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Substituting for arbor screws


Jun 25, 2016
Sometimes there’s no correct arbor screw for holding a face mill to an NMTB50 arbor and we use a SHCS and thick washer cut down to fit the hole in the face mill. See pic. Is this particularly dangerous or something everyone does? I found “real” arbor screws at Shars reasonably and ordered a few but they only sell 4 sizes.

Is there a minimum clearance between the work and the big head of the arbor screw? Sometimes the head is at about the same vertical distance from the work as the inserts, realizing of course that the cut will increase this distance when work feeds part moving inserts.

Also I have no doubt you observant folks will bust me for substituting one insert different from the rest, which I wouldn’t do except we ran out of matching ones and we’re only doing rough cuts with this setup. The only thing I think the different insert might screw up is the surface finish. Agree or not?


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Aug 31, 2015
The Moridor
I don't see any problem with using a washer and bolt. I've done it and didn't have any issues other than the Sandvik rep making fun of me for my "lame" homemade washer. He was probably just mad that I didn't buy one from him!


Cast Iron
Jan 21, 2011
Troy mi
If the washer is not hardened, the capscrew will loosen with vibration. Washers needs to be hard enough so the screw head won’t yield the surface and as thick as can be packaged. The thickness of the washer is the major part of the stretch length the screw gets. Cutting down the height of the socket he’d will allow a bit more washer thickness.