The ER32 collet holder I purchased years ago had a bolting circle of 82mm with holes tapped M10 (the lathe spindle BC being 84mm, 8mm dia holes) and also a different register bore.
I had fitted it by machining a thin aluminium adapting plate and three M10 brass plugs, through drilled 6mm securing the holder to the spindle with 3 M6 socket head screws and nuts. Not that I liked that so much....
Time for a change: a properly fitted backplate with studs and the usual 14mm hex nuts I've got on the chucks and faceplate.
A heavily rusted (see bore in photo below) leftover provided the material, which I chucked, faced and bored to fit the spindle register: fortunately, my 3jaws is fitting very precisely to the spindle, so I could remove the chuck itself and test the workpiece on the flange with reasonable expectations to set it back in the original position. Of course I did not remove the workpiece from the jaws.
A few cut and tries brought a very good fit, in the end. Mostly out of luck, tho: after the last cut I could sense a little play when fitting the plate to the flange. "Little", but still play.
Exactly what I did not yet know I wanted: in fact, the workpiece was very hot and shrinked to a perfect fit when it cooled down.
- Lesson learnt, and kept well in mind on later stages -
Next, I clocked the bore on the mill and drilled the three holes for the studs, to be tapped M8.
At this point, I had to make some studs: made (12 of) them from M8 bolts, to take advantage of the already threaded end.
Also... ...a nice discover into the metal shelves: I had already made most of the backplate work, years ago.
Completely forgot! :-(
Now I had the studs, I secured the backplate to the spindle, faced it, and turned an oversized register for the collet holder: let it there cooling down for a good while before cutting to size.
Here's why I had dumped the 'other' backplate: no way to secure it with M10 bolts from the spindle side of the backplate, as the heads would interfere with the recess. Either I drilled new holes on a larger bolting circle on the chuck (which is at least surface hardened) or bolts from the top, as they were before.
Not wanting to have bolt heads protruding from the front of the chuck (again) I had to study some fancy way of securing it: I drilled through and cut short lenghts of an M10 bolt, to be screwed into the M10 holes of the chuck, with the idea of fitting some screws resting on them into the holes.
A picture's worth a thousand words...
The heads were still a few thous too large, used a jig to take a skin cut on them without ruining the threaded part
Tapping the holes for the screws: that tap cuts steel like butter!
READY!
One day, I will make a new plywood box for the collet holder....
Marcello
