Educate me about taps

[PSS]

I have been messing around with building muzzleloaders. Specifically Leman Trade rifle, southern mountain rifles and have a Vincent Caleb rifle half done that was a TOTW "kit". I started with the Vincent Caleb "kit" and realized quickly that it was actually going to be easier to build from scratch than trying to fit parts into semi inletted spaces. I started several project, focusing on the wood working. Inletted several barrels, made ramrod hole drills and shaped the forends. It's worked out pretty good. I feel comfortable with that now and want to move on to the metal work. Barrels are draw filed. Now I'm needing to tap the barrel for the drum and nipple. There's a few other uses for taps too. I bought what I thought was a decent tap set. Found out quick that I wasn't going to be happy with it. I've heard good things about Kodiak Cutting Tools so I'm getting a numbered drill set (1-60) from them and buying just the taps I'll be using.

My question is this. Noticed that with a tap, say a 10-32 that there were several but with different H numbers. Found out that it was the H limits dealing with tolerances. For Gunsmithing purposes which H limit is desirable, best?




H1 = Basic to Plus .0005
H2 = Basic Plus .0005 to Plus .0010
H3 = Basic Plus .0010 to Plus .0015
H4 = Basic Plus .0015 to Plus .0020
H5 = Basic Plus .0020 to Plus .0025
H6 = Basic Plus .0025 to Plus .0030
H7 = Basic Plus .0030 to Plus .0035

[BPTactical]

https://www.rntap.com/tap-technical-information/tap-recommendation-2-3-2b-3b-unified-threads.aspx

[henpecked]

The tighter the tolerance the more torque it will take to tap the hole. Increasing your chance of breaking the tap.

[rondog]

Broken taps are SUCH fun.....

[DLI Chip Maker]

I generally run H2 or H3. H1 will get real tight with a lot of fastners. H4 & bigger produce "looser" threads, which ain't a big deal if the fasteners are just holding parts together, but if the thread or fastener itself serves any function in alignment, you don't want a sloppy fit.

As for the taps themselves, I recommend OSG spiral flute bottoming taps for most purposes. Expensive, but about the best there is. I've tapped hundreds of holes in all kinds of materials with OSG #10-32 taps and not broken them, and I rigid power tap in a 3 HP knee mill. Spiral flute taps will push chips out the back, allowing you to thread without interruption.

Also, remember, the foremost cause of broken taps (especially small ones) is lateral pressure, followed by lots of back & forth or interrupted cutting. If you can keep them straight, keep them turning and not back up, you'll have great success.


The tighter the tolerance the more torque it will take to tap the hole. Increasing your chance of breaking the tap.

The tap tolerance has nothing to do with that. The "tolerance" you're referring to is a function of hole diameter; 100% thread will have more resistance than 75%, no matter the tap. And a hole under the minor diameter size means the tap is also drilling, which is a problem. That said, see above; rotational torque is not the cause of most broken taps.

[PSS]

I generally run H2 or H3. H1 will get real tight with a lot of fastners. H4 & bigger produce "looser" threads, which ain't a big deal if the fasteners are just holding parts together, but if the thread or fastener itself serves any function in alignment, you don't want a sloppy fit.

As for the taps themselves, I recommend OSG spiral flute bottoming taps for most purposes. Expensive, but about the best there is. I've tapped hundreds of holes in all kinds of materials with OSG #10-32 taps and not broken them, and I rigid power tap in a 3 HP knee mill. Spiral flute taps will push chips out the back, allowing you to thread without interruption.

Also, remember, the foremost cause of broken taps (especially small ones) is lateral pressure, followed by lots of back & forth or interrupted cutting. If you can keep them straight, keep them turning and not back up, you'll have great success.



The tap tolerance has nothing to do with that. The "tolerance" you're referring to is a function of hole diameter; 100% thread will have more resistance than 75%, no matter the tap. And a hole under the minor diameter size means the tap is also drilling, which is a problem. That said, see above; rotational torque is not the cause of most broken taps.

The info I wanted! Thanks