Drill Bit

[tbroye]

I bought a "B" mandrel from AS. I want to make some Delrin bushing to use when finishing a Churchill kit. I measured the shaft with my trusty HF digital mic. It measures .287 or 7.31mm. where can I get a drill bit that is the same size as the shaft. Do they even make a bit that is 7.3mm Looked at my chart and couldn't find a fractional, number or letter bit that was close. Any help would be appriciated.

Tom

 

[jthompson1995]

I've heard that the B mandrel can be held with a 5/16" collet, but that would be closer to .3125 than what you measured.

You could get some extra 8mm tubes. drill 8mm hole in the delrin bushings and epoxy the tubes in. It should give you a good fit, htough I'm not totally sure about the epoxy sticking to the delrin.

 

[Randy_]

Looks like your HF caliper let you down or you got a severely undersized mandrel. The Berea "B" mandrel is supposed to be 0.291" +0.0" -0.002". The mandrel I got from Berea measures 0,289" and the one I got from Joe Collazo measures 0.290".

An "L" drill bit is supposed to be 0.290" which might be a hair snug for a spec mandrel and a "M" drill bit is supposed to be 0.295" which is probably a bit loose. A 7.4mm drill bit should be 0.2913" which is probably the best you can do; but I have no idea where you could find one. An Internet search may turn up a source.

If it were me, I would get a "L" bit which should not be too hard to find. If your mandrel really is 0.287", the "L" bit should be just right. If the bushings turn out to be too snug, you can always polish the holes and take off a thou or two and loosen up the fit.

 

[Rifleman1776]

Is this were I go into my weirdo drill bit size rant? [:0]

 

[tbroye]

Went out to the shop this moring after ready you replys. I can get .290 or .289 depending on how I use the mic. I think is was more a case of operator error. I think, I was clamping, for lack of a better word to tight on the manderl and thus coming up witht the smaller measurement. Has anybody come up with chart or some kind of cross reference for the various kits names drill and bushing size and tube size from the different manufactures and distributors? It seem like even though the kits are basicly the same they all require different drill, bushing and tube sizes, it drive me nuts, more than I already am when trying to get every thing I need. Rant off.

Tom

 

[wdcav1952]

Originally posted by Rifleman1776

Is this were I go into my weirdo drill bit size rant? [:0]

Go for it Frank; we love your weirdo rants!! [}]