Machinery's 20th

[PeterT]

Neither had 1/4' x22tpi Whitworth which is what I was after

I less familiar with Whitworth but is 1/4-22 even a standard thread? I see 1/4-20 (BSW) and 1/4-26 (BSF) and G1/4 BSPP (Whitworth pipe thread) = 19TPI.
I mean theoretically you can make any thread form to match some specialty fastener situation if you know the underling formulas, but there seem to be fewer online calculators of Whitworth.
I don't have the Blackbook so I cant confirm its in there. I'd be kind of surprised but who knows.

Whitworth British Screw Threads Size Chart BSW&BSF

Whitworth British Screw Threads Size Chart BSW & BSF

www.engineersedge.com

BSPP Whitworth Pipe Thread DIN ISO 228 (DIN 259)

 

[Downwindtracker2]

I thought I might luck out and find it in the MH Collector's first edition, no luck. It's an obsolete thread from the late 19th century. I have an old Starrett thread guage and it had 22tpi where as the newer PEG ones didn't.

 

[Susquatch]

I have an old Starrett thread guage and it had 22tpi where as the newer PEG ones didn't.

Not sure it matters, but 22 tpi is a standard thread pitch on my lathe.

 

[trevj]

Not sure it matters, but 22 tpi is a standard thread pitch on my lathe.

I've got a vague itchy memory that 22 TPI was used on older, Pre-Unified (late 1960's-ish) Brit Motorcycles. Memories from working after hours, at a Brit bike shop just off the Base I was posted to at the time, where bulk lots of hardware that had been sent out for CAD Plating, needed to be sorted by TPI, diameter and length.

I think the Cycle Engineering Institute, an old Brit bicycle makers Standards setter, had the right idea. IIRC, they just set 36 TPI as the standard thread pitch, and it didn't matter what diameter you were making, it was threaded 36 TPI !

 

[Downwindtracker2]

I have 22tpi on my lathe, too. My son and I had a XIMA 250mm x 600mm (10x22) It didn't have 13tpi but did have 12 tpi. I think it was more of a gearing thing.

Stanley planes used some odd ball diameter Whitworth screws. They were off the shelf screws when the plane were first made. I think Whitworth was the international standard at one time. pre-1900 ??

 

[PeterT]

Well I assume you make a 55-deg HSS tool with the proper nose radius similar to a conventional 60-deg thread.
- you have the pitch setting on your lathe
- I pasted a Gemini response calculating diameters to the custom pitch
- link shows Whitworth specific wire diameters to measure PD (unless you have matching anvils for a thread mic)
- now how to make that nice thread round-over... Ugh, you're on your own there!

The Three Wire Method Of Measuring Pitch Diameter

Measuring thread pitch diameter can present difficulties. Thread Check discusses 3 wire thread measuring, thread measuring diameters and pitch diameters.

www.threadcheck.com

GEMINI
To calculate the pitch diameter (E) of a Whitworth thread, you can use the formula: E = D - 0.6495 * P, where D is the major diameter and P is the thread pitch. Alternatively, you can calculate it using the formula E = K + 0.4330 * P, where K is the minor diameter.

Explanation:
Major Diameter (D): This is the largest diameter of the thread, measured across the crests of the external thread or between the roots of the internal thread.
Thread Pitch (P): This is the distance between two adjacent threads.
Minor Diameter (K): This is the smallest diameter of the thread, measured between the roots of the external thread or across the troughs of the internal thread.

Methods for Finding the Pitch Diameter:
1. Using Major Diameter and Thread Pitch:
Identify the major diameter (D) and the thread pitch (P) of the Whitworth thread.
Use the formula: E = D - 0.6495 * P.
For example, if the major diameter (D) is 20 mm and the thread pitch (P) is 2 mm, then the pitch diameter (E) would be:
E = 20 - 0.6495 * 2 = 18.701 mm.

2. Using Minor Diameter and Thread Pitch:
Identify the minor diameter (K) and the thread pitch (P) of the Whitworth thread.
Use the formula: E = K + 0.4330 * P.
For example, if the minor diameter (K) is 15 mm and the thread pitch (P) is 2 mm, then the pitch diameter (E) would be:
E = 15 + 0.4330 * 2 = 15.866 mm.

Additional Notes:
Whitworth threads have a 55-degree thread angle.
The pitch is specified in threads per inch (TPI) in the British Standard Whitworth (BSW) system.

 

[Warlock]

I less familiar with Whitworth but is 1/4-22 even a standard thread?

The thread I think was a probably designed and made to prevent others from using it in their products. That practice you see a lot with industrial sewing machines particularly old Singers even today with Juki machines and the clones (counterfeit) machines. A simple little bolt similar to a #10 about a 1/2 " long will cost between $3 - $9 each if you can get them. Sometimes you are lucky and there is enough metal to re-tap the hole to a more conventional size.

I was lucky about 2 years ago and managed to get a box of 100 new ones for $150 ($1.50 each) while the same ones were being sold for $6.00 US ($8.25 CAD) each.

 

[Downwindtracker2]

As usual, we have wandered off topic, but screw threads certainly are part of the machinist trade. They even figure in millwrights trade knowledge, as millwrights bolt things together. I'm a retired millwright, so I'm not going to rate expert in anything.chuckle

Whitworth thread pattern is a better thread design than the later American National . The rounded roots and tops make for a stronger thread. And easier to make by rolling as well. Though the use of 55* instead of a more normal 60* is odd . The use of 60 is a result of our use of Arabic mathematics . In the latter part of the 19th century, Great Britain was the world technological leader. Likely thanks to all those Scottish scientists. By the end of the century it was passed by both Germany and America. It was from that time that my 1/4"x 22tpi came from and the odd ball threads used on Stanley metal hand planes.

I was simply looking for the Major Diameter of a 1/4" x 22tpi . I guess I will take the difference between 20tpi and 28tpi Whitworth and divide by 4 . The part is not critical., a little undersize will not hurt.

 

[PeterT]

I was simply looking for the Major Diameter of a 1/4" x 22tpi . I guess I will take the difference between 20tpi and 28tpi Whitworth and divide by 4

I think the major diameter of external thread will be the same 0.250" regardless of pitch. The minor diameter & pitch diameter is different.

 

[Downwindtracker2]

Sorry, I got that wrong, my note reads the effective diameter.

 

[Susquatch]

I guess I will take the difference between 20tpi and 28tpi Whitworth and divide by 4 .

I think that is a reasonable approximation. In fact, it might even be precise. I'd have to think on that for a while to be sure. But for your purposes, it should work regardless. The profile geometry is all linear so an interpolation should get you damn close. If it isn't linear its only out by the small difference in the ratios which is a neglidgeable difference for your tpi.

Don't forget to use your 4th on the right end...... LOL. Ask me why I give that advice.......

 

[trevj]

I think that is a reasonable approximation. In fact, it might even be precise. I'd have to think on that for a while to be sure. But for your purposes, it should work regardless. The profile geometry is all linear so an interpolation should get you damn close. If it isn't linear its only out by the small difference in the ratios which is a neglidgeable difference for your tpi.

Don't forget to use your 4th on the right end...... LOL. Ask me why I give that advice.......

Whitworth thread were very similar to BA threads, in that they stuck to a series of rules for deciding their dimensions, and the dimensions of the subsequent nut or bolt head. Off the top of my head I cannot plainly state that they were proportional through the sizes as BA was, but they also follow a set of rules.

 

[kstrauss]

You're certain that it is 22tpi? I believe that 1/4-24 was once used on Harley motorcycles and is even available from KBC (https://www.kbctools.ca/itemdetail/1-372-116). Curiously, a 1/4-24 thread is used in the US Army's WWII vintage M94 cryptographic device.

 

[Downwindtracker2]

I first looked it up to be sure, my memory isn't what it once was, then I checked with a thread guage. It is 22tpi.

 

[trevj]

I first looked it up to be sure, my memory isn't what it once was, then I checked with a thread guage. It is 22tpi.

The mere fact that it is included in the choices for thread pitch on both Lathe gearboxes, AND thread pitch Gages, pretty much states that it was a Standard SOMEWHERE. Have yet to find a thread Gage that goes up through ALL the numbers, just in case...

That said, I HAVE seen a blueprint for a screw made by the Winchester Firearms Company, that was considered to be a bit of a mystery, until the print was dug up and it specified that the thread pitch was 36 and 1/2 TPI! Pretty much the same deal mentioned with sewing machines (with which, I am familiar, and they seem to run the same as always have!), where they were pretty insistent that the only place that you could get the Proper replacement screw, was going to be through the original maker!

Pretty sure my approach would to be to deepen a female thread with a smaller than maybe correct defined tip radius, based on the threads near 22TPI and make the male threads a little less deep, with a slightly larger tip radius. Use thread measuring wires, to ensure the pitch diameter is correct, as they measure on the flanks of the threads, rather than on the diameter, and they will fit well together, as well as not causing any undue strain on things.

'Course, if it were for anything not subject to inspection by rivet counters with magnifiers, for detail. I would likely just skip the radii and use a 55 degree tool and most of the UNF thread form to make a male thread with a 25 percent of pitch flat and 12.5 percent (IIRC!) pitch flat on the Female...