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I have a small vintage benchtop lathe with a MT1 taper in the headstock.

I've been using a modern ER16 collet perfectly well with this setup for a couple of years, but it only goes up to 10mm. I want to work with larger stock, with 20mm being the minimum and 25mm would be nice. This requires an ER32 or an ER40 collet respectively.

But they don't seem to exist. I found exactly one MT1-ER32 and it was for fancy pen-turning and was priced to match.


How can I get ER32 or ER40 collet holder on a MT1 taper?

One idea was to buy the right collet holder but on a larger taper, and turn it down. Either a Straight sided one as pictured, or a MT2 and reduce it. These are much cheaper but still a cost.

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Buying a bigger lathe would be a nice option, but that's out of budget.

I understand turning larger stock means more forces potentially breaking the taper, but I'm already turning the same stock in a 4 jaw chuck successfully - it's exclusively Aluminium not steel.

I've already done something similar at https://diy.stackexchange.com/a/189181/44550 by turning a MT0 taper onto a drill chuck stub, but that was soft and I don't know if a MT shank would be harder to turn.

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Turning it down is likely to be a problem, as it's likely hardened, ground, and polished. Grinding it down might work if you have a toolpost grinder. Or you could potentially anneal the shank.

If you have appropriate tooling, turning the whole thing from non-hardened stock and threading it is an option.

Beware the funkiness of Morse taper angles.

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