hand chasers

I have aquired three buckets of hand chaser from WW2 with stamps of USS SAE Their are heaps of 1mm external/5mm internal and the following sizes 20/26/38/50 external and 48 internal.has anyone any idea what thiese were used for.

Frank

presumably to finish form rough cut threads.

Probably sent over herein bulk to help us Limey's convert our Whitworth threads to UNC and make adaptors for captured continental thread equipment. Your buckets being the stores clear-out some while later when we went all metric.

In addition to the previous post there are a lot of toolpost chasers 13 tenths " stamped ESC13 TPI USS CS The 50 on the previous post has SAE stamped on.

Frank

Thought that 13 tpi sounded as if it might be a pipe thread, since 1/2 BSP, 5/8 BSP 3/4 BSP and 7/8 BSP are 14 tpi, and NP thread pitches seem to differ from BSP by 1 tpi.

Unfortunately, Kempe's Engineer's Year book, 1982 does not admit the existence of national Pipe threads, nor does Tubal Cain's Model Engineer's handbook nor Martin Cleeve's Screwcutting in the lathe.

1/2 and 3/4 NPT and NPS appear to be 14 tpi

Zeus charts show no 13 tpi threads.

Tracy Tools catalogue shows no 13 tpi threads, so sorry, but what thread is 13 tpii remains a mystery to me.

Howard

Howard

The old US Standard 1/2" thread is 13 tpi.

Apparently the Americans stayed with the 1/2" Ø 13 tpi and 1" Ø 14 tpi SAE (Society of Automotive Engineers) after all other sizes were switched to the UNC, UNF and UNS (Unified Special) standards.

Don't know if the detail tolerance and clearance specs were updated to conform with Unified or not.

Clive

Plenty of new 1/2" 13TPI UNC items on eBay from UK sellers. taps, dies, studding, nuts etc

Possibly, but I guess the main reason was quick repair of damaged threads. During WW2 the Allies all used gigantic quantities of American made equipment - vehicles, weapons, machines, ships, aircraft, radios etc. Most of it came with US threads that caused serious difficulties to everyone because Whitworth was also in somewhat less gigantic quantities of British made gear : British trucks couldn't be fixed with almost identical American parts and vice versa.

As military equipment must often be quickly repaired in wartime, being able to chase damaged threads is a useful workaround. Probably avoided as much as possible, but I can imagine British Repair Units urgently fixing US made gear by chasing something from their huge stock of Whitworth into something like a US thread. And chasing dinged US threads back into usable form was probably common too.

Only Inspector Meticulous would rather be killed by the enemy than permit a chased thread to be used to fix a broken down truck just so he can escape in it!

Dave

My Zeus books shows ½" UNC as 13tpi, as do my taps, dies and chasers.
If anyone needs a set, Tracy Tools do supply.
https://www.tracytools.com/taps-and-dies/UNC-taps/1-2-x-13-tpi-unc-spiral-point-flute-fluteless

Bill

Edited By peak4 on 25/07/2022 16:07:21

Quite right! 1/2 UNC

That's what becomes of becoming obsessed with pipes! Logic goes down the tubes!

Howard

How do you use a hand chaser ? Whenever I have tried, it digs into the work or alternatively doesn't remove any metal. I appreciate they are for just putting the crest / roots on or perhaps for cleaning up threads.

I think in the very old days they actually cut threads from scratch with them. But I reckon it was a dark art. I have seen old books that refer to it but never really delve into the "how".

Edited By Hopper on 26/07/2022 09:40:37

I have seen some of the woodturners doing exactly that when making screw top turned wooden boxes - fascinating to watch !

John

I've seen a brass worker do it too.

Roy

A support close to and long enough to run past the threaded area to be cut, a substantial wooden handle for the chaser and a slow speed. Preferably some pre-cut thread and allow the chaser to follow the thread to clean and round off the crests. Not often used on steel unless cleaning thread. Mostly brass threads chased and fairly long threads (Fine threads) like on traverse screws on an Instrument or a microscope, I have not chased one greater than 8mm diameter.