Disassembling and Reassembling of the Form 2 / re-calibrating Tank-Tray

[Frew]

I absolutely agree that there’s a great deal of utility in having resources available that show users how to disassemble the machine. I largely want to make sure that new users don’t attempt this as a first step and instead troubleshoot with our team. For less experienced users, disassembling the machine could potentially cause more errors than it corrects.

One of the main reasons we’re unable to provide tray calibration in the field is because vertical towers at each corner provide an imperfect measure of tray level. They have a great deal of utility for other troubleshooting steps but don’t dial in tray level to the level of precision we aim for. For your applications, it sounds like the process has been adequate and I’m glad that’s the case, but it’s not quite accurate enough to achieve our desired tolerances.

As an example of relative measures, the tilt of the tray is calibrated relative to the tilt of the accelerometer. Slight deviations in tray tilt likely won’t cause issue here but it’s something to watch out for. Different positions of the tank relative the capacitive level sensor is a bit more worrisome as slight deviations will have a more significant impact. In any case, I’m excited to hear that this worked for you, and this technique could provide reasonable levels of accuracy. It just might be something to err away from for newer users and factory calibration will provide greater levels of precision.

[fantasy2]

Is the tray calibrated relative to the accelerometer of is the accelerometer calibrated relative to the tray?

From a mechanical point of view, there is a fixed position of the build platform that can not be calibrated in any way, as the holder, arm and linear slider are all fixed and assumed reasonably perpendicular. So this would be the reference point/datum.

From there you have the resin tank where the PDMS needs perfect alignment and be parallel to the build platform or you will cure an uneven layer of resin. This should be the biggest influence factor on accuracy, taking into account that you didn’t touch the calibration of the Z axis and optics(not influencing laser focal point).

From there you would have to align/calibrate the accelerometer to the resin tank, to make sure the resin is perfectly level, as the accelerometer is on an undefined space on the PCB which is mounted to the bottom of the machine.

Then, when everything is level, you need to lower the build platform relative to the capacitive sensor so it senses a full tray… this is in my opinion less critical.

If you have print layers of 25 micrometer, you might desire and accuracy in parallelity of 1/10th of that, which I fully agree is not possible to do with a standard calliper(check the datasheet on accuracy!) and you need to make an accurate measurement block to do this. I could imagine you guys have a block with dial gauges(or some other electronically measuring magnetic sensors) on each end. For us end users we could do something fairly simple: calibrated, spring loaded pins that make electrical contact once touching the build plate. This technique is used to calibrate industrial machines as well.

Correct me if my order is wrong, but this is how I would do it.

Anyway, @Jens_Schnabel, thanks for sharing the video’s! We had a very bad resin spill, all electronics, steppers, gears and sensors were filled with white V3 resin after the parts broke off mid-print. We managed to completely disassemble the machine, rinse it and put it back together without much trouble. -> Not something I would recommend for the casual/regular normal user!!

[rodrigo_antonio]

Very Good !!!

[Jens_Schnabel]

Accelerometer - The Machine level sensor has nothing to do with the absolute accuracy of a built part. Which is what’s at stake when “messing” with the tank-tray as I call it - there is the carrier, which is mounted to the optical housing then the tray that holds the tank, which is the only part that can be adjusted. Just to clarify my use of words.

The machine level sensor or better it’s display is not particularly accurate as the system accepts the machine to be level even if the small circle is not dead center. Even if it looks to be dead center visually, it still can be off slightly, since it’s a visual calibration in the end… so we have an inaccuracy here already.

Further the accelerometer has to be calibrated to the building platform not to the tank. The building platform is fix and therefore the only reference to the accelerometer, and tray. The accelerometer is dialed in by the factory so I assume it is right on out of the box, if that is so this won’t cause any problems when re-calibrating the tray as everything else stayed the same (Machine level sensor, laser unit), unless it’s been “messed” with.
Possible that when reattaching the base plate it won’t be in the exact same position as before therefore throwing the accelerometer off. Unlikely and if it’ll be so slight that my machine didn’t detect it.
The Z-Axis is fix, the carrier is fix, the PCB is fix - as you say @fantasy2 we assume the Z-Axis is perpendicular to the PCB and all other horizontal planes (to absolute precision).
I also assume here that we have an accurate PDMS layer - if we don’t that is not too critical as, again the tray can be adjusted to a slight imbalance, unless we have “waves” within the PDMS, which can happen but is unlikely within such a small surface area. This however is another point of possible inaccuracy. The play of the Z-axis and the tank unit within itself is rather small but there is some play, not so much the tank unit, but Z-axis. More potential inaccuracies.
The Form 2 still kicks out some layer shifting, right out of the box, rarely but it still happens.

Having this said - it is important to have the machine level or else we might encounter a resin level imbalance, which could cause spilling, therefore the accelerometer. If the machine is not level it won’t work - or better if it’s not level enough…
For the machine to spill resin (without parts or particles floating around) the tray would have to be off by quite a bit, we’re talking millimeters.

Yes @fantasy2 essentially the final calibration is the distance PDMS surface to build(ing) platform. Even with my crude calibration techniques. Let me add here that my brother bashed me for trying what I did and wanted to drag in his calibration equipment - he also was the one checking the PCB and resin sensor board in the video - I wouldn’t know where to start looking if I had to test the PCB myself or any other circuit board for that matter, so I do have some good help if needed in that field.
The machine nevertheless was dialed in with my crude tools as this is what I wanted to test. Most don’t have any calibration equipment and for those this is a possibility to get the machine back on track. The final question, which I don’t seem to get an answer for is how close is this calibration. Far off or not quite accurate enough to achieve the desired tolerances (that doesn’t help) what are these tolerances @Frew? I understand that you most likely are not allowed to tell me (us).

Of course I agree 100% that with my crude ways I won’t be able to get it dialed in to absolute perfection.
The machine - as all machines, operates within a certain window of accuracy - that window starts at a certain point and stops even if the machine can be dialed in better. The question here is how far am I away from that window with my crude way of calibration - it looks like I am at least close to it, judging by the parts it kicks out.
Thanks @fantasy2 for the numbers - 1/10th of 0.025mm I am not so sure if the machine can be dialed in to that then again maybe it can, maybe even more accurately …@Frew?
In any case thanks for chiming in here @fantasy2 - crazy the spilling on your machine - I heard that from a few people - I did have one part breaking off but luckily no spilling even when resin was stuck on the PDMS. The new tank is apparently spill proof…and lasts 20 times longer - i want to see that - 20 liters instead of 1 (which is typically what I get out of a tank 1-1.5 liters), that would be something!
I did have the resin sensor error and I also get - off and on - the no resin cartridge error, even though the cartridge is inserted…and we are talking about accuracy here…

Here is an Optical test, using a file my good buddy from the support team sent me. There are 2 tiny parts on there which I need for my latest project - no problem for my machine as “off” as it is, to get this optical file done “perfectly”.

[adzaroo]

can you post the calibration spheres you used in the corners?

[Jens_Schnabel]

The ones I used in the beginning of the video? Those are elements I took from a model I was working on. They are basically half spheres with an outside ring attached to the flat side and rather useless compared to Formlabs’ optics test file.
I suggest just using Formlabs’ test file instead.

I tried to attach the optics file but it’s too big in terms of file size. Ask Formlabs’ support for the optics test file, they’ll be happy to give it to you.

[adzaroo]

i ended up printing 10mm cubes and got them calibrated within +/- 0.25mm.

This inaccuracy should only affect the first few mm printed right (i.e. only the first few layers should be distorted)?

thanks for posting your video.

[Jens_Schnabel]

You’re welcome (for the video)
When you say +/- does that mean you have a combined difference of 0.5mm? If so try to get to a maximum of 0.25 all together. Or simply test your machine with a good part and see how well it comes out. Every machine is slightly different so what might be the right number for me might not be right for you. Once your machine builds a good base and connects all supports properly you’re in the right ballpark with a good working machine.

[rodrigo_antonio]

Do you have these print test files?

[Jens_Schnabel]

Antonio,
I have the file but it’s too large to upload here - but you can go to Formalbs’ Customer service and ask them to give you the optics test file (which is exactly what I ended up using), they’ll be happy to do so.
You can also simply make 4 small cubes in your modeling software and place each in one corner of the building platform. That’s besiclly all it is. Let the machine go and you’ll be able to measure each one and adjust the machine accordingly.

[Chris_Estelow]

OPTICS_Test.form (274.2 KB)

Optics test file attached.

Chris

[Jens_Schnabel]

Chris,
thanks for uploading the file.
Interesting that your version is only 274KB mine somehow is 5 times larger (1.1MB)but show the same objects as I checked briefly (4 columns and the center object). Byt that’s the one.

[Chris_Estelow]

I was a little confused when you said the file was too big…LOL, Just for your reference the file I uploaded was supplied to me on 2/1/18. When did you get your version?

Chris

[Jens_Schnabel]

August 16th, 2017 is the date on mine.
Jens

[rodrigo_antonio]

Many thanks for submitting the file!

[eaelec]

I found a much faster way to align the corners of the tray carrier with the build platform:
A. Remove the resin tank.
B. Set the printer to open mode.
C. Start a print, the build plate will come all the way down.
D. Unplug the printer.

Now that the plate is stopped at the bottom, get out your trusty spark plug gapping tool,
set the tool for a 7.5 mm gap. Adjust the gap at each corner by inserting the tool between the tray carrier and the bottom of the build plate, then adjust the screw at the same corner. You will need a #10 Torx Security driver, not a plain Torx and you should go around more than once because each adjustment can affect the other corners.

At this point I printed a test file which is shown below.

The result I’m getting is 4 good pyramids on the corners but the center pyramid doesn’t print, just leaves one layer stuck to the bottom of the resin tray. That’s the problem I will tackle tomorrow. Any suggestions?

[eaelec]

Increased the gap between the build plate and the tank carrier to 8.4 mm in several steps and it had no effect, corners still good, center still bad. I checked the optical window, the main mirror and the acrylic window on the tank, can’t see anything wrong. I’m beginning to think the PDMS layer on this tank has been damaged in the center.

[wimvanvlasselae]

got it solved?

[eaelec]

I had even bigger problems to deal with, see here:

This is definitely going to void your warranty

The resin tank contacts on the carrier plate of my Form 2 had been gradually failing. It got so bad that just closing the lid on the printer would cause it to lose contact with the tank. Then I would have to pull out and re-insert the tank numerous times until contact was restored. Then one day it failed and no amount of pushing and pulling could fix the problem. So … Top of Carrier Plate [carrier_plate_top]

I have switched over to a new resin tank but haven’t tried printing any part with long rafts like the ones that failed.

[eaelec]

Looks like a new tray did not fix the problem completely: