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View Full Version : Yet another cool toolblock:



Doc Nickel
12-16-2004, 03:13 AM
Picked up some TNMC 4xx carbide inserts and managed to finish up another one of my toolblocks. The TNMC is a triangular threading tool that sits in the holder vertically, rather than flat, so the "pocket" is on the side of the holder.

http://www.docsmachine.com/machineshop/carbideholder4.jpg

Again, the tool height is fixed with these, so I made another solid stop. These particular ones are zero rake, but the same insert is available in 5 degree and 10 degree built in. So with a "level" pocket, I can vary the rake just by changing inserts.

The brunt of the cutting force is on the walls of the pocket, the button-head machine screw is just to hold it in place. That's about as low-profile as I can get for cutting to a shoulder, if I need to. http://bbs.homeshopmachinist.net//biggrin.gif

Here's a close-up of the tool in the pocket:

http://www.docsmachine.com/machineshop/carbideholder5.jpg

There's plenty of "stick out" to the insert and clearance to the block, to make some pretty mongo threads. Probably bigger than I can actually do on this little 3/4HP 11" lathe. http://bbs.homeshopmachinist.net//biggrin.gif

I also picked up some trapezoidal CNMG type inserts (double sided negative rake) for the fourth and last block. Time, however, is as usual against me.

Doc.

John Stevenson
12-16-2004, 04:58 AM
Doc,
Nice work.

I had thought about putting about 8 or 12 of these around a circular disk and running them from a geared motor mounted on the crosslide to make a poor mans thread milling attachment.

I know it's been done before but I've never seen an inserted cutter.
At least using these you aren't limited y revs.

John S.

Spin Doctor
12-16-2004, 05:57 AM
Doc, hopefully with these you won't have the problems I have had with threading inserts in the past. The small ones can be very fragile and if your are not running into a relief groove at the back they are suseptible(sp) to breakage if you over shoot the back of the thread

Doc Nickel
12-16-2004, 07:32 AM
Spin- Considering that the insert is pretty huge, comparatively (1/2" IC, overall OD of the triangle is about the size of a quarter) and the lathe is a relatively small 11" with a cone-pulley belt drive, I suspect I'd have to work pretty hard to badly damage an insert.

But we'll see. http://bbs.homeshopmachinist.net//biggrin.gif

John- Eight or twelve? How big a wheel do you need? http://bbs.homeshopmachinist.net//smile.gif For something like that, I'd look more at those "Thinbit" inserts- cheaper per insert, and you could get more on a wheel.

Just make sure you have a skookum blade guard on that puppy! http://bbs.homeshopmachinist.net//biggrin.gif

Doc.

nheng
12-16-2004, 02:25 PM
Doc, That holder is to die for !

Spin, I've had some problems with small Thinbit threading inserts and have to use a relief groove with them. They will not tolerate the tip digging in much.

Den

Spin Doctor
12-16-2004, 04:08 PM
nheng, that's why I almost always use HSS for threading. There are two exceptions and that is in a Hardinge Tool Room lathe or a CNC where the tool pull-out is controlled by the machine. But with carbide threading inserts I always plunge straight in as it helps to keep the cutting forces split evenly between the two sides