# Steps/ mm calculator.

Posted by CVRIV
 Steps/ mm calculator. January 12, 2021 02:42PM Registered: 4 years ago Posts: 51
I printed a 20 x 20 x 20mm test cube and the print was amazing and the dimensions were so nearly close. The X and Y measured 19.67mm. I wanted to tweak my steps/ mm so I decided to try the Prusa stepper calculator and yea.... whats going on with that? I had input my parameters: 1.8deg, 2mm pitch, 20T, full step I think?, 2mm pitch belt preset? I told me my steps/ mm was 5. LOL.

I changed the micro stepping and non of the results were even close. The version of marlin im running has a default of 100 for x and y. That was so close. I m testing with 102 now just to see what happens.

What am I doing wrong with that calculator?
 Re: Steps/ mm calculator. January 12, 2021 04:38PM Registered: 10 years ago Posts: 6,077
Nobody runs full step! (its obnoxiously loud and jerky movement)

most likely you have 1.8 degree steppers, 1/16 micro stepping, 2 mm belt pitch and 16 tooth. This is 100steps/mm
 Re: Steps/ mm calculator. January 12, 2021 05:01PM Registered: 8 years ago Posts: 5,549
20 mm is too small to calibrate your axes (unless your printer has a 25 x 25 mm bed). A 20 mm cube prints so fast that the print quality degrades as the print builds up because you're dumping hot plastic on top of hot plastic. Where do you measure it to decide if it's 20 mm on a side?
Print the largest object you can accurately measure and use it to calibrate. A large object will print with better quality so your measurement is likely to be a better representation of the true size of the print.

Every measurement comes with some error. The error is a larger part of a 20 mm cube than it is a 100 mm cube. A 100 mm cube lets you measure diagonals to verify squareness of the axes with a 6" caliper. If you measure a 20 mm cube and use it to calibrate, then print any object larger than 20 mm, the error in the 20 mm calibration will be multiplied. If you print a 100 mm object and calibrate, when you print smaller objects the error will be divided. In both cases the percentage error remains the same, but the absolute error is what matters in the real world, not the percentage.

A 20 mm calibration cube was a bad idea when someone first came up with it, and has propagated through time like so many other bad ideas (4 point bed "leveling" for example- which the world seems to finally have come to realize is a bad idea).

Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
 Re: Steps/ mm calculator. January 12, 2021 11:42PM Registered: 4 years ago Posts: 51
Ahhh this all makes sense now. The number of teeth, 20, is the number of the new pulleys I bought for a new machine build. They looked similar to the ones on my old machine so I just assumed they were the same.

As for the 20mm cube being a bad idea due to the erroring you explained, that makes perfect sense to me. My bed is about 200mm so I'll print a 100mm test. Thanks so much.

Edited 1 time(s). Last edit at 01/12/2021 11:42PM by CVRIV.
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