Boring Hole Issues

[usajet]

I have a Bridgeport J Head mill that I converted to a cnc. Installed ball screws on the x, y and z. I doubled checked my calibration on all axis and all is good.

I am using the Masso G3 Touch with these stepper motors, https://www.automationtechnologiesinc.com/products-page/nema42-kits/3axisbridgeportkit

Well every time I try to bore a hole in aluminum or steel it does not come out as a circle more like a freehand circle.

Since then I replaced my spindle bearings, shimmed my x and y gibs. I haven't looked at my knee gib yet.
I tried just doing hole boring after I did all the above with no luck.

I am running the spindle at 2720 rpm and using a mister for lube, 8mm end mill and air.

Is there anything I could try or look at?

Thank you for the help, Nathan

 

[BajaFire]

Since then I replaced my spindle bearings, shimmed my x and y gibs. I haven't looked at my knee gib yet.
I tried just doing hole boring after I did all the above with no luck.

So in between posting this exact same question in a different subforum yesterday and posting here today, you still didn't check your knee gib?

There is The H0bby-Mach1nist

 

[CarbideBob]

Bore with knee or quill or profile the hole in x-y?
Maybe 8mm endmill is a clue but maybe it is a 8mm hole??
Funny at 12 a clock, 3:00, 6:00 and 9:00?
If profiling perhaps backlash compensation?

 

[usajet]

I replaced the steppers with servos and it still stops during milling process at 12 o'clock, 3 o'clock, 6 o'clock and 9 o'clock. Plus the circles are still not round. The Knee gib is good.

 

[atex57]

I replaced the steppers with servos and it still stops during milling process at 12 o'clock, 3 o'clock, 6 o'clock and 9 o'clock. Plus the circles are still not round. The Knee gib is good.

Servo's do not gain you anything if the ball screw or its mounting is loose even .001". I have a couple CNC knee types and even after a lot of tinkering and upgrading they still give a hole .0015 out of round. Do not expect a knee type to have the rigidity in the screws and drives to do that.

Ed.

 

[memphisjed]

If everything is reasonably tight with the monkey test (grab the table and shake it- if it shakes it is not snug) then you are looking at control/motor issues.
Look ahead and smoothing values would be first settings I would play with.
Is the gcode g2/g3 or lots of g1?

If you put a sharpie in the spindle and have machine draw a circle is it round?