# Specific 3D Printers, Scanners, & Hardware > Peachy Printer Forum >  Possible hole fix - Drip those holes away!

## NoctumSolis

Hi, I've been following the Peachy Printer project for a while now and have also supported it via backerkit, but alas I'm no beta tester. If I were I'd try this idea myself, in lieu of which I can at least suggest it here.

Like many others I suspect that the holes in prints are caused by surface tension during the raising of the resin level. To fix this, while keeping costs down and continuing in a very _Peachy_ style, I suggest a second drip feed or, more accurately, a drip _drain_.


Attach a new drip that is able to drain the printing tank; a drip drain.Use the existing drip feed to raise the level further than desirable for the new layer, ensuring that the resin overflows properly.Lower the level via the drip drain, reducing the thickness of the layer.Print the layer.

This has certain advantages over other techniques. 
Because we're not moving the printed object or displacing the water by pushing something into it, no waves are introduced.Because the drip drain would be mechanically identical to the existing drip feed, established techniques could be easily adapted.Because the drain and the feed would operate at different times, both could be controlled through the same audio jack. Just use software to track which drip is operating.
Of course, there are also disadvantages.
It's extra hardware, so extra cost (but hopefully not much).The drained fluid has to go somewhere, presumably a third tank. Cumbersome, but perhaps acceptable. Just stack the print tank on top of the drain tank.

But, if it works, it could save a LOT of hassle.

----------


## jstrack2

I think that this is an interesting idea. It definitely may be helpful. One thing that you did not mention that I think could be a problem is that the drip drain may have to drain a lot each layer to deal with the surface tension. I don't know how much, but it may be too much to have this method as you stated it make sense. For example if you wanted 10 micron layers and it required a 100 micron drop to each layer to properly deal with the surface tension then you would need to use 11 times more liquid. This could be really obnoxious, especially when trying to print something fairly large.

I was working on this idea in this thread: http://3dprintboard.com/showthread.p...y-Prints/page2

At first I was thinking of having a hole or something in the bottom of the printing tank that go in and out to change the liquid level. But then I realised that I would be fighting the water pressure too much. So I came up with the design I showed in the video. I did this for a three layer variation where salt water, fresh water and resin is used (instead of just salt water and resin) and in that case adding a sheet of plastic between the thing that goes up and down prevented surface waves from forming. I explain why in that thread. However I don't know how well it will work for the standard two layer approach. I will fairly soon make an update to it and try it out with both two and three layers, as well as just improve the overall design. Also I should point out that my method requires a solenoid, which of course adds some cost.

----------


## mike_biddell

A mobile phone vibrator might allow the resin to overcome surface tension. Turned ON when the laser is OFF. The ripples wud die down quite rapidly in a viscous fluid.

----------


## Feign

I was also thinking something similar, though less a vibrating motor and more a subwoofer speaker (because I have a few just sitting around in the basement) against the side or bottom of the tank to put a low-frequency noise into the fluid between layers.  With a speaker playing a tone, you can get nice fine adjustment of the output to find just the right tone for your tank.  (oh yeah, that's right, _more_ things to calibrate!  :Roll Eyes (Sarcastic):  )

----------


## NoctumSolis

> I think that this is an interesting idea. It definitely may be helpful. One thing that you did not mention that I think could be a problem is that the drip drain may have to drain a lot each layer to deal with the surface tension. I don't know how much, but it may be too much to have this method as you stated it make sense. For example if you wanted 10 micron layers and it required a 100 micron drop to each layer to properly deal with the surface tension then you would need to use 11 times more liquid. This could be really obnoxious, especially when trying to print something fairly large.


This is a very good point. Initially I imagined, without giving it any thought, that the technique might double the water used, but I have no reason for such a low estimate. Ideally we'd be able to pump the drained water back into the feed tank, but pumps are not cheap and cost is a driving concern here. (Such a pump could be an optional extra, of course.) The alternative is to drain into a jug (for instance) and tip it back into the feet tank.




> I was working on this idea in this thread: http://3dprintboard.com/showthread.p...y-Prints/page2
> 
> At first I was thinking of having a hole or something in the bottom of the printing tank that go in and out to change the liquid level. But then I realised that I would be fighting the water pressure too much. So I came up with the design I showed in the video. I did this for a three layer variation where salt water, fresh water and resin is used (instead of just salt water and resin) and in that case adding a sheet of plastic between the thing that goes up and down prevented surface waves from forming. I explain why in that thread. However I don't know how well it will work for the standard two layer approach. I will fairly soon make an update to it and try it out with both two and three layers, as well as just improve the overall design. Also I should point out that my method requires a solenoid, which of course adds some cost.


I'd seen some of this but missed some details, sorry. I hadn't noticed that you had a working solution to the ripple problem. Obviously though, costly things such as solenoids are exactly what I was hoping to avoid. But if it works, it works.

----------


## NoctumSolis

> A mobile phone vibrator might allow the resin  to overcome surface tension. Turned ON when the laser is OFF. The  ripples wud die down quite rapidly in a viscous fluid.





> I was also thinking something similar, though less a vibrating motor and more a subwoofer speaker (because I have a few just sitting around in the basement) against the side or bottom of the tank to put a low-frequency noise into the fluid between layers.  With a speaker playing a tone, you can get nice fine adjustment of the output to find just the right tone for your tank.  (oh yeah, that's right, _more_ things to calibrate!  )


I'm not too well up on fluid dynamics, but I would imagine that to get decent coverage this way a fairly substantial disturbance would be required. Since the waves will lose energy with increasing distance from the source the amplitude would also be different depending on depth. Right?

----------


## jstrack2

> I'd seen some of this but missed some details, sorry. I hadn't noticed that you had a working solution to the ripple problem. Obviously though, costly things such as solenoids are exactly what I was hoping to avoid. But if it works, it works.


It was my fault, I was not very clear in that thread. When I post an updated video sometime I will show things a lot better. A five dollar solenoid will work. I am currently working on making a solenoid for something else that would require well less than a dollar in materials, but a little labor. It should also be strong enough.




> I'm not too well up on fluid dynamics, but I would imagine that to get decent coverage this way a fairly substantial disturbance would be required. Since the waves will lose energy with increasing distance from the source the amplitude would also be different depending on depth. Right?


I think that there can be not that much loss depending on how things are set up. Since it is a wave it can just propagate through the liquid to the surface. However if the wave goes directly towards the surface (in other words normal to the surface) it will just pass on through to the air without creating a surface wave. So in that sense having a deeper tank will force the angle to be on average smaller which will cause more of the waves' energy to pass through into the air rather than creating surface waves. Regardless though I don't think it will be hard at all to create the surface waves. They can be tricky to get rid of, but are darn easy to make!

----------


## Aztecphoenix

The biggest problem with a dual drip system is it will extend the print time to almost double, having to fill up and then drain out for each layer, I had suggested in another thread about using a simple displacement piston that displaces 1mm of water and then returns the level to normal every layer, a simple build using PVC pipe, a solenoid, and a few other minor materials, having the system places below the surface of the print area should eliminate most if not all waves and ripples in the print.

----------


## User_Defined

Hey guys,

I've been following the thread and thinking about possible solutions.

So  far I think you are all on the right track, and that something needs to  break that pesky surface tension. From what I've seen, top down SLA  printers do it by submerging the part completely and then bringing it  back up to printing level. This is super easy with those systems because  of the linear motor controlled track the Z is on. But the Peachy doesnt  have this!

So, based on this and judging from your past posts it  would for sure work if the resin level could be accurately raised and  lowered between laser blasts. To do this 100% you would need some kind  of plunger either fixed into the base of the print basin, or on a float  above the print basin, the first being more precise. The problems I see  about this are cost and implementation. In other words it would work,  but it might be better left as a final option than a go-to.


Waves:

Others  have suggested making waves on the surface by rocking or vibrating or  hitting the print basin. While the idea sounds good, I dont think that  manipulating the whole of the print basin with a physical disturbance is  a good idea. What could work, however is a vibrating float. Another  possible cheap solution could be a tiny fan to blow air on the resin and  make little waves in between layers.

Something that could  possibly work is to vibrate the print bed inside the basin, and it might  be just enough to disturb any surface tension bubbles. I dont know how  it will affect print robustness.

Maybe a spinning wiper float?  Could simply by a floating octopus like thing with thin flat arms slowly  spinning above the resin and acting like a wiper, seems impractical.

Another  suggestion, and this may seem radical and not work, is to consider the  possibility of the resin bath liquid being in a very slow circular  motion during the print. It may be enough to over come the surface tension.

If  the guys at peachy can figure out why and when these bubbles happen,  they can always use the laser to add support structures that can block  them from occurring. Could be as simple as little rods coming off the  surface. 


that's all I can come up with, nothing that I am happy with but I hope it sparks an idea from one of you!


-UD

----------


## jstrack2

Having a solenoid lift something floating both above and below the resin is what my video shows. By having it float the solenoid does not need much strength to change the height of the resin temporarily. However to avoid making waves a sheet of plastic must be placed between the object that displaces water and the actual print. This causes waves to reach the surface at small angles, which prevents surface waves for a reason I will explain here.

When making this demonstration I looked up information about how the surface waves are created. It happens when a wave runs into a lower index of refraction medium at an angle too great for the wave to pass through to the lower index medium. The energy of the wave is then dumped into the interface between the two mediums and a surface wave is generated there. If the angle is small enough then the wave will just carry on to the lower index of refraction medium and no surface wave will be created. The equation for the minimum angle to cause surface waves is angle = arcsin(n2/n1) where n1 is the higher index  and n2 is the lower. Water and the resin have a much higher index of refraction than air. So in this case n1 is resin and n2 is air. Therefore if you disturb liquid then surface waves will result unless the waves travel in a direction pretty much normal (directly) to the air-liquid boundary. The sheet of plastic forces the waves generated from the moving floating object to be pretty normal to the air. 

It is just like total internal reflection with a laser, except that instead of the wave reflecting it just dumps itself onto the surface causing waves. Here is a good video demonstration of laser light total internal reflection:




I think that it is pretty interesting that it works this way.

----------


## User_Defined

Jstrack, I dont really understand what kind of waves you are talking about, your video shows light waves.

One more thing has come to mind about these holes, and that is the peachy printer look-alike, the Hardcotton Elemental. 
They use a pressure controller instead of a drip to control the fluid level, but I dont think they have up and down control of that level.

Here is their functional diagram:
http://3dprint.com/wp-content/upload.../07/hard-3.jpg

And here are their test prints:
http://3dprinterplans.info/wp-conten...-printer-4.png

There aren't any holes! 

Now maybe, they just printed things until there were no holes, or maybe the problem is simply a question of Rylan printing with walls that are too thin in problematic areas.

I was taking a closer look at these holes, remembering that the peachy build bottom-up and almost all of them originated on Yoda at heavy wrinkles. 

https://s3.amazonaws.com/ksr/assets/...jpg?1407365420

- The lowest one on his right side has it's bottom point of origin at a heavy indentation on his shirt.
- The two next ones are almost flush with lateral wrinkles in his shirt.
- Lastly the most prominent one came from the corner of his mouth.

It could be that although the peachy can produce overhangs very well, these overhangs may be too steep for the wall thickness, and they may be losing contact when the laser forms them, creating a bubble with nothing for the new material to stick onto.

I am fairly sure that if they print with a thicker wall, that this will be overcome. And in the future, have some kind of material detect in the software that can see these problems in advance, and thicken the walls right before steep overhangs.


-UD

----------


## jstrack2

> Jstrack, I dont really understand what kind of waves you are talking about, your video shows light waves.


I mean that it is _like_ total internal reflection with a laser. The waves that I am talking about here are sound waves. I am just saying that how the sound waves travel here is similar to light waves, so that it is easier to visualize. So if you create a sound wave in the liquid that is heading toward the surface, you can kind of think of it like a laser shining up at the surface. If the wave is normal to the water then it will pass through into the air (without creating any surface wave at all). If the sound wave is at a significant angle then instead of passing through to the air it will cause a surface wave (where as if it were a laser the light will reflect instead of causing a surface wave). So I posted the video of the laser just to give an intuitive sense for how the sound waves are working. The stuff in the video involving a flashlight and after is not relevant. Let me know if I am still unclear.


I think that the pressure system is basically the same thing as the drip system (without the ability to count drips). I mean pressure ultimately controls dripping, so I think that they are not as original as they claim haha. So yeah it seems Peachy clones are coming!

I would guess that you are correct about thicker walls fixing the issue. That is an interesting idea having the software make the walls thicker automatically in areas that could be trouble. Ultimately though I would like to really understand the exact causes well so that thin walls in areas that curve dramatically still print well. I think that eventually this printer will be able to do really amazing prints, while still being super cheap.

----------


## Feign

> Now maybe, they just printed things until there were no holes, or maybe the problem is simply a question of Rylan printing with walls that are too thin in problematic areas.


Both of these are likely.  Also, the Hardcotton printer is able to raise and lower the resin level as well as dwell on a layer as long as it needs to, meaning it can print the solid pieces, spending as much time as needed on each layer.  The Peachy has a time limit for each layer, necessitating the hollow shell printing in most cases.  Though it printed the Rook solidly, and there were definitely no holes in that.  If he had printed the Yoda with three layers in the shell rather than just one, I'm pretty sure there wouldn't be any holes at all and still have all the resin economy you could want.

I wouldn't call the Hardcotton printer a Peachy Clone, as the only similarity it has is being a top-printing SLA machine.




> I mean that it is _like_ total internal reflection with a laser. The waves that I am talking about here are sound waves. I am just saying that how the sound waves travel here is similar to light waves, so that it is easier to visualize. So if you create a sound wave in the liquid that is heading toward the surface, you can kind of think of it like a laser shining up at the surface. If the wave is normal to the water then it will pass through into the air (without creating any surface wave at all). If the sound wave is at a significant angle then instead of passing through to the air it will cause a surface wave (where as if it were a laser the light will reflect instead of causing a surface wave). So I posted the video of the laser just to give an intuitive sense for how the sound waves are working. The stuff in the video involving a flashlight and after is not relevant. Let me know if I am still unclear.


The problem here is with your core assumptions.
First, a wave will only remain stationary where it is _exactly_ 90o to the fluid's surface, any angle at all will cause a wave to propagate along the surface.  This is because viscosity carries energy between molecules in a liquid even if the direction of the force itself doesn't pass between them.
Second, mechanical waves in a liquid or solid propagate radially, similar to how light waves propagate from a light bulb.  There's no way that I know of to form an actual cohesive mechanical wave through a fluid (though there are ways to fake it through amplifying and cancelling waves, but those cause all kinds of incidental vibrations that you don't want.)

----------


## jstrack2

That is cool that the Hardcotton can do that. I think hopefully the Peachy will have those features soon. But I think it is very similar to the Peachy in that it is using liquid's auto-leveling properties to make the prints. Perhaps calling it a clone is unfair. There are some differences for sure. Maybe it is a partial clone (offspring?) haha


When you say the wave stays stationary do you mean a standing wave? Anyway when going from a high to low index of refraction at enough angle there can be increased interaction at the interface which does not support waves in either the low or high index of refraction medium, and thus the energy becomes surface waves propagating along the interface of the two mediums. If the second medium's index isn't enough lower than the first or the angle isn't great enough then pretty much all energy will just pass through two the second medium. I am not saying that all energy is perfectly sent along in this manner, but more or less this is how it works.

Also it is true that these waves propagate radially, however by the time they reach the air interface the part of the wave that hits the interface can be travelling pretty normal to the interface. So yeah it is true that in this way it also doesn't behave like a laser, but still it works as I am saying. I just used the laser analogy since it is simple, but it seems it has been more confusing than anything. :/ I think that you can form sound waves in liquids that are pretty cohesive in different ways by the way, but they definitely are not here.

----------


## Feign

> That is cool that the Hardcotton can do that. I think hopefully the Peachy will have those features soon. But I think it is very similar to the Peachy in that it is using liquid's auto-leveling properties to make the prints. Perhaps calling it a clone is unfair. There are some differences for sure. Maybe it is a partial clone (offspring?) haha


Considering that the very first 3D printer back in the 1970s was a top surface SLA that used the natural leveling properties of the liquid and changed the surface level to move up the layers rather than lowering a platform, it's more accurate to call the designs 'cousins' than anything.




> When you say the wave stays stationary do you mean a standing wave? Anyway when going from a high to low index of refraction at enough angle there can be increased interaction at the interface which does not support waves in either the low or high index of refraction medium, and thus the energy becomes surface waves propagating along the interface of the two mediums. If the second medium's index isn't enough lower than the first or the angle isn't great enough then pretty much all energy will just pass through two the second medium. I am not saying that all energy is perfectly sent along in this manner, but more or less this is how it works.


No I mean that only that part of the wave goes directly up and then directly back down without propagating out over the surface of the fluid.  Indexes of refraction are almost entirely a property of a material's _permissivity_, or the resistance the material has to the energy passing through it.  Mechanical waves propagate based on a material's _viscosity_.  While the two are sometimes related, the two properties are independent, there are very very refractive fluids that are very low viscosity.  (Mercury is an example, though the refractivity of Mercury is generally a moot point since it is opaque to light, but it's refractive properties come into play with very lower frequency radio waves.)




> Also it is true that these waves propagate radially, however by the time they reach the air interface the part of the wave that hits the interface can be travelling pretty normal to the interface. So yeah it is true that in this way it also doesn't behave like a laser, but still it works as I am saying. I just used the laser analogy since it is simple, but it seems it has been more confusing than anything. :/ I think that you can form sound waves in liquids that are pretty cohesive in different ways by the way, but they definitely are not here.


The problem with using light analogy to this is that with light, the permissivity of water is lower than air, allowing there to be a point where the light passes through without being reflected.  If you were to shine the laser down from the air and into the water, even at an exact 90o angle, you would get some amount of reflection back up toward the laser.

Further, in order to make a proper analogy between water and light, you would have to find an interface that has similar differences in _permissivity_ that water and air have in _viscosity_.  Air is about as viscous to mechanical waves as say, milk is permissive to light, and water is about as viscous as air is permissive (roughly).  If you were to shine the laser downward on the interface between air and milk, you would get a more accurate indication of what kind of behavior you would get back from mechanical waves.

... I hope I was able to get that to make sense.  Physics is hard to explain sometimes.

----------


## jstrack2

> Considering that the very first 3D printer back in the 1970s was a top surface SLA that used the natural leveling properties of the liquid and changed the surface level to move up the layers rather than lowering a platform, it's more accurate to call the designs 'cousins' than anything.


Ah I didn't know that, I should learn about the history.  So cousins it is!




> No I mean that only that part of the wave goes directly up and then directly back down without propagating out over the surface of the fluid. Indexes of refraction are almost entirely a property of a material's_permissivity, or the resistance the material has to the energy passing through it. Mechanical waves propagate based on a material's viscosity. While the two are sometimes related, the two properties are independent, there are very very refractive fluids that are very low viscosity. (Mercury is an example, though the refractivity of Mercury is generally a moot point since it is opaque to light, but it's refractive properties come into play with very lower frequency radio waves.)_


I think you mean permittivity, which along with the magnetic permeability determine the refractive index for electromagnetic radiation. The higher the refractive index the slower the wave travels. I think that the analog for mechanical waves is also called refractive index, but this may be wrong. Also, I am interested in surface wave generation, not how much of a mechanical waves is reflected or transmitted (which can be pretty complicated). Viscosity attenuates a wave, but doesn't change the speed of it (or it could some technically, but generally it is not what determines it.) The speed of a wave in a fluid is proportional to the square root of the of bulk modulus divided by the fluid density btw.

So anyway as I was saying I think surface waves can form when you have waves hit a higher lower index of refraction (high speed) at a high enough angle and then from surface interactions can't reflect much so they form surface waves. When I say refractive index I mean the index for mechanical waves. Again this may not be correct use of the term, but mechanical (and all) waves can refract in the same sort of way as light does. It is just a matter of entering a new medium where the speed of the wave will be different.




> The problem with using light analogy to this is that with light, the permissivity of water is lower than air, allowing there to be a point where the light passes through without being reflected. If you were to shine the laser down from the air and into the water, even at an exact 90o angle, you would get some amount of reflection back up toward the laser.
> 
> Further, in order to make a proper analogy between water and light, you would have to find an interface that has similar differences in _permissivity that water and air have inviscosity. Air is about as viscous to mechanical waves as say, milk is permissive to light, and water is about as viscous as air is permissive (roughly). If you were to shine the laser downward on the interface between air and milk, you would get a more accurate indication of what kind of behavior you would get back from mechanical waves.
> 
> ... I hope I was able to get that to make sense. Physics is hard to explain sometimes._


Water has a higher permittivity than air. Of course some light will always be reflected, but this is not relevant to what I am talking about. I am just interested in surface wave formation. Permittivity and viscosity do not matter so much for total internal reflection of mechanical waves. Of course other stuff can cause surface waves to form too, like moving the container.


Anyway I just added the laser analogy to make things more clear, but obviously miserably failed here! haha Also this topic is supposed to be on holes in the prints, this has gotten way off topic.

----------


## jstrack2

Yeah I am pretty sure that the refractive index is only for light (since it is a number relating the speed of light to the speed radiation passes through a medium). Sorry for the confusion this caused. The way I was incorrectly using it I just meant how much a mechanical wave will refract when going from different mediums that have waves travel at different speeds. Man I really sent this discussion off topic!

----------


## rylangrayston

> I was taking a closer look at these holes, remembering that the peachy build bottom-up and almost all of them originated on Yoda at heavy wrinkles. 
> 
> https://s3.amazonaws.com/ksr/assets/...jpg?1407365420
> 
> - The lowest one on his right side has it's bottom point of origin at a heavy indentation on his shirt.
> - The two next ones are almost flush with lateral wrinkles in his shirt.
> - Lastly the most prominent one came from the corner of his mouth.
> 
> It could be that although the peachy can produce overhangs very well, these overhangs may be too steep for the wall thickness, and they may be losing contact when the laser forms them, creating a bubble with nothing for the new material to stick onto.
> ...


Very Observant of you!! 

Indeed we noticed this too.. 

We have another theory that could explain this also, Stray laser light. 
We have an alarming amount of light scattering far away from the focal point of the laser. 
in arias that are more complex ( like the ones you point out ) the aria around that complication may get enough stray light to cause the surface of the resin to partially cure, to become so viscose that it has trouble flowing in over the printed wall. 

Been working on  better laser focus along side about 5 other theories , hopefully will have it solved soon. 
The laser focus problem has been fun, iv been staring at beautiful diffraction patters for days, and learned about electro polishing, and how to machine very very small holes.  
Light has some mind boggling property's.

----------


## Aztecphoenix

> Very Observant of you!! 
> 
> Indeed we noticed this too.. 
> 
> We have another theory that could explain this also, Stray laser light. 
> We have an alarming amount of light scattering far away from the focal point of the laser. 
> in arias that are more complex ( like the ones you point out ) the aria around that complication may get enough stray light to cause the surface of the resin to partially cure, to become so viscose that it has trouble flowing in over the printed wall. 
> 
> Been working on  better laser focus along side about 5 other theories , hopefully will have it solved soon. 
> ...


as for focusing the light, I was wondering what about having the focal lens after the aperature, in the assembly videos they show mounting a small aluminium disk with a small hole punched in it stuck on top of the laser module after the focusing lens, if you reversed it you would be focusing the small beam instead of restricting an already focused beam, this might solve the stray light problem as well as possibly producing an even finer beam allowing for even better than your already awesome resolution.

----------


## rylangrayston

Aztecphoenix Altho I haven't printed with it yet putting the aperture in front of the lens as you suggest dose produce much less stray light! 
Time will tell if this fixes the problem.

----------


## User_Defined

This all sounds very promising! 

Would this also make the resulting prints have smoother finishes? I notices some wavyness in many of the prints that other SLA printers dont have (maybe it is becaue youre printing in clear resin, it is hard to tell from pictures!)

I remember coming across this DIY project for SLA 3d printing, he uses an iris a bit further away from the laser:
http://www.instructables.com/id/Buil...ography-at-Ho/


- UD

----------


## Aztecphoenix

I've been thinking more into the surface tension problem and have been trying to think of an easy and inexpensive way of adjusting the surface level temproarily between printing layers and I think I've got a viable solution using a small servo, two syringes, a length of hose, and some laser cut parts, the most expensive part being the servo at a couple of dollars (cheaper in bulk) you can create a pneumatic piston that raises and lowers the build surface between layers.

you attach the hose to the tips of both syringes, place the build surface on the plunger of one syringe, using a laser cut actuating system between the servo and the second syringe, this way, when the servo pulls the syringe plunger up it suck the air from the second syringe causing the second syringes plunger to drop lowering your build surface, this allows the resin to flow over top of the entire surface to fill in any holes, then the servo reverses pushing the plunger down pumping air back into the other syringe raising the print back up to print the next layer.

the best part of this is it's scalable, you can use a 60cc syringe connected to the servo that is hooked up to a manifold connected to four smaller syringes (one on each corner of the build surface) for printing larger objects.

----------


## Feign

Attenuating a beam into a fine point is a serious pain.  When I worked on beam attenuators I figured out a little trick for making them pretty cheaply that maybe could apply here.

The best method of attenuating a beam so that there is no scatter is to have a series of apertures spaced along the beam and perfectly lined up.  In most cases this is a crazy machined assembly that's nearly impossible even at the 10mm beam diameter scale.  But if you want a similar effect to the big expensive attenuators, just use a threaded hole with the thread ID the size of the beam you want (provided the material you use isn't at all reflective.  I'd recommend a black anodized nut with the tiniest thread you can find.

----------


## Aztecphoenix

> Attenuating a beam into a fine point is a serious pain.  When I worked on beam attenuators I figured out a little trick for making them pretty cheaply that maybe could apply here.
> 
> The best method of attenuating a beam so that there is no scatter is to have a series of apertures spaced along the beam and perfectly lined up.  In most cases this is a crazy machined assembly that's nearly impossible even at the 10mm beam diameter scale.  But if you want a similar effect to the big expensive attenuators, just use a threaded hole with the thread ID the size of the beam you want (provided the material you use isn't at all reflective.  I'd recommend a black anodized nut with the tiniest thread you can find.


what about using a series of varying aperatures, with the largest nearest the diode? wouldn't this work similarly but reduce the problem of alignment?

----------


## Feign

> what about using a series of varying aperatures, with the largest nearest the diode? wouldn't this work similarly but reduce the problem of alignment?


Well, the problem is that as light passes the edge of the aperture, it gets scattered just slightly.  So what you want is it have apertures that only interact with the scattered light.  The first aperture reduces the beam width, but the edge scatters some of the light right at the edge of the beam.  The next aperture is to block the scattered light, but you want it to not touch the rest of the beam.  Of course, some of the scattered light does hit the edge of that aperture and scatters again instead, necessitating a third aperture and so forth...

Of couse, two should be enough for the Peachy, since the first one only scatters about 10% of the light at even at a small scale.  The next one of course only scatters 10% of that and so on.  Two apertures and you've filtered 99% of the scatter.

----------


## rylangrayston

Feign Thank you so much for the suggestion ... ive been using a bunch of razor blades stuck to a hollowed out magnet, by sliding the blads up to the beam scatter I can reduce it, but i love the threaded hole idea.... i have a piece of solid graphite ( quite black ) im going to try threading that now. 

I have been theorizing exactly the scatter reduction technique you speak of on our white board, good to know with some confidence that multiple apertures is worth trying.

----------


## Aztecphoenix

you may also try an electro-etching template on some thin steel to make the aperatures, if the template is made properly the only trouble with alignment would be in your frame assembly.

lots of info on electro-etching can be found online, however if there is a sword smith or black smith nearby they may be able to help you get set up.

just remember, the thinner the steel is, the smaller you can make the aperture 

@ Feign,
in regards to the apertures, do they have to be an opaque solid with a hole through it or, can it be something like acrylic with a coating of black paint with a speck of unpainted area that the light can pass through? if so then maybe we could silk screen print some apertures.

----------


## rylangrayston

Hey Feign 
The Graphite worked really well, I didnt have any tap nearly small enough to thread a .3- .5 mm hole,  so i just machined a tapered hole that is 1cm deep. 

so currently my best setup is some thing like this    laser diode-- 3mm-- first aperture--Lens--- 100mm---1cm thick taperd Graphite aperture---->  

Id like to get that 100 mm down alot but the light needs space to scatter, 
and I think that my first aperture being right up against the lens is probably bad, im going to try giving it a .5 mm gap, and making the first aperture out of graphite too. 

any other suggestions, Ill probably try printing with the best thing iv come up with late tomorrow.

----------


## Aztecphoenix

> Ill probably try printing with the best thing iv come up with late tomorrow.


please post a video, it doesn't have to be anything high end like all your other videos, but just something showing the current state of the peachy and how it looks printing, I know I'm not the only one who would like to see this.

----------


## Feign

I like the idea of using solid graphite.  And the setup you have is definitely in the right direction.  It makes sense to have the second aperture a distance away.  Since there is a good dark band between the beam and the first diffracted band, your second aperture doesn't need to be as precisely placed if it's just blocking the band.

I can't remember the formula for the angle of diffraction through a hole, but I do remember that it's dependent on the wavelength, so you've got one of the toughest possible scenarios with this.

Unfortunately, this little revelation adds parts that need machining and I can't for the life of me figure out how you can get it so the end user can calibrate a multi-step attenuator easily, since you have to aim the laser _exactly_ through both of the holes.

----------


## NoctumSolis

> Unfortunately, this little revelation adds parts that need machining and I can't for the life of me figure out how you can get it so the end user can calibrate a multi-step attenuator easily, since you have to aim the laser _exactly_ through both of the holes.


I'm showing my ignorance here, but... wouldn't it just be a matter of extra snap-together parts designed to hold the pre-machined parts in position? If the emitter is mounted to the circuit board then its position, along with all dimensions, are known quantities.

I realise there are plenty of fiddly, moving parts to calibrate, but wouldn't a static attenuator be easy enough to ensure consistent placement for?

----------


## Feign

Maybe, maybe not.  Basically, you have a disk with a small hole through it that you have to shoot the laser through without touching the edge of the hole (or else you get the scattering all over again.)  There's about 0.01mm of leeway for the second disk if there is good separation between the first and second apertures and the laser diode is lined up _just right_.  I'm not sure how tight a tolerance the snap fit can make.

Here's a good picture of what the scattered light looks like for the red spectrum, as wavelength goes down, the spacing of the rings also decreases.  
pinhole2.jpgWhat you really want is the beam to be on-center enough that the edge is in the first dark region between rings.  However this picture was probably taken in a dark room at about five feet from the wall.  Trying to find the rings at 10cm in UV wavelength would take a microscope.

However, if the second aperture is two or three times the size of the first, and you don't have it exactly lined up, you only get a few pairs of _points_ on the second aperture where light is getting re-scattered, and they are from the rings, which have much less light in them anyway.  It all boils down ti where the magic "good enough region" lays.  In any case, it's a thing that would need calibration.  Not something that I would trust to laser cut acrylic tolerances.

----------


## Feign

Just found the formula for it!  The distance between the rings of light (y) is based on the equation  y=D((mλ)/d)  Where D is the distance from the aperture and d is the diameter...  m is a constant whos origin I don't know...

Here's a handy little calculator (physics department websites are quite handy):  Circular Aperture Diffraction  Plugging in the numbers, for a .5mm first aperture diameter and a 10cm spacing between the first and second apertures, the minima (dark space between rings) has .01cm of wiggle room to calibrate the placement of the second aperture.

But like I said, you don't have to get it _exact_ to get the scatter down significantly.

----------


## erikk

> ...  m is a constant whos origin I don't know...


m = 1 for the first ring, 2 for the second... etc. 
Its means the 10th ring is 10 times the angle from center as the first ring
Edit: maybe m isn't exactly nice numbers but there's an m for every minimum/maximum ring

----------


## jsondag

What if you used a pump like this. http://www.ebay.com/itm/6v-dc-Dosing...item2ed1c1d0d1
You can reverse the direction. Pump in some water, pump out some of it, and repeat.  You can raise the resin over the print and back down. All it takes is a little attiny85/45 or something, which are a dollar or two, and a small H-bridge chip. You could integrate it into your board fairly cheaply, or let people use an arduino or similar. This would solve your drip inconsistency, as well as a number of other problems.

----------


## Aztecphoenix

> What if you used a pump like this. http://www.ebay.com/itm/6v-dc-Dosing...item2ed1c1d0d1
> You can reverse the direction. Pump in some water, pump out some of it, and repeat.  You can raise the resin over the print and back down. All it takes is a little attiny85/45 or something, which are a dollar or two, and a small H-bridge chip. You could integrate it into your board fairly cheaply, or let people use an arduino or similar. This would solve your drip inconsistency, as well as a number of other problems.


I'm not so sure about using the reverse feature, but make sure you use varable speed otherwise you can't adjust the flow depending on the size of your print

----------


## User_Defined

> Feign Thank you so much for the suggestion ... ive been using a bunch of razor blades stuck to a hollowed out magnet, by sliding the blads up to the beam scatter I can reduce it, but i love the threaded hole idea.... i have a piece of solid graphite ( quite black ) im going to try threading that now. 
> 
> I have been theorizing exactly the scatter reduction technique you speak of on our white board, good to know with some confidence that multiple apertures is worth trying.


Easy fix for this:

Make some kind of foil holder mechanism that will attach onto the laser diode module. Inside this foil holder will be three discs of aluminum foil (basically like your instructional video, except with three foils within it).

Then perform the same hole making action but pierce through all three foils at once. The only thing is that it would need to be very straight. 

You could probably try it easily with some big washers for spacers, with foil folded between them and crumpled on the sides to hold it all together.

For the actual implementation, have the foil holder as part of the peachy frame, and use 4 laser cut plastics before the first foil to line up and guide the hole piercing probe and ensure it being straight. This should keep everything aligned with the laser cut frame and reduce human errors.

Or, make an alignment tool with 4 laser cut plastics for when you need to pierce the triple hole.



- UD

----------


## jsondag

> I'm not so sure about using the reverse feature, but make sure you use varable speed otherwise you can't adjust the flow depending on the size of your print


You can use PWM from the attiny to control the speed. The H-bridge is what reverses the direction. It's just an input line on the H-bridge to reverse the polarity, and thus, direction of the motor.

----------


## jsondag

> What if you used a pump like this. http://www.ebay.com/itm/6v-dc-Dosing...item2ed1c1d0d1
> You can reverse the direction. Pump in some water, pump out some of it, and repeat.  You can raise the resin over the print and back down. All it takes is a little attiny85/45 or something, which are a dollar or two, and a small H-bridge chip. You could integrate it into your board fairly cheaply, or let people use an arduino or similar. This would solve your drip inconsistency, as well as a number of other problems.


Thinking about this, it actually makes sense as an external add on. It would have an output for the pump motor, and an output to the sound card to simulate drips. One adjustment knob to change drip rate independently for calibration to container size, and another main knob to change motor speed. The main knob would adjust speed, and drip pulses linearly.

If anyone were interested in this as an add on, once I get my peachy, I could easily draw up a PCB, make it a kit, and open source it.

----------


## Aztecphoenix

> You can use PWM from the attiny to control the speed. The H-bridge is what reverses the direction. It's just an input line on the H-bridge to reverse the polarity, and thus, direction of the motor.


I meant, I don't really see the point in using the reverse, I don't feel as though it could be precise enough to pump out exactly enough water to bring the level back to proper height to resume the print or even whether it could pump out fast enough so the prints don't take hree times as long, but I do agree with the PWM for speed control

----------


## jsondag

> I meant, I don't really see the point in using the reverse, I don't feel as though it could be precise enough to pump out exactly enough water to bring the level back to proper height to resume the print or even whether it could pump out fast enough so the prints don't take hree times as long, but I do agree with the PWM for speed control


I guess it would just have to be tested to find out. If not, you could use a stepper motor pump. That should give some good precision. It's going to add more money to the cost of the printer, and yes it could make the prints take longer, but it's an option. And still cheaper than any other printer on the market. In either case using a pump like this could certainly solve the drip metering problems.

----------


## Aztecphoenix

the biggest problem I see with any pump system is it would have to be a completely closed system, just the slightest bit of air in the system and kiss any degree of acurasy goodbye, meaning before you start any print, the whole line will have to be primed (see the promo video when he is explaining about the drip system to see where my concerns lay).

with that in mind, some food coloring in the salt water would make it easy to see if the line has any air pockets in it, does anyone know if the resin has any reaction to food coloring?

----------


## jsondag

It shouldn't be any harder than the drip system. Just run the water a bit before you start the system, and tap the lines a bit to get the bubbles moving.

----------


## jstrack2

I am confused about why an aperture is being used. I know that it is for attenuation, but is it also to focus the beam? I am not sure if this is the way to go. How about using a colored plastic sheet to attenuate the beam? The material cost of this would be effectively zero and it would attenuate the beam without hurting the beam quality much at all or adding other significant complications (although this will reflect the laser so shielding from the dot that is reflected will be needed). Using an aperture creates multiple modes and increases beam divergence as Feign pointed out with the equation y=D((mλ)/d). Therefore using an aperture will always significantly diminish print quality.

Focusing the beam is a trickier matter. It is not possible to have a super long tight beam because of fundamental physics. The best way to get a tight long beam is to focus it then collimate it (have the light rays be parallel again). To do this we could just use two opposite facing identical convex lenses (or alternatively a convex and a concave lens). The focus on the laser could be adjusted to eliminate the need for the first lens so only one lens would be needed. I think that a convex or concave lens could be obtained for 25 cents pretty easily, and possibly even significantly cheaper. The laser would focus the beam, and then the external lens could collimate it so that you would have a tighter beam that has almost parallel rays.

However the beam will not stay super tight. If the beam is a perfect Gaussian (which it won't be so things will be worse so this is best case) then the beam will diverge by the equation θ = λ/(π*ω). In this equation θ is the divergence, λ is the laser's wavelength, π is pi and ω is the radius of the beam at its smallest point. So focusing the beam will cause it to diverge faster. For example, if λ equals 405 nm, and ω is focused down to 0.1 mm then θ = (405*10^-6)/(3.14*0.1) = 0.00129. The diameter a given distance (l) away from the smallest diameter is approximately d = 2*l*θ + ω. So it would be 2*300*.00129 + 0.1 = 0.874 mm. This is not that great. If the beam wasn't initially as tight then close to 0.5 mm beam diameter 300 mm away would be _theoretically_ possible. Also there will be a big difference in detail between the top and bottom of a print which won’t look good. I think that this final diameter could be cut significantly further (close to in half) if the beam was slightly converging after leaving the second lens so that it had a minimum diameter half way to the max distance of 300mm. In this case then the middle of the object would be capable of the highest detail and the top and bottom would be the least. This could be pretty decent, especially for the basic Peachy.

Therefore if real small features are desired then either the beam must be focused closer to the target, or there must be adjustable focus. Focusing closer to the target could be done by either moving the laser optics with a platform that floats so as the resin rises the optics are always close to the resin (I believe this has been discussed some on the forum), or by just saying that only small prints can have very high detail (this may not be so bad, since prints will only need to be small in one of the three dimensions). Also multiple higher detail small parts could be printed and then glued together later.

Adjustable focus would allow for super high detail throughout the entire print. Perhaps a super cheap servo motor could control it. I don’t know if it could be included in the basic kit, but having it would be a big step towards ridiculously high quality prints.

So anyway does what I have just posted seem correct? It is definitely possible that I made one or more mistakes. Also sorry for this post being so darn long!

----------


## jstrack2

Erikk is correct that m in the equation that Feign first posted does not have to be an integer. It is for a slit, but not a circular hole. I should have viewed the link about circular apertures that Feign posted! Therefore I deleted my post.

----------


## ijmok

Forgive me if this has been tried, but I've been stood looking at one of our objet machines at work, and something popped into my head,

Has anyone warmed the resin?

Would this fix the flow and thus the hole issues,

I only say this because all our resin machines run warm (60 degrees C or so), the heads can get as hot as 90 degrees C when building, and i can only conclude its to allow the resin to flow easier,
but being as I don't have resin, a printer or a way to test this scientifically I thought I'd ask on here first

Rob

----------


## Chayat

If warming it works for getting the resin to flow would you not also distort the Z as the salt water absorbs the heat and expands?

Or if the whole thing is toasty then you'll need to insulate it all because you'll get Z movement from cooling too.

----------


## Zypher

Ok the whole Peachy 3d printer revolves around the drip raising the level of the resin to prepare for the next slice..you should never mess with the timing the laser itself cures at the top of the saline and bottem of the resin first, simultanuesly curing the next few layers.  That is why the Peachy prints with such little perosity and since the laser is curing so quickly the Peachy is able to make 20 passes where the standard 3d printer make 1 which makes a total hands down winner! I can't tell on the Beta from pictures but on the very first model you see the saline drip is falling freely into the render tank. I think more likely a tunneled resevoir stretching from the top of the saline basin (drip tank) oriented from top to bottem of render tank with open sides would be a more approriate attempt at a fix. This would cut down on surface disturbance and also give the saline an open place to return to the volume of saline below the resin. Since in the earliest model I didnt see this feature, without a Beta model I can't be certain but perhaps the drip itself is spreading on the surface of the the Resin.  Even a minute droplet that enters in the the path of the laser during curing can refract or deflect the beam long enough to create a porous state...As for the linear deformation that occurs evenly almost seamed, I believe they have fixed with a software patch that allows for the Laser to Zero itself at an overlapping point.  But this is just conjecture on my part without actually having a Beta to inspect or test,  :Smile:

----------


## jstrack2

Ijmok: Yeah I think that changing the resin temperature or other adjustments are quite interesting, but I don't know if anyone has really tested it thoroughly. For me personally I am working on a bunch of hacks that change all sorts of stuff so I haven't tried playing with the temperature yet. Also experiments with all different kinds of resins in the future will be really interesting. I could definitely imagine such experiments leading to significant benefits though.

Chayat: I think that this definitely needs to be considered, though I don't think that it should be too hard to address. Off the top of my head I would think that you would heat both the salt water and resin and then if you know the temperature then software could address any size increase. I think water expands about 1% with a 50 degree C increase so the effect isn't giant, but still worth noting. Also if the Peachy later has the ability to continuously measure resin height then this problem would be automatically addressed.

Zypher: Yeah I think that it is definitely important to have the drips go underwater rather than just dropping on the resin. The instructions do call for this and it works well. It is definitely important to have the resin clean of other things. Bubbles are also something to watch out for.

----------


## User_Defined

Has the print holes problem been solved yet? From the update it sounded as though it was a software/programming bug, but there havent been any updates since.

One thing to try would be to run the peachy inside of a sonicator bath and turn it on and off between layers. 
Maybe even sound from an underwater speaker or transducer could do it? Just ideas!


- UD

----------

