Hello CJ,

I have done this sort of picking up on a part cut thread by combined movements as you describe many times and it is easier than one might think too.

Regards

Brian

Clearly not ‘best practice’, but when ‘needs must’ many of us have done it! Even Doubleboost has succumbed on occasions – not removed from the chuck, but having to make a new cutter half way through an internal threading job on one of his u-toob videos.

Personally, on a job like that I think I would make a plain thread to get the fit and then make the item. Not too bad with a coarse thread, as yours, but I would not relish rechucking with a very fine thread.

Of course, the re-chucking (the really naughty bit) could be avoided by cutting the threads between centres so that alignment is not a problem, leaving only adjusting the thread starting point as the much less of a problem, even for finer threads.

For fine adjustment of threads you might find a hand held thread chaser of some benefit. No need for realigning part with a leadscrew or even running super true in the chuck.As another benefit you can also get correct thread form on rounded Whitworth threads. Do Tracy Tools still do their chaser sets?

chriStephens

Do

Standard way to deal with this sort of dilemma is to leave the half nuts engaged and work with the topside set the parallel to the bed. Exact replacement position becomes a non issue as the topside provides the necessary fine adjustment to give proper alignment between thread and tool.

As Neil says its important to use the threading feed to run up to the approximate position to take out backlash.

For final adjustment I prefer to cut on the front edge of the tool as its easier to set up a very fine skim.

Can be a pain in the backside keeping track of cuts. Best way is to start by touching the tool off the workpiece.

Set the cross-slide dials to zero.

Crank the saddle clear of the workpiece and run the cross-slide in by the book thread depth (plus an allowance for tool tip shape if yours is too pointy).

Set the cross-slide dial back to zero.

Cut thread as per normal using only cross-slide feeds. When the dial gets to zero thread should be the calculated book depth.

Remove, test fit and adjust as needed.

I normally use the zero2zero threading method where the lathe self generates the required in-feed with the topside set at close to half the thread angle so this is a simple modification to my standard process.

Got me a left hand 26 TIP thread wheel bearing retaining ring in the "Please fix this for me" box that will need this approach. On machine trial fits are a bit impractical with a 19" diameter motorcycle wheel. With a simple job like that its easiest to make a test piece then revert to the zero2zero method for proper job as the final cross slide dial reading give the extra in-feed needed beyond the original setting so the proper depth can be used.

Clive.