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Breaking Taps

Captain1201

Plastic
Joined
Apr 18, 2020
I'm installing a steel bullet guide in the trunnion of a Saiga 7.62 x 39mm rifle. I'm in the process of converting the magazine well to receive standard AK47 magazines. The bullet guide just alters the height of the trunnion about an 1/8" or less, so the rounds will properly feed using standard AK47 magazines.

I am hand tapping a thru hole to fasten the bullet guide to the trunnion of the rifle using a round socket flat head screw. I always use plenty of tapmatic oil, and make a practice of going very slowly.

I've been using a drill/tap kit supplied by the vendor, which includes a 6-32 H3 tapered tap, drill, 6-32 socket flat head screw, and an allen wrench But, the taps have a tendency to break very easily. Breaking taps creates a real mess, trying to get the broken taps out of the hole. They break off right at the surface of the bullet guide, and they're a real pain to remove.

I realize that the vendor of the bullet guide kit isn't probably supplying me with the highest quality tap, probably mediocre quality, yet still affordable, and I don't want to spend a fortune either.

There's a "YG" brand tapered tap for around $6 on Amazon.com, which I would expect to be higher quality than the vendor is supplying, if it's not a fake, knowing Amazon.com these days, not to mention that six bucks sounds cheap for a "YG" tap.

Should I being using a different tap than a tappered tap in order to acquire some added strength in the body of the tap?

Should I drill a slightly larger diameter hole to reduce the amount of stress on the threads/body of the taps?

I'm not really sure of the drill size the vender is supplying in the drill/tap kit. There isn't really a lot of stress on the bullet guide, it just acts as a ramp that the rounds slide over so that the rounds chamber properly into the barrel. I blue locktite the screw as a precautionary measure so the screw doesn't back out from the recoil over time.

So, tapping a drilled hole that is slightly larger than recommended by the handbook for a 6-32 thread might provide sufficient holding power on the screw along with the locktite. If so, what drill size would you suggest?

Any advice on how to potentially remedy this issue would be very greatly appreciated!
 
my knowledge on this exact application is very limited. but speaking from a strict machining standpoint I would check a few things.

make sure the drilled hole is the correct size, chamfer or at least edge break the hole before tapping, use a better tap as you mentioned. that surface might be work hardened or mildly heat treated? you said it breaks pretty much in the very beginning of you tapping? make sure you are giving it a counter clockwise little turn to break the chip. not trying to assume you DONT know certain things, just would rather tell you something you may already know than skip it and assume you know it. goodluck!!
 
6-32 is a very poorly designed thread. Try using a 6-40 tap / screw instead. McMaster has taps (about $6) and screws. I would drill with a #32 (0.116) drill.

Fine thread series taps are often called 'gun smith taps' for a reason.
 
6-32 is a very poorly designed thread. Try using a 6-40 tap / screw instead. McMaster has taps (about $6) and screws. I would drill with a #32 (0.116) drill.

Fine thread series taps are often called 'gun smith taps' for a reason.

I like this answer

40 years ago I was told by the lead machinist supervisor to never ever tap 6-32 or get the heck out and don't come back. On staff engineering and drafting were pretty much told the same thing. It was really good advice then and I carry that with me still.
 
Pay the bucks and get an American made tap. I have been down this road and was lucky to have a friend with a Elox EDM machine to burn out the broken stuff. The American made will be better material and sharper.
 
For taps, "american made" is not enough to go by.

unfortunately, Vermont American and Irwin sell real garbage in the blister packs in hardware and home centers, "proudly made in USA.. those are finished with a bead blast from what I can tell, "factory dulled to work like crap" . ridiculous. I think they do it to produce a "uniform finish" and disguise the fact they just toss these in bins of thousands with no concern. only good for soft brass.

I buy Widia and Hertel these days on sale. nice.
 
You are right on Vermont, any tap they sell at the big box store is junk. I just finished mounting a base with a 6-48 Hansen and it worked well.
 
I agree 6-32 is a pain in the butt to tap. I avoid it as much as possible, If I must tap that size I do it 2 ways. (1) get the complete set Taper, Plug and Bottoming from a good HSS Tap maker. Then tap in sequence, first the taper until the torque gets you concerned, change to plug then bottoming. Repeat the sequence changing the tap type each time the torque required gets a little concerning. (2) I also Power tap 6-32 without problems. I have a tap driver such as USED SPI QUICK CHANGE TAP ADAPTER COLLET W/TORQUE ADJUSTMENT #6 H.T. (75-913) | eBay though I do not recommend this one because it's used. The holder is preset to the correct torque required and will not break the tap! However it is adjustable and should be marked as to where it was adjusted by the factory to correct torque limit. I have the complete set from #4 to 1/2" that have never adjusted the torque plus a few others that I've adjusted the torque for my needs. I have made a simple holder so I can hand tap with them plus I have the Tension/Compression holder they fit. When using the holder with factory settings I have never broken a tap even the lousy 6-32!!! I do have a Tapmatic with adjustable torque settings but it has to be changed for each different size so adjusting to the correct torque limit is not easy especially if it's unknown. This type holder is for one tap size only, other sizes will not fit. Checking ebay for similar holders like Blitz or Nikken I'm sure a new one can be found. If you do buy that used one you can message me and I'll check mine for the correct factory setting.
Those big box store taps are Junk!! Most of them are Carbon Steel. HSS is much better! Emuge taps are good too but not cheap!
 
I think the issue of the broken taps was caused by a number of variables. I ended up getting an OSG spiral point plug tap, and it cost around $10. It worked, thank goodness! But, this time, before I tapped the hole, I noticed that the material must be pretty stringy, or at least I noticed that the drilled hole seemed to have some pretty substantial hanging burrs in the hole. It could even be that the drill supplied from the vendor of the bullet guide tool kit, which had a very high helix, may have failed to break the chips properly as the hole was being drilled, resulting in material being left in the hole, causing pretty substantial burrs to be created in the hole. I also noticed that the position of the drilled hole was drilled right next to the wall of the trunnion itself, and those trunnions are very hard. So, I suspect there was more resistance in the hole than should have been there. I made sure to drill out the hole more thoroughly this last time. I almost think that the previous attempts made to tap the hole where the taps broke, that maybe the hole wasn't fully opened up. The other thing I noticed was that the couple of tap wrenches I had access to just didn't hold the tap securely. Tap wrench collets just don't seem to close in around the tap shank to hold the tap securely when you get down to the 6-32 size. You have to be careful using the tap wrench because if the tap slips in the collet, I think it causes a shearing action that breaks taps that are really too fragile or cheap to withstand the side pressure of being used in tap wrenches that don't hold the tap securely in the collet. So, I had to really, really take it slow, clearing chips often, backing off quite often, removing the tap to clear chips, retightening the tap wrench, plenty of lubricant, etc...I do think the added strength of using a high quality tap also contributed to my not breaking the tap this time, and that the tap supplied by the vendor of the bullet guide was probably junk. But, this time it worked out after considerable evaluation and awareness of these various factors that seemed to possibly all be contributing to the breakage.
 
Use a straight tap handle, not a T. I think that you get better control with the plain ole straight handle.
 
Use a straight tap handle, not a T. I think that you get better control with the plain ole straight handle.

I had two hand tap wrenches in my stash, and both have the type of "T" handle where the "T" handle can be moved horizontally, and also completely removable, but if you removed the handle there would be no way of using it without the "T" handle. I think you must be referring to another type I also have...I also have a tap wrench where the chuck is in the middle, and the the handle extends out horizontally in both directions from where the tap is chucked. I didn't like that one because it felt like I was just putting too much torque on the tap due to the handle and chuck all being in line, but mostly because of clearance issues with the trunnion, I needed the clearance and reach that the "T" handle wrench provided. I tried looking for an alternative tap wrench to use with the 6-32 tap, and could never find one that was a reasonable price, which I'm sure was also part of my problem...too cheap. But, to tap a couple of holes, I didn't want to make a pricey investment. If you have time, please post a link to the type of tap wrench you think would have worked better in my application, just so I can visualize it. I'm always open to learning something, and maybe I was just unaware of other better types of tap wrenches that are out there.
 
Tap quality

I agree with Cyanide kid, Widia taps (Hanson too I think) are of good quality, any tap you see or for that matter comes out of a "home gamer set" are crap. Yes I have such a set to get me out of a jam or cleanup an already tapped hole, but that is it for the set. A good rule of thumb, which most of you probably know, a tap with a matte finish is useless for anything barring chasing or tapping plastics or other polymers.
Flying R/C helicopters I tap a lot of very small holes and have found a few things worthy of mention when doing so.

Make sure out your tap is perfectly perpendicular to the work surface.
Use a tap block if possible.
Go slow, one turn back off break chip, rinse and repeat.
Choose the correct tap for the hole, blind or through.
Blind you want a tap that pushes chips up and out.
Through either or.
Use the appropriate cutting fluid if indicated.
Lastly if you don't have the feeling of when the tap is going break practice on some scrap.
After tapping thousands of holes I know with 99% confidence when to stop back out blow out the hole clean the tap and continue.
Lastly second if tapping your gonna break some taps, but due some forensics when this happens, why did it bust clean half in two you can learn a lot from this.

But yes stay away from matte finish taps, they are a home gamer item.
Having said all the afore mention garbage I have begun to thread mill when ever practical. I started T. milling out of necessity, doing 5" 8 TPI hole is an ideal candidate. Wen I first took over machining these they were using a collapsible style tap and it was a grand PIA. Now milling has knocked the tapping op from 20+ min per hole to ~2 minutes per hole.
 








 
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