Build Your Own SLA/SLS

Hi all,

I have been building bottom-up printers for the last two years now and still having issues with peeling. Tried a lot of different things with only average results and things get even worse or impossible when going big. All these issues seem to vanish or become obsolete when switching to the top-down concept. Almost all of the big companies only offer the big machines with this concept as it was invented 30 years ago. So in the end, for the moment, I think top-down has more advantages than bottom-up.

As I am completely new to top-down systems -> what are the typical problems I'd have to face? I'm interested in any kind and like to build a small list!

I bet there are more than:
- consistent layer height only possible with wiper
- needs a lot of resin (when not using another liquid where the resin floats on)
- reliable resin level measurement
- a lot of mechanically moving parts
- pigment settling

Thanks,
radi2k

Hi,

No one every worked with top-down or never built such a printer? I bet there are many people out here that have a good knowledge of that concept but are too lazy to answer So please give me some suggestions, tips, ...

Thanks,
radi2k

Ok, I'll bite.

I found top-down to be messier, the smell of the resin was stronger, the surface of the liquid has to be perfectly motionless so walking around the printer can impact layer accuracy. I also found layer height to be more difficult to control. I like to store my resin in the bottle so it doesn't stink up the whole room, doing that with a top-down system is tedious.
Setting up an automatic liquid level control (whether it is passive or using some kind of sensor) is an extra step I didn't want to deal with.
Setting up a wiper is annoying, and waiting 30 seconds for the resin to settle between layers is also annoying.

It is easy to get a top-down printer working, but it is hard to getting it working perfectly.

That's my take anyway, others will have different opinions and experiences. You should try it and let us know what you think!

I've switched to a top down print setup, and i've found the following issues and work around's

Resin surface tension that effects the layer height: I run a resin heater to keep the viscosity's consistent between printing at different times during the day / night, I aim for 25 deg C and use the following external controller

This will help with consistent results for your given resin

Wiper system: I've set this up on the X axis and uses the tilt control in creation workshop, setting this up as a short stroke distance, so it keeps the wiping time to a minimum, I see people don't like to add this complexity to their setups, but if you have the ability to build a diy printer, then this shouldn't be an issue.
The best part about a wiper system is you don't have to worry about the different resin viscosity's at different temperatures

Resin print level: In my resin tank it runs a overflow system (a hole 10mm down from the top of the resin tank) to maintain a consistent surface height as the build plate moves deeper in the resin and displaces the resin.
The overflow is connected to a fishtank pump and recycles it back into the resin vat at a slow rate, the pump is controlled by a PWM motor controller.

The pump returns the resin to the bottom of the resin tank, via a aluminum tube (bent to suit), this also solves the mixing and pigment issue, as before printing, I run the pump at max and the heater to mix the resin and to bring it up to temperature, before printing.

Needs a lot of resin: the price of resin has been dropping a lot since the wide spread uptake of DLP printers, I'm in New Zealand and I can land resin here for $50 NZD per liter, my build tank is 6 liters to fill so its quite cheap when compared to the total printer build cost, and its just a one off cost for that resin.

Smell: this is a problem, I've built doors on the printer with red polycard, this is to try to seal in the smell and keep natural UV light out, I've added intake and exhaust fans that vent to outside, but this only helps so much.
Best bet would be to build an air sealed room / space for it, with an external vent / breather pipe so it pulls the air from the room like a chimney.
Seems excessive, but until there is nil to low odor resin is available

Future plans for my printer is that since DLP printing is a resin, it allows adding of external additives to change the printed items mechanical properties, like chopped carbon fibre (30um - 50um), aluminum or titanium spheres (15um - 50um), much like how composites like carbon fibre etc work.
By adding the pump, temperature control and wiper system, I'll be able to keep the viscosity high (thick) so I can slow the material from falling out and settling in the bottom of the resin tank, by continual mixing at a slow rate during printing.

I think this is were DLP printing will really be the 3d printer of choice, for strength and prototyping as the resin allows for adding of external additives and when fully cured the layers are completely interlinked.

Ill post some photo's once Ive ironed out my current printing problems

Thank you so much for your answer danthehuman!

I'd be really nice if you could share some images anytime soon. I'm still on that project!