[FuriousGeorge]

So I was testing out a new finishing tool by cutting a simple 6061 aluminum boss and noticed that my mill is almost Perfect in X and off by about 0.0015" in Y. I milled a square boss with a Nominal Thickness of 0.85" and when I measured with a micrometer I got X:0.8501 Y:0.8485. It's not really a problem since I don't need that kind of accuracy, but I'm curious as to how I could get that. Gib Adjustment? Different feeds and speeds? I tried a few cuts and methods and found that my Y dimension is ALWAYS smaller by about 0.001"


Cut 1:
Nominal 0.85" square
Measured: X:0.8501, Y0.8485
Tool: Variable Flute LakeShore Carbide 1/2" 2 Flute End Mill
Feeds and Speeds: 60 IPM 5100 RPM
Finish Pass Parameters: 0.005" WOC, 0.75 DOC, 1 spring pass.

Cut 2:
Nominal 0.84" square
Measured: X:0.8411, Y0.8397
Tool: Variable Flute LakeShore Carbide 3/8" 2 Flute End Mill
Feeds and Speeds: 50 IPM 5100 RPM
Finish Pass Parameters: 0.005" WOC, 0.75 DOC, 0 spring pass.

Cut 3:
Nominal 0.83" square
Measured: X:0.8304, Y0.8295
Tool: Variable Flute LakeShore Carbide 3/8" 2 Flute End Mill
Feeds and Speeds: 30 IPM 3000 RPM
Finish Pass Parameters: 0.005" WOC, 0.75 DOC, 1 spring pass.

[popspipes]

I would think the backlash in the axes would have a bearing on this as well.
I had one instance when this made a difference, it was fitting two profiles together that were cut in opposite directions. When they were cut in the same direction the problem dissapeared.

I am pretty sure it was related to to backlash.

[MichaelHenry]

There's a section (might be 9.5.1.2) in the Tormach manual that goes into backlash, friction, and lost motion that bears some study and can lead to a solution for these sorts of issues.

A while back I ran into the same thing and after a fair amount of troubleshooting, traced the problem down to loose SHCS mounting screws on the X-axis ball nut. It might also be a good idea to verify that your Y-axis is getting enough lube - maybe one of the delivery tubes or a manifold port is plugged.

[philbur]

I tried a few cuts and methods and found that my Y dimension is ALWAYS smaller by about 0.001".

Cut 2 and 3 look pretty good in Y.Backlash may or may not show up in one axis depending from where and in what direction you started the cut.

Phil

[FuriousGeorge]

Did some more tests and measurements.

Lost motion in X:0.00015"
Lost motion in Y: 0.0003"
Lost motion in Z: 0.00045"

So my backlash is well within what I would hope. Would this account for a 0.001"-0.002" in cuts on the X and Y axis? Or could something else be going on?

[philbur]

Did some more tests and measurements.

Lost motion in X:0.00015"
Lost motion in Y: 0.0003"
Lost motion in Z: 0.00045"

So my backlash is well within what I would hope. Would this account for a 0.001"-0.002" in cuts on the X and Y axis? Or could something else be going on?

Wow that's very much better than the test certificate minimum requirement of:

Lost motion in X: 0.00098"
Lost motion in Y: 0.00098"
Lost motion in Z: 0.0013"

Are you sure the decimal point is in the right place. How did you do the measurement. What does your test certificate say the measured values were when new.

Cut 2 and 3 are still find on the Y axis????? so it's not clear why you say "I tried a few cuts and methods and found that my Y dimension is ALWAYS smaller by about 0.001"

Phil

[CadRhino]

Hi Michael
Do you check if it is getting enough lube by removing the oil feed lines and turning in the oiler or is there an easier way?
Thanks

There's a section (might be 9.5.1.2) in the Tormach manual that goes into backlash, friction, and lost motion that bears some study and can lead to a solution for these sorts of issues.

A while back I ran into the same thing and after a fair amount of troubleshooting, traced the problem down to loose SHCS mounting screws on the X-axis ball nut. It might also be a good idea to verify that your Y-axis is getting enough lube - maybe one of the delivery tubes or a manifold port is plugged.