Z-axis always too big (mostly by factor 1.3)

Hi to ereryone…

ervery print is perfect in x or y axis. But in direction z (height) all layers seems to be between factor 1.3 … 1.6 too big. E.g. an object with 1 mm height is 1.3 mm if printed in 0.025 mm resolution. The same object (multiplied in PreForm" by 2) is then 3.3 mm height and not ‘only’ 2 mm. This is reproducible.

The effect will happen regardless of the resin (I have tried white, black, clear and grey resin).

What to do? Are there any calibration steps needed/possible? Is this an expected behaviour?
Remodelling by a calibration factor of 1.3 of my modells is not an option - i need them as a proof-object of the given 3d layout.

Regards, Martin Bauer

Remark: I do not use “supports” - i print it always directly onto the build platform.

(I use a special wax and a liquid (after it is not wet any more) which will seperate the platform from the object by a thin layer which can be washed away with water.

What is this wax and liquid technique?

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In general, the procedure is:

  1. calculate the scale (to be set in preform on a per-pbject basis) to use to get the Z output physically correct.
  2. compensate for x and y in the preform fine tuning section.

Now, for every part you print, you’ll need to scale it by the factor you determined in step 1 above. The x and y settings will persist.

If what you meant is it comes out at 2.3mm instead of 3.3mm the problem is likely that your platform height is about 0.3mm too high.

Go to Help > Fine Tuning > Platform Height and use the slider to lower the platform 0.3mm.

The amount the platform is spaced from the tray can vary pretty heavily across the build area is they aren’t parallel. To check the difference across it all I use the following test print.

All four squares are supposed to be 2mm thick. Just print it and adjust your platform height till all four are as close to 2mm as you can get them. If you do use it please report back your measurements I’m always curious what they are on different machines.

What is this wax and liquid technique?

It was invented from manually work with resin and a negative-form which must be protected. The ‘negative’ form of the original model is at first waxed (cere) and then covered with a thin film of liquid which will seperated the resin from the model after it is dried. This stuff can be bought from the typical warehouses selling resin.

So it is very easy to pulling away the printed form from the build platform - and (like my case) i won’t need any supports and get very flat surfaces on the bottom of the form.

But - there is a negative thing: If you use too much wax or your form is too heavy - if could fall down and/or warp away while printing. So - you have been warned! But don’t worry - everything what will happen is that your printed form is lost.

uhhhhh … bad thing…

No. It has a scale factor and not a ‘single’ offset.
I played around with this height setting - but i does not help.I have now seen another interesting thing:

It is happening if i print it in 0.025 res. in 0.1 res. everything seems to be correct - so far …

IIRC, z-offset is used to fine tune platform compression to the PDMS layer, and not to make the z scaling/accuracy correct. I could be wrong here, but that is what I believed it was for. I have had to use it get support bases to adhere to the platform, and it does work for that, so that is the basis for my reasoning. I can’t imagine having to decide between adhering or being accurate.

Anyway, I went this direction instead. Using this model,

which is 10cm in x, y, and z, in 1cm steps

Using the xy+scale method I mentioned above, I’ve tuned my machine to about ±.0015 throughout that envelope. The model is printed with X and Y zero’d out, but z-offset can be whatever you need it to be (for good adhesion) @ 100% scale. I used an excel calculator I made, where I caliper every step dimension and plug these in. I then average each axes. I’m using Z is the datum dimension, and it is scaled to be correct. X and Y scaling is then calculated, and these are entered in the fine tuning.


The PDMS is a little compressible, and the entire build tank is suspended on a spring loaded mount. So the build plate can actually start at a “negative” Z-height that’s below the PDMS surface “zero”. Until the printing Z-Height has increased to a layer that’s above this zero point, every layer prints with minimal or possibly zero thickness. The final print will come out a a lower height than it’s supposed to.

If on the other hand your build plate is already too high, objects will come out too tall because the first layer printed it much thicker than necessary. But. If you change the Z-Height calibration the thickness of that first layer is going to change in proportion to how much you change the calibration. The no-base-or-supports-print’s Z thickness has to measurably change if the Z calibration measurably changes.

If you’re printing directly on the platform without a base or supports, the Z-Height adjustment has to make a difference to the final height of your part. If it didn’t, it’s because you didn’t change it enough to be within your measurement accuracy, or the build platform is still too close/low to the PDMS because you moved it in the wrong direction or by not enough. There’s no other possible explanation (at least, that I can think of).

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Thank you very much. I’ll will investigate this. In fact - all my pritings arenot so tall (1 cm -. 2 cm) - so a z-axis starting problem could be an correct answer to my problem.

Considering you height is usually quite small and the problem only occurs at 0.025 this really sounds like the Platform Height. 0.025 is worse about this than 0.1 because it has more layers and even wIth compression they deposit some material.

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