The Craftmans Shop > New from Old
The Sequel - Oh Blimey I bought a CNC Lathe (Beaver TC 20)
awemawson:
Well I couldn't leave it at that - could I :clap:
So out to the workshop and I swapped the insert for a TPKN 1603PPTR which is the one with the odd two facets rather than a radius.
It actually gave a pretty good, and certainly acceptable, surface finish on this test piece of EN8 steel at 700 RPM. I just need to work out graphically if there are any implications for the male taper nose profile where it protrudes from the base metal - it may be within the chamfer of the chuck, but I need to check that they won't clash.
(The value "BS" in the picture is 1.47 mm)
jiihoo:
It is definitely looking better with the 2nd insert!
awemawson:
Oh yes Jari - and I've tried a few random ones today !
Today's job was to see if there was any way to cut an undercut at the root of the taper where it meets the body of the adaptor. This is to prevent any problems mating with the chuck body. Chuck body has a very small (just over 1 mm) 45 degree facet here but with the tips I have I can't get the root radius small enough to sit in that facet.
Normally I'd just use a parting tool or diamond tipped tool to form a groove at the root, but here I am working out side of the envelope where normal tools can reach.
Trying to push the TPKN 1603PPTR to it's limits to make a groove there I ended up with a nasty crash, pulling the EN8 bar end out of the chuck :bugeye: Lucky this is an experimental test piece! Tidying it up on the manual lathe I got it back to a state where I could experiment cutting ever smaller tapers I've come to the conclusion the with a TPUN160304 tip (ie 0.4 mm tip radius) I should be able to get away with it - I have TPUN160308 tips but in a carbide grade suited to aluminium - so too soft and too large a radius.
TPUN160304 tips on order in P40 grade (steel and alloy steels)
All a bit of a pain but this is why I'm making numerous experiments before working on the adaptor itself - don't want to wreck that at this stage
nrml:
Can't you do the undercut on the manual lathe at the end? It shouldn't affect the mating of the chuck to the adapter.
awemawson:
Thanks for the suggestion.
The face where the under cut should be has to contact the relevant bit of the chuck absolutely and precisely when the tapers close together.
As the taper wont close without the under cut I cannot be sure the sizes are right, and dismounting it would be counter productive concentricity wise,
I had already thought that I could 'half machine' the taper, mount it on the manual lathe for undercutting, remount it on the CNC and finish the taper but it's fraught with introduced inaccuracies
. . . .it's all a blooming palaver !
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