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Ian Parkin22/03/2011 12:54:37
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1174 forum posts
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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
elanman22/03/2011 13:22:39
47 forum posts
4 photos
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 stephens22/03/2011 14:03:27
1049 forum posts
1 photos
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 Parkin22/03/2011 14:32:26
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1174 forum posts
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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
ady22/03/2011 14:39:22
612 forum posts
50 photos
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.

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

Keith Long22/03/2011 15:17:24
883 forum posts
11 photos

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

mgj22/03/2011 15:20:24
1017 forum posts
14 photos
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 stephens22/03/2011 16:13:17
1049 forum posts
1 photos
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 Builder522/03/2011 19:17:00
2878 forum posts
248 photos
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 Parkin22/03/2011 19:25:08
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1174 forum posts
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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?
JasonB22/03/2011 20:18:03
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25215 forum posts
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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

mgj22/03/2011 20:30:06
1017 forum posts
14 photos
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 Stevenson22/03/2011 21:43:36
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5068 forum posts
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Ian,
Is Nottingham J25 / M1 any good ?
Got drawers full of cycle and specials and can cut virtually any thread.
 
John S.
Terryd22/03/2011 22:01:27
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1946 forum posts
179 photos
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 C23/03/2011 11:18:47
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7468 forum posts
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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 C24/03/2011 10:46:45
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7468 forum posts
230 photos
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 Stevenson24/03/2011 12:36:27
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5068 forum posts
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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.
JasonB24/03/2011 13:18:10
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25215 forum posts
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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 W24/03/2011 16:19:07
2011 forum posts
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.
JohnF24/03/2011 23:42:19
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1243 forum posts
202 photos
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.

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