Do you lower the knee to to avoid rubbing the tool?

[pinstripe]

I know what half of you are thinking. Stop smirking, it's a serious question

This question comes from the "Squaring up a part within .0002" on a knee mill" thread http://bbs.homeshopmachinist.net/thr...on-a-knee-mill

Steve said that he lowers the knee to avoid rubbing the carbide inserts as he goes back to the "home" position. I've never done that, thinking that it wouldn't make much difference. Does anyone else do the same? Any idea what impact it has on tool life?

BTW, thanks for the video Steve. I'm going to try some of your tips next time I square a block. I'm also putting an indicator on the fixed jaw to see how much it deflects.

[michigan doug]

Most tooling, hss or carbide, does not benefit from rubbing. I avoid it when I can, but I don't lose sleep over it if it happens once in a while.

Usually, I cut both directions unless there is a specific reason not too, thus, no rubbing.

[lakeside53]

I raise the quill or drop the knee more for cosmetics on the work finish that worry about "rubbing". Face mill particularly.

[Arcane]

I sometimes will reposition the table so the workpiece is to the side of the cutter. Saves futzing with the table height and eliminates any difference in cutting depth between passes.

[chipmaker4130]

I sometimes will reposition the table so the workpiece is to the side of the cutter. Saves futzing with the table height and eliminates any difference in cutting depth between passes.

Same here. I don’t have a Z-axis DRO so moving the knee up and down while trying to meet extreme tolerances is insane. I just go off the part for re-positioning. That won’t work for a pocket, of course.

[polaraligned]

I thought the same thing after seeing that video. Why not move off the part in X or Y? Seems to me it would be more accurate. I always avoid moving the knee when possible.

[lakeside53]

If anyone is worried about re-positioning the knee.. a DTI on a rod from the head to the vise or table works well.

[pinstripe]

The cutter he was using was wide enough to cut across the part. So he was going to move the knee up to take the next cut anyway. I too would prefer to go around if I was taking another cut at the same height. Or as Doug said, take a cut on the way back.

[Viperspit]

The cutter he was using was wide enough to cut across the part. So he was going to move the knee up to take the next cut anyway. I too would prefer to go around if I was taking another cut at the same height. Or as Doug said, take a cut on the way back.

Hi pinstripe,

I usually take most of my cuts so that I am throwing the chips away from me rather than at me. Even with the chip guard some chips do get through. Also, by throwing chips toward the guard the guard will get marred up faster and it will get harder to see through. On the return pass where I lowered the knee to prevent the insert rubbing the part I was using rapid travel on the power feed and this in my experience is not a good for the inserts. In the video the outside dimensions of the block were not being held tight (+-.005"). The accuracy was on flatness and squareness not the overall dimensions. Most of the work I do on the mill I leave grind stock and will use the Surface grinder, Jig Grinder and hard turning. There are times I will do very tight tolerance work on the mill but most of the time it is easier with the other machines. Thanks for watching the video and starting this thread.

Steve

[754]

How big are your chips at 0.00 depth of cut ?

[Viperspit]

On a blank pass none just the rub. If you cut both directions then whatever amount you raise your knee.

[RB211]

Is this no different on a lathe, turning down a diameter? I only retract on the the finishing cut.


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