[How do I?] Lathe/mill A Converging, Internal Angle Deep Inside Part

[knoq]

there is enough room to use a thin boring bar to form the left taper
in alu with tiny cuts that should be no problem

That would be the smallest boring bar I've seen.... rough estimates are about a 1/4" diameter boring bar and that's with part of the tool post inside the nozzle section. I'm sure they exist, but getting my hands on one would be the tough part

 

[John Hasler]

That.... could work!

I have a QTCP and rotating that is fairly easy.....
The angle of attack on the cutting face may be off, but I could get a HSS boring bar (ideally a blank) and grind that to the correct face.

That's a lot of overhang for a 3/8" bar though. I might be tempted to turn an offset 30 degree cone and a short 3/8" stub onto a chunk of 1" steel shaft and then drill the stub for a HSS cutter and setscrew.

 

[knoq]

That's a lot of overhang for a 3/8" bar though. I might be tempted to turn an offset 30 degree cone and a short 3/8" stub onto a chunk of 1" steel shaft and then drill the stub for a HSS cutter and setscrew.

It is a lot of overhang.
That is one of the things I followed up with Robert about (second link, still no reply). I would expect serious chatter at a minimum or much worse on the extreme case.

I'm not sure I follow the cone bit though....
I can picture the "cone on a stub" but why would the stub hold the cutter? what would the point of the cone be then?

 

[janvanruth]

That would be the smallest boring bar I've seen.... rough estimates are about a 1/4" diameter boring bar and that's with part of the tool post inside the nozzle section. I'm sure they exist, but getting my hands on one would be the tough part

what about a 3/16 solid carbide long shank endmill

 

[John Hasler]

It is a lot of overhang.
That is one of the things I followed up with Robert about (second link, still no reply). I would expect serious chatter at a minimum or much worse on the extreme case.

I'm not sure I follow the cone bit though....
I can picture the "cone on a stub" but why would the stub hold the cutter? what would the point of the cone be then?

It's a stub on the end of an offset cone. You could put the tool right through the end of the cone but the stub would give you a bit of extra clearence so that you could reach into the throat.

 

[knoq]

It's a stub on the end of an offset cone. You could put the tool right through the end of the cone but the stub would give you a bit of extra clearence so that you could reach into the throat.

Ah, so if I'm understanding, it's to avoid putting a square thing in a conical hole by putting a cone in a conical hole.
Thinking about how to machine it, but could be a good solution.

 

[John Hasler]

Ah, so if I'm understanding, it's to avoid putting a square thing in a conical hole by putting a cone in a conical hole.
Thinking about how to machine it, but could be a good solution.

Just put the chunk of 1" shaft in your four-jaw, offset it so that the lathe centerline is half the stub diameter into the shaft and turn the stub. It will be an interrupted cut, of course. That will give you a 1" shaft with an off-center stub sticking out the end. Then set your compound to 30 degrees and taper the shaft back from the cone (interrupted cut again). Draw it up first to be sure the dimensions are right, of course. 3/8" may be too big for the stub.

[Edit] Will a real machinist please chime in and tell me if I'm full of it here? I'm just working this out in my head.

 

[kd4gij]

I have what you need but couldn't find one on a quick search. Extra long 1/2" shank boring bar for a boring hear the tapered part is 4 " long.

 

[knoq]

So is this just a longer boring bar with a cylindrical/tapered tail end? Or is the head the important part where it hold the bars at a 0 or 90(deg) angle?

sorry... just hard to tell from that picture and I'm far from knowledgeable on the more exotic tooling.

 

[JimDawson]

Here is a boring bar holder that I made for my BXA (205) tool holders. These happen to be 3/4 inch shank, but 1/2 and 3/8 shank are readily available. Also these happen to be carbide tipped, but HSS is also available. Here is a whole page of them http://www.use-enco.com/CGI/INPDFF?PMPAGE=198&PMCTLG=00



The holder is a chunk of 1.5 inch CR shafting I had kicking around. The key is just that, a piece of 5/8 key stock. The holder has a shallow key slot milled into it and the key stock is simply bolted on with some 1/4 inch socket head cap screws.



It is perfectly acceptable to grind clearance on the back of the bit as needed to get the job done. I have boring bars ground into all kinds of strange shapes.



With some creative setup it might be possible to do all of the bores in one setup working from the large end. I would have to draw it up and draw the tooling in place to see.

If I had to do more than about 2 of these I would turn my lathe into a mechanical tracer lathe, something on the order of a taper attachment, but spring load the cross slide, so it will only need to work in one direction. That way you could easily make changes to the nozzle shape just by changing the pattern.