Tapered thread chaser ? my Zeus book states 22 tpi as 5/16 BSF, must be a home made special.

George.

Not home made,…it's a product of Thomas Chatwin makers of fine threading equipement mainly for industry, and it's for 'chasing' or repairing/polishing threads. Its used in the top slide which is set to the right angle for the particular thread and then can be fed into the thread until the required finish is atained.

Thread burnishing?

Hope not to appear too stupid here (well, not much more than normal), but wouldn't a chaser or die be needed to round off a Whitworth thread that had been screwcut?

Brian

.

Not stupid at all, Brian

Three answers:

1. Hopper, speaking as a practical man, says "Not really"
2. If you use a 'full form' cutting tool [*], No
3. If you use a conventional single point cutting tool; and you [or QA] care about accuracy of thread form,  then Yes.

MichaelG.

.

[*] See the excellent illustration by Andrew Johnston, here: 

https://www.model-engineer.co.uk/forums/postings.asp?th=137131

… noting, of course, that he shows ISO Metric thread form, not Whitworth.

.

Edit: Here's an 'external' insert of Whitworth form:

https://www.rileyshutt.co.uk/ProductGrp/00160003001f0002

Edited By Michael Gilligan on 19/10/2018 10:00:30

Edited By Michael Gilligan on 19/10/2018 10:08:10

Has anyone here besides me tried hand chasing a thread?

It is very definitely a skill' and worth a try just to see what's involved!

Neil

I've seen straight chasers with a tapered tang that looked as if they were made for a file handle, but not one with that angle before.

I'd guess it was designed to work in an angled toolpost close to a chuck or other workholder, avoiding collisions with projections.

Edited By Mick B1 on 19/10/2018 11:53:07

For anyone interested in seeing hand chasing, here is a link to a fascinating video about Japanese fountain pen making:

Edited By ega on 19/10/2018 12:07:47

Edited By Neil Wyatt on 19/10/2018 19:29:05

The tool looks just like a hand chaser as would be used by a woodturner. Very commonly done in some forms of wood and exotic material turning. I once watched the now deceased Bill Jones make up a chess king out of about 6 pieces of ivory (or more likely imitation ivory), all individually turned and hand threaded to fit together to form the finished piece in order to maximise the use of the material. Hand threading lidded boxes is pretty commonly done nowadays, usually in boxwood, African blackwood and other very dense timbers to take and hold a fine thread. There is definitely a knack to doing it but if you are shown the technique by someone who knows, you will have a fair chance of making a functional male and a female thread within an hour. Lots of stuff on Youtube as usual eg **LINK**. Hand chaser sets are available for wood turning. I know nothing about hand chasing metal, you may not be surprised to hear ….

A lack of fillet radii – cannot be over stressed.

Okay, I am playing with words here but in the light of the above remark …

The radius is more theory than practice …

and with due respect to Hopper (assuming we are referring to thread root and not thread crest), in the many years while I was ‘doing’ technical service, the vast number of moulded products that failed in service, failed through lack of adequate fillet radiusing. This included a wide variety of threaded components, e.g. caps, closures, water filter canisters, and on through a wide assortment of moulded parts, big and small.

The source of the problem was often tool design or mould-making oversight, i.e. sharp edges left on the external corners of mould cores and profiles.

For further reading – Google ‘Fillet radii’ and a myriad of examples will appear.

My apologies if I’ve covered this somewhere else.

Regards,

Sam 

BTW – when I bought my (now long gone) ML7, it came with a box of thread chasers, mostly with tangs for hand chasing.

That's a fascinating video of pen making, especially the method of closing the lathe collet.   

Edited By Sam Stones on 20/10/2018 00:19:38

I often run a die down my coarser machine cut threads – unless the thread is one that I don’t have a die or chaser nut. Saves having to get that final cut at the right depth and with a good finish, while the thread will be dead straight aligned without worrying about a crooked start. Easier on the arms, as well as the die, for the larger diameter threads I deal with.

When I first learned about single point thread cutting in the lathe, it was Whitworth threads, round root and crest, and a hand chaser was used to finish the thread.

In later years I have read of early thread cutting on the lathe using a hand held thread chaser to form the complete thread without the assistance of a lead screw(internal and external threads), I think I first saw this in the first volume of Model Engineer 1898.

Ian S C