what thread is this?

[Ian ParkinParticipant @ianparkin39383]

Hi there

I have a motorcyle front wheel spindle that I’m making some nuts for ..

Its a french 1930 terrot

the thread measures 12.15 mm and pitch is 1mm and left hand for good measure. Its in fine condition considering its age.

I bought a LH 12 x 1.0 tap and made a sample nut and no way will it go on.

What do I do? machine the spindle down to 12mm and buy a die (£ 58 eek) or any other ideas? Is it a special thread? or another I’d not considered

 

Ian

[Ian ParkinParticipant @ianparkin39383]

[elanmanParticipant @elanman]

Ian,

IMHO if it’s 12.15mm o/d then the nominal diameter of the thread is larger than that. I would guess at 1/2 inch. Also 1mm pitch is very near 24 tpi. Tracy tools list cycle thread of 1/2″ * 24tpi. It’s in the taps and die/ cycle threads section on their web site.

Just a suggestion.

Or re-make the spindle and use what thread size you want.

Cheers

John

[chris stephensParticipant @chrisstephens63393]

Hi Ian,

John might be right about it being 1/2 but not about 24 it is nearer to 26 which is a cycle thread. (26-25.4 not 24). Cycle threads as the name suggests were common on, er, cycles.

Do you have a lathe and can you cut threads?

Cleaning up your spindle to fit the newly made nut might be an option, although the old vehicle owners I know prefer to keep everything as original as they can despite the easier alternatives. Making a new nut is easy enough if you have enough experience or are willing to gain that experience.

 

Some manufactures, in those days, didn’t use standard threads but made them all in-house. Very frustrating trying to work out what it is meant to be, only to find it an oddity. Is it worn or is it special? Turning bits yourself might be the best option, as you can keep machining till it fits.

christephens

[Ian ParkinParticipant @ianparkin39383]

Thanks for your replies guys

the thread is definately 1mm with my pitch gauges 24,25 and 26 tpi dont fit at all

Its just the odd diameter

I do have a lathe and have cut quite some threads but never left hand and so small internal..

Is anyone near sheffield who would be prepared to do the job?

I have ordered a 12mm die from china but delivery is 2 weeks or so

 

 

Ian

[adyParticipant @ady]

I wouldn’t experiment with steel nuts.

 

Use something like delrin or aluminium, you can bore and cut a thread in minutes with softer materials on a lathe until you get it hunky dory, then do it in steel.

 

edit:

Maybe it’s a multi start thread…lol…I keep reading about them guys but I haven’t met one yet.

Apparently they are very strong.

http://www.neme-s.org/Multi_Start_Threads/multi_start_threading.htm

 

 A left handed internal multi-start thread…yup, sounds like something the French would do.

 

Edited By ady on 22/03/2011 15:03:53

[Keith LongParticipant @keithlong89920]

Hi Ian

You can mount the tap in your tool post and use it like a chaser to cut the internal thread. Machine the nut id to a suitable size (male thread od minus twice thread depth). That way you can cut the odd size with the equipment you’ve already got. You’ll need to set the lead-screw to give you the 1mm pitch and you might have to keep the half nuts engaged if you’ve got an imperial lathe. It might be better to use a hand crank rather than cutting with power.

Keith

[mgjParticipant @mgj]

Or make your own tap out of SS. For a one off it can be pretty crude. A lot less than £58 and some weeks delivery.

 

Don’t be frightened about a LH thread. Its just an RH one with the feedscrew reverse engaged.  Nothing special.

 

A few quid and one evenings work.

Edited By mgj on 22/03/2011 15:23:10

[chris stephensParticipant @chrisstephens63393]

Hi Ian,

LH threads should be easier to cut than RH, in a nut, because you start at full depth, hole not thread, and come out into free air. On Sunday I cut a RH 8.5mm by 20TPI nut for an auto- jumble purchase thread form tool holder, yes mixed units to match original, it just needs a small cutting tool. If I can do an 8.5, doing a 12 should be a doddle.

chriStephens

[Speedy Builder5Participant @speedybuilder5]

Just another thought – What is the thread angle ? 55 deg would suggest a British thread (Of Whitworth form) and 60 degree would suggest a metric one. 5 Deg doesn’t sound like much, but would be enough to foul things up. There is another dodge, make your nuts half thickness and use two of them. It would allow for a bit of ‘slop’

[Ian ParkinParticipant @ianparkin39383]

How do you accuratly check the thread angle on such a fine form?

I have lots of pitch gauges and only the 1mm fits perfectly.

what other thread form would correspond to 12.15mm and 25.4 tpi?

[JasonBModerator @jasonb]

A VG 12 thread (Valve thread) has a major dia specd as max 12.243 and min 12.091 but its a 26tpi

 

J

Edited By JasonB on 22/03/2011 20:18:24

[mgjParticipant @mgj]

The thread angle – bear in mind that this is pre a lot of standardisation.

 

If your 1mm pitch gauge fits well- hold it up to the light is what I do – go for it on that. Use the formula for depth unless you are intot wire depthing. Just cut an internal thread, and pull the x-slide back and forth a bit if its a bit tight. (See Grays remarks about commercial slop)

 

The trouble with these old non standard threads is that sometimes you have to invest a bit of time getting it right.

 

Go for it – aint that difficult, and doesn’t matter if you do get it wrong. You just have to do it again! We’ve all been there – more than once.

 

Edited By mgj on 22/03/2011 20:30:52

[John Stevenson 1Participant @johnstevenson1]

Ian,

Is Nottingham J25 / M1 any good ?

Got drawers full of cycle and specials and can cut virtually any thread.

 

John S.

[TerrydParticipant @terryd72465]

Posted by Ian Parkin on 22/03/2011 19:25:08:

How do you accuratly check the thread angle on such a fine form?

I have lots of pitch gauges and only the 1mm fits perfectly.

what other thread form would correspond to 12.15mm and 25.4 tpi?

 

Hi Ian,

 

You could scan the thread with a computer scanner and then enlarge it. You can then use any technique you prefer to measure the angle. Even a schoolboy protractor is accurate enough to measure 55 vs 60 degrees.

 

We used to use a similar technique in industry called a ‘Shadow Graph’ and I think the name is self explanatory It is quite accurate and simple.

 

Regards

 

Terry.

[Ian S CParticipant @iansc]

Graham, Germany dropped the Whitworth threads about 1934 from what I remember, I,v done some work on Lanz bulldog tractors, making new parts, and was suprised when I found the threads were whitworth, after that they changed to a metric thread.

1/2″ should not be too small, the first internal thread I cut was 3/8″ bsf, at that stage I had’nt cut many external threads, so fingers crossed and away , a few miniuts later a perfect nut. It was for a compressor at a local engineering shop, they could’nt do it and were worried that the might not be able to get a castelated bsf nut from the supplers in Christchurch. Some engineers that lot. Ian S C

[Ian S CParticipant @iansc]

Hi gray, have replied, there may be a delay with some information, things have been moved about a bit over the last few months, some thing to do with earth quakes, but it will be there, some where. Ian S C

[John Stevenson 1Participant @johnstevenson1]

A lot of cycle stuff was special.

Cotters are still 17/64″ x 26 to this day.

Triumph speedo cables are 0.715 x 26

Threads on Amal carb bodies are 15 thou undersize so if you use standard threads they suck air .

 

The list is endless and not many are in tables.

 

John S.

[JasonBModerator @jasonb]

Problem is a lot of French cycle threads differed from the normal british threads, such as bottom brackets, pedals,freewheels, headsets and cotters. Mostly they were a close metric equivalent but not the usual ISO as that was not about then.

 

As a lot of these early motorcycle builders were originally bicycle makers its very likely that their odd threads carried over.

 

Jason

Edited By JasonB on 24/03/2011 13:20:00

[Gordon WParticipant @gordonw]

You probably know this, Terot, along with most makers in those days, bought in a lot of stuff, probably including wheels, certainly they used Jap engines. So could be any thread! Not much help. If you intend running the thing ,I would make a new spindle, then use any fine thread. Quite important the old front spindle.

[JohnFParticipant @johnf59703]

Hi Ian,

The simple answer is screwcut a LH nut to suit the wheel spindle–a simple operation providing you have a 127 or 63 tooth change wheel [only if your lathe is imperial]. If metric you can do the job even easier.

To check the thread angle use a powerfull magnifier and offer up a threading tool of known angle and you will see which fits correctly.

I do many “funny” threads but I use a toolmakers microscope to assertain the specification regarding angle,pitch, etc.

Quite often old products–mostly older than yours–interchangability was not a criteria so “funny” threads that were close to standard sizes appeared and the man who made them made his own taps and dies–so long as they fitted together that was fine!!

Good luck John F.

[Richard ParsonsParticipant @richardparsons61721]

Ian Checking the thread angle is quite easy if you have a good quality set of thread gauges (not those made by the yellow peril). I use the Whitworth set. If I cannot find a match its metric, so I try the metric gauges, if it don’t fit the metric it’s a BA (47.5&#176. or God knows what. If it fits the Whitworth gauge I hold it up to the light. A good fit it is Whitworth/BSF (55&#176. If it is not a good fit it is a ‘Unified’ (60&#176.

Over here in Hungary much of the old Russian army gear is ‘Unified’ not metric. This seems to drive the locals ‘round the twiddle’. There was heaps of the stuff about, but the Orientals turned up with suitcases of forint and everything disappeared including some new pylons they were putting up.
Regards

Dick

[Richard ParsonsParticipant @richardparsons61721]

Confounded auto insert “smilies”.

Edited By Richard Parsons on 25/03/2011 06:03:56

Edited By Richard Parsons on 25/03/2011 06:04:33

[Ian S CParticipant @iansc]

Dick was it Hungary where some one nicked a bridge afew years back? Ian S C

[Ian ParkinParticipant @ianparkin39383]

Well after all you guys fine advice, I decided to buy a chinese die to match my tap so it will be 12mmx1.0 LH and hopefully just run the die down the spindle so it will be reasonably standard then …just the delivery time from china…it was only £8 in total though.

 

Problem with making a new spindle is thats theres a bearing cup threaded onto the middle of the spindle so making a new one of those starts getting complicated …so if i just leave the bearing cup on the oversize thread and cut down the exposed thread on each end.

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