A method to bore a very narrow taper

[Tokarev]

When I had to bore a taper, to match the pictured part, for the swaging of narrow cones, I had to come up with a way to bore the hole out to the taper.
As I do not do it more often than once a year or two, buying a $50 micro boring bar felt like a waste.
What I ended up doing is taking a stub of a broken 0.08 drill bit, putting it into the 45 degree boring bar holder, and using it to bore.
Initially, I went 0.001 a pass, at 200 RPM, advancing about 0.001 per second. Then I upped to 0.0015 a pass.
Yes, it took me almost 1 hour to bore the taper, but the $50 tool would have paid for itself only after a few years, and it could not bore as narrow as the drill bit.
Attachment 259128

[akajun]

Glad you got it done but why didn't you just grind the proper boring bar from a HSS bit? Even a busted Endmill or old tap would have worked? That drill bit is pretty flexy

When I had to bore a taper, to match the pictured part, for the swaging of narrow cones, I had to come up with a way to bore the hole out to the taper.
As I do not do it more often than once a year or two, buying a $50 micro boring bar felt like a waste.
What I ended up doing is taking a stub of a broken 0.08 drill bit, putting it into the 45 degree boring bar holder, and using it to bore.
Initially, I went 0.001 a pass, at 200 RPM, advancing about 0.001 per second. Then I upped to 0.0015 a pass.
Yes, it took me almost 1 hour to bore the taper, but the $50 tool would have paid for itself only after a few years, and it could not bore as narrow as the drill bit.
Attachment 259128

[John Taylor]

A "D" reamer is easy to make.

[garandsrus]

I would probably have turned a piece of drill rod to match the taper you want (external taper so no special tools) and then milled/cut it in half to make a D reamer as was mentioned. You would need to harden the tool after milling it and cutting in some relief on the cutting edge, which is normally the left edge.

Have you tried the die yet? My guess is that your cores are going to stick in the die and not be easy to remove. The finish probably won't be smooth enough for them to eject easily, which is still true if you used a micro boring bar. Too much flex/chatter.

[Tokarev]

All right, next time I will just keep it to myself.

[Win94ae]

Well, I think it is genius; because I have no idea what you are talking about.