Build Your Own SLA/SLS

My prints, they print out squashed, like by around 15%, using the FEP Vat. Using the Petri they print out perfect. I did not change the build size. I don't understand what in the world could be happening. Anyone else have this happening? Any ideas?

X&Y or do you mean Z?

I've just found that retensioning the vat shifts the vat floor down, so I need to recalibrate the size. Not entirely sure the FEP isn't still stretching either; wonder if working with a thicker film would be sensible?

As far, as I know, FEP Vat's base are higher than Petri dish bottom. So, there is no way to print at same focus distance as with Petri.

I want to buy closeup lens for my Acer P1500, to solve that issue.

I thought the build plate determined the size? Now I am confused.. Anyway x,y is squashed. I guess the question is, when using the FEP vat what needs to be calibrated since the vat floor sits up higher than the petri. How do you determine this?

The build size in CW coupled with the Z height that the build plate sits at rest dictates the final size of the model; focus needs to change if you change the height of the build layer too. Look at http://www.littlerp.com/?page_id=55 (Calibrating Printed Object Sizes) for more detail (and cal object STLs).

Maybe I should chime in here.

The flexvat "focal plane" sits approximately 21mm above the LittleRP base plate. As noted above if you just adjust focus the image on the focal plane will be larger than on the petri dish (xy resolution is lower = resolution in microns is larger = bigger pixel size) so your xy resolution in microns would go from, for example, 35 microns to 42 microns but you vertical resolution must also match (must go from 35 to 42 microns or your model will be squashed). With the flexvat you can print larger models at slightly lower resolution but your new xy build size in CW must match the actual projected image size if you do this the z axis will be correct. All of this is pretty much automatic when you adjust the build size in CW (actual projected image width by image height). If you adjust your image to be the same size on the flexvat as it was on the petri dish (by using the projector focus and zoom) x y and z axis settings in CW do not need to change but you will probably not be taking advantage of the larger build size.

This post gives you information that allows you to control your build resolution and model sizing for any sized build area:
http://projectsinterestsandetcetera.com ... -workshop/
This post was written some time ago for a previous version of CW but the basic procedures are the same.

A note:
The gasket clamp bolts on the flexvat should be tightened all the way down until the gasket is fully crushed, this will allow you to put a considerable amount of tension on the FEP film using the tensioning bolts. The tension on the FEP film should be high enough so that when your build plate drops for an exposure any slight downward bulging of the FEP is squeezed out before the exposure is made. The FEP should be quite rigid and should make a high pitched drum sound (almost bell like) if you tap the side of the vat with your finger.

And since I'm on a roll here, more notes and maybe a tip or two:
The base layers tend to be critical for making sure your model sticks to the build plate, you can make extremely long base layer exposures but only if the layers are thin (I would say 100 microns max). If you try to make a long exposure on a very thick single layer the resin can get so hot that it can reach the FEP's melt point (about 260C, 500F) or the temperature that the FEP will begin to sag and you will ruin or damage your FEP window. You should take care that the build plate and FEP are as close to parallel as you can get them and that the FEP is taught if you are going to make long base layer exposures.

A trick I use for particularly difficult models is to paint the build plate with a thin coat of resin with a small shop brush and cure it with a uv light source before printing. I use an old dental curing lamp but a $15.00 ebay uv flashlight would probably work as well. You will probably want to print on supports if you do this or you risk breaking your model when you try to remove it from the build plate. Also, the uv curing lamp is useful for repairing imperfections or damage on printouts (toothpicks and small brushes to dab resin on the problem area, sandpaper and diamond files to clean it up)

The best money you will spend all week: http://www.sciplus.com/p/SET-OF-10-6-OV ... ILES_51826

BTW thanks to all that purchased the vat (40 and counting)

HTL

Thanks HTL for your concise write up. Z is the squashed plane not x,y my bad. I am still processing the info, but I am sure I will get it figured out. Great job on the FEP vat by the way.

I think you can get your setup corrected quickly by using the following information as a template.

make sure your image is in focus and square, there are tips on this in the link I mentioned earlier.

measure the width of the image (a cheap harbor freight digital caliper is perfect for this), do not measure the height, always measure one dimension and calculate the other.

lets say as an example that the image width measured 70mm

for a high def projector (1080 x 1920) do this:
divide 70 (the width in mm) by 1920 (the projector width in pixels)
this gives you 0.03645 Which is also your resolution (0.03645 mm, 36.4 microns)

multiply 1080 (the projector height in pixels) by 0.03645
this gives you the image height 39.375 mm

In CW (Build Size mm)enter 70mm X and 39.375mm Y and a slice thickness of 0.0364 (in Slicing Profile, I round to 4 decimal places)

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for a low def projector (1024 X 768) with a 70mm image width:

divide 70 (the width in mm) by 1024 (the projector width in pixels)
this gives you 0.0683 Which is also your resolution (0.0683 mm, 68.3 microns)

multiply 768 (the projector height in pixels) by 0.0683
this gives you the image height 52.454 mm

In CW (Build Size mm)enter 70mm X and 52.454mm Y and a slice thickness of 0.0683 (in Slicing Profile, I round to 4 decimal places)

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CW should take care of the rest.

FEP Vat's base are higher than Petri dish bottom.
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