Parting-off Tools for Small Lathe

Parting blades or tips, with a central groove reduce the risk of swarf jamming in the slot, because the swarf is now two streams, each much narrower than the slot being cut.

As a plug for rear toolposts, where possible; for a long time I ground the tool at an angle so that any "pip" was on the raw material rather than the work. This results in swarf that is wider than the slot, and has the additional disadvantage of tending to force the blade sideways. With the tool set with zero top rake, and light lubrication with soluble oil, a dig in was pretty rare event.

With the tool ground square, and zero rake, I am now brave enough to use a fine power cross feed for parting off.

No doubt this is pride coming before a big fall!

Howard

I chose the flat-topped blade and holder because it was smaller than the v topped blade and holder. After ordering it I realised that the v topped chipbreaker type comes in different sizes.

Hey, ho.

James

My own view is that parting under power is a bit of circus trick. You can get excellent feel for how fast you can advance the tool doing it by hand, and there are often conditions where it may be practical to vary the feed rate as you plunge in - especially going extra slow as you near the cutoff point in order to minimise the pip or ring. I can't see that you'd reliably save time with power feed in most situations outside a repetition shop.

My own view is that parting under power is a bit of circus trick.

I nearly always part off with power feed. Likely takes a little longer than hand-feeding, but leaves me with one hand for lube/cutting oil and the other ready to trip the power feed before it falls off, if It is a large lump, or to catch the part rather than losing a small part. I’m not working at piecework rate!

I tend to part off under power on the manual lathe and by hand on the repetition lathe.

Andrew