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Author Topic: Bad precision with arcs  (Read 1564 times)

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Bad precision with arcs
« on: May 24, 2013, 12:55:59 PM »

As a novice machinist, I have a issue about precision of arcs in Mach3, or maybe it's me the problem !

Need very precise holes in hard aluminium, for eg. 10 mm. But it is never accurate, like 9.75 - 9.85 mm with digital calipers.
First I thought it was drill flex, but after slow feedrate and second pass it is the same. It seems it always loose 0.1-0.2 mm whatever hole size,
even on different drills.

-Tried incorporated wizards, also imported Aspire simple circle test
-Rectangular patterns is spot on 10mm. Tested longitudinal length mill 100mm = 100mm +/-0.01mm on calipers, correct.
-Checked Mach3 on pause, coordinates and radius are right.
-Using Climb Conventionnal with a HSS quality drill
-Tried very low feed, 20mm/min at 15000 rpm.
-The machine is a Heiz 1000T, very precise to 15 microns.
-Using 25khz, processor usage is 5-10%

I don't know what else to try. It makes this high precision CNC useless if you can't even make a hole precise !

Re: Bad precision with arcs
« Reply #1 on: May 25, 2013, 01:18:59 PM »
I found the solution.

it was simple... tool deflection. Sorry guys.

With arcs or circle the force vector on drill of milling deflection can vary due to different direction.. and desired shapes aren't recoverable by finishing pass sometimes.

Since straight movement is less affected (parallel force vector) and I didn't thought it could be that magnitude, I couldn't find where was the catch.
Well, with lower step depth and lower feedrate, second pass are near 30 microns ! Incredible...

Thank you anyway,