I now need to make the nut. but first , I need to grind an internal threading tool. given the size free hand was out , so I made a holder for the proxxon multi tool. then it was a case of mounting the small grinding wheels and thining down somw 3/16 tool steel. I used a cut-off wheel to get a sharp corner as the pink wheels are quit soft and left a radius
the rest of the tool was finished free hand - not the best preparation for cutting an internal square thread
I faced of a square blank, drilled a tapping hole, set up the thread follower and began cutting the nut
it did cut , but I could visibly see the tool flexing, and i realised i would need better tool grinding facilities or come up with a different method
so i tried making a tap from silver steel ( drill rod) using the proxxon free hand to cut the flutes.
no way was it going to finish the threads and broke quite easily the first try.
having cut the male thread , I didn't want to give up just yet, so tried to think of another method.
having had some success removing taps I wondered if it would be possible to reverse the process as it were, and form the nut round a sacrifial stud, then disolve it out leaving the nut.
so I drilled out the blank clearance size, set up the thread follower and made a small stud.
I then dropped it into the nut blank and heated it up to a good red heat and then proceeded to knock the hell out of it with a 2lb hammer. As an anvil I just put a block of steel on the garage floor - there's no way my wooden bench would be up to it. sorry no photos - with hammer in one hand, pliers in other and torch in vice not possible.
I soon stopped as A) It wasn't doing the floor much good, and B) It looked like the bronze was splitting by the hole.
I tried drilling out the centre of the stud to give me less steel to disolve, but this was a mistake as it was difficult to hold the now mis-shappen nut square in the vice an the drill looked like it had wandered.
I then started to disolve out the mandrel using alum powder. It took the best part of a day . I ended up using about 2/3rds of a 100g bag, but i have no idea how to make up the solution - I just kept topping up the water and spooning the powder in whenever the stream of bubbles looked like it was tailing off.
I would take it out every now and then to check progress and see if I could loosen the bolt. eventualy I was able to get a punch behind it and twist the las bit out
here you can see the remains of the stud next to the nut.
the nut was a bit dissapointing. the drill hadn't wandered too much , but I hadn't been able to hammer enough bronze into the threads.
The nut tried to go on the threaded bar but was very tight - i had foolishly made the sacrificial mandrel the same size as the original bar, so there was vertualy no clearance on the o.d.
Eventualy, with the help of some timesaver lapping powder, I got it started and then merrily would wind it on a bit , back it off , on a bit etc. etc. and I began to make progress. Unfortunately I got carried away , wound it on too far and it locked up - not to worry - i'll just back it off. and then 40 odd years of using right hand fasteners kicked in , and instead of backing it off ( it's a left hand thread) I turned it the way you would to loosen a right hand thread , screwed it on even more, and sheared the bar. No point in stopping, so clamped the stud in the vice and carried on. I eventualy got the nut to run on what is left of the bar - in fact it runs quite freely .
hopefully I've posted the link to the video O.K.
http://s1184.photobucket.com/user/PEATOLUSER/media/NEWNES/DSCF0464_zps373bdcc7.mp4.html7/32 O.D. 8TPI Lefthand twin start thread
all is not lost . the stud is repairable and I think there is enough depth in the nut to be usable. But I may remake them anyway.
For the nut, I'm thinking of casting it around another stud, and the maching / dissolving away the excess as before.
And I would like to remake the stud and get the threads equal length.
I may be back in the middle of the woods, but this time I think I have found a path out!
any way i have a couple of weeks to think it over as we are of to sunny Spain on sunday for two weeks!
thanks for looking
peter