Roll pin tension

[JWF III]

Tension may be the wrong term here.

I am building 2 Colt “clone” 9mm carbine/sbr’s. I’m using Colt brand, pin in, mag well blocks. (Don’t ask why. Short answer is “because”.) I have a Brownells roll pin kit with miscellaneous roll pins ranging from 1/16” to 5/32”. Measuring my factory Colt with a caliper, the holes are 9/64”. And my 5/32” pins measure exactly 5/32”, and 1/8” is exactly 1/8”. So I would assume, if I could find them, 9/64” would be 9/64”.

My question is, how much smaller should the hole be than the roll pin? 1/64” seems like an awful lot, specially putting a steel roll pin in an aluminum reciever and block. But the same size wouldn’t give it enough “tension” to keep it in place.

Any help would be greatly appreciated...

Wyman

 

[doubleh]

I believe roll pins have the correct tension for the size of hole they are to fit. In other words if you have a 1/8" hole you put a 1/8" roll pin in it and everything works correctly. That's the way I've always done things and none have ever come out without being driven out..

 

[Shimitup]

Here's a chart that should give you an Idea of the tolerances.
https://almabolt.com/pages/catalog/pins/springroll.htm

 

[edwardware]

https://almabolt.com/pages/catalog/pins/springroll.htm

Wow. So, 0.001-0.007 for a 1/16 pin, and 0.003-0.0240 for a 0.5" pin. Sounds like ye olde 'beat to fit' spec. I wonder what the spec is for coil pins. . .

 

[JWF III]

Thanks for that great link there, Shimitup.

I had always thought and drilled them as there call size. But I haven’t done them in anything like a reciever before. Specially an aluminum reciever. The aluminum had me a little concerned, that’s when I put the caliper on everything. Could be the pins I measured were a little on the small side. Or it could be my cheap”er” dial caliper. I’ll have to dig my digital set out from the reloading bench and get a battery for it, and check everything again. Probably just worrying about nothing.

Thanks
Wyman

 

[doubleh]

I think you are worrying about nothing and if I wanted really accurate measurements I would get a decent micrometer to measure with.

It's been my experience that using a drill bit that has been resharpened with the center point slightly off center will result in an over sized hole and the worse the center point offset the worse the oversize.

 

[Shimitup]

I think you are worrying about nothing and if I wanted really accurate measurements I would get a decent micrometer to measure with.

It's been my experience that using a drill bit that has been resharpened with the center point slightly off center will result in an over sized hole and the worse the center point offset the worse the oversize.

Agreed, even with a fresh quality bit I expect them to give at least a .001 over hole. For instance if I want a #36 hole I drill with a #37 first in follow with the #36, that's usually awfully close. Very seldom do I need that precision anyway that's why they invented roll pins with a nice wide hole tolerance, their invention did wonders for mass production.

 

[beag_nut]

Thanks for that great link there, Shimitup.

I had always thought and drilled them as there call size. But I haven’t done them in anything like a reciever before. Specially an aluminum reciever. The aluminum had me a little concerned, that’s when I put the caliper on everything. Could be the pins I measured were a little on the small side. Or it could be my cheap”er” dial caliper. I’ll have to dig my digital set out from the reloading bench and get a battery for it, and check everything again. Probably just worrying about nothing.

Thanks
Wyman

When I was the supervisor in the "prototype dept." of a surgical-instrument maker, the machine-shop leader was a tool&die master. He (Dino) always said that "Calipers will get you into the ballpark", but that a mike was the umpire.