[mike_mccue]

Hi,
I've been learning the basics of working a metal lathe. I joined a maker space club that has an old Craftsman 101/Atlas 618 and they have left me to teach my self how to use it. I am currently working with a 2-1/2" dia. aluminum rod that I want to carve into something similar to a cup. It has side walls and a bottom.

Last night I plunged a drill into the face and began the process of hollowing out the interior. I worked at a low RPM and the drilling went very smooth.

I have purchased a kit of the imported brazed carbide tip boring bars and tried to use them to enlarge the hole. I didn't have much luck with those tools. They seemed to cut crudely.

I did find that an old HSS bit that I was using for facing did a great job of cutting the face down. I also use a cheap brazed carbide tip cutter which worked well, and finally I tried a indexed carbide tip tool I had purchased and it worked pretty good.

My general observations was that the boring bars I just bought should be returned and that I should find a better product.

I would like to avoid a carbide vs HSS debate, but it seemed like the HSS worked great and I was surprised at how the carbide, even the ones that worked well, seemed to cut the Aluminum less gently. I tried various SFM looking for a sweet spot.

Which brings me to; I have found two boring bars with HSS index inserts and I am considering ordering one of them.

One uses Diamond shaped inserts and the other uses Triangle shaped inserts.

It seems like the triangle would be ideal for a plunge cut while the diamond might be good for a both a plunge cut and a bit of facing where the wall meets the base.

I'm hoping to get some comments about real life practical use of the two shapes.

Thank You.

[RICHARD ZASTROW]

The triangular bits are positioned at different angles in various boring bars. They are less expensive per edge than the diamond shapes because you generally don't use 2 of the 4 edges in the diamond shapes.

Also, you will find more tip radii available with the triangles as well as smaller insert sizes. Many are specially made for boring with sharp nose radii.

Time to snoop in the tooling catalogs to see what's available.

Dick Z

[mike_mccue]

Thanks.

I ended up buying a 1/2" shank with a triangular index insert and it seems like it is going to work much better.