Possible hole fix - Drip those holes away!

[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.