Build Your Own SLA/SLS

Hi Makers,

the reason why we all have to struggle with PDMS, Teflon films (FEP), or similar, is because we have built (or purchased) bottom up systems.
The projector or laser diode sits underneath the resin tank with transparent bottom and a non-stick surface (such as PDMS or FEP / Teflon)
and points upwards to cure the resin.

Is my assumption correct, that the only advantage with the bottom up type of 3D SLA Printers is that only very little resin is required,
instead of having to fill a large tank of several liters?

I think the disadvantage of having to fill a large tank full with Resin makes up the with the disadvantage of having to use PDMS or FEP,
provided that you are printing a lot, and need to use a lot of Resin anyways.

Do you agree or disagree ?

Do you see any other disadvantages, or technical problems, if switching from bottom up style to top down style 3D printing?

For me, the big disadvantage to top down, aside from needing way more resin in the vat, is layer height control. With bottom up, layer height can be pretty precisely controlled, but with top down the surface tension of the resin plays a part in dictating z-resolution.

Hey Glacian,

thank you for those concerns.
Do you have any idea as to what kind of minimum layer thicknesses would be possible, with a standard Resin like from SpotAMaterials or FTD or similar?

I am thinking also about one more problem:
As the buildplattform is lowered into the resin, the rod that holds the build plattform adds volume to the resin
and should raise the resin fill level... - Or does the software account for that ?

Also, when the Resin is cured, it shrinks, which again leads to lowering the volume and the fill level,
is that accounted for in the software, or just ignored ?

Haven't a clue, sorry. My own personal experience is only with bottom up...I was just theorizing about top down.

I'm playing around with top-down right now. Liquid control is a bit of an issue but the longer you let it settle between layers, the less of a problem it is. I'm thinking of putting a wiper setup together to test as well. Industrial SLA machines work with a wiper and they control the layer height very well without dealing with sticking to the vat. Part quality is very high compared to the FFF/FDM process - even with the issues I'm having currently.

The biggest problem I am having is resin shrink, which is common to both top-down and bottom-up systems. I'm working with SubG+ right now. Has anybody tried different colored layers. I'm wondering if my pure white light from 6 inches away is just too intense. I vaporize resin when flashing a large flat cross section...

With a top-down set up if you have a piece of glass on the top and allow the build plate to push against the glass would the resin that's sandwiched in between the build plate and the glass form a consistent thin layer for printing without any issues due to the Van Der Waal force like you would have to deal with in bottom-up designs?

Anyone know of sources to read up on both designs with their pros/cons of each design?

I've been thinking...would top down have a harder time with steep undercuts VS bottom up? I figure with top down if you're printing something with a V shape, there's nothing to support the upper layers vs having the vat/gravity to support using bottom up.
-Vaughan

I am using the top down system for a couple of months now with a inverted u as a wiper, the resin is cappilairy pulled into it and delivers resin to the lower areas that are created when the part is lowered 1 layer. Trick is to have the wiper not at resin level, but slightly above it , a few tenths of a millimeter. Best is to lower your object 0.05 mm more then a layer heigth and after wiping let it come up this 0.05 mm. Stabilisation time after this is 3 seconds.

Hi Bendelange,

I can't figure out about the wiper... could you post some picture please?

thanks!

Hi, I made a quick drawing of what i mean by the inverted U, its metal with thin walls, as thin as possible, i made the walls from 0,3 mm steel. The wiper (recoater) is making a single forward or backward move after each illumination. This way the dent in the resin above the lowered object is filled from the resin supply in the inverted U. This idea is not mine, search for recoater in combination with sla. I hope i made it clear, if you have any question, feel free to ask.