Possible hole fix - Drip those holes away!

[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 90^o 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 90^o 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'spermissivity, 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 90^o 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.

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

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.
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.

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.