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25th Apr 2021, 11:55 AM #1
Whitworth fittings on vintage machinery.
I have a 1960s English wood machine I'm restoring . All BSW / Whitworth threads . The fit of the bolts through cast iron and other metals is nice and fine . Not a sloppy fit .
I tried using a Whitworth tap through one of the dirty holes to clean it out and it shaved enough away to loosen that fine fit . I only did that once !
Some other damaged threads I had to do anyway to get them working again . No other option .
What are the options with this situation ?
Do you find a Whitworth tap and die set that happens to match buy buying a few and trying ? Do they differ between makes ?
Or in the past did the sets come in various fits?
Or is that just the way it goes and you try not to do it unless necessary ?
Thanks. Rob
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25th Apr 2021, 01:09 PM #2Member: Blue and white apron brigade
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Are you sure it was a Whitworth tap - might it have been a UNC?
If its just for cleaning out threads you could always always make a slightly smaller tap using an adjustable die?
Or if you have spare bolts of teh right fit, you could always cut vertical slots in those to use as thread cleaners.
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25th Apr 2021, 01:27 PM #3Gear expert in training
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Perhaps WD40/turps/kero plus compressed air would clean the gunk out without having to resort to a tap?
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25th Apr 2021, 02:19 PM #4Most Valued Member
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25th Apr 2021, 02:35 PM #5
Chaser
I think you need a chaser ? These are different to normal cutting taps. You could make a chaser using a BSW bolt of the correct size
"Taps and dies are designed for creating new threads. If you drill a hole in a piece of metal that you want to run a bolt into, you'd use a tap to cut threads in it. ... Thread chasers aren't designed for cutting new threads, only for cleaning rusty or damaged threads."
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25th Apr 2021, 05:58 PM #6
Yes its definitely a Whitworth Tap . Its a Japanese small boxed set . Cheapies I think which could be the problem. Playing with a bolt would do it too .
Just WD40 and air would be better than nothing . Its just that Ive read of this being done on metal restoration . Maybe it was car resto ?
On quite a lot of the threads its been ok . Others were worse.
I'm starting to think maybe some of the holes Ive done possibly through pressure have threads that have distorted and me putting a tap though has cleaned the hole back to normal shape and the distorted bolt that lived in there now has a wobble .
Its not much . I was out there before and screwed a 3/8 16tpi stud in a dirty hole . Its was tight and half way in there was no wobble sideways. I then passed a tap through and caught what came out on the under side. They were fine grains like castor sugar of cast iron mixed with the oily dirt . And I could definitely feel the tap re cutting iron . The stud re fitted half way in now had a 1 to 1.5mm sideways wobble . Normal for a Bunnings nut and bolt maybe . But not on this older English made machinery I think , or thought. Plenty of the clean oiled fittings are nicely fitted I think . The worst one I did the other day which started me thinking of asking this question was a 5/8 11tpi and when I passed the tap I got curly shavings and maybe a 2mm sideways wobble half way in .
I have to get some better Whitworth Tap and dies as well . Im trying to tap a 3/8 16 tpi and I don't trust the feel . Its about to break on a test Im doing on mild steel . I cant get past half way though a 10 mm section and the drill hole was slightly over sized. Think I need the tapered starter first . Not just the Plug Tap maybe?
Thread chasers Ill look into as well . Are they just slightly smaller or softer ? They don't cut but just push the crud out ?
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25th Apr 2021, 06:37 PM #7Most Valued Member
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25th Apr 2021, 06:39 PM #8Gear expert in training
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25th Apr 2021, 06:52 PM #9Golden Member
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25th Apr 2021, 06:54 PM #10I break stuff...
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Well, in theory Whitworth was made obsolescent in 1948, when the UK, US and Canada all signed on the Unified standard (I believe in large part to issues throughout WWII with the interchangeability of bolts, an issue that had previously been raised during WWI). The reality of course is that different industries and manufacturers changed over whenever they felt like it. Some went straight from Whitworth to metric in the 70s, some used Unified for some or all of the interim period, and some got an early start on metric....
So the answer is probably "just about anything".
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25th Apr 2021, 07:04 PM #11Gear expert in training
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25th Apr 2021, 07:13 PM #12Golden Member
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I once owned a perfect example of this confusion, a 1953 MGTD. The engine was all metric (as were all old MGs), but the fasteners all had Whitworth sized hexes! The gearbox and body fasteners were Whitworth/BSF. The back axle used UNC/UNF, since it was sourced from the Austin factory due to the recent merger of Morris Motors and Austin, who had already converted to the unified threads. All piping was BSP, and the Lucas electrics used BA fasteners. It's no wonder why I seem to have collected a fairly wide range of taps and dies over the years.
Frank.
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25th Apr 2021, 07:14 PM #13Gear expert in training
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Sounds like the kind of thing that'd make a mechanic jump of a bridge
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25th Apr 2021, 07:35 PM #14Most Valued Member
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25th Apr 2021, 07:40 PM #15
Hi Guys,
Just after the war manufacturers started automating production machinery, a lot of automatic threading was done using specially ground taps, some with very short tapers and often slightly undersized. Also thread rolling of bolts rather than cutting tended to produce undersize threads as well, depending on how well the rolling machines were set up.
However that doesn't entirely explain tight taps and loose bolts unless the threads have been stretched ! Threads in cast iron tend to strip rather than stretch.Best Regards:
Baron J.
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