I had no idea that I would have to use non standard arbors. Thanks for mentioning that.
This casting made by Gary Martin, what is it and how do I get one?
Nichols arbors have an
9/16" pilot [corrected] while standard style A arbors have a 23/32" pilot. Conveniently for Nichols, 9/16" is a standard size for needle roller bearings. Unhappily for me, 23/32" is not, which is why I planned on an adjustable bronze bushing.
There were exactly two of these castings made, to my design, and this is a picture of both of them, still in to-do state as received from heat-treat, together with my factory arbor support. The arbor pilot enters from the right in this orientation.
If I were doing this again, I would use the more modern (I think) Nichols design for the clamping bosses, where there is basically a continuous tab across the top of the support, with two clamps and one central screw for forcing the support open. I have to knock wedges into the slot on my Nichols-original support so it will slide onto the overarm; the factory castings close up that much.
As a bonus, here's a photo of a Nichols 1" arbor and a standard NMTB40 1" arbor.
Since you have a Nichols mill, you already know the spindle doesn't have driving lugs. Instead you just put one or two socket head cap screws into the face of the spindle. As you can see here, the Nichols arbors don't have driving notches. A 1/4" dowel, secured by a setscrew, makes a fine driven lug. You can also see the Nichols pilot is considerably smaller than the NMTB40 pilot.
The remaining pieces in that photo are the double-ended drawbar. It's a little-known fact that the ASME standard for milling arbors specifies two drawbar threads for each size of NMTB taper. For NMTB40, the two sizes are 5/8" and 7/16". Almost all commercial NMTB40 arbors use the larger size. Nichols arbors use the smaller size. The drawbar will accommodate either size, by reversing the double-ended rod and nut. IIRC, Doc got fed up with the two-piece drawbar and make his own, dedicated to one size.
I should say, that you can probably do quite a bit without the overarm. So don't forgo arbor-mounted cutters just because you don't have a support that fits your available arbor pilots.
I can't imagine that Gary still has the patterns for these castings around, but you certainly have my permission (and I'll put it in writing if Gary wants) to have castings made from the patterns if they exist. You will probably find it prohibitively expensive, especially because you still have to do a couple of fussy jobs to turn the raw part into a functional support, but at least you won't have to pay for the patternmaking.
