Do you trust your end mill holders to keep the correct tool height?

[beanbag]

Normally I use the ER collets, but occasionally I have had to use the 3/8 end mill holders, the ones with a set screw on the side. Considering the pulling and pushing forces from ramping, profiling, plunging, etc, how do you know the endmill height isn't changing? There's about an 1/8" of room where the tool can slide up or down due to the width of the flat ground into the end mill. Is there some standard procedure, where you pull out the tool as far as it will go while the set screw is still in the flat, and then tighten the screw fully? Or do you push in the tool all the way?

[David Bord]

I use carbide em's with no flats and and it will pull out of the machine before moving by the set screw....

David

[philbur]

The standard practice is to pull the endmill down against the setscrew, assuming it is a normal right hand spiral flute. The cutting forces tend to try to pull the endmill out not push it in.

Even the cutting forces when plunging tend to pull the cutter out unless of course you plunge feed rate is to great.

Phil

Normally I use the ER collets, but occasionally I have had to use the 3/8 end mill holders, the ones with a set screw on the side. Considering the pulling and pushing forces from ramping, profiling, plunging, etc, how do you know the endmill height isn't changing? There's about an 1/8" of room where the tool can slide up or down due to the width of the flat ground into the end mill. Is there some standard procedure, where you pull out the tool as far as it will go while the set screw is still in the flat, and then tighten the screw fully? Or do you push in the tool all the way?

[LeeWay]

Mild cuts and smaller end mills are what I use in these holders. No problems at all. Anything over 3/8" though and I use a collet instead. Sharp cutters work better of course. Dull cutters start to become problematic.

[philbur]

I think the conventional view point is that collets are used for small diameter cutters, (because of the greater impact of any run-out) and the set-screw holders are used for larger diameters where run-out is not so critical. Set-screw or Weldon holders as they are often known are very widely popular, they do work well if used correctly.

Of course at the end of the day - whatever works for you.

Phil

Mild cuts and smaller end mills are what I use in these holders. No problems at all. Anything over 3/8" though and I use a collet instead. Sharp cutters work better of course. Dull cutters start to become problematic.

[beanbag]

The standard practice is to pull the endmill down against the setscrew, assuming it is a normal right hand spiral flute. The cutting forces tend to try to pull the endmill out not push it in.

Even the cutting forces when plunging tend to pull the cutter out unless of course you plunge feed rate is to great.

Phil

Thanks for the advice. But I have peck drilled using an end mill on a manual mill, and the forces are definitely pushing for even light feeds.

[philbur]

Well of course you need some force to start the cut, you have the set screw to resist this force. On a CNC machine, once the cut starts the forces are trying to pull the cutter out of the holder.

You need to compare apples with apples. Drilling manually is somewhat different. When you say light feed you possibly mean light feel (of a resisting, upward force). When you manually feed it is normal to feed as fast as the work will take it without showing excessive resistance. However the fed rate on a CNC machine is fixed and constant and takes no account of "feel". If the feed rate is less than the removal rate then the act of removing and moving the cut material away from the cut surface produces a reaction force in the cutting tool that is attempting to pull the cutter out of the holder. You can exceed this force if you feed fast enough but the in CNC machining your feed rate would, under normal circumstances, be too high.

On a drilling machine or with a lathe tailstock (without drawbars) it is not uncommon for the taper to pull out if the feed rate is not maintained to ensure positive pressure.

In any case I think the plunging issue is a red herring. The real issue with pull-out is side milling, due the the combination of flexing with the pulling effect of the spiral flute.

Just a few thoughts for consideration.

Phil

Thanks for the advice. But I have peck drilled using an end mill on a manual mill, and the forces are definitely pushing for even light feeds.

[TXFred]

In theory, an end mill can move in a set screw holder. That's why the screw should be tightened while you are pulling the end mill out of the holder. If the end mill moves in the holder, it would have to move inwards. That would cause it to cut too shallow instead of too deep. The part would not be scrapped if this happened.

But, I've never had it happen to me.

Frederic

[LeeWay]

I have had the TTS tool holder slip out of the collet before. Not the end mill out of the set screw holder though. I don't use the flats either. I have different style tools and they all have the same offsets, but the flats on the tools are in different spots. It works for me and keeps it all very simple.

When the TTS does pull out, it was in need of cleaning. Totally my fault really.

[philbur]

Good point.

Phil

If the end mill moves in the holder, it would have to move inwards. That would cause it to cut too shallow instead of too deep. The part would not be scrapped if this happened.

Frederic

[Jaynboom]

When I started at an aerospace contractor, I asked the guy training me about grinding flats. He said he didn't. I asked how many endmills he'd had pull out of set screw holders. He said "in thirty years, zero".

I was there three years, and I never used flats either, and I also never had an end mill pull out.

We ran the machines in that shop pretty hard too.

I may have been lucky, but his experience was the reason I never started grinding flats.

Heck, even cutting copper, the work would come out of the vise if the pull was too great.

[TXFred]

When I started at an aerospace contractor, I asked the guy training me about grinding flats. He said he didn't. I asked how many endmills he'd had pull out of set screw holders. He said "in thirty years, zero".

I was there three years, and I never used flats either, and I also never had an end mill pull out.

Bear in mind, the set screws on the TTS holders are pretty cheap. I wouldn't count on them to hold a tool without a flat.

If you replace the set screws with good ones, you can get them a lot tighter. And then I suspect that you will be proven right.

Frederic