Mini-Lathe: Adapting a Five Inch Four Jaw Chuck Adapter Plate

The kludge required to trim the coaster rims disturbed the silt enough to reveal a long-lost 5 inch 4 jaw chuck that fit neither the old South Bend lathe nor the new mini-lathe. In any event, the chuck does have an adapter plate on its backside, it’s just not the correct adapter plate for the spindle on my mini-lathe.

Making it fit required enlarging an existing recess to fit the spindle plate, a straightforward lathe job with the plate grabbed in the 3 jaw chuck’s outer jaws:

5 inch 4 jaw chuck - boring spindle recess
5 inch 4 jaw chuck – boring spindle recess

Carbide inserts don’t handle interrupted cuts very well, but sissy cuts saved the day. The plate is kinda-sorta cast iron, so the “chips” are dust and a vacuum snout reduces the mess; you can see some chips inside the bore.

A faceplate for the mini-lathe lathe located three holes matching the spindle plate, after I noticed the amazing coincidence of both parts having 26 mm bores. Making an alignment tool from a scrap of 3/4 inch (!) Schedule 40 PVC pipe was an easy lathe job:

5 inch 4 jaw chuck - adapter plate alignment
5 inch 4 jaw chuck – adapter plate alignment

Transfer-punching those holes produced pips on the chuck side of the adapter plate:

5 inch 4 jaw chuck - spindle bolt spotting
5 inch 4 jaw chuck – spindle bolt spotting

I thought about freehanding the holes, but came to my senses:

5 inch 4 jaw chuck - adapter plate drilling
5 inch 4 jaw chuck – adapter plate drilling

Of course, the Sherline lacks enough throat for the plate, so each hole required clamping / locating / center-drilling / drilling / finish drilling. With all three drilled, hand-tapping the threads was no big deal:

5 inch 4 jaw chuck - rebuIlt adapter plate
5 inch 4 jaw chuck – rebuIlt adapter plate

Those are M8×1.25 studs from LMS (although the ones I got look like the 30 mm version), with the long end sunk in the adapter plate to put the other end flush with the nut on the far side of the spindle plate:

5 inch 4 jaw chuck - installed - spindle nuts
5 inch 4 jaw chuck – installed – spindle nuts

And then it fits just like it grew there, although the jaws don’t have much clearance inside the interlock cover:

5 inch 4 jaw chuck - installed - front view
5 inch 4 jaw chuck – installed – front view

Now I’m ready for the next set of coasters and, if the jaws stick out too far, I can gimmick the interlock switch for the occasion.

If the truth be known, I ordered two sets of those studs along with the 4 inch 4 jaw chuck intended for the mini-lathe, so, if anything, I’m now over-prepared.

The description of the 4 inch chuck seems inconsistent with its listed dimensions, which may be why I ended up with the larger chuck in the first place. You can never have enough chucks: all’s well that ends well.