Many of my models are coins, lapel pins and generally flat thin parts. Printing flat without supports gives me a superior surface finish but I have to scale the objects on the z access to compensate for the initial compression layers.
Printing these on the edge or at a slant with supports cause all kinds of poor results because of the thinness of the objects.
If supports are not used and the part is less than .xxx in depth could you have it not compress the layers or only have it automatically compress when supports are used?
The skewing is the mushrooming from the initial compression.
Here is a pic of a job I’m working on, I’m having a hard time trying to compensate for the thickness difference but you can see how clean the background is. This will make a really nice mold and the metal will polish up nice.
My other option is to model the halves on a post or cylinder almost the diam of the final part that I can mount and trim off in my metal lathe. Not a big deal for me but most people don’t have metal lathes floating around to do this. Print time will be much longer and material use will be higher. But seems to be the other only work around.
So contrary to how it may seem this is a complicated topic. The problem is complex enough that formlabs does not support printing straight to the platform.
To fix the compression there is a tool under fine tuning options celled z-offset that you can use to remove some of it, however when I asked if they would allow it to adjust more so I could remove more compression they said they wouldn’t do that without giving any reason, so you can only fix some of the compression.
The next problem is that the objects print skewed. The amount of skewing varies from machine to machine and can be quite bad on some machines. This is because in their calibration process they make no attempt to make the tank and build platform parallel. They only calibrate the laser to draw the layers correctly on the tank. Then use the softness of the PDMS to cram the platform down into the tank resulting in compression and a base thick enough to absorb the resulting slop. This means anything printed to the platform will show the effects of this slop in calibration, all you can really do here is hope you got a fairly well calibrated machine, which in my limited experience is unlikely.
The next problem is holes building pressure pockets. This problem is a problem for any print but is significantly exaggerated on the early layers with all of the compression. The problem comes when there is a closed pocket of unprinted area surrounded by printed material. During the peel and return process the pressure in this pocket fluctuates quite a bit and the result is that a path from this pocket is often blown out. This happens less on overcured parts of the print, however Formlabs refuses to give us any control over how much curing we get so you can’t use that to your advantage. I’m also fairly sure regulating peel and return speed would help but Formlabs refuses to give us any control over that as well so that won’t help. This leaves trying it and hoping it works.
Depending on what exactly you want to accomplish there are a couple more considerations, but the ones listed above are the main ones.
That is interesting. maybe I’m lucky because even the thinnest of prints have been really accurate in thickness, No sloping that I could see. I guess my other option is to build may own standoff and mount the model on that allowing me a post I can mount in my lathe and part the final from that.
I seem to have more failures with their auto support system resulting in tons of artifacts in the resin that I then need to screen out. I have much much better results manually adding supports and orientating the model so the longer supports are towards the hinge side.
What is disappointing is I had a part printed by Formlabs under the assumption this wouldn’t be a problem then proceeded to purchase the machine based off the sample print.
If I had known this to be an issue up front I may not have purchased the machine in the first place.
In the meantime I’ll try some more workarounds. Really not a fan of the supports generated by the software. Most likely I can model something better.
I agree with @RocusHalbasch, the supports are also very important for less obvious reasons like the error mitigation he mentioned. Have you tried printing it straight up? Normally this is bad advise but for a coin shape with very little relief on the face this might be good advice. Just be sure to put the supports thick near the platform and wider further away to ensure a good start. Then I would finish with some light sanding on the coin’s edge after removing the supports.
This orientation would prevent any support marks from being on the back of the coin. And sanding on the edge should be far less noticeable.
Printing straight up creates the worst finish on a flat. Not all layers are even steps, some bulge more than others. I did that as a quick run off of the coin and had the same results on a very expensive Polyjet and Objet. The post finish work is just not reasonable.
I have a manual support structure that should resolve both the possible bubble issue that I haven’t had any issues printing flat as well as allowing me to be able to part it on my lathe.
Coins typically aren’t that thick or big so flat is giving me the best results.
Layer bulging is normal, it sounds like the finish you want is beyond the Form1+ abilities. And by printing it flat you are getting blowouts above the letters A, M and N in the word tournament. You could fuss with the thickness of the model until it is perfect, print flat, and repair the blowouts… would that work for your needs?
I don’t mind the minor repairs on the letters, very easy to repair these with raw resin and my uv pointer. What is impossible is to sand out imperfections on a background on this type of art.
I have a support I am going to try that doubles as a fixture I can part on my lathe, haven’t had a chance to test it yet, just so busy.
I agree with you that what you are trying to print is best printed flat. I’ve been back and forth with Formlabs about the lack of support for printing to the bed, because of how superior the results are for prints like yours. However they really don’t seem to understand that their just print it tilted with supports no matter what advice results in significantly worse quality for some cases
Since your tray and your platform are almost definitely not parallel some areas of your printing surface will print with less compression. If you figure out which way your tank leans you can find which of the four corners of the print area has the least compression, hopefully for any tank if you print straight to the platform in the corner with the least compression the z-offset feature should be enough to eliminate most of the compression.
Another option if thickness doesn’t need to be exact and you don’t mind a bunch of work is to print flat with supports. The finish on the back of the coin will be awful at first, and getting it off of the supports will be tedious, but with a good amount of sanding it can be made nice and flat.
I tried flat with supports as well as a test yesterday that had the object on a 5’8" hollow post that I could part on my lathe and both prints failed horribly.
Seems anything under 1/8" directly on the platforms works the best.
Maybe I am really lucky but my tank seems to be dead on flat all around. Wondering if there is a variation between tanks where the pdms isn’t perfect on all tanks?
I’m on my first tank and it seems to be holding up really well so far. If there are variations on the PDMS I’ll probably go and re-coat my tanks as I need.
For the small flat items, for now I’ll just adjust my models to compensate for the difference. These parts just need to look good and tolerances are pretty loose. X,Y accuracy is really nice on this machine, so far the edges all match up to my gates perfectly.
Are you at least using z-offset? You could ask Formlabs to increase the z-offset range maybe if enough people ask they will do it.
As for the tanks they do vary some but mainly only in thickness. You are lucky your platform is nice and parallel mine is only about 0.4 degrees off but that makes for a very noticable difference in thickness of objects printed in different areas. Anyway another possible solution is to replace the pdms in your trays with a thinner layer, it would take some trial and error and the z-offset for fine tuning but should work.
I have a feeling there is a variation in the PDMS thickness between tanks or batches of tanks made. Maybe they are not all perfectly level. I don’t know because I am pretty new and only have the 1 tank at the moment. Doesn’t seem that difficult to re-coat them and with the z fine tuning shouldn’t be a big issue.
Ideally level adjustment screws on the tanks platform to fine tune the tank to build platform would be the best option. Simply lower the build platform and gently snug the tank into place. Maybe something the could consider in the future if this is the case.
As far as the compressed layers the model is actually distorted at the bottom portion so scaling sort of works to get me by.
There is definitely variation in thickness of different tanks, however they all seem pretty level. However I have measured using an inclinometer the difference in angle between the platform and the tray housing on all 3 machines I have had and all 3 have been off.
As for level adjustment screws that would work if they calibrated the machines so the lasers drew the path undistorted on the surface of the platform, but unfortunately from my discussions with them I’ve gotten the impression they calibrate them to draw it undistorted on the surface of the tray. This means if you adjusted the tray to be parallel with the platform you would introduce distortion to your prints. Which is a real shame as there already are screws you can adjust to level the tray housing. There is even a YouTube video demonstrating the process.
My other thought is maybe the build platform walks just a little and it isn’t the tanks so much.
I had to adjust the tension on the lock clip already on mine. If that isn’t parallel then you would have the skewing. To me that seems more like the culprit rather than the tank being off itself.
If thats the case then it would be easy to use some shim stock between the aluminum and head to tweak the size.
Still want to be able to turn off the compression layers when no supports are used. Sounds like the easiest fix.
Yeah with just rough measurements with my inclinometer in the past, it seemed if you assume the column housing the threaded rod runs reasonably parallel to the z-axis that the plane of the platform was quite close to perpendicular to the z-axis, while the plane of the tray housing was not.
The important thing to avoid skewing is that the planes are perpendicular to the z-axis. I’ve explained they have not been on any of my machines and Formlabs has assured me this is all compensated for in the calibration process, and that this process takes place both in the factory and in the software, but they can tell me no more. I can detail more of the extensive conversations I’ve had but to some it up after much poking and prodding and extracting data that May or may not be correct I’ve come to some theories about what they do to 'calibrate" these machines but they refuse to admit or deny any of it. One thing they have openly admitted repeatedly is that making the platform and the tray parallel is not a part of the calibration process, and they don’t even really try to do so.
If your platform is loose tighten the screw in the top some it should be snug and stable. I will check my measurements again tonight. You can check your machine pretty easily if you would like. Most smartphones these days have bubble level apps if you don’t have a digital inclinometer.
Four of that model, one in each corner, should suffice. Also my tanks have definitely varied in thickness, but only slightly. Also like I said they all seem to be really even thickness. I also rechecked my machine with my inclinometer and the plane of the platform is quite close to perpendicular to the z-axis, while the plane of the tray housing is way off so it is definitely the tray.
Yeah although the variation in height due to tanks being non-parallel is a bigger problem. I’ve only seen about 0.2mm difference in thickness across about 5 tanks, however there is about .85mm diffrence in thickness between different corners of my print area. So they need to compensate for slop from calibration more than variation in thickness.
