Problem- My machine is not cutting exact!

[greasetattoo]

Hey All,
Well, I have been using my Sherline CNC for over a year now..
I did do some changes to the machine, fixing here and there..
I did put new leadscrews (x and y axis) on the machine about 6 months ago.

I just noticed something..
It is not cutting exact..

I cut some holes for some bolts and low and behold the bolts holes were a tad to small..
The bolts would not fit into the hole.
I measured the hole and it was not to my measurements (the size of the bolt) I used in Vectric's Aspire software.
Now the question..

Is there a template or a way I can see if my machine is machining correctly?
I realize I could cut some squares or circles and measure them with my Vernier digital caliper.
But is there a better way?
A certain template or cutting template, one uses?

Ok, let's say I did measure, and my square, I cut was off?
How do I compensate for the off-ness?

I realize I have to go to my machine setup and adjust the STEPS PER INCH.
But is there a formula, you use?
Or do you just add or subtract a little amount from the steps per inch and just keep playing with it,
until the square I cut is to my measurement?

I hope I made some sense here.

I am using DeskCNC for my post processor.

What about the Z axis, how do you measure that?
Also, whatever I change on the Y axis, do I do the same with the X axis?

I did use the formula that came with my controller (Imservice) and Globe motors. (steppers?)
My leadscrews are 4 tpi. (.250 lead) dual start threads, my X and Y.
My Z stayed the same as I did not change my Z leadscrew. (10 pitch)

I did determine the Max velocity (speed) of my machine.
I thought I followed the directions here:
http://www.imsrv.com/deskcnc/setup/index.html

Also, do you guys check your machines often?
Or once it is set, you are good to go?

Sorry about all the babble..
But I am just trying to figure this out..

Thanks
Grease

[greasetattoo]

Thanks everyone...
I figured it out...

Works like a charm now..
Cuts dead on..

[laszlozoltan]

It would be helpful if you would provide how you fixed your problem - just in case...

[altonj2008]

Hey Grease, I'm having an accuracy problem with Deskcnc. Exactly what was wrong with yours and how did you fix it?

[altonj2008]

Oh, I forgot to mention. I bought this machine from the internet. It appears to be a great setup. It has a Deskcnc controller, Anaheim drivers, individual 48v power supplies for each motor, and Anaheim motors (630 oz/in in bipolar). These are more than enough. I have tweaked the setup as best as I can. I slowed the cutting down to 30 ipm on a 3" raster pocket cutout and cutting air. I am still losing steps. I am suspecting high frequency noise. My spindle is a Colombo 1 1/2hp. None of the wires are shielded. I would appreciate your findings on your problem. Maybe mine is related somehow. If anyone else can offer input, I would be grateful. Thanks

[greasetattoo]

altonj2008,

Yep, you hit the nail on the head...

high frequency noise

My brushes were bad on my spindle motor.
That was causing the high frequency noise.
Which in turn, was losing steps.

Tried putting new brushes on the motor, but Sherline's older motor makes it nearly impossible to change brushes without breaking the brush holder.
So, in turn, I bought a brand new motor and WA-LA, she cuts like a charm...

Check your motor and brushes.
Good luck and if there is anything else, let me know.

Let me know if you figure it out!

[Joe S.]

I would try some .01UF caps bypassing both brushes to ground too. Be sure they are of appropriate voltage and insulate to prevent shock.