.

With apologies for any confusion that I may have caused …

I have re-weighed my 'threaded body' Pratt-Burnerd 6" on some good [but uncalibrated] Kitchen Scales, and the indicated weight is 4358g … Which seems consistent with Nick's weighing.

It appears that my Bathroom Scales are reading low [… now there's a surprise! ]

MichaelG.

Hi Micheal

Yes thats pretty much how i would go about it , the only bit i have a bit of a problem with, is how does one ensure a good fit of the mandrel screw thread in the new bush. When i did similar mod, fitting a 4 inch lever scroll chuck to a 3/4 inch mandrel, the chuck was internel threaded 24 x 1.5 mm, the mandrels threaded 3/4 x 10w. But i had another lathe to make the bush with, i removed the 3/4 mandrel from the lathe so i was able to use the mandrel to test the internal thread when i was getting close to finished size, cutting with single point tool using lead screw, so was able to use the mandrel to gauge and get best possible fit,

Next the 24×1.5mm male thread was cut again using single point tool again thread was tested using the chuck to gauge the thread to get best fit, next face off the bush just enough get clean square end, the bush was then counter bored, as the 3/4 mandrel has straight 3/4 register about a 1 or 1 1/2 tpi, so the mandrel can now be screwed fully home,,( it is of course now the wrong way round ) remove mandrel

Part off… Then set mandrel up on the lathe with fixed steady using pair of clock gauges to set running true, then screw bush onto mandrel counter bore for register and face off the parted off surface, about 1/2 a thou concave, remove bush from mandrel turn through 180` refit to test ( the bush is now the right way round ) and very light facing cut with tool to make shoulder side of bush very slightly concave, these last two opps ensure the mating surfaces are full contact across the diameters

Fit chuck check and test , all`s well , reunite mandrel with lathe.

Just a slight variation Micheal, and think your list of opps is fine , will the bell mouthed chuck hold true! If really bad one could use a longer blank and use a fixed steady, this would remove the wobble factor of the bell mouthed jaws so all the chuck has to do is revolve the work piece

There was bit more to the above in as much as the blank i used was long enough to make two adapters, the other one to be threaded male 11/8 myford so that was faced off and bored and screw cut 3/4w and counter bored for register before removing from chuck, the myford thread can now be finished at later date on the 3/4 mandrel lathe.

Simple`s…………..b

PS If you blow my one and only pic up you can see the bush fitted to the chuck, the chuck is jaws down on the boring table , right hand side near the top , sorry its such poor res…. if i proof read this any more it wont get posted hope it makes sense…………..b

edited for typo error and may still have missed others !   oops……………b

Edited By bodge on 10/07/2016 00:17:48

I should of added that the myford threaded adapter is so as i can use 80mm 3 jaw i have that has 11/8 myford back plate and 4inch 4 jaw ind, if and when i get round to buying one, 

Edited By bodge on 10/07/2016 00:32:46

Thanks for the 'sanity check' on my list of ops, bodge

… It really doesn't seem difficult, and the only tricky work is being done on 'a bit of bar' [repeat until satisfied]

As you say; if the old bell-mouthed chuck is really bad; a fixed steady might be needed … but that could be a disposable item, knocked-up from a few bits of wood.

MichaelG.