Oversize print

Hi, I have been trying to get my printer to print the proper size, I have been trying to print a 20mmx20mm cube and one dimension come out about 19.8 and I'm OK with that as i'm fairly sure is a just a little bit of backlash but the other dimension come out close to 21mm, I'm not sure how that can happen, what can cause that? I have opened the object in netfab and it says it is 20x20x20

probably irrelevant info:
techzone huxley with RAMPS and Chinese J-head
cura engine
repeiter host

Edited 1 time(s). Last edit at 08/16/2014 08:38AM by mrkaras.

Most likely it's caused by a bad steps/mm setting in your furmware. Have you properly calculated your values?

Try the calculators here or here.

yes, I've calculated the values and are using the same value for x and y, Y is OK but X isn't. as near as I can tell manually moving 20mm does actually move 20mm. I believe that first link was the page I used. Perhaps I should deliberately set it wrong so it come out the right dimensions, I just cant see how I can need to.

Perhaps it's mechanical. Are the belts loose, or is there any binding in the movement of the axis?

the belt is tight, I tightened it some more and it didn't seem to make a difference but wouldn't both of them give undersized prints not over size? I'll have a closer look and make sure nothing is binding anyway

Are your pulleys printed or metal? A printed pulley, if not "round", can cause too much and too little movement. If you are using metal pulleys, make sure there's not too much space inside where the motor's shaft goes. When tightening the grub screw, if the motor shaft is too far to one side this will cause the pulley to be off center and cause the same problem as a deformed plastic pulley.

Are the pulley screws tight?

Make sure your belts are perfectly level from your motor pulley, x-carriage, and idler bearing. Any stray from that path will make the travel go further, if say... the motor was higher, it will try to pull the carriage up. Since it's on a linear path, it will just move closer to the motor. This can cause a wider path.

Its a printed pulley. my belt looks straight. maybe I'll swap some pulleys around and see if the problem moves. this pulley fits tight on the motor because unfortunately the way techzone desigend it there is no room for a screw, but I'm fairly sure its not slipping (and again, I would think that would give undersized)