Milling with a lathe

Page 2

ER collet system

Next I looked at a suitable collet chuck to hold the  milling cutters.

I purchased an industrial grade ER32 chuck and 10 collets from an online store - $174 AUS. About 40% off local prices including postage.

Since then, online prices have reduced considerably.  Quality is as advertised, and I have had no issues.

ER32 is cheap, compact and available with a Morse No. 4 taper to fit my spindle.  

The ER series is a good choice as it will securely hold virtually any metric or imperial round shanked mill, drill, thread or rod, is quick to change and easy to use - self releasing and no stuck collets.

It also has a 20% longer grip axis than any other system, for potentially less runout.

er32

The collets tilt to push in and remove.  Some people seem to have trouble figuring this out.

The ER32 holding range is up to 20 mm.  Most basic ten piece collet sets are comprised of nominally even sizes (eg. 2, 4, 6, 8 mm etc.) which will compress to hold anything in between.

The recommended compression range is 1 mm, but they will go down to near 2 mm.  The only exception is for sizes below nominal 6 mm, which will only compress to 1 mm.  Therefore you will need to buy a separate 3 mm collet to cover the range 3 - 2 mm.

The full set of collets (20 piece) has both even and odd nominal sizes which gets around this issue, and makes inserting and removing cutters near the nominal size easier.  I would recommend you buy the full set.

While the basic single point "C" wrench that comes with the collet chuck works reasonably well, it's worth spending a few extra dollars for a safety wrench - seen below on the left.

ER32 safety wrench

This allows you to tension the chuck to a higher level, and can't slip.

Draw bar

A draw bar had to be made up to secure the Morse taper collet chuck in the spindle of the lathe.

The components are seen below - (A) Morse taper collet chuck, (B) draw bar through bolt, and (C) draw bar bolt end locator.   

ER collet draw bar

(B) is simply is simply a length of standard 16mm metric threaded shaft - commonly available in most hardware centres.  Weld a nut onto one end.

(C) has a stepped collar which fits into the bore and a shoulder to pull up against the end of the spindle (drive belt end).  I recessed a flat washer into the face to assist in tensioning.

draw bar nut

You can use a self centering cone shaped end locator as an alternative.

To fit the ER collet chuck, the standard chuck and any mounting bolts are first removed.

(A) is then inserted into the Morse taper at the chuck end of the spindle, (C) is fitted into the other end of the spindle, (B) is inserted through (C) and screwed into the back of (A).

Lightly tension the draw bar with a couple of wrenches.

Note: The draw bar will pull the Morse taper together very tightly, and the collet chuck will have to be knocked out to remove it.

To do this safely I unscrew the draw bar a few turns and then gently tap on the outside edge of the draw bar nut, while slowly rotating the spindle by hand.   This avoids damaging the rear spindle bearing from hammering in the one position.

The Morse taper should release quite easily.





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2014