I think it is a tight push fit in order not to contribute to play in that axis. Mine does not have a centre dimple but has a steel sleeve evident suggesting it was bushed to tighten it up. It is also very slightly proud of the surface while yours is flush. I suspect yours has been peened to tighten it.

The dimple does not mean it was threaded but might have been turned to size between centres as that was common back then. Often older parts have a boss cast in to make the centre, perhaps opposite a turned section which can look a bit out of place subsequently. (the over arm of some small die filers is a very good example – see my Excel die filer album)

However I'm interested to hear your findings as I still have to take mine apart sometime 

Edited By Bazyle on 19/09/2022 18:15:43

I take it you have removed the gib from the front of the saddle.

Great news, now if you can make a deep chamfer in the hole, you can fit a matching washer and a screw to hold it when it gets rebuilt.

I havejust realised that the nut os not for the cross slide, but offset to the right for a central leadscrew. Is there anything to keep the swarf off the leadscrew? Maybe a tube on the left of the saddle which just stops short of the left end of the gap?

Edited By old mart on 19/09/2022 21:12:22

I tend to agree with Jeff about the screw / washer idea. I've come across many similar setups over the years and have never seen one with a holding screw.

As they are fitted, they provide a tiny amount of 'wiggle room' for alignment and so are naturally self-aligning. 'Locking' them would probably result in excessive wear in the long run.

regards Mike

You can see the other centre in the base that they needed for turning the spigot. This method would have been a lot faster for production that trying to set up in a (uncommon at the time) 4 jaw chuck. Interesting also to see the hole in the base that the nut needs for removal. I wonder if they thought of that in the first pattern for the prototype.
The Boxford cross slide nut has a threaded hole down the middle, a hole going sideways and the idea is that a suitably shaped screw pushes a short wedge ended rod against the side of the hole to hold it.
The drawing for the assembly that is around on the net shows it the nut the wrong way round so that the cutting force is taken by the rod not the larger area of the spigot. I don't recommend this method.
Also some lathes have a hole down the spigot to the thread for oiling but that attracts swarf.