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markotjo

Calibration of the X and Y axis

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Hello

I'm mark and with some students we have bought a ultimaker original in November. since we have printing a couple of things we discovered that the dimensions we want arn't right. For example I printed a part that was 50x50x10mm. When the print was done is was 49.1x49.1x10. So Z axis is good. Since we want to produce some technical prints we hava a problem with it. I was looking on the internet to solve this. I found some ppl with formulia's and such. I understand the formulia but where can I put this number then? Also I read somethings about the marlin firmware. But i don't understand how this works. Can someone tell me this?

 

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I think the recommended approach would be to use Cura to rescale the object in the XY direction. See "Scaling your object" here: https://www.ultimaker.com/spree/uploads/38/original/Cura_User-Manual_v1.0.pdf

The firmware has a mapping of (stepper) steps per unit distance (mm I guess). However, I've seen in another post that the UM person (Daid or possibly SandervG) recommended not changing them.

If you really want to change them, I think the three ways to do so is:

Through the ulticontroller if you have it

Via the start gcode using (I believe) M92

Modifying the firmware defaults and rebuilding it.

I think the default steps per mm is correct but the difference you see is due to shrinkage. I think the reason why they recommend you don't change the steps/mm is because different materials or the same material from different batches or vendors will shrink a different amount.

Also, the issue with any of the three ways above is that you cause the XY axes to move every so slightly more than Cura expects when it calculated the volume of material to extrude. So you will have an ever so slight underextrusion. When you scale the model, Cura adjusts the extrusion rate as required.

So try scaling the XY axes with a factor of 1.018 or 1.019 and see if the size measures up.

And in case you are wondering, I think the reason why the Z axis is accurate is because as the layers shrink, the layer above is constantly compensates for the shrinkage when it is extruded. Until the last layer which in and of itself doesn't shrink a measurable amount. However, in the XY direction, no such compensation occurs.

 

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All the issues above are true and in addition you may hit the end stops early if you print something 205mm long in X or Y.

So best to scale in Cura.

There are many other accuracy issues - the biggest issue is with vertical holes that is caused by 3 factors (shrinkage is only 1 of the 3 issues with holes). The best solution in this case is to print twice - after the first print measure everything and then adjust the cad file by the error.

With experience you can get it right the first time in CAD for your particular PLA and print settings. But simply changing the qty of edges in a circle in your CAD will change the size of the hole and there are other issues that you have less control over.

 

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Thank you all for your help.

I tried to scale it up and 1.02 is fine and works perfect! my product is now in the right size so it was the shrinking. The only part now is that if I remove the object from the bed there is a line that was laying on the bed. That line is a little bigger then the rest. But I can remove that line.

Thanks you very much

 

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there is a line that was laying on the bed. That line is a little bigger then the rest

 

Your leveling is slightly off then. I recommend the bottom layer is .3mm to reduce the sensitivity to levelling. Anyway you want to level slightly higher than you have been. This is very quick as your 3 screws you don't need to touch most likely. So do the procedure, set to very roughly 1mm in first portion then continue continue until time to insert paper in the back - make it so the paper feels a little tightening but not much - less tightening on the paper than you tried before. Or maybe you used paper too thin - it should be normal copy paper. Then skip right through the front two screw leveling steps.

Again - you can do all of this without touching any of the 3 screws!

 

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