Can get round holes

[Almost Scientific]

Hi All,

I've got a PRS Alpha.

I'm cutting a series of 0.5" holes in some 0.25" thick Baltic birch with a 0.25" 2 flute down cut bit.

I've tried a whole range of cutting speeds and cutting depths but I cant seem to get perfectly round holes.

The all have a flat regions that run mostly along the X axis with a slight angle towards the Y.

I tightened the gears on the x steppers and reset the steeper mount tightly but it persists.

I've had my bot since Sept and it's been running well, but hard since then.

Can anyone suggest what I should jigger around to get more perfect holes?

Cheers

[BTP]

1 pass for this.

Cut from inside out. add a lead

if the ply "can" it will bend down as the z is going down.
That might be the angle you are seeing.

Is the ply secure?

The trick is to make the "mark", IF there is one, where the cutout will be, and not the perimeter

[Almost Scientific]

Thanks Alex,

The ply is held down with a Vac table and is not moving during the cut. I do cut from the inside out and also ramp into the wood.

I discovered some backlash in the X and Y carriage because the set screws on the pinion gears on the steppers was loose. I tightened these and re mounted the steeper and that helped a bit, but the holes are still not round.

Anything else I can check?

[gc3]

have you tried spiral ramping?

[Sean24]

You may have to look into the settings for your bot. the software sees arcs as segments. The more segments the more accurate. look under unit values. There is also something to read in the manual about this. I hope this helps.

[LeapTime]

This non circular problem is intresting to me... I have had this same issue for a very long time and have read many of threads on it and presitantly check all the things that everyone has suggested.... but still have oblong holes as well. The only thing that I have found that leads me to think it may be a problem is that my actual gear rail mounted to X rail is slightly out of position from side to side. This is the way it came and never thought much of it.... What do you guys think?