Need help with disc shaped object not being perfectly round

[Bommes 0]

Hello,

 

I'm using my Ultimaker 2+ to print a disc shaped object with a diameter of 124mm, but despite showing the correct diameter in the slicing software the finished print is slightly oval with a diameter difference of up to 0.8-1mm between the x- and y-axis (for example 123.8mm and 124.6mm). It's obviously not much, but since the finished print is intended to rotate at a few hundred rpm I'd prefer to get it as perfectly round as possible to get rid of as much unbalance as possible and keep the stress on the part as low as possible.

 

Has anyone encountered similar problems and knows how to get a better result? I've tried both Cura and Simplify3D as the slicing software with no difference between the two.

 

Thanks for your help!

Edited January 6, 2018 by Bommes

[gr5 2,094]

What kind of printer?  It's the printer, not the slicer.  Make sure the belts are of equal tension in X and Y and maybe calibrate and also make sure the X and Y axes are perpendicular.  The most common problem on a UM printer would be that the two rods going through the head are not perpendicular.  If it's a UM printer then push the head to the 4 walls and make sure the blocks hit at the same time.  If not loosen some of the set screws and re align and then tighten the hell out of those set screws and double check.  The symptom would be errors in the diagonal direction - in otherwords bottom left of the desk to top right would be a different diameter than the perpendicular measurement.

 

If X and Y are not exactly equal on your printer then you would get different distance in those axes instead.

 

Another common problem on the old UM originals was the pulleys were not colimated - in other words the hole through the pulley was not through it's center.  This results in for example if the head is supposed to be moving at a constant speed it instead speeds up and slows down each time the pulley rotates once.

 

But you should also consider putting a shaft or hole in your disk so you can mount it on a drill or lathe and file/sand it down a bit while it's spinning fast to get it better.  *and* also consider adding bits of glue or other weights to make it well balanced.  I took apart an old cassette player recently and was amazed at the heavy round part that was connected to the capstan (the primary speed control shaft).  Even though it spun kind of slow it had all kinds of last minute adjustments to make it perfectly balanced.  And it was clearly made very accurately on a lathe at some factory yet they still had to drill out a few chunks to balance it.

 

[Bommes 0]

Thank you very much for your suggestions, I'll go through them tomorrow and report back!

 

The printer is an Ultimaker 2+ which has gone through quite a bit of print time by now. I haven't done much maintenance other than keeping the rods mildly oiled and making sure it's calibrated for use, all parts are clean etc.

[gr5 2,094]

Then check that belts are equal tightness (including the short belts on the steppers!!!)

 

And look straight down on the printer and see if the rods through the head appear to be perpendicular.

[Bommes 0]

We checked your suggestions and found one of the rods was indeed not perpendicular, so after fixing it we're hopeful there are no more problems with our prints  Right now I'm waiting for the print to finish and then we'll know for sure.

 

At one time in the past one of the axles came loose during print (probably because it wasn't screwed in properly in the first place or came loose over time) - the misalignment most certainly happened then.

 

Thanks again for the help, I'll do a quick update via edit once the print is finished!

[gr5 2,094]

It will be much better I'm sure.  But possibly not good enough if you want it well balanced.  So you may have to come up with a procedure to adjust the balance or to machine it a little such that it is more round.