Scaling with Smoothieboard

I have a Smoothieboard and I'm having a heck of a time getting the size of my prints to be correct. The prints are printing at about 90% their actual size.

I have played with the stepper settings for steps/mm. If I set the steps/mm to 88, I will get correct x/y dimensions, however any circles print in a somewhat oval shape. If I dial the steps back to 80, circles are fine but dimensionally the piece is incorrect. I have resorted to scaling in Slic3r, but that to me seems like a kludge. There is a GCODE command (G51) that will apply scaling, but that does not work in RepRap. Is there some sort of scaling or tuning that can be done with Smoothieboard that could compensate for this?

You should not have to do any scaling to get circles to come out as circles.
Are the X and Y axes drives identical mechanically (same size pulleys, etc.)? If circles come out oval, one axis steps/mm is different from the other or something else is wrong. Did you create the model file yourself?

Are the printer's axes aligned?

What sort of printer is it: Cartesian, CoreXY, delta, or something else?

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

It's a Cartesian printer (QUBD TwoUp) Both steppers are identical.

The QUBD came with a geeetech printrboard cloan. It committed seppuku and is no longer in service. However, with the printrboard attached I had no problems like this.

Attached is an image from a test file I made I get if I set the steps to 88 steps/mm for both x and y

With the steps set to 80, the circles come out fine, which leads me to believe there is no issue with any slop or misalignment with the axes.

I have a 100x100x100 test file I tried as well. With the steppers set to 80steps/mm, the x-y dimensions came out at 90x90. At 88 steps/mm, the test file prints at 100x100

Edited 2 time(s). Last edit at 06/17/2015 08:12PM by RickRap.

What slicer did you use? Sometimes slic3r does goofy things. Try slicing with Cura and see if the printer behaves itself.

When I first installed my smoothieboard I had problems with X axis layers shifting. After tweaking literally every possible variable and checking and rechecking wiring and mechanical stuff for about 2 weeks straight, someone suggested I try a different uSD card on the smoothieboard. I tried it and all the weird problems magically disappeared. Maybe it's time to try a different SD card.

I know you'll say "but my computer sees the card and the files on it and reads and writes to it just fine". So did mine. The problem seems to be with a voltage level or timing (or ?) on the smoothieboard that makes it hard for the smoothie board CPU to read some cards.

Hey !

If you give the same steps per mm for X and Y to Smoothie, it should print circles. This is very straightforward inside Smoothie, no reason whatsoever for it to print ovals.

I would look for the source of the problem elsewhere : mechanical issue, or a slicer issue.

Cheers !

If there was something mechanical wrong with the printer, it would not print circles correctly regardless of the steps/mm.

And I'm still not sure the Smoothieboard is innocent. With BOTH steppers set at 80 steps/mm, circles are circles. They are spot on. Setting BOTH the steppers to 88, I end up with the oblong pictures shown.

I suppose there could be something with slic3r. I will try a different one. Or perhaps I need to use different settings for each stepper.

Or try changing uSD card. I was having all sorts of problems that made no sense until I changed the uSD card.

If the steppers are 200 steps/rev and the pulleys are the same size, they should use identical settings.

Did you use the M500/M503 commands ? Is there a config-override file on your SD card ?

Are they 18 tooth pulleys? If so they are 88.88 steps/mm. 16 and 20 give round numbers.

Sounds to me like the config isn't saving correctly...check to see if the file is on there 2 times (like 1 .txt and 1 "any type")

Notepad++ likes to save funny sometimes...you have to save as "any/all types".

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Thanks for all the info.

I solved the issue. I had to have different settings for x and y steppers. Setting x to 90 and y to 88 solved the problem. Not sure where the ratio difference is. The X-axis uses a 12-tooth pulley. Not sure about the Y. It's possible that's different.