Crown Distorted

Hello fellow MPCNC builders

I am at my wits end …

This MPCNC is make up of components provided by Ryan ( PLA parts, Electronics and Motors ) with conduit from one of the local Portland, Oregon big box stores.

I have been through the forums and double and tipple checked my build but no matter what I do I always get this same distorted crown. Printing circles results in egg shaped things that sort of resemble circles with bigger ones looking better than smaller ones, but printing straight lines or squares works just fine.

This latest one which I double printed because the first run was too far off the base but since it is very close to duplicating the lines that tells me that the machine is doing very nearly the same thing with the g code.

I have checked the base for square and it is within 1/32 over the nearly 44 inch diagonals and the gantry is as square as I am able to get it.

Today I pulled the motors out to check the mechanism for movement and both axis move with the same amount of effort in both directions.

Played with belt tension and that seems to make little difference until it is too loose when skipping starts happening.

So I am at a loss … Help


Bill Mullikin



Looks to me like pulley(s) on driving the y axis might be loose on the shaft. This appears as huge “backlash”. When the motors are energized can you move the gantry a little bit by hand or is it rigid? If it can move, look for the location of the movement.

Yeah I would guess one of your steppers is not moving or the pulley is loose.

Thank You both!!!

Checked with holding current on the motors and one motor can be moved, the other three no movement.

Found that Y2 motor wiring was bad, one wire does not conduct electricity!!!

So now I know what I am doing tonight.


Again thank you very much

Bill Mullikin