Using square hss blanks in round boring bar

[Clunker1]

I've acquired a set of various size round boring bars with square holes for hss tool bit. Hole on one side positions the bit at 90 degrees to bar axis and the other end at an angle. As I have a box of hand me down hss blanks. I'd like to use these rather than buying more boring bars of the insert or cemented carbide variety.
I've looked at the profiles of cemented carbide boring bars and reviewed the "Boring Primer" on the forum. As I understand, my exposed end of a hss tool bit should be as short as possible, have a small nose radius, a neutral or slightly positive lead angle ( angled back away from cutting direction for tight tolerance), adequate relief from part radius, a relief on end away from cut surface, and zero or slightly positive back rake ( away from radius). However this is my understanding for cemented carbide and inserts from reading the primer.

Should the geometry I grind into HSS be the same? Secondly, should I be using the 90 degree slot or the angled slot in these boring bars?
Thanks

 

[GeneT45]

Use the 90* slot for form tools - like internal threading. Use the angled slot for most boring - it lets you reach past the tip of the boring bar to bore full length and/or cut a flat bottom. If you're boring a through-hole it really doesn't matter.
Grind your tools mostly like you'd grind lathe cutters. The biggest difference is that you will need more front clearance. The exact amount varies with the size of the hole being bored (not the final size, the size you start with). The smaller the hole, the more front clearance you'll need for a given size cutter. A CAD program can be really helpful if you want to calculate a size. I usually just grind a pretty sharp clearance on the bottom of the leading edge when I need a tight hole - but it depends on whether you're setting up for a particular job or for general use.
Definitely use as short a protrusion as possible, and extend your bar only as much as necessary.
The rest of your geometry is as you describe. You haven't mentioned any numbers for your angles, but I usually grind HSS "sharper" than the inserts I might use. I'm probably excessive in this respect, but I don't mind touching up an HSS cutter for the next job.

GsT

 

[Clunker1]

Thanks GsT. My first application is boring a mt5 to mt3 sleeve to make a 5c collet adapter for my lathe. I have some Rex 95 blanks to make bits which I think should cut this chinese sleeve material.

 

[mickri]

I have two or three of those round boring bars. I use them all of the time. Mostly the angled end. The tool bit should be as short as possible. I posted my tool bit on Mikey's thread on grinding HSS tool bits. Here is the tool bit I use most of the time. The geometry is a little different because you are cutting on the front edge of the tool bit.