A kind person gave me some weird old collets, and two rough Hercus spindle thread holders/adapters (ER25 & ER32).


Step Description Pic.
1) The collets They are 24mm diameter. The front looks just like an ER25,
but the whole collet is much longer - 45mm.

Taper is 8°, compared to 16° on an ER.
I eventually found the spec – Q24/16. Grips up to 16mm
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2) The holder An ER25 holder is a compromise – even this unfinished
one which has some extra metal in the taper.

The nut end of the taper is loose,
and the tapered section is shorter than these collets,
but I think it should grip over half of the collet
IMG_0479.jpg
3) Taper setup I mounted a collet on a rod (drill) in my chuck,
and used a dial gauge on the toolpost
to align the compound slide angle to the collet's taper
IMG_0481.jpg
4) Boring A few passes at 4 or 5 thou, and trial fitted a collet.

It was stuck out too far, so a few more passes.
Cleaned up with a little grinding stone
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5) Testing Tightened the nut on a collet,
and used dial gauge to check runout.

It wasn't good – about 3thou.
Tightening the nut more got it down to 2 thou.

Decided it was just these rusty old collets
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6) ER32 Unmount this hacked holder,
borrowed ER32 collet on rod, align compound to taper,
ER32 holder on spindle, final machining of the taper.

TRO much better. About half thou. Same as my spindle
IMG_0485.jpg
7) Fiddling Back to the hacked holder. Fitted it more carefully.

Noticed that the spindle thread is a little loose.

Padded the flat section with some paper.
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8) Re-machine In its better centred/mounted position on the spindle,
polished a few micron off the taper.

Collet is now about a thou TRO
IMG_0483.jpg



So, not exactly precision holders, but more accurate than my 3jaw chuck, and totally free!

(until I buy some ER32s to fit in that holder)
Attached Images




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