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utopia · 23-03-2017, 05:14 PM

Parting off with a centre fitted is never a good idea because it can cause the part to jam between tool and barstock as it falls away.
The best method to use will depend somewhat on the lathe in question and the tools available, but ...
I'd make them one at a time.
Either way around really, but if you do them "flange outwards, there will be a smaller diameter at the part-off position.
I would only have just enough barstock sticking out of the chuck to make one part, plus clearance for the parting/turning tool/s, and I wouldn't use a centre at all.
Face and turn both diameters, then drill for tapping, and countersink for a lead on the thread.
Then, with the headstock drive disconnected, fit the tap in the tailstock chuck and enter it into the bore, then tap a short distance by pushing on the (unclamped) tailstock while turning the headstock chuck by hand (using the chuck key as a lever).
When it becomes too hard to cut any more by hand, undo the tailstock chuck and withdraw the tailstock leaving the tap in place. You can then finish tapping by hand with the part still in the chuck if you like, or remove the tap, part it off and finish tapping in the vice.
The swarf falls away better if the hole is vertical in the vice, but its easier to hold in the chuck, so you takes your choice.

If you made them "flange inwards", you could perhaps hacksaw them off leaving a bit extra, then replace them in the chuck and face the end afterwards ... BUT realise that a 3-jaw chuck is somewhat self-centring but the part will not run dead true when replaced (it may be true enough though .. depends on the part and its function.
Doing them the other way round eases the parting-off process and leaves both ends true (though you will need to remove some residual metal by hand with a file as it wont break away entirely cleanly).

Doing them one at a time reduces the length of hole to be drilled too, which is also very much better.
Centre drill first.
I sometimes drill undersize then set a tiny boring tool to clean up the hole to finish size .. and this helps the hole and the resulting thread to run dead true, as the drill on its own will probably run off somewhat. Again, it depends on the requirements of the particular part in question.

Use paraffin for everything .. turning, drilling, tapping and in particular for parting-off.

23-03-2017, 05:14 PM	#99
utopia No turn left unstoned Join Date: Jun 2010 Location: leicester Bike: M750 Posts: 4,545	Parting off with a centre fitted is never a good idea because it can cause the part to jam between tool and barstock as it falls away. The best method to use will depend somewhat on the lathe in question and the tools available, but ... I'd make them one at a time. Either way around really, but if you do them "flange outwards, there will be a smaller diameter at the part-off position. I would only have just enough barstock sticking out of the chuck to make one part, plus clearance for the parting/turning tool/s, and I wouldn't use a centre at all. Face and turn both diameters, then drill for tapping, and countersink for a lead on the thread. Then, with the headstock drive disconnected, fit the tap in the tailstock chuck and enter it into the bore, then tap a short distance by pushing on the (unclamped) tailstock while turning the headstock chuck by hand (using the chuck key as a lever). When it becomes too hard to cut any more by hand, undo the tailstock chuck and withdraw the tailstock leaving the tap in place. You can then finish tapping by hand with the part still in the chuck if you like, or remove the tap, part it off and finish tapping in the vice. The swarf falls away better if the hole is vertical in the vice, but its easier to hold in the chuck, so you takes your choice. If you made them "flange inwards", you could perhaps hacksaw them off leaving a bit extra, then replace them in the chuck and face the end afterwards ... BUT realise that a 3-jaw chuck is somewhat self-centring but the part will not run dead true when replaced (it may be true enough though .. depends on the part and its function. Doing them the other way round eases the parting-off process and leaves both ends true (though you will need to remove some residual metal by hand with a file as it wont break away entirely cleanly). Doing them one at a time reduces the length of hole to be drilled too, which is also very much better. Centre drill first. I sometimes drill undersize then set a tiny boring tool to clean up the hole to finish size .. and this helps the hole and the resulting thread to run dead true, as the drill on its own will probably run off somewhat. Again, it depends on the requirements of the particular part in question. Use paraffin for everything .. turning, drilling, tapping and in particular for parting-off.