Ovals instead of circles??? X4

[zaebis]

Ok just decided to check how round my interpolated circles are. Openned a few round pockets from 1" to 3" via Mach3 wizards. Grabbed my trusty bore dial caliper. Bloody hell ! I have about 10 thou greater circle on Y than on X. X measured bang on for the radius but Y was greater.

I checked backlash on Y against 1-2-3 block and an indicator in a spindle and coudnt see any perceptible backlash on Y.

What may be the problem here?

How can I fix it?

[gabedrummin]

You might have to adjust your steps . I had a similar problem with a home built cnc . My x and y had differet pitch screws so screw resolution was critical . I used a 3 .0 inch gauge block and zeored off one end then indicated the other edge . Then adjusted the steps to make the move were it had to be .Then my cicrles were round . I did have to check ball screw preload , end block supports , shaft couppling , thrust bearings , ballnut carrier , everything connected to saddle screw and machine base abd table .If you tell the machine to move 3 inches in y dose it move three inches ?

[zaebis]

You might have to adjust your steps . I had a similar problem with a home built cnc . My x and y had differet pitch screws so screw resolution was critical . I used a 3 .0 inch gauge block and zeored off one end then indicated the other edge . Then adjusted the steps to make the move were it had to be .Then my cicrles were round . I did have to check ball screw preload , end block supports , shaft couppling , thrust bearings , ballnut carrier , everything connected to saddle screw and machine base abd table .If you tell the machine to move 3 inches in y dose it move three inches ?

I will check if it does accurate 3" on Y. In the meantime how one adjust the steps? Is that in Mach3?

[gabedrummin]

I dont use mach 3 but all control software I have seen lets you set the steps per revalution My machine has 5mm ball screws my steppers do 200 steps for one full revultion. One full turn of my screw moves .19685 divided by 200 steps , makes each step=.000984. so one inch divided by .000984 is 1016.26013 steps to move one inch . So in my software I have 1016.260 set as my x axis resulotion.

[metalworkz]

Hello,
You should check the motor couplers on your X an Y axis. The set screw can work lose and add enough play into the system so that when the axis change direction(90º intervals) like on circles you end up having egg shapped or flat circles. My SX3 had come lose on the X axis and was cutting flats and after fixing that the circles were fine. I hope this helps.

Regards,