Milling a part-sphere with a boring head?

[Tim StevensParticipant @timstevens64731]

I have been trying to mill a male part-sphere on the end of a bit of hex stock, using a dividing head with a boring bar with the cutter facing the wrong way and the drive going backwards. The head was set to about 25 degrees and the shape was generated by turning the dividing head handle until the work had gone more than 360 degrees.

All went perfectly, and I produced several parts, but … the boring bar is on a threaded MT adapter with no locking device, and could easily come undone – especially as the cut is interrupted.

So, does anyone supply tooling for the commercial boring head with the tips on the other way round, ie cutting on the left corner rather than the right with the tool pointing away and the top face upwards, so I can use the drive forwards?

Thanks

Tim

[Tim StevensParticipant @timstevens64731]

[JasonBModerator @jasonb]

Can't you just grind a internal one to suit running backwards, I do that to get them to machine externally rather than internally

[Tim StevensParticipant @timstevens64731]

Yes, I suppose I could, but I am hoping to recommend this technique to others who may not be confident about grinding carbide.

Tim

[JasonBModerator @jasonb]

Then use an off the shelf HSS one

Or a simple holder to take an old crt drill that can be ground to shape

[Les Jones 1Participant @lesjones1]

Hi Tim,
Here are two holders I made to allow the use of round and square HSS tools in the boring head.

HSS tools could be ground to cut on the outside of a cylinder with the boring head rotating in the normal direction to avoid it unscrewing from the arbor.

Les.

[Tim StevensParticipant @timstevens64731]

I had something similar in mind, but my first priority was to find a source of the right (left-handed) cutters commercially. Ho, hum, it's back to the shed again and make something to do the job on the lines of your helpful suggestions.

One other thought I had was to modify the screw-on boring device by unscrewing the body, drilling and tapping a couple of holes in the MT fitting flange (parallel to the spindle axis) and make matching dimples in the body. Then a couple of grub screws (or set screws for our friends over the pond) should prevent any unscrewing in use, while allowing it if needed in future. So, perhaps I might suggest that as an alternative.

Cheers, Tim

[ANDY CAWLEYParticipant @andycawley24921]

MSC Industrial Supply do do them but they are not shown in their online catalogue, they are however in their paper catalogue but only in 12mm shanks not 1/2".

I've just done a recent job where I had a similar need and couldn't wait ( and spend the dosh) so I tightened up the boring head on the shank using a big adjustable whilst holding the shank in the lathe chuck.

All held and I was taking an intermittent cut.

The material was aluminium and I took the precaution of taking light cuts.

[Jeff DaymanParticipant @jeffdayman43397]

Andy you've got the movable part of the head quite far out for this cut – any further out and the head would be held by only one setscrew on the gib strip. I mention it as a safety caution to others – just because the tool WILL extend out that far does NOT mean it is safe to do so.

I'm glad it turned out OK but do please be careful. A cranked boring bar or a 90 degree extended bar mounted through the horizontal hole would be safer, again for very light cuts on aluminum – no hard steel hogging with that sort of long extended tooling.

JD

[ANDY CAWLEYParticipant @andycawley24921]

Jeff, surely it's the adjusting screw that stops the thing from flying apart?

I did see the Arc Euro extension bar and have stored it away for future reference however we do not always have the luxury of doing things the "perfect" way.

[JasonBModerator @jasonb]

Andy a lot of the heads at the lower price range have a threaded MT shank that the head screws onto or off of if run in reverse! Look a little further down teh link Bogs posted and you can see what I mean.

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