Boring Deep But Small Holes

[awemawson]

Background: I need to bore a set of 32mm thick soft jaws to accept 10mm copper bar. (This is on my Traub CNC lathe)

So not only is the finished hole fairly deep relative to it's diameter, it'll be an interrupted cut, and not only that, but with the jaw clamping ring in place fitted close access to the jaws is limited so the overhang needs to be getting on for 60 mm

I'm tempted to just run a long series 10mm end mill through them but it seems a tad crude, and although hole size isn't needed to be accurate to much more than +  /- 10 thou concentricity is important.

[Fergus OMore]

No doubt that there will be other replies but the classic way is to pull the tailstock poppet out and replace it with a piece of round with a 10mm hole bored right through. This is the steady- used by ALL bagpipe makers.

The tool is nothing but a piece of 10mm round silver steel with a D Bit sufficient to drill the full depth and a little bit.
 Temper the end of D Bit- and simply peck away with the tailstock steady right up to the work.

I've done holes 13" long and 3mm diameter in African blackwood and Lignum vitae this way.
The trick is to clear continually- or it will all wander or seize.

OK?

Norman

[awemawson]

An interesting approach Norman, thank you. No tail stock as such on this lathe, it has an 'opposing spindle' driven by a tiny little 12 kW motor  but I could certainly program it to peck away with a D bit.. Not sure what the effect of the interrupted cut would be though.

[Fergus OMore]

32mm deep isn't a lot. Of course you could just bore it- jaw by jaw. Or - wait for it put a piece of round in it- with a split in it- and then drill a 10 millie hole- and nip the rod. A sort of like a split die? Then  you have your soft jaws unmachined- eh?

Well, he did ask

Cheers

Norman

[awemawson]

Thanks for the suggestion Norman, but the split collar won't work in this situation. This is 'widget production '.
The copper bar is in 1 meter lengths, is griped in the soft jaws, part turned in main spindle, opposing spindle advances grips the part which is still attached to the bar. Main spindle releases it's grip and bar and part are pulled out 45 mm. Main spindle grips again, both  spindles spin up to speed in synchronism, the part is parted off. Opposing spindle withdraws and second operation is performed on its left hand end (drill and tap).. The parts catcher comes out, opposing spindle stops, parts ejector pushes part out as flushing coolant washes the collet for next time. The the whole cycle repeats until the bar is all used. Nb main spindle has a sleeve reducing it to 10.2 mm to prevent bar whip.

[Fergus OMore]

Sounds awfully complicated! Me, I am still in the chalk and slate era .

Seriously though the thing becomes one which needs a basic solution- and that is to grip 10mm and I would have thought that if a 10mm drill was a possibility( poor possibility), mine with a D Bit acting like a sort of one edged reamer might be suitable.

We await results with baited breath.

Cheers

Norman

[John Stevenson]

Tapered bush to fit the spindle behind the chuck if it has a tapered spindle ? with 10mm hole in for reamer support.
Reamer held in the turret.
Close the jaws a tad at a time and spin the chuck by hand, you only need to get witness marks on the jaws

[Stilldrillin]

Tapered bush to fit the spindle behind the chuck if it has a tapered spindle ? with 10mm hole in for reamer support.
Reamer held in the turret.
Close the jaws a tad at a time and spin the chuck by hand, you only need to get witness marks on the jaws

That's a great idea!  Supported at both ends.

Or a boring bar, with central tool.......

David D

[awemawson]

Nice one John - but no tapered spindle bore

It's going to get a 3/8" (9.5 ish mm) end mill up it's jacksy, followed by a 10 mm spiral reamer and if it doesn't like it tough 

[sparky961]

Sounds like you need a collet chuck.

[awemawson]

Got a collet chuck, and collets for the larger sizes (up to about 55 mm) but nothing below 20mm and they are silly money - well over £100 each - J56 is their name iirc and I've never been able to locate used ones which is why I fitted the hydraulic chuck and soft jaws. I'm sure my solution will be fine ..... Probably !

[PekkaNF]

Can you use slightly under size undersize carbide endmill and contrarotate it slightly off-centre?

Like live tool setting on drilling.

Pekka

[S. Heslop]

Would it be possible to take them out and mill them?

[awemawson]

No they need to be in situ and clamped with the same (hydraulic) closing pressure that they will be used under.

I've done the job now with an end mill followed by a reamer. If you look at the arrangement in the picture attached to the original post, you will see an adjustable plate with pegs that engage with the jaw mounting holes. Pegs slide in curved slots to set the jaw spacing, and the clamping force is taken by those pegs.

There is a very narrow tolerance on exactly where the 'fully clamped' position of the jaws ends up. Movement of the clamping cylinder is monitored by a pair of proximity switches. If the 'clamped' position doesn't lie between these limits the controller will not let you start the spindle.

[PekkaNF]

....
I've done the job now with an end mill followed by a reamer. ...

Helical reamer?

Pekka

[awemawson]

Yes

[Pete W.]

....
I've done the job now with an end mill followed by a reamer. ...

Helical reamer?

Pekka

mmmmm, I wondered about that. 

[awemawson]

I thought a helical one would be best due to the intermittent nature of the cut, but as John S said it only needed witness marks clean across the depth of each jaw. I had the main spindle turning about 100 rpm and the opposing one counter revolving again about 100 rpm, and fed the tool in by hand and it was far less painful than I'd feared. Although steel, the jaws are in the soft state.