Undercutting With a Tee slot cutter

Toms Wheels · Jan 30, 2018

I need to undercut a 1.8" blind hole about .250
X.500. I've done it before with a hand ground single point cutter that is .300 x.200 going about .250 into AL. Done on a lathe works but cuts slow.

I have a 1.125 x .125 keyway cutter HSS. I am thinking of reducing the shank to 1/4" and mounting it into my 1/2hp toolpost grinder. The motor can be slowed with a DC drive that I have, and slowest pulleys mounted.

Anyone see an issue with this idea, there are a dozen undercuts to be done.

This needs to be done on the lathe.

Bobw · Jan 30, 2018

Biggest issue I see is getting a GRINDER to run slow enough for running a 1" plus HSS tool..

since you are being cheap, use the key cutter as a dead tool.. Just because its round doesn't mean
it has to spin, use one tooth at a time like its a boring bar, when the one tooth gets dull rotate it
over to the next tooth.

HuFlungDung · Jan 30, 2018

Toms Wheels said:
I need to undercut a 1.8" blind hole about .250
X.500. I've done it before with a hand ground single point cutter that is .300 x.200 going about .250 into AL. Done on a lathe works but cuts slow.

I have a 1.125 x .125 keyway cutter HSS. I am thinking of reducing the shank to 1/4" and mounting it into my 1/2hp toolpost grinder. The motor can be slowed with a DC drive that I have, and slowest pulleys mounted.

Anyone see an issue with this idea, there are a dozen undercuts to be done.

This needs to be done on the lathe.

Maybe I'm not getting the picture but you're cutting a groove, it sounds like. Why not a boring bar then? You're not going to get good chip clearance out of a woodruff cutter, plus it doesn't really facilitate getting the tool into the hole to begin with. Sketch it up, perhaps?

brian.pallas · Jan 30, 2018

What Bob said. Grind away teeth as needed for clearance as use it as a lathe tool. I've done it a few times

SIP6A · Jan 30, 2018

Even if you can run your tool post grinder the correct speed, it won't have bearings anywhere heavy enough for the job.

JRIowa · Jan 31, 2018

I've done that when thread milling mold inserts years ago. Extremely slow.

I'd make a boring bar with a piece of parting tool silver soldered to a 1" bar.
JR

Limy Sami · Jan 31, 2018

SIP6A said:
Even if you can run your tool post grinder the correct speed, it won't have bearings anywhere heavy enough for the job.

Nor I doubt will you be able to run the lathe slow enough, .........unless I'm 180 out in picturing the part, that's a turning job, and JRIowa's method is both proven and easy peasy.

HuFlungDung · Jan 31, 2018

If it is a boring bar job, Iscar does make boring bars with deep grooving inserts. Pricey (especially if they make you buy a whole box of inserts) but might be of interest. These will plunge as well as taking light lateral cuts, and give a superb finish in most applications I've used them on.

Toms Wheels · Jan 31, 2018

Yeah, I'll scratch that idea, go with what I used before, a hand ground single point boring tool.

I have a heavy metal Top Notch BB, but the standard cutters do not project near enough to .250 depth.

Thanks All

randyc · Jan 31, 2018

I've used stationary router cutters in a lathe many times, much simpler than modifying a milling cutter (and cheaper, for HSS cutters). Make a bar for a HSS rabbeting cutter, grind away unnecessary material if required.

My needs have mostly been decorative contouring in aluminum. It was ten minutes work to make a tool holder that secured a router cutter in a 4-way toolpost. Didn't need to modify any of the cutters.

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