On my BL12-24 (and presumably their look alikes, Warco BH600, Chester Craftsman etc) behind the regicster is flange. On the back of the chuck is an extension with two diametrically opposed M8 tappings.

These are used to secure two dogs which hook behind the flange, so that IF the chuck tried to unscrew, the dogs would prevent any forward movement.

Retrofitting something like this for a Myford, or similar lathes, might be more difficult, but worth exploring.

I would not be keen on just using a grubscrew, because of the risk of danage to the thread or register, but a setscrew with a plain end, inro a shallow drilling, might be effective.

When I had a ML7, I did not have a problem with chucks coming loose when reverse running (But being aware of the risk was careful) Lathes with heavy braking facilities, can cause this sort of problem.

(Not long ago, I read of someone saying that he had a chuck land in his lap! Fortunately, from a small lathe)

Howard

On 14 October 2024 at 12:29 John Haine Said:

[…] IIRC the instructions are NOT to fully tighten this […]

That’s an interesting subtlety, of which I was previously unaware John … thanks for mentioning it.

It effectively means that there is no pressure on the safety mechanism unless and until it is needed … very clever!

MichaelG.

I made a clamp for the museums Smart & Brown model A which is much more sophisticated, so much so that when I described it in an earlier forum thread, people were not interested. I needed the turning, and milling with a rotary table to modify the lathe spindle and complete the adaptor. Most of the backplates can be fitted with the lock if needed, which is not often.

On 14 October 2024 at 17:13 john fletcher 1 Said:

…neither of us has actually spoken to person who has had the chuck come off whilst reversing.

How does the 80 year combined length of both your and his ownership correlate with the number of people you have spoken to?

Is it a linear, polynomial or exponential relationship?

Smart & Brown mention in the manual that when using reverse, only slow speeds are used, mainly when threading, so the cutting forces are low. I have accumulated some left hand boring and threading bars and the advantage of a left hand threading bar is that you can produce a right hand internal thread by cutting away from the chuck. The left hand boring bar allows a much better view when starting a cut.

I watched the forman at my firm back in the 70’s switch on a brand new Super 7 with a single phase motor for the first time and the chuck that was not tight unscrewed and bounced off the bed, over the stand and onto the floor, unfortunately missing the fools foot. I dressed the bed before we had cut any metal.

I do occasionally run my S7 & Warco720 clone in reverse for turning operations, as opposed just to reversing for metric threading.
The last time I recall was for machining internal and external tapers with the same top slide setting.

For my 4 jaw independent chuck, the hole through the backplate is slightly smaller than the throat of the chuck.
A simple large washer, nut and a drawbar through the spindle keeps everything in place.

My 3 jaw Griptru has the same size throat and bore on the backplate, but I have a recess machined in the backplate behind the chuck.
Again I can use a drawbar and washer, the main difference being that this washer has two sides cut off, so it slides down the bore of the backplate, and then can be twisted to fill the gap twixt backplate and chuck.

Obviously this precludes the ability to turn long workpieces using the spindle hole, but a fixed steady could be used.
I’ve never got round to it yet, but a thinwall-tube/hollow-drawbar would at least allow slightly smaller long workpieces to protrude into/through the spindle.

Bill

A suggestion I have previously read about, but not implemented as I have threaded body chucks with no rear spigot.

If the chuck backplate has a reasonable width of spigot at the back, about the same diameter as the spindle shoulder, or a bit larger, then a clamp ring can be put round it. Relying on the requirement that the backplate is already a close fit on the spindle register, the spigot can be sqeezed enough to hold tight on the register. A split ring with a cap-head clamp bolt would do.