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Old 08-21-2019, 01:46 AM   #1
1930 roadster
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Default Which tap and die set

Hi Guys,

A question from the metric side of the ocean.

A model A is build up with Lots of bolts and nuts. Even metric so iíve noticed.
Iím planning to buy a tap and die set, but Iím not sure which to buy.

What do I need for my model A? UNC/UNF or BSW/BSF?

Anyone?

Thanks!
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Old 08-21-2019, 06:05 AM   #2
Bruce of MN
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Default Re: Which tap and die set

I was going to say that I think it is safe to say that there arenít any BSW/F threads on a Model A, but who knows about the UK models with their smaller motors, etc.?
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Old 08-21-2019, 06:24 AM   #3
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Default Re: Which tap and die set

Buy a decent thread pitch gauge set. looks like a bunch of different pitch and height saw teeth and some decent digital calipers. This will help immensely. Trust nothing, verify everything because not only did they use oddball stuff prewar but you have 90 years of fingers in there too.
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Old 08-21-2019, 06:55 AM   #4
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Default Re: Which tap and die set

As a starting point, I'd suggest a set of UNC and UNF taps and dies. (Unified National Coarse and Unified National Fine). That should do you except for those strange "gauge threads" no one else understands - well, I don't. Maybe I am about to learn something too.
It should be noted that BSW and UNC are the same up to 1/2" so far as the TPI goes but the thread form is 55 degrees vs 60 degrees. At 1/2, BSW is 12 TPI and UNC, 13 TPI. Weird, the way they changed so little for UNC!
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Old 08-21-2019, 07:56 AM   #5
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Default Re: Which tap and die set

Here in USA the model A's has many fine threads. Way more than one might have expected.
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Old 08-21-2019, 08:23 AM   #6
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Default Re: Which tap and die set

Whitworth..
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Old 08-21-2019, 08:54 AM   #7
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Default Re: Which tap and die set

Ford used rather tight clearance tolerances on many fasteners. If you buy the average tap/die set it will be fit class 2A/2B and you will ruin parts if you use the taps/dies to clean up nicked threads. You need a set with 3A(external) & 3B(internal) clearance tolerances.


My go-to for taps/dies with the clearance specs I want is MSC Industrial Supply Direct Co. Inc. (US)
https://www.mscdirect.com/
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Old 08-21-2019, 09:28 AM   #8
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Default Re: Which tap and die set

Quote:
Originally Posted by Railcarmover View Post
Whitworth..
While Whitworth generally follows the UNC/UNF thread TPI convention, the taps/dies themselves have a 55 degree included angle.

In my basement I have a circa 1860 Wood turning lathe made by one the early Worcester, MA machine tool builders (Likely Lathe & Morse or their predecessors.) The headstock bearing caps are threaded 7/16 -14 BSW - It was common for pre-Civil War American machine tool builders to "import" their tooling for threading.

A 7/16-14 UNC bolt will not screw into the hole more than about 8 turns.

I was tempted to drive a 7/16-14 tap into the hole to allow use of UNC dies to make the machine cut bolt - but I resisted opting instead for a $24.95 BSW die from Ebay.

Originality matter in historic machines. At least in my mind/wallet.

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Old 08-21-2019, 09:31 AM   #9
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Default Re: Which tap and die set

Mike,

As we know the differential bolts and case are a tighter thread than common taps and dies.

Are those 3A and 3B or are they a different, even tighter tolerance?

Transmission cases also?

Thanks





Quote:
Originally Posted by MikeK View Post
Ford used rather tight clearance tolerances on many fasteners. If you buy the average tap/die set it will be fit class 2A/2B and you will ruin parts if you use the taps/dies to clean up nicked threads. You need a set with 3A(external) & 3B(internal) clearance tolerances.


My go-to for taps/dies with the clearance specs I want is MSC Industrial Supply Direct Co. Inc. (US)
https://www.mscdirect.com/

Last edited by Benson; 08-21-2019 at 09:51 AM.
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Old 08-21-2019, 01:30 PM   #10
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Default Re: Which tap and die set

Quote:
Originally Posted by Benson View Post
Mike,
As we know the differential bolts and case are a tighter thread than common taps and dies. Are those 3A and 3B or are they a different, even tighter tolerance? Transmission cases also? Thanks
Tough question since Ford, and the industry in general at the time, did not use today's grading standards for either strength or fit. You would have to find the prints/specs (Benson Ford Research) and both old '20's and modern copies of Machinery's Handbook to compare the tolerances.

That said, I have run class 3 cutters over differential, trans, and engine threads and fasteners without removing anything more than the deformed metal. A class 2 cutter would leave the walls of the thread cut or scraped down to new metal- bad, bad, bad.

In any case that type of clean up is a last resort after steel bore brushes and 60 degree die sinkers files fail to give the desired outcome.

Another option is thread forming rather than cutting taps, also available in various tolerance specs. I used those a lot on AlMag castings when I had a foundry back in the 70's & 80's.

As far as dies go, the adjustable versions permit dialing in the clearance you want. Not something for the casual user.
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Old 08-21-2019, 06:16 PM   #11
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Default Re: Which tap and die set

All the old USA built Ford stuff with some minor exceptions is Unified type for the most part. I don't know about the UK built cars. It depends on how much was shipped from the USA. The Dagenham Ford plant was still under construction in the first few years of the Model A production.

I've always kept British Association and British Standard tooling around due to work on Rolls Royce aero engines and all the old British cars and motorcycles I've owned over the years. Thread pitch gauges are invaluable to identifying fasteners. The stuff is all still available from UK sources. My BS and BA wrenches & socket sets are all Snap On since there were so many Rolls Royce aero engines back in the day. The old Merlin engines and Dart turboprops were all popular back when.
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Old 08-22-2019, 02:52 AM   #12
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Default Re: Which tap and die set

When cleaning old threads DO NOT be tempted to use taps and dies. There are thread restoring tools out there that are designed to do the job. A classic example of the "wrong way" are back axle banjo bolts which have been "restored" with a die. Then there's the torment of stopping lubricant leaks past the threads.
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Old 08-22-2019, 03:32 AM   #13
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Default Re: Which tap and die set

Thanks!


Wow, I thought I had a simple question. But learned much
My Roadster is an American made by the way. But I didn't know that the british made cars, could be different. Which is to be expected of course.
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Old 08-22-2019, 08:08 AM   #14
Benson
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Default Re: Which tap and die set

Mike,

Thank you very much. for the help.

We use MSC-direct at the shop

Last edited by Benson; 08-22-2019 at 10:14 AM.
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Old 08-22-2019, 09:18 AM   #15
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Default Re: Which tap and die set

Quote:
Originally Posted by tiger.1000 View Post
When cleaning old threads DO NOT be tempted to use taps and dies. There are thread restoring tools out there that are designed to do the job. A classic example of the "wrong way" are back axle banjo bolts which have been "restored" with a die. Then there's the torment of stopping lubricant leaks past the threads.
I agree. I hear of so many people using a tap to "chase" the threads in their block for the head studs to "clean them up". Makes me cringe.
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Old 08-22-2019, 06:25 PM   #16
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Default Re: Which tap and die set

Quote:
Originally Posted by tiger.1000 View Post
When cleaning old threads DO NOT be tempted to use taps and dies. There are thread restoring tools out there that are designed to do the job. A classic example of the "wrong way" are back axle banjo bolts which have been "restored" with a die. Then there's the torment of stopping lubricant leaks past the threads.
My '30 CCPU was "restored" in Minitoba, Canada. The guy who did it chased the banjo threads and I had that problem but it is easy to fix. I drained the oil, flushed and removed the bolts one at a time, I then used brake cleaner or carburettor cleaner (could use wax and grease remover) on a strip of rag to clean the thread. I did the same to the tread on the bolts, put some Permatex No 3 on it and screwed them back in. now, 9 months after returning the oil to the diff, it hasn't leaked a drop. I think we sometimes get a little precious about how things should be done, especially when we think about how these cars have been treated during their "just another old car" days.
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