Newbie alignment issues

[mooreaa]

Hi guys,

I am trying to cut parallel edges on both sides of a 1/4" plate. I hold it in my vice and take a pass on one side with my 1/2" end mill.

I get a very nice clean cut and I mark this location as 0.25" (half my cutter width), now I scroll to -6.85" inches to the other side, and make a cut, take another pass at -6.75" and measure.

I'm seeing 6.48" using my digital calipers. I tried this a few times taking light passes thinking maybe it was tool deflection or something but it doesn't appear to be so. I know that my tool might not be exactly 1/2" but with this method, i would have thought it would have errored on the greater side.

I'd appreciate any ideas on where I might look to solve this issue.

Thanks

[philbur]

What mill are you using.

Phil

[Gerry Sweetland]

Never mind :-)
Gerry

[g3jeff]

Is the tool runnimg true? or how much run out is there?

[mooreaa]

philbur: This is a Tormach PCNC1100 Series 2 with upgraded motors.

g3jeff: I put a dial indicator on the tool and spun it and see less than 0.0005" of run-out. The bit is held in a 1/2" TTS holder.

The tool is an OSG 541-1100 4F Cobalt cutter with a 1.25" LOC.

[john2532]

Is there any chance it could be a backlash issue or a setting in Mach3 that is compensating (or over-compensating) for backlash? I haven't performed the backlash setting procedure on my machine yet so I'm pulling this info out of some vague memory and it may be way out in left field.

Good luck and I will be definately interested reading the solution.

John

[philbur]

Check the axis movement corresponds with the DRO by using a dial indicator. Run the same path as the part with the error (including start and finish directions, to allow for potential backlash).

With a DI and a bit of thought it should be easy to find where the error is.

Phil