My machine is still cuttign a bit small.

[knight_toolworks]

I got one of the new pinion gears and replaced the y pinion. Then I did some test cuts with a ¼” bit and a ½” bit.
This is on a prt alpha.
I am getting about the same cuts a 2” square box comes out about 1.98 or a bit larger in the y axis and 1.99 or so on the x axis.
I was cutting some mdf at .2 depths and I tried regular and climb cut. I tried .5 1 and 3ips. It got worse the faster I went. But we are not talking a lot but still .02 is a fair amount on a light cut. The ¼” bits measure around .247 the cut was better with a ½” bit closer to 1.99 then 1.98
But I don’t know why it is on in the x but not the y. I don’t find any play in the y axis when I tug on it.
Climb cuts are pretty much right on.
the multiplier settings are all default and are the same for the x and the y and the z.
my depth tends to be off by about .01 though not always .01 not deep enough.

[rcnewcomb]

Have you measured the hole when the square is cut? The hole should be the width of the square plus 2 times the bit diameter. Is the hole undersized as well?

What I am looking for is runout vs. motion in the X or Y direction. Runout would make the hole larger and the part smaller. Check with both climb and conventional cutting to see if there is any difference.

What are your Units values?

[dubliner]

Why "plus 2 times the diameter of bit"?

[rcnewcomb]

quote:Why "plus 2 times the diameter of bit"?
Once for the left side and once for the right side.

9083

[knight_toolworks]

I just checked as I had forgotten looks like with the 1/2" bit the cut is 1.99 with the y and 1.98 with the x. I have not changed the pinions yet on the x I should have them today.

[erik_f]

You have to add two times the bit diameter because its a 1/4" on every side of the work piece. So if you are measuring across a hole made from cutting out a 2" square...the hole would be 2.5" in an ideal world with a 1/4" bit. Am I making sense or just saying the same thing Randall said with different words.

[mims]

When I was adjusting my cnc (not shopbot), I used a 1/4 bit that was really .243". I made a toolpath that was essentially a capital E, where each 'finger' of the E and each gap was .5".

If each finger and gap were equally away from the .5" dimension measured with quality calipers (say finger was .52 and gap was .48), I knew the machine was set correctly and then I just needed to adjust the bit size in the toolpath program.

[dubliner]

Randall & Eric, got it!, about one second after I hit send I realized what you meant.

[knight_toolworks]

ok got the pinions all changed and I get 1.99 on both sides of the square if I cut at 1ips. if I cut at 3ips it goes to about 1.97-8 but that's only cutting .2 deep in mdf with a stubby 1/2" straight bit that came with the machine.

[gerryv]

Coming from being a metal lathe/mill tinkerer, any significant deflection you get is not going to be from a 1/2" dia. stubby bit unless they're a lot skinnier through their "waist" than a typical metal mill bit is. You should be able to rule that factor out as I see it anyway. But, in fairness, a router is not designed to match a HAAS or Bridgeport in terms of rigidity either :-)