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Old 11-22-2017, 04:25 PM   #1
BuzzSaw7
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Default Gas port inquiry

I've been working on a Polish underfolder for the last few weeks, and at just about every turn, I've run into some sort of obstacle or issue that has caused me a great deal of headache. It is almost like this parts kit is possessed like a certain well known Plymouth Fury.

I'm using a Polish Radom barrel that I purchased from AK Builder, and this thing is literally so hard that I can't get any of my drill bits, including brand new ones from AK-builder to bite into the barrel to drill the gas port. So far today, two brand spanking new AKB gas port drill bits and a #31 drill bit have kicked the bucket in a short period of time.

I'm at a loss of what to do at this point. Any ideas or suggestions would be greatly appreciated.
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Old 11-22-2017, 05:02 PM   #2
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Slow down your speed, if you are smoking drills you are going to fast. Be patient and go slow, you will feel it start "thumping" as you almost break through, at that point reduce pressure so the bit doesn't grab and break.
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Old 11-22-2017, 05:38 PM   #3
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Try a cobalt bit
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Old 11-22-2017, 07:07 PM   #4
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a carbide tipped drill bit will cut though anything. they are user friendly and arent brittle like solid carbide bits are. mcmaster carr is the place to get them. they are decently cheap since they are not solid carbide. but they cut the same. guaranteed it will cut it with no issues. if doing with a hand drill, be sure to back off the pressure alot when you feel the bit start to break through the bore and increase speed of the bit. going slow when the bit is braking through will guarantee a broken bit! just ask around lol. oil or cutting fluid etc necessary! shouldnt be much of an issue with carbide though, still back pressure off regardless. you will feel what i mean.

part numbers to save you the searching for carbide tipped size #31
31575A444 (standard 2-3/4")
2940A434 (standard 2-3/4")
2854A454 (12" long extended length)
$8.83-19.90 make sure you get a bit that is long enough. you will like the way it blasts through without much effort.

part #'s for a carbide tipped#30 $9.30-$20.29
31575A443 (standard 2-3/4")
2940A433 (standard 2-3/4")
2854A453 (12" long extended length)
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Old 11-22-2017, 09:51 PM   #5
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If it is a nitrided barrel it will be hard as Chinese algebra but the good news is it is only a couple thousandths deep. Use a Dremel to grind off the surface until you see the bare metal then drill your hole. If you don't have a steady hand, tape around the port area to protect the barrel from an OOPS.
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Old 11-22-2017, 09:54 PM   #6
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Also. if you can slide a 1/4 inch dowel into the bore it may help from going too deep. Be careful when breaking through into the bore, that is where the drill will grab so go slow and use some oil.
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Old 11-22-2017, 10:37 PM   #7
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Here's a tip that will help you. The density of the steel is one thing, and I think you are binding the tip of the drill bit and breaking the corners of the margins. The gas port drill bit is normally smaller than the gas port of the gas chamber block, and the point of this bit can "walk" and bind.

Use a vise and clamp the barrel so the gas port is "level". This will allow you to make sure you are pushing "straight".

Use a pilot drill bit that is the same size as the gas port of the gas chamber block. Do not drill into the rifled bore! You only want to make a shallow divot to help the gas port drill start without binding. It does not have to come to full tip diameter.

Now use the gas port drill bit and be mindful when you can feel it breaking into the bore. Clamping the barrel as I describe gives you a lot of control. I have simple cobalt bits that have drilled many gas ports in cold hammer-forged, nitrided, and button-rifled barrels and they are still on their original grind. Just a bit of cutting oil helps as well.
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Old 11-23-2017, 12:52 AM   #8
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I managed to finally get it drilled after about 5 hours of running around various hardware stores, rummaging around through various drawers in my workshop trying to find something that would work. Total number of casualties ended up being about 7 ( however lucky that number is supposed to be ) drill bits and my sanity. Pretty sure there were a bunch of new words learned during the process too.

I think it is time to invest in better tools and scrap the rickety piece of [censored] [censored] 50+ year old wooden workbench with wooden vises. Most of my tools I've had for over 20 years now ( many were purchased for me by my dad when I was a 6 or 7 years old learning how to work with wood ) and are a bit worn out now.

As for the clamping, I managed to kludge something together that worked for the time being with what I have at the moment.

I also appreciate the information on a source of drill bits. I've got about 3 more kits in the queue and I don't feel like going down this road again. I'm going to see about turning down a piece of aluminum to act as a sleeve on around the drill bit so that it has a snug fit around into the gas port ( if entirely possible ) when I've got more time to tinker around with the old South Bend this weekend.

and Rforbus, you were right about the bit binding and breaking off the edges of the tip and the breaking of the bit. In fact, at least two that ended up taking the entire angled portion of the bit in the process. I sacrificed one of my last surviving horror freight transfer punches by turning it down until it was a snug fit in the gas port location to mark the hole.
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Old 11-23-2017, 09:51 AM   #9
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Here is a photograph of the tools for AKM. I have a stop collar on the diameter 4,0mm drill bit so I do not go too deep.

I don't assemble barrels for a long time now. When I made a lot of assemblies I would occasionally have a gas chamber block with a larger, say up to diameter 4,5mm port. I generally just select a number drill that will work and since I do not need to drill very deep the jobbers length drill bits are fine for making the divot.

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Old 11-23-2017, 10:09 AM   #10
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I have built a couple rifles on the polish barrels. These were the first batches to come in. How long ago did you purchase yours? Reason I'm asking is I'm still on my original gas port drill bit from ak builder with no issues. I have never had an issue with the polish CHF barrels, they were never that bad to drill. Now the nitrided ones suck and to do it properly you need carbide tooling and should be using a mill due to how easy carbide breaks. For nitrided without a mill you need to mark were you want to drill then remove the nitrided surface and then drill. I have only built on one nitrided and I was taking tooling very serious towards the end.
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Old 11-23-2017, 11:58 AM   #11
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Roberts advice is spot on.
Use a larger bit first to get a centered divot that will center the correct bit.

I have just used a transfer punch that fits the GB as well to center punch also.

I use a slightly under size bit than final port size to drill through with on 7.62x39 barrels . I then final drill . This leaves a smaller or no burr in the bore.

On a 223 and other barrels with small ports I use the final bit to drill through.
Breaking off a .065 bit sucks so I use the largest one first.
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Old 11-24-2017, 12:35 AM   #12
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Antifreezer, this barrel was purchased a month or so ago. It could just be something on my end with my ineptitude, or it could be something that Bolesław messed up while thinking about the Czernina he had the night before at his girlfriend's parent's house. ( for the record, I'm 1/4 Polish, which in might explain a whole lot in and of itself or why this build is turning into a major cluster of compounding problems )
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