Flat bottom parts need supports?

New to SLA and Form 1+ and I have only printed a couple parts so far. One of the parts was basically flat, so I chose not to use supports and it came out just fine.

I read where if I don’t use supports, even on a flat part, it may be dimensionally inaccurate. What would make this difference between a flat part using supports, vs. the same flat part not using supports?

I print many such parts and would really like to do this without the added time and materials - and extra finish time

Happy New Year 2015

Hi @Carter_West,

Great question.

Some prints come out fine with no supports printed right on the build platform. If your parts work, and are dimensionally accurate enough for your purposes, feel free to print with no supports.

Larger parts often print better with supports because you can angle them to minimize the area of each layer. Layers that have smaller areas are much easier to peel from the tank, and often, this results in a better print.

We also recommend angling flat prints with supports so that resin flow is optimized and so that resin does not end up “pooled” on flat surfaces during the print, which can result in lost details. If flat works for you, by all means print things flat!

You must be very conscious of layer area and resin flow while printing with an SLA printer. Often, you can optimize these (and subsequently, the quality of your print), but angling a part with supports. There are benefits to each method of printing (flat, directly on the platform vs. angled with supports). As you experiment more with the printer, you will learn when each one is best.

Hope this helps,

You will probably need to adjust your model some since there are compression layers. From what I understand the exact thickness varies between tanks and maybe machines. Mine runs at .022" which i pad the bottom of some parts that need to be flat based on 25µ and a little more with the 50µ. I have had problems with layer tear and blowouts on objects exceeding 1.25" dia. that had rims or details inside. Raw resin trapped in an area as it compresses may blow out the sides usually the side opposite of the hinge.

First, thank you Aaron, excellent response.

How very interesting Ken. I in fact just printed two parts that ‘should’ measure 4.5mm in the Z. The X and the Y are measuring very close indeed, but the Z is coming up .5~.7mm (roughly your .022") short. I guess this is on account of the resin flow that Aaron was explaining.

You say you ‘pad’ the thickness to compensate. Is that done in the CAD model, or is that done in the fine tuning?

Many thanks guys!

Compression layers are the first few layers that are pressed more to make them stick more to the build platform. Without them the model may peel off the build platform or simply fall off.

I did a step block test and the printer compensates for this over a distance, longer the piece the more accurate it seems though my test was done at 100µ layers which will cause some inaccuracies.

For low profile objects such as items under say 1/10" simply pad the bottom of the object in your modeler by the difference as long as the bottom isn’t critical or require any detail. In my case I make challenge coins and other flat items and I print both sides as halves then with a 404nm laser pointer I fuse them back together with some raw resin.

The supports base pretty much zero out the models accuracy and probably why Formlabs tries to edge people to use them rather than printing flat.

If your object has a rim and recess in the middle it may cause blowouts as the raw resin is compressed and trapped within the cured rim. If there is a blowout you will most likely see it on the non-hinge side where the forces will build up the most. So try if possible to have the more fragile side towards the hinge.