ak barrel pins

[nicitaja]

So, I already posted in the WTB, looking for yugo length (36.6mm) oversized (8mm/.315) barrel pin. Then I noticed that even curtis's (but out of stock anyway) 8mm pins were profiled after romanian trunions and not the length I would like for a bulged yugo.

I did a quick search for 8mm tool steel, was able to find grade A2 8mm tool steel / Drill Rod @ 36" locally at fastenal, Im going to assume that its oil hardening drill rod which comes annealed and at Rockwell B approximately 100, Rockwell C approximately 20 as I pick it up. Or this is how I understand it, Im not really sure though.

So the question is, anyone know how hard the barrel pins will need to be? Im thinking this stuff might actually already be pre hardened (but unsure), or the simple heat to bright orange and drop in motor oil, and the 700 degree heat and let air cool would be good enough?

Thanks in advance,

-John

[Richard Erichsen]

So, I already posted in the WTB, looking for yugo length (36.6mm) oversized (8mm/.315) barrel pin. Then I noticed that even curtis's (but out of stock anyway) 8mm pins were profiled after romanian trunions and not the length I would like for a bulged yugo.

I did a quick search for 8mm tool steel, was able to find grade A2 8mm tool steel / Drill Rod @ 36" locally at fastenal, Im going to assume that its oil hardening drill rod which comes annealed and at Rockwell B approximately 100, Rockwell C approximately 20 as I pick it up.

Pre-hardened tool steel dowels from McMaster Carr or Misumi USA are the better choice in my opinion. Length would be 40 mm as your closest increment, then you'd have to trim off the excess.

So the question is, anyone know how hard the barrel pins will need to be? Im thinking this stuff might actually already be good to go, or the simple heat to bright orange and drop in motor oil, and the 700 degree heat and let air cool would be good enough?

56-58 HRC would be about perfect, which is about what the trunnion hardness is and about the hardness of the dowels. Make sure the hole is well reamed and straight.

R

[ott1]

As I've mentioned in another thread, the steel dowels Richard mentioned are case hardened. Personally, I would use a drill blank which is through hardened to about 65 HRC. I can trim to length. Someone else mentioned that the M2 HSS isn't the right material to use but it'll work just the fine if the hole is drilled and reamed properly.

M2 HSS contains tungsten that A2 tool steel does not. Here's a technical chart comparing high speed steels and tool steels.

http://www.drillblanks.com/technicalinfo.html

[Gowking]

Ott1,

Is that drill blank already hardened or are you cutting them to length and then hardening them? What's your process?

-MRA

[nicitaja]

Thanks James, I actually mis-spoke, not A2 but I believe O1.

have you purchased from drillblanks.com before? 8mm x100mm is only $7.77 (which is more $, but not ridiculous)

I did try to look up what Richard was talking about before I posted about going with the O1 drill rod, .313 and nothing near the other size I wanted, .302, I've already got the Size N/(.302) and 8mm/.315 in 36" lengths coming, *BUT* tool steel is always something to have around.

BTW James, I know you also got the .315 from Brownells and it was short for a buldged trunion, so I should have spent more time in the PM talking to you, sounds like you already did this once. Whats the rest of your process, if you are hardening and annealing this drill stock?

Thanks
-John

[ott1]

Ott1,

Is that drill blank already hardened or are you cutting them to length and then hardening them? What's your process?

-MRA

The HSS drill blanks are already hardened. I cut slowly with a little bit of cutting fluid as to not alter the heat treatment.

have you purchased from drillblanks.com before? 8mm x100mm is only $7.77 (which is more $, but not ridiculous)

You can get the 8mm from Reid Supply. You may be able to find it elsewhere for less. I believe you can find metric sizes in 0.1mm increments. McMaster-Carr has M2/M7 blanks for a bit more. It all depends on how much you buy to make the shipping cost worthwhile.

[Richard Erichsen]

As I've mentioned in another thread, the steel dowels Richard mentioned are case hardened. Personally, I would use a drill blank which is through hardened to about 65 HRC. I can trim to length. Someone else mentioned that the M2 HSS isn't the right material to use but it'll work just the fine if the hole is drilled and reamed properly.

M2 HSS contains tungsten that A2 tool steel does not. Here's a technical chart comparing high speed steels and tool steels.
http://www.drillblanks.com/technicalinfo.html

The Misumi are definitely not case hardened, they are through hardened. The type of steel used in the McMaster Carr is not typically case hardened either, so I believe both are through hardened.

R

[ott1]

The Misumi are definitely not case hardened, they are through hardened. The type of steel used in the McMaster Carr is not typically case hardened either, so I believe both are through hardened.

R

Here's what another company says about their dowel pins. One of Misumi's dowel pin is made 52100 bearing steel. Maybe not the same steel as other manufacturer's dowel pin, so I can't say for sure that every dowel pin out there are only case hardened and not through hardened.

Hardened ground Alloy Steel Dowel Pins do not bend, dent, or break very easily because they are case hardened to Rockwell HRC 60 and have a core hardness from HRC 52-58. Alloy Dowel Pins are excellent for applications where high strength is required. Though these pins are not corrosion resistant they can be coated with a black oxide finish to help reduce their tendency to rust.

Unless you get the black oxide dowel pins, I wouldn't use them because they aren't readily available in odd sizes.

[nicitaja]

Well, I already ordered the O1 drill rod, I have a couple of AKB standard size pins, I've drilled them out before, so I know they are not too hard (thats figurative), but Im pretty sure there are 100's of ak's built on his pins, so I have to assume that I can make the O1 work.

I'm sure someone will confirm (or blast me :] ), but I have to imagine with how hard it is to get the barrel in, that the barrel pin is one of the few things that is not overly critical on particular hardness.

Now, if I can get someone to guess whether 1600 degrees, oil quench, and 750 degree air cool will be sufficient that is the question. I suppose 60 mins at 375 in the wifes oven might be better for the annealing
-John

[Richard Erichsen]

Here's what another company says about their dowel pins. One of Misumi's dowel pin is made 52100 bearing steel. Maybe not the same steel as other manufacturer's dowel pin, so I can't say for sure that every dowel pin out there are only case hardened and not through hardened.

52100 is ball bearing steel, not case hardening steel. Based on the comment you posted from some other manufacturer, they don't seem know what case hardening is. A typical finished hardness range would be 57-60 HRC for a through-hardened dowel part, whereas a case hardening steel (like AISI 9310) would have a similar surface hardness but a core hardness in the 30s range.

Given how small a pin is and the typical reason you case harden (produce a tough part with a hard wear resistant surface), the case hardened part would be more expensive to produce. Throwing a bin full of pins into the furnace for an hour at 1550 F and through hardening them is a lot cheaper and better suited to how these pins are used. Even if the pins were case hardened, it wouldn't compromise their function at all.

The reason you want a bit more hardness than the unhardened state of the pin is to prevent the assembly (in this case the barrel) from distorting the pin by the thrust of the assembly pushing against it. The barrel is already a lot softer than the pin (about 28-35 HRC depending on alloy), the pin is going to win. Anything harder than the barrel should be sufficient. A pin that is in the mid 50s to high 50s HRC will just have less trouble scraping any burrs out of the way as it is pressed into the trunnion. Much harder than this and it will likely be brittle performing a function that benefits more from toughness than peak hardness.

R

[Richard Erichsen]

Well, I already ordered the O1 drill rod, I have a couple of AKB standard size pins, I've drilled them out before, so I know they are not too hard (thats figurative), but Im pretty sure there are 100's of ak's built on his pins, so I have to assume that I can make the O1 work.

I'm sure someone will confirm (or blast me :] ), but I have to imagine with how hard it is to get the barrel in, that the barrel pin is one of the few things that is not overly critical on particular hardness.

Now, if I can get someone to guess whether 1600 degrees, oil quench, and 750 degree air cool will be sufficient that is the question. I suppose 60 mins at 375 in the wifes oven might be better for the annealing
-John

750 degrees sounds too high (I recall it being closer to 450-500 F) if you want a finished hardness in the high 50s range. Anything in the mid-50s HRC and you'll match what many of the dowel pins are. You can test with a file and the edge of a pocket knife. Most pocket knives have an edge somewhere in the mid-50s. Your home oven should be enough to get into this temperature range, though it might require the "self cleaning" setting if I recall where that is on the temperature setting.

R

[nicitaja]

Thanks Richard, going all from memory rather than looking it up,

thanks again.

-John

[ott1]

Given how small a pin is and the typical reason you case harden (produce a tough part with a hard wear resistant surface), the case hardened part would be more expensive to produce. Throwing a bin full of pins into the furnace for an hour at 1550 F and through hardening them is a lot cheaper and better suited to how these pins are used. Even if the pins were case hardened, it wouldn't compromise their function at all.

If you look at those dowel pins from Misumi, they are all chamfered on one end and radius on the other. Given that there are dowel pins made from different steels, you would have to be careful to choose the right one. I still wouldn't use one as a barrel pin.

I'm not going to discuss cost as it's a variable that can vary quite a bit due to quantity involved.

[Richard Erichsen]

If you look at those dowel pins from Misumi, they are all chamfered on one end and radius on the other. Given that there are dowel pins made from different steels, you would have to be careful to choose the right one. I still wouldn't use one as a barrel pin.

I'm not going to discuss cost as it's a variable that can vary quite a bit due to quantity involved.

The trunnion and barrel are made from different steels, as are the various bits that are pressed and pinned to the barrel. It won't hurt anything. Thermal rates of expansion and that sort of thing aren't going to be a problem, if that's what you are worried about.

R

[tujungatoes]

Now, if I can get someone to guess whether 1600 degrees, oil quench, and 750 degree air cool will be sufficient that is the question. I suppose 60 mins at 375 in the wifes oven might be better for the annealing
-John

For 01 you want to bring it to 1500 and hold it for 1 minute per inch of thickness and then quench in oil. Given the relatively small size of the pin 30 seconds ought to do it. Then heat to 600 degrees and allow to air cool. This should leave you with somewhere around Rc50 which should be far more than needed for a barrel pin.