Maxnc-10 all circles not round

[Shelby5041]

hi
i bought this old maxnc10 used a few years ago..never really used it until now

my max nc is very old version is from 1997-1998

all original components..no mods

using the orig maxnc software in DOS and using mach3 software to control machine produces same results

all circles are not round see photo

i have calibrated xy steps and are very accurate
stepper motor couplings are tight
lowered feed rate to 4ipm..no change

im thinking this could be a backlash issue or maybe worn out stepper drives that affect when xy move at same time

i did about 10 holes in aluminum and also HDPE at various depths and all looked very similar ....i did some squares and overall the squares were ok.

any thoughts on this?

note: in the image i attached i used the cad file and node editing to simulate the look of the hole when machined on the max...the hole in cad is round.

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[fc60]

Greetings,

My CNC had a similar problem.

I run LinuxCNC with Stepper motors.

Withing the LinuxCNC configuration is a parameter to compensate for backlash on each of the drives.

Roughly an hour running the machine forth and back with an indicator allowed me to remove a great deal of the error.

Not ideal; but, with light cuts the machine is fairly accurate now.

Remember to restart the program to read the changes made, if any, to the config files.

Cheers,

Dave

[Dean448]

So your cutting a .250 dia hole in aluminum using a smaller cutter and inside cutting the circle? Then accurately measuring those 8 points in the aluminum hole?
Probably not as you would just drill a standard hole like that.


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[awerby]

The problem is worse than backlash. On those machines, the screws are not held in place by thrust bearings; they are directly attached to the stepper shafts and float freely back and forth as much as 1/8" or so, since the motor shafts aren't really fixed in place. It's not surprising that those holes aren't round.

[Shelby5041]

Yeah i noticed that when i removed steppers.to add flats to the shafts...today...all shafts need flats...the designer dhould have been fired ....hes a dumbass ..its just a poorly designed machine period.....avery so basically the gen 1 maxnc non modified is not capable of milling round holes consistently?...and everyine who owns one has same problem as me?

[Shelby5041]

Not sure if mach3 has a compensation for backlash

[Shelby5041]

update:
fc60 yes you be right issue is indeed backlash..which was one of my initial thoughts


.014 in x
.008 in y

[dazp1976]

Not sure if mach3 has a compensation for backlash

Yes it does.
Not perfect but it does work. I set it to 100% speed if I need it. default is 20%.

[Shelby5041]

hi daz..thanks..i enabled backlash compensation in mach3 and put in values and set at 100% and now my circles are round and accurate as well as squares...did 4 .250 circle pockets and 4 .250 square pockets and all were within .001 much much better and definitely acceptable for my hobby use....egg shaped circles were not acceptable. and i have no idea how anyone who owns a maxnc could even make parts with the horrible backlash it has ...when the manuf made the machine what were they thinking? the orig stock software for maxnc has no backlash compensation built into it that im aware of and there is no mechanical feature to prevent backlash so there is no way the machine ever could have made good parts