Can I get away with using 20 TPI for a 1.25 mm metric thread

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woodfarmer

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pretty much all in the header.

just need about 1/2 inch or less 10-12mm of thread to fix a nut to.
My lathe only does Imperial threads and I need to make something using 12mm steel rod.. should have though more about it and ordered 1/2 inch :( Of all the 8 mtres of rod I only need to thread two ends, rest is welded.
 
If threads are very tight, some cutting/grinding paste will ease them, but wash it clean afterwards. You will only need a dab on your finger so perhaps a local garage workshop would oblige,or someone who does cars or bikes will have it.

Best wishes.
 
I'd turn to 12mm OD, rough out on the lathe screwcutting at 20tpi and then take the last few thou off with the 1.25mm pitch die (M12 iso fine I think)

MM
 
Myfordman":228eg55c said:
I'd turn to 12mm OD, rough out on the lathe screwcutting at 20tpi and then take the last few thou off with the 1.25mm pitch die (M12 iso fine I think)

MM

Trying to avoid spending £20+ for just two threads

may just weld the stainless 12mm rod to a SS flange and use a couple of bought stainless /nuts & bolts.
 
Is there a particular reason why you can't screwcut the thread on your lathe? Metric approximations can be made on an imperial lathe using the standard gears. The only issue is you have to leave the leadscrew engaged and reverse the lathe back to the starting point.
 
DTR":ifwmescs said:
Is there a particular reason why you can't screwcut the thread on your lathe? Metric approximations can be made on an imperial lathe using the standard gears. The only issue is you have to leave the leadscrew engaged and reverse the lathe back to the starting point.

On my ninety year old lathe screwcutting is from a gearbox. just move the lever to the TPI you require from 4 to 28 TPI .

Metric threads are somewhat difficult . Normally I buy imperial bar or if bigger just make whatever size suits. but cant sensibly cut 12mm internal thread. If I had thought about it more thoroughly I should have bought 1/2" bar and not 12mm. Then I could have threaded the bar and just bought a couple of stainless steel nuts. Just sort of painted myself into a corner :(

Just this week made a toolpost mount for my woodcut bowlsaver (1 inch bar with a 1/2" UNF threas on the end).
 
woodfarmer":oncfmdcr said:
DTR":oncfmdcr said:
Is there a particular reason why you can't screwcut the thread on your lathe? Metric approximations can be made on an imperial lathe using the standard gears. The only issue is you have to leave the leadscrew engaged and reverse the lathe back to the starting point.

On my ninety year old lathe screwcutting is from a gearbox. just move the lever to the TPI you require from 4 to 28 TPI ./quote]

A gearbox! #-o That would make sense then
 
DTR":29zdevrd said:
woodfarmer":29zdevrd said:
DTR":29zdevrd said:
Is there a particular reason why you can't screwcut the thread on your lathe? Metric approximations can be made on an imperial lathe using the standard gears. The only issue is you have to leave the leadscrew engaged and reverse the lathe back to the starting point.

On my ninety year old lathe screwcutting is from a gearbox. just move the lever to the TPI you require from 4 to 28 TPI ./quote]

A gearbox! #-o That would make sense then

Like this...

P1020530.JPG
 

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woodfarmer":7n33i2l3 said:
On my ninety year old lathe screwcutting is from a gearbox. just move the lever to the TPI you require from 4 to 28 TPI

file.php

Can you add new gears on the outside (left hand of your photo) ?

BugBear
 
bugbear":ngrypfo4 said:
woodfarmer":ngrypfo4 said:
On my ninety year old lathe screwcutting is from a gearbox. just move the lever to the TPI you require from 4 to 28 TPI

file.php

Can you add new gears on the outside (left hand of your photo) ?

BugBear

It might be possible, but many are on fixed centres so they would have to be made in pairs.
 
woodfarmer":2l6q87fq said:
Can you add new gears on the outside (left hand of your photo) ?

BugBear

It might be possible, but many are on fixed centres so they would have to be made in pairs.[/quote]

Tricky. And an extra jockey wheel would reverse the motion :-(

I was thnking (of course) of a 127, or 65 (introduces a very small error) gear.

Maths

BugBear
 
bugbear said:
woodfarmer said:
Can you add new gears on the outside (left hand of your photo) ?

BugBear

It might be possible, but many are on fixed centres so they would have to be made in pairs.

Tricky. And an extra jockey wheel would reverse the motion :-(

I was thnking (of course) of a 127, or 65 (introduces a very small error) gear.

Maths

BugBear[/quote]

I can reverse direction with a lever :) (for cutting LH threads and reverse feeds.

One day i will try to count the teeth on the last two gearwheels.

But back to my original question..12mm metric fine is 1.25 mm 25mm of thread uses 20 turns, and 20 tpi does 20 turns in 25.45mm so 1/2 a mm runout over and inch.. about 0.2 mm over the length of a nut. Think I will buy a couple of staonless nuts and just cut the 20tpi threads until the nut will go for its length and see what it looks like.
 
In answer to your original question, it will work if you cut a 20 TPI thread to fit a 1.25mm threaded nut but the bottom line is it won't be very strong as the thread mesh will only effectively be in one place.

The other option would be to buy a cheap carbon steel imperial tap to make a nut and thread-cut your rod to match that. You can pick up a 3/8" or 1/2" UNC carbon tap for £3 from Chronos. Or with a short piece of silver steel you can even make your own tap.

HTH
Jon
 
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