View Full Version : facing with triangle inserts

11-09-2007, 05:04 PM
Finally got my QC toolpost mounted on the South Bend 10K lathe and have some triangle inserts and holders but the inserts have a sharp tip and I'm not sure how to face with them. Or do I need some with a radius on the tip?

I am building a disc sander and the 1/4 inch thick aluminum disc that I am making needs to be faced to get it to run true. It has about .030 wobble and when I tried to use my lantern toolpost to face it off, it squealed so loudly that it hurt my ears. It squeals less with the QC toolpost, but I am not sure how to use the triangle inserts.

My friend said that I am probably turning the disc too fast and that slowing it down will help. It already is in the slowest speed without using the backgear speeds.

11-09-2007, 05:11 PM
Squeal suggests to me that something is rubbing instead of cutting.

11-09-2007, 05:12 PM
You are probably going to want some radius on the insert. Maybe try to turn it so you get ~30 lead angle?

On a disk that big, surface speed is going to be a problem too. It's quite likely you are too fast on the outer portions. Not to mention warpage from both pressure and heat effects, if you let it heat up much at all.

Maybe fasten it to a larger plate, perhaps a face plate? Not sure how, perhaps toe clamps and glue? That would cut down on shift/flex and also lower resonance reducing chatter.

But I'm just guessing, I don't recall having tried to face a thin aluminum plate that large.

11-09-2007, 05:37 PM
Are you sure you have a positive insert in a positive holder? Or a negative
insert in a negative holder. If you have a negative insert in wrong holder it won't work.

Spin Doctor
11-09-2007, 06:34 PM
Use two sided tape to mount the disc on the face plate (check the face plate with an indicator to see how flat it is). Feed from the outside edge in towards the center. Set the tool at an angle the makes sure the chip won't curl in between the tool and stock on the back side of the cut. Run at low speed (I'd use HSS myself). Before you take the cut wipe the stock down with a rag sprayed with WD40 or LPS1. This will provide enough cutting lube to make the job easier without generating clouds of coolant. A flood coolant will cause problems with the tape delaminating

Paul Alciatore
11-10-2007, 10:50 AM
I'm with Spin, it is more likely the work than the insert that is causing the problem. I bought some tools that use the triangle inserts and find them to be just fine. Of course, be sure the inserts are properly mounted in the holders - no chips under them, etc.

The 1/4 inch thick disk does need good support. I like the suggestion of glueing it to a backplate.

11-10-2007, 10:55 AM
Ran it in back gear (lower speed) and that helped the squeal. It is now lower in pitch and not as loud. There are still some grooves and pits to face off. I have been using one edge of the triangle insert almost parallel to the disc and it seems to work OK. I'm sure that there is a proper way to use these inserts.

11-10-2007, 11:02 AM
The disc is mounted on an expanding mandrel mounted in a collet. Maybe I can use the face plate between the collet and the mandrel to steady it more. Using the face plate alone would make me have to dial it back in again. Thanks to all--Mike.

J. R. Williams
11-10-2007, 11:16 AM
Sticking the plate to the lathe's face plate will not solve the problem as this will make the disk conform to the surface plate and the stress in the disk will restore it to a warped surface when removed. The carbide inserts have a feed/speed cutting window that must be followed for reasonable service. Grind a sharp cutting edge on the insert with a lot of top clearance and take a small cut at a slow RPM.


11-10-2007, 02:55 PM
your running the edge of the triangle parallel to the work - so the cutting edge is the entire side of the triangle?

Peter N
11-10-2007, 03:06 PM
your running the edge of the triangle parallel to the work - so the cutting edge is the entire side of the triangle?

Maybe he's trying to polish it smooth instead of cut it :D

Mikem, turn the toolholder round a little bit so that you have a small clearance angle between the edge of the insert and the work.
You need to be cutting with the nose of the insert contacting, and the rest of it clear of the work for facing.


11-10-2007, 05:04 PM
The angle wasn't quite parallel, so there was some clearance. It works best from the inside out. From outside toward the center, it digs in and leaves a spiral gouge. These inserts were some that I got at a surplus auction, so I don't know what metal or purpose they are to be used for. Some have such weird shapes that I don't know what mounting or holder they should use. I have a bunch of different ones. Boy, are they heavy--the drawer full of inserts seems like it weighs a ton. Thanks to all--Mike.

11-10-2007, 05:41 PM
Well if it was me, i'd find an insert that is round or has a radius on it, or better yet, get a piece of HSS and grind the nose round. Then set the bit just a little bit above center, take a light pass from the outside in with a slow feed.

If your getting a spiral pattern in its because your feed is too fast and you might be taking too heavy of a cut. For a good finish take a fairly light cut with slower feed.

<edit> the reason why it works best going from inside out is that it is dragging a larger cutting surface across the work - this tends to cause chatter and be hard on the inserts, in my limited expierence.