doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Action pin clearances ...

Assume a good quality gun; what would be the accepted (or most desirable, not always the same thing) clearance between the action pins and any part rotating upon them?

Has anyone any measured data on clearances in various makes and grades?

Eug

I wouldn't know how to measure gap in such small holes but I'd say the fit of sears and triggers in American classic/vintage/well-known/well-thought-of doubles ain't no squeaker. Maybe the difference from one wire drill size to the next smaller.

jack

A pin is of course quite easily measured with a micrometer. For the small holes the most convient & sufficiently accurate method is with a set of precision ground pin gages. I would think that if you haad a pin measuring .125" for instance if you could ream a perfect hole at .1255" you would be about perfect, these parts definitely do not need a sloppy fit. I can't recall offhand the sizes of all those little wire size drills without going to a chart but I think in most cases the difference between two consecutive numbered ones would give an excess of slop.

Another piece of this is the taper on some pins. My understanding and practice is in from the left, out from the left. When I make custom pins, I put .0005 to .001 taper on them so they tighten up as they go in.

Hi Miller:

Did you mean to ream the hole .1255"?

I know that my math skills are very weak, but I can not make any sense out of what you posted. How does one ream a .125" hole to .0255". lol

Good shooting,

Franchi

I would doubt that any one outside a drawing office has ever even considered this .There are parts of a guns mechanism were it matters ,say in a single trigger and other places were it is of little consequence .Obviously any wear on an axel can cause problems as can an over sized hole or undersized pin.In general I would say its down to individual assessments.

I don't think it is down to individual assessments. I think it should follow sound engineering practice, which can be found in the 'bible' Machinery's Handbook chapter on 'Fits' page 1506 onwards.
Enjoy.

Thanks gents (and Salopian ),

The current (28th) Machinerys Handbook gives five classes of clearances for shaft and hole; "loose running, free running, close running, sliding and locational." I'm taking it that when a tumbler moves on an action pin it should be either close running or more likely sliding.

Just for background, I'm setting myself a project to take a rattly coarse action, and then render it smooth and silky by adopting the best fits, smoothest mating surfaces, spring strengths and correct hardening.

If this means a bit of turning, reaming and polishing, great, thats just what I want to do.

Eug

Franchi;
Yes, an emphatic Yes, what a BooBoo I made there, thanks for catching it. I have edited my original post to read correctly.
Incidently the first Double shotgun I ever owned, a J Stevens Arms & Tool Co model 325 began doubling on me if the rear trigger was pulled first. The problem proved to be the holes through the sears had become worn to an extent the sears could "Wobble" enough for their tails to bind against one another. The right sear tail sat a bit higher than the laft one so it never doubled if I pulled the right trigger first, but one day I went to try a long shot & pulled the back one first & got a very loud Bang. The pull on that trigger simply lifted both sears simultaneously.
Take my word for it "Fit" can be important.

Fraid Miller is correct even about things he can't precisely recall. Wire size twist drills don't change size by a consistent increment but 3 to 6 thousandths" seems about average. Far cry from 5 ten/thousandths" difference bore to shaft which I assume gives a "sliding" fit. For instance in the roughly 1/8" range we're considering, a #30 twist bit is .1285" dia. A 29 is .1360" dia. or .0075" difference. Maybe I should play a machinist on TV as my idea of clearance between axles and bores is only off by 14 or 15 magnitudes! Oh well!!

jack