Holes larger at top than bottom

[Ed Williams]

I have checked everything I know of on this machine. I have ball screws linear rails and a spindle. I have checked motor alignment on X an Y. I have checked spindle alignment. My holes are larger on the top than they are on bottom. The bottom is the right size but the top is 2 to 4 hundreds larger. Any idea of what this could be. It just started all a sudden.

Thanks Ed

[ger21]

What size holes, what size tool, and how are you cutting them? I'm guessing there's some slight play in the machine.

[Ed Williams]

I can't find any play. I'm using a .125 bit. Holes are 20mm. I'm dry cutting at 22000rpm .o2 depth. It has been working for a long time it just started doing this. But no matter what size hole, it is larger evenly around on top.

[Pplug]

Bad or worn bearings in the spindle or a loose spindle mount?

[Ed Williams]

Mount is very tight and spindle is only 2 months old with .0005 runout and .001 on bit.

[dertsap]

sounds like the tool is wandering . are you spot drilling the holes first ?

[ViperTX]

Well, what I would do is put a long piece of very accurate drill rod (diameter of your cutter)...approximately the length of your preferred cutter. Measure the total run out at the tip...1/2 inch from the tip and 2 inches from the tip.

I suspect that you have a runout problem or an alignment problem.

What material are you cutting?

Paul

[Ed Williams]

6061 aluminum. I have checked the runout on a long bit and it was less the .oo1. I had thought the same so I had ordered new collets. Still same problem.

[ViperTX]

Ed,

Have you changed your brand of end mill? Have you slowed down your cutting speed to some riduciously low value. Just wandering if aren't suffering from some flex in the cutter.

Paul

[Ed Williams]

Yes I changed brands and that didn't help.

[Hirudin]

What is the total depth of the holes? Can you watch the holes getting larger?

Is this your machine? If not, can you post (or link-to) a picture of your Z axis? To me (a beginner) it looks like the Z would be more rigid on the bottom of it's travel on that K2CNC machine. Could that be contributing to greater accuracy on the bottoms of holes?

[SORCHEROR]

sounds like a backlash error to me,check the backlash with and indicator,maybe something came loose or a bad thrush bearing