Long tap

[GrahamRounce]

Hi - can anyone suggest a source of a range of thin-but-long taps? I want to make a thread about 20 or 30mm long, M1.5 or M2

It sounds like it would be a bit of a strain on the thin tap. I can't tap in from each end, as the threads probably wouldn't match up! Unless there's a way to ensure that?

Or is there a totally different way of doing it?

Thank-you,
Graham R.

 

[Torx]

What material?

 

[TheTiddles]

You don’t usually go beyond 4D on a female thread as it’s plenty possible for the threads of the male fastener to clash and still be in tolerance with a standard ISO course, so no need to tap that deep either. If you’re just using a section of that thread you’ll be ok, but that’s a pretty funny design, what are you making?

 

[GrahamRounce]

Probably brass.
I want to replace the 2 or 2.5mm shaft of a dc motor with one that's threaded.

What's "4D"? Anyway, I guess you're saying the thread's likely to be too long to mesh reliably? Now you nention it...

Maybe a better idea would be to tap a 5 or 10mm thread, then drill out the rest of the shaft? I'd like to thread the middle 10mm of a 30mm shaft though, so I guess do it the other way round: drill out 10mm at each end then thread the middle bit. Can I take it that the shank will be the same diameter as the thread?

Lot of questions! Thanks again.

 

[TheTiddles]

Probably brass.
I want to replace the 2 or 2.5mm shaft of a dc motor with one that's threaded.

What's "4D"? Anyway, I guess you're saying the thread's likely to be too long to mesh reliably? Now you nention it...

Maybe a better idea would be to tap a 5 or 10mm thread, then drill out the rest of the shaft? I'd like to thread the middle 10mm of a 30mm shaft though, so I guess do it the other way round: drill out 10mm at each end then thread the middle bit. Can I take it that the shank will be the same diameter as the thread?

Lot of questions! Thanks again.

4 diameters, sorry

yes that’s it, it might be fine, but if it wasn’t it would still be correct, which would not help you. You plan sounds better, or drill it out larger and press in a threaded insert

For a small tap the shank is often waisted down, so tapping a deep hole sometimes means grinding back the shank (yuk)

 

[GrahamRounce]

I was afraid of that!
Thanks anyway

 

[J-G]

I haven't seen one as small as M1.5 or M2 but you might find a 'Nut Tap' which would have a long and narrow shank. I doubt that it would be cheap though.

As 'The Tiddles' has said 4xD is about as long as you'd get under normal conditions; and that would have a shank probably 4mm Ø. In extremis I have ground the shank of an M3 tap down to get a longer reach but there comes a point beyond which the strength of the shank is below the force needed to cut the thread and I suspect that M2 - and certainly M1.5 - would pass that.

Tapping a long thread, even in Brass, is asking a lot and the chance of breakage high unless you take extreme care and extract the tap to clear swarf every half turn which would be a real bind.

 

[sometimewoodworker]

For a small tap the shank is often waisted down, so tapping a deep hole sometimes means grinding back the shank (yuk)

All my tiny taps have a significantly larger shank than the thread. I am sure that a tap that small with a shank that small would be a special order. Also grinding the shaft though possible I completely agree on the yuk factor and I would have at least 1 spare.

I don’t completely understand the need for a thread section that deep but redesigning would probably be better. Possibly threaded at one end with the main section being a clearance fit on the shaft would be a more stable design and certainly easier to thread.

 

[GrahamRounce]

Thanks. Yes, I suppose the thread doesn't really need to be in the middle of the shaft, 4mm at one end would do. I was sort of revising it as the comments went along! (I nearly wrote "thread" instead of "comments" there, which might have been confusing : )

I've browsed for ready-made clock parts, such as the spacers separating the big plates, but without any luck.

 

[clogs]

threading brass is a nightmare at the best of times......have enough trouble doing 5/16" UNC......

 

[GrahamRounce]

Yes, ok, not brass then! Steel, I suppose.

 

[Fergie 307]

Brass will thread easily in the sizes you are talking about. You can also try using machine taps which have spiral rather than straight flutes and clear much better. Still not probably going to help with such long holes.

 

[GrahamRounce]

Thank-you.
Whizzing off into realms of fantasy, I could try and mould it somehow, I suppose... Hmm now I've said it, it doesn't sound all that practical! Perhaps I'd better stop now. Thanks, people, as always, for all the info and advice.
Graham