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parts are the wrong size
« on: February 11, 2013, 07:23:50 PM »
hi, i have been using mach for a while now on a cnc router that i built myself completely from scratch.

here is the situation. i have calibrated all the axis. everything moves accurately. ie if i move the x axis 1" or 30" it goes exactly that far +/- .005"

when i use any of the mach wizards, or g code from a cam program. the parts come out the wrong size.

if i run a hand written g code program they come out the right size.

here is an example of a simple g code program i wrote to cut the inside of a 1" square. i am using a .125" (1/8") cutter

Code: [Select]
g01
m03
z-.125
x-.9375
y.9375
x.9375
y-.9375
x-.9375
y0
z.1

and here is an example of the squares it cuts.



and here is an example of what happens with the mach 3 pocketing wizard.



as you can see they are not the right size. i am at a loss as to what could be causing this to happen.

i have also cut some parts with multiple passes for depth. ie. .100" doc. 5 times for .500" total. all of the steps line up exactly so i dont think i am loosing steps. and the manual code is also right on.


any ideas or help are greatly appreciated.
Re: parts are the wrong size
« Reply #1 on: February 11, 2013, 09:02:35 PM »
Cutter diameter?
Re: parts are the wrong size
« Reply #2 on: February 11, 2013, 09:03:46 PM »
Ooops. disregard. Didn't notice it was off .050"

Offline Hood

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Re: parts are the wrong size
« Reply #3 on: February 12, 2013, 03:03:10 AM »
Strange one indeed, the pockets actually look more in proportion than the profiles but that is likely just a trick of the camera.
Do you have backlash comp enabled
Are you feeding both at the same rates?
Hood
Re: parts are the wrong size
« Reply #4 on: February 12, 2013, 09:00:55 AM »
Backlash comp is off, but I will double check it again.

Both are being cut exactly the same. I have every thing set very low. Feed rate is 6 ipm  accel is set equally low. The g force is .009
Re: parts are the wrong size
« Reply #5 on: February 12, 2013, 11:47:41 AM »
Servo's?  If set up on loose side this may be your issue.
Re: parts are the wrong size
« Reply #6 on: February 12, 2013, 12:19:20 PM »
The machine uses stepper motors. Sorry, I should have specified that.

Offline BR549

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Re: parts are the wrong size
« Reply #7 on: February 12, 2013, 12:33:33 PM »
YOU really need to run the drawing test to eliminate lost steps during cutting. The test are not really equal the way you did them as the pocket test runs from inside out and has a LOT more cutting involved before you get to finish size.

In the drawing test run the first set of code and on the secound test cut only run the last set of perimeter code.

Looks like lost steps to me.

(;-) TP
Re: parts are the wrong size
« Reply #8 on: February 12, 2013, 09:50:45 PM »
where does one find that drawing test?

Offline BR549

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Re: parts are the wrong size
« Reply #9 on: February 12, 2013, 09:53:32 PM »
Put a pen or pencil in your spindle and draw the objects.

(;-) TP