The Craftmans Shop > New from Old
The Sequel - Oh Blimey I bought a CNC Lathe (Beaver TC 20)
AdeV:
Ah, ok; one wonders then, would they necessarily be "gnat's cock" accurate, if they're effectively roughing collets? Can you get 2nd op/finishing collets in that size?
awemawson:
Oh yes, and they are £140 each new :bugeye:
AdeV:
Yikes!
Time to figure out a program to make your own?! :smart:
awemawson:
Yes a bit pricey aren't they !
It was suggested quite correctly by Ade that the surface of the previous test bar could be the cause or at least contributing to the observed run out of the collet chuck. After all it was just a bit of MS bar stock.
So this morning I mounted up a piece of 30 mm bar that I had parallel ground to a good finish in the J&S 1300 cylindrical grinder and measured it's run out. It's a different collet of course being a different diameter but this probably is typical of what the chuck can achieve at the moment with the rather old collets that I have, and it's state of wear. Perhaps 15 microns run out.
Now I reckon that most of this is going to be in the taper that the collet is pushed into to close, so I'm scratching my head how I can possible grind or lap this in situ on the lathe.
As always, suggestions would be welcomed.
awemawson:
I'm trying to find figures for what degree of concentricty I should expect from these Crawford Multibore M673 collets but have drawn a blank. However I have found one manufacturer for collets who quotes 30 micron for 'standard' and 20 micron for 'precision' in the 30 mm diameter of the last test where I was getting 15 microns.
Am I chasing ghosts - it seems a lot of run out to me.
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