roll pins - why use them instead of solid pins?

[jaredr]

PM'ing my primary AR and wrestling with re-inserting the roll pin that secures the ejector spring. thing is so small there's actually no roll-pin starter for it in my brownells kit... finally got the pin started without mucking it up, have to wonder - what's the benefit of using roll pins that leads manufacturers to use them over solid centerless ground pins? Are they really that much cheaper to manufacture these days? I understand every penny counts when you're manufacturing but man I've grown to hate them...

[razerok1]

i think its cause the roll pin is compressed when inserted and constantly trying to expand hence locking itself into place kind of how a lock washer works with a bolt. If it was a solid pin it my loosen its way out on its own during cycling and cause the bolt to either scratch the carrier or not allow the bolt to go back into the carrier.. i think.

[Outsydlooknin75]

A roll pin exerts constant tension and allows for a wider range of tolerances. Next time take a file and knock the outer edges off one end and insert that end first. It'll make it easier.

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[whistlepig]

Roll pins are frequently used in an application where the pin needs to stay still. The gap in a roll pin lets it compress. When the right sized pin is used, the pin is compressed a small bit when inserted and friction keeps it in place. If a roll pin starts traveling out it's hole, it is either tired and needs replacing or it was undersized to start.

[Toolguy]

What's cheaper is the hole, mainly. A roll pin can be used in a drilled hole that varies in diameter a few thousandths. A solid pin has to have a very precise hole that is reamed to an exacting press fit tolerance. It's much harder to maintain a precision hole size in production quantities than to just drill and be done.

[jaredr]

man, i really love this place. thanks for everyone's replies, i actually learned something here today. that'll make up for the last week at work...

much obliged, jared

[Sean Gaines]

What's cheaper is the hole, mainly. A roll pin can be used in a drilled hole that varies in diameter a few thousandths. A solid pin has to have a very precise hole that is reamed to an exacting press fit tolerance. It's much harder to maintain a precision hole size in production quantities than to just drill and be done.

+1

Much cheaper to buy roll pins than it is to manufacture them!

[Mark Gale]

PM'ing my primary AR and wrestling with re-inserting the roll pin that secures the ejector spring. thing is so small there's actually no roll-pin starter for it in my brownells kit... finally got the pin started without mucking it up, have to wonder - what's the benefit of using roll pins that leads manufacturers to use them over solid centerless ground pins? Are they really that much cheaper to manufacture these days? I understand every penny counts when you're manufacturing but man I've grown to hate them...

Roll pins are cost effective and they work. In this application, thermal expansion is another consideration. A roll pin has the ability to do its job while being subjected to heat without stressing the bolt any further as it has room to expand and contract. A solid pin would have to be an interference fit and may stress the bolt with an increase in temperature. I have to believe that it would also be much harder to remove/replace than the roll pin.

Edited July 9, 2011 by Mark Gale

[BHE]

Roll pins (spring pins) have constant tension to keep them in place.

To aid in installation, Insert your roll pins about 1/3rd of the way into a cordless drill chuck and tighten. Run the pin in the drill against a running belt sander at a 45*angle to chamfer the end of the pin a small amount. Now you have a nice "lead-in" for inserting the pin. A dab of white grease will keep it in place while you start it. I bought a Stanley Tools punch set from Wal-Mart that has the correct small punch for this job. Hope this helps!!!

BHE

[Hamma Slamma]

On a side note, i don't think it was mentioned, but don't re-use your roll pins.

[Mark Gale]

Roll pins (spring pins) have constant tension to keep them in place.

To aid in installation, Insert your roll pins about 1/3rd of the way into a cordless drill chuck and tighten. Run the pin in the drill against a running belt sander at a 45*angle to chamfer the end of the pin a small amount. Now you have a nice "lead-in" for inserting the pin. A dab of white grease will keep it in place while you start it. I bought a Stanley Tools punch set from Wal-Mart that has the correct small punch for this job. Hope this helps!!!

BHE

I have to politely disagree. Having removed and installed a couple of thousand ejector roll pins in my time, I can assure you that dressing a roll pin is unnecessary. Having an good ejector tool and a quality pin and starter punch set is all you need.

That being said, I am not aware of a drill motor that has a chuck that will hold a 1/16 roll pin that is only 3/8 of an inch long. Most chucks will not grab something that small in diameter unless it is nearing an inch in length.

[BHE]

"I have to politely disagree. Having removed and installed a couple of thousand ejector roll pins in my time, I can assure you that dressing a roll pin is unnecessary. Having an good ejector tool and a quality pin and starter punch set is all you need.

That being said, I am not aware of a drill motor that has a chuck that will hold a 1/16 roll pin that is only 3/8 of an inch long. Most chucks will not grab something that small in diameter unless it is nearing an inch in length."

OK...

Edited July 10, 2011 by BHE

[jaredr]

I can assure you that dressing a roll pin is unnecessary. Having an good ejector tool and a quality pin and starter punch set is all you need.

That being said, I am not aware of a drill motor that has a chuck that will hold a 1/16 roll pin that is only 3/8 of an inch long. Most chucks will not grab something that small in diameter unless it is nearing an inch in length.

thanks - think I know what the pin and punch are, but what is an ejector tool?

re: dressing the pin to get it started, maybe not necessary but certainly helped me knock the burrs off of the pin i had to re-use maybe I'm just lucky, but had no problems chucking in the ar ejector pin in my sears craftsman 3/8 drill. ymmv.

-jared

[Mark Gale]

thanks - think I know what the pin and punch are, but what is an ejector tool?

-jared

An ejector tool gives you the ability to fixture the bolt for disassembly. It depresses the ejector so it removes tension from the ejector pin so it can be removed easily. Two 1/16 punches speed the job also. A shortened version is for breaking the pin free and the longer version is to complete removal. At some point, you WILL bend the a long one if you use it to break the ejector pin free.