Internal keyway in 4140

Discrepancyform · Apr 28, 2018

Having horrible tool life and trouble with the cutter getting sucked up in the material and either stalling the machine or exploding the cutter. More pressure on the cutter bar only seems to make it worse. Running about 18 sfm and .001-.002" a whack using a hydraulic mitts n Merrill that I've made 3" chips in 304 with. Cutter is m42 with 3° clearance and about that much positive rake (I think) Depending on the bore size and setup I can use, I'm roughing 3/4-1 1/4 to finish 1 1/4-2. Thinking about negative rake but worried about chatter.
Thanks

HuFlungDung · Apr 28, 2018

I don't understand your roughing terminology, but anyways, I always open a keyway with a narrow tool that the machine can handle without too much chatter, and then widen it by about 1/4" at a time (while feeding down at fairly aggressive chipload).

Other than that, can you chamfer the lead in side of the keyway so the tool doesn't have to hit the wall every stroke? When possible, I drill out most of the material in a big keyway (but I don't do anything as big as what you are doing).

Discrepancyform · Apr 28, 2018

HuFlungDung said:
I don't understand your roughing terminology, but anyways, I always open a keyway with a narrow tool that the machine can handle without too much chatter, and then widen it by about 1/4" at a time (while feeding down at fairly aggressive chipload).

Other than that, can you chamfer the lead in side of the keyway so the tool doesn't have to hit the wall every stroke? When possible, I drill out most of the material in a big keyway (but I don't do anything as big as what you are doing).

The cut seems to start fine but dig in as it goes down the bore. I've had to tear down and remove the part to chisel out a 1/16" chip and blend smooth before continuing. These are couplings with tapered bores 6-10" dia and about 8-12" long kw sizes run from 1.25" (rough .75") to about 2" sometimes bigger I'll rough out at 1.25 or 1.125". I do this in cf-3 (cast 304) all the time with much better success so I have to imagine the setup is plenty rigid

Milland · Apr 28, 2018

Some pictures of your setup, and ideally a video with good sound might help with suggestions.

James H Clark · Apr 28, 2018

Discrepancyform: I have run into that with soft metals such as Aluminum and others. What is recommended for this is to lay the cutting edges of the broach, down on a fine grit stone such as an India stone and running it back and forth. Yeah, I know, this sounds crazy but it works. This is the method recommended by by duMont Company. This actually dulls the cutting edges a little.

JH

Limy Sami · Apr 28, 2018

Try a neutral top rake.

Myrmidon · Apr 28, 2018

James H Clark said:
Discrepancyform: I have run into that with soft metals such as Aluminum and others. What is recommended for this is to lay the cutting edges of the broach, down on a fine grit stone such as an India stone and running it back and forth. Yeah, I know, this sounds crazy but it works. This is the method recommended by by duMont Company. This actually dulls the cutting edges a little.

JH

That's to put a neutral wear land on its not crazy, it's the same concept as why in some materials "broken in" cutters work better.

basalt · Apr 29, 2018

Worn dovetail

I had this problem and it was because the dovetail groove in the bar was worn and the cutter rode too high up and was not supported by the tapered wedge directly behind the cutter bar.

HuFlungDung · Apr 29, 2018

I was thinking this was being cut on a slotter, not a keyseater. My bad.

Discrepancyform · Apr 29, 2018

basalt said:
I had this problem and it was because the dovetail groove in the bar was worn and the cutter rode too high up and was not supported by the tapered wedge directly behind the cutter bar.

Hmmm, our 4" cutter bar dovetail is pretty worn out but this also happens with our 2" "super bar" where the cutter is held by shcs

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