PDA

View Full Version : Tram and tool rubbing/work hardening.



Black_Moons
12-20-2009, 11:30 PM
Hi. it just occured to me, if your tram is perfict with an endmill or flycutter, and you are endmilling/facing a workpeice, the face of the cutter is allways rubbing on the peice on the back stroke, and leading up to the cut. as theres nothing left to cut there, isent this causing extra wear on the cutting edge, and possabley work hardening the metal by having the cutting edge rubbing against it?

Would tool life in work hardening/diffacult materials improve if your tram was off for your roughing passes to reduce rubbing?

mechanicalmagic
12-20-2009, 11:39 PM
Would tool life in work hardening/diffacult materials improve if your tram was off for your roughing passes to reduce rubbing?

With work hardening SS and similar materials, YES. Set the head to a few tenths toward the cut if possible.

dp
12-20-2009, 11:41 PM
Some people, I'm one of them, like to see symmetric machine marks on a fly cut piece. It indicates a well-trammed machine. Others prefer to see the leading machine marks only. That produces a concave surface, of course, and across adjacent paths the surface is scalloped. I don't know if it produces longer tool life as I always touch up the fly cutter before each pass. My HSS end mills don't seem to be bothered by near-perfect tram.

lazlo
12-20-2009, 11:43 PM
Some people, I'm one of them, like to see symmetric machine marks on a fly cut piece. It indicates a well-trammed machine. Others prefer to see the leading machine marks only. That produces a concave surface, of course

Dennis, the idea is you tram the head with the head a tenth or so toward the cut, so that when the head flexes in the cut, it brings it back on tram. I've seen guys on PM go as far as to measure the head flex with a fish scale, and tram the head low by that amount.

Same reason the table on a turret mill is high on the front edge, so that when you put a heavy workpiece on it, it settles back to level.

Personally, I don't do that, because the resulting tram is for that particular cutter diameter, depth of cut, etc, but for a production shop that running the same job over and over...

mochinist
12-20-2009, 11:45 PM
With work hardening SS and similar materials, YES. Set the head to a few tenths toward the cut if possible.Just when I thought I had read it all on this forum:rolleyes:

dp
12-21-2009, 12:10 AM
Dennis, the idea is you tram the head with the head a tenth or so toward the cut, so that when the head flexes in the cut, it brings it back on tram. I've seen guys on PM go as far as to measure the head flex with a fish scale, and tram the head low by that amount.

Same reason the table on a turret mill is high on the front edge, so that when you put a heavy workpiece on it, it settles back to level.

Personally, I don't do that, because the resulting tram is for that particular cutter diameter, depth of cut, etc, but for a production shop that running the same job over and over...

Yes - that is dynamic tram (probably not the right word for it) and it does depend on the setup and a bunch of other variables I never get near at home. This is another area I agree with Frank Ford on: http://www.frets.com/HomeShopTech/QuickTricks/TramTime/tramtime.html

My greatest tram problem was actually on the Y axis - I had to shim my column as I could feel the edge of adjacent passes. That's fixed now and it leaves a beautiful surface with the flycutter.

oldtiffie
12-21-2009, 12:47 AM
Hi. it just occured to me, if your tram is perfict with an endmill or flycutter, and you are endmilling/facing a workpeice, the face of the cutter is allways rubbing on the peice on the back stroke, and leading up to the cut. as theres nothing left to cut there, isent this causing extra wear on the cutting edge, and possabley work hardening the metal by having the cutting edge rubbing against it?

Would tool life in work hardening/diffacult materials improve if your tram was off for your roughing passes to reduce rubbing?

You differentiated between between roughing and finishing cuts.

The cutter will deflect under roughing cuts anyway and your "problem" may not be a problem at all.

A high-speed out-of-balance fly-cutter may certainly not be as well "set up" as it was when it was "set" statically.

For an instructive exercise,I suggest you get a flat (a lathe face-plate will be fine) say 8" diameter(the same as you tram your mill over) and pack one end/side (shim) by 0.002". Now work your way around the plate from the "low" side (where it is touching the table) until you can fit a 0.001" shim under it.

You are in for quite a surprise.

That set-up is linear and so reduces proportionately for a 4" disk (half) and 1" (an eighth).

So - a bit less talk and needless worry and a bit more constructive thinking will work wonders.

An end-milling cutter is relieved and has a 178 degree (~) cone at the end as well as positive rake and clearance angles and can quite well cope with "dragging".

An end-milling cutter with sharp pointed tooth-ends is far from an ideal fly-cutter - and it shows.