Odd tapping day - educate me if you dare ;)

[oxford]

A long time ago I bought a set of taps and dies in a very nice case. There were three of each size tap. Wow that is quite nice I thought. I had lots of trouble using those taps. Then a member pointed out to me that what I had were hand taps and they were intended to be used in a series leading up to the finished size. The rings on the tap shank designated which to use first and so on. I didn't know such a thing existed. Live and learn. I know this is probably not the case in your situation as there is no ring on the shank to designate it to be a starter tap. I threw out the hand taps and replaced them with really good quality German made taps. Did I mention that they came in a really nice case?

We’re they all the same type of tap in the set? I’ve seen some sets of 3 hand taps but they were a set of tapered, plug, and bottom.

[Black Forest]

We’re they all the same type of tap in the set? I’ve seen some sets of 3 hand taps but they were a set of tapered, plug, and bottom.

Yes they were all the same except they differed in how deep they cut the actual thread.

[old mart]

I would mark it and use it as a roughing tap to use on difficult materials, it would save stress on a full size one used in one pass.

Serial Hand Taps - Metric Fine - Arc Euro Trade

[Bob Engelhardt]

[snip]
I threw out the hand taps ...

I wish that I lived near you, so that I could go through your trash.

[Black Forest]

I wish that I lived near you, so that I could go through your trash.

You need to come over pretty quick. I ordered a container to be delivered next week. I am going to throw out a lot of stuff that I have bought over the years. Lots of projects that I just haven't had either the time or interest to complete. I intend to be ruthless. My goal is to have a very organized shop before spring. My shop is only 10m x 20m but it has 20m x30m worth of stuff in it.

[mattthemuppet]

Yes they were all the same except they differed in how deep they cut the actual thread.

from what I've read that seems to be a very European thing. I've heard of them alot from European members but never seen them or heard of them in the US. I imagine they'd be handy for tapping tough or hard materials. Also for high % thread depth in steel too.

[tom_d]

Thanks Dan that's an excellent idea and why I didn't think of it....

Great idea, but............Just remember that some of the more difficult to machine alloys are that way because they tend to work harden. The undersized tap will work fine, but it could leave a hardened surface that is impossible to shave a small amount off.

[JoeLee]

The tap is designed to cut undersize. The designation code letter G is for Ground thread, the letter L is for the pitch diameter to be below basic size, and the 1 should be below basic by .0005"
Typically we see taps designated GH, where the H is the thread above basic pitch diameter with a number designating how much oversize.

I use H1 taps all the time and I've never run into this problem.
Is is there more to it or am I missing something?

JL ....

[J Tiers]

Progressing through multiple taps sounds like extra monkey-motion... What's wrong with one taper tap that ends up at the same place, but starts with a shallow cut?

You need to come over pretty quick. I ordered a container to be delivered next week. I am going to throw out a lot of stuff that I have bought over the years. Lots of projects that I just haven't had either the time or interest to complete. I intend to be ruthless. My goal is to have a very organized shop before spring. My shop is only 10m x 20m but it has 20m x30m worth of stuff in it.

"Only" 30 x 60! I'd not want a shop that BIG, at the moment! If I had 30 x 60 I'd be running a commercial shop at least part time..... I'd have a planer and a medium sized Bullard in there, as well as a big mill and a 25" swing lathe. and, of course a couple CNC so the place would actually make money. What I have now would be the toolroom for the shop. Oh, yeah, and I'd have at least one or two employees.

And that sounds like work..... I'm retired....!

[eKretz]

It's not a European thing to use three taps in sequence. It's an old thing that's not commonly done anymore. They're called serial taps, and yes they are meant to be used in sequence. Generally they aren't very common for normal threads, but are still somewhat commonly used for things like Acme threads.

[eKretz]

Funny, was looking for a link to a site further explaining their use and found this:

https://www.merriam-webster.com/dictionary/serial%20tap

[Illinoyance]

The tap is not marked as a serial tap. What was its purpose?

[tom_d]

I use H1 taps all the time and I've never run into this problem.
Is is there more to it or am I missing something?

JL ....

The L designation taps cut an undersized thread. The H designation provides some clearance with a slightly oversize thread. H1 designation is for a tap that will cut a thread that's going to finish anywhere from basic pitch diameter to .0005" over basic. An H4 designation will cut threads from .001 to .0015 larger than basic pitch diameter. It's standard practice to use a tap that cuts slightly above basic pitch diameter to provide some clearance, so they're the ones most readily available. The information about size designations is available in older Machinery's Handbooks. I'm not sure about their latest edition.

[tom_d]

The tap is not marked as a serial tap. What was its purpose?

The tap is designed to leave an undersized thread. Pure speculation here, I'm going too suggest the tapped hole would accept a stud, rather than a bolt, with the intention of the stud being held captive by an interference fit on mating part disassembly, and an interference fit to aid in structural integrity in a high vibration application.

[oxford]

The tap is designed to leave an undersized thread. Pure speculation here, I'm going too suggest the tapped hole would accept a stud, rather than a bolt, with the intention of the stud being held captive by an interference fit on mating part disassembly, and an interference fit to aid in structural integrity in a high vibration application.

Does anyone know what the standard would be for this if there is one?

I ask because I have bought studs in the past that had slightly over size threads on one end for this situation.