Securing workpiece for parting in lathe or 'left feed'

Martin, John. some good ideas. I have used a metal rod of the right diameter where the workpiece has a centre hole. The rod held in a drill chuck which works well but only if the piece has a centre hole!. I'll look at the ER collet idea.

The 10mm shaft helps because the I can pull the piece in tighter to cut off. Also, the 'tail' sticking through the spindle means that the piece is unlikely to come out of the chuck, though it might flex!

As to the left to right movement, I've avoided it recently by using the parting tool to get a neat 'right hand side' edge. I cut a lot of pulleys!

Stuart

??? Sorry, this still makes no sense to me! I think the Sherline spindle BORE is 10mm diameter, it has an MT1 taper. Chuck fitting is 3/4 - 16 so the spindle OD must me significantly more than 10mm - in fact the bearings have a bore of 20mm so that's the OD in the bearing section. What's a metal rod of the right diameter and why is it held in a drill chuck and which piece has to have a centre hole to use it? Where do you put the 10mm shaft and why does it allow you to pull the piece in tighter? If you could be clearer in stating your problem, possibly posting a photo, it would be easier to give specific suggestions!

John,

Mia culpa if I've used poor descriptions but its actually quite straight forward.

The ID not OD of the spindle is 10mm and the Lathe chuck - 3 or 4 jaw is as you say 3/4 - 16tpi. This means that the spindle with the chuck on it has a 10mm hole right through is axis.

A stock piece to make say, a brass pulley, which is 10mm OD fits nicely through the hole and is clamped in place with the chuck. I then bore a hole in it with a 'drill' chuck fitted to the tailstock, say 3mm.

I can then place a 3mm rod into the tailstock drill chuck and use this as a dead centre poking it into the hole in the workpiece. When parting the workpiece can slide further onto the rod but is supported laterally.

Alternatively, if working from stock with a max diameter of 10mm I can position it so that it extrudes from the lathe chuck by say 25mm. Work on the end then loosen the chuck and slide it out another 10mm. This is not ideal as I lose indexing but with care this can be re-established. Ergo, the piece remains well supported laterally.

Following on from John's question above, from my answer you can see that I am not into heavy engineering; no steam engines. Mostly small components for radio controlled yachts/power boats which are made from Brass or Aluminium.

I've taken to using delrin rod for pulleys of late. I had managed to reduce the parting off problems with Brass but are finding them more acute with delrin (or sometimes nylon). I expect this is because these plastics, however rigid and machinable they are, are more slippery than brass.

I also make components on a sherline mill - cases, cogs, small steering boxes etc. I'd like to try using Delrin here but buying sheet delrin is very pricy. Any sources of reasonable prices materials or suitable 'plastic' substitutes?

Thanks, that is clearer. I suspect that if you drill a 3mm hole then use a bit of 3mm rod it won't give much lateral support because of play between the rod and hole. Better is to centre drill and use a standard dead or live centre.

What sort of parting tool are you using - carbide? If so I can understand having problems with plastics because they need a very sharp tool. Best grind your own from an HSS blank - you can get parting blade holders for small lathes with narrow HSS blanks from the likes of RDG or Arc. Actually I see Arc have ready-sharpened blades.

Corian is a lovely material to machine and make small components from. Find a friendly kitchen fitter who will let you raid his waste skip.

John,

Yes, I use a HSS blade and regrind it regularly.

Corian - heh, I'll give it a try but my wife might spot the hole in the kitchen worktop!