I also have a 6mm lathe although mine is a Lorch. I bought it second hand and seem to have been lucky as it works surprisingly well for what I use it for.
However, the previous owner managed to make a repair to a very similar problem by putting a right angled piece of metal in and tapped holes in the casting to hold it together. It works well although it is very tight fitting now so it is a bit of a pain to take on and off. Fortunately I don't use the cross slide very much and prefer the hand held graver.
I haven't cleaned everything yet but here is a picture of the repair:
Failing that, cast materials will braze as long as you are careful with the temperature which is another possible way of repairing it. I haven't done much brazing, welding or silver soldering before so I don't know about the practicality of that idea.
I'm afraid its a lemon and is of Chinese origin Elliott did not start production of platform escapement mantle clocks until the 1920's and used very good quality platforms of french origin and then later very good platforms by Rotherham's eventually switching in the 1950's to L'epee escapements, you could always try and send the clock back stating its not as listed because I can tell you with certainty its not by Elliott.
As a side note I have bought from the seller you purchased from, a Gillett and Johnston clock last year, he's a retired clock repairer and jeweller so should know better.
I was going to say, I have a couple of 1970s HMT (Citizen) movements marked for LH threads.
There are a number of co-operations between the French watch making industry and the USSR industry.
For example -> http://www.ranfft.de/cgi-bin/bidfun-db.cgi?10&ranfft&&2uswk&Zvezda
... and ... -> https://en.wikipedia.org/wiki/Slava_watches
Also worth a look is the Lorsa 8FA on 17jewels.info
So the most likely candidate is a Lorsa 8FA derivative, followed by perhaps one of the USSR era licensed copies of a similar French movement derivative.
Well worth the not very much you paid for them, even of only for the history lesson . I think they are going to clean up very nicely though.
Can someone here who actually uses a 4-jaw on a watchmakers lathe for case finishing comment on its use, as per the original poster’s query?
There’s no point in speculating about them. I strongly suspect not everyone here discussing them even owns a watchmaker’s 4-jaw
Here’s my experience:
I have a 3-jaw and have only used it for circular brushing and polishing of bezels and case backs. It works perfectly well for that application and is sufficiently concentric.
Yes, a floating barrel or “suspended barrel”.
In the UK, the Geneva stopworks are regularly removed. Some watchmakers decided they were better without. For an excellent description of why they were implemented, David Boettcher’s website is excellent.