Might want to consider milling a bit off the top slide to allow for a floor on the 4 way. That was my method atleast.

My first move would be to replace what looks like a bit of B&Q studding currently used for a toolpost stud, with a properly machined stud that is a snug fit in the bore of the 4 way toolpost.

That way, clamping down the tool holder on to the cutting tool should eliminate, or at least cut down considerably, the tilt to the tool holder that is currently occurring.

Alternately, depending what model of Denham you have, the centre height appears to be around 5". A 5/8" tool is pretty hefty for this size of lathe, so you may be able to fit a different 4 way tool holder with a floor on it, along with 3/8" or thereabouts cutters, thus eliminating the issue another way.

If you went for the latter, I would still get rid of the bit of studding and go for a plain snug fitting tool stud, regardless.

Because there is effectively only half of a 4 way toolpost, i.e. the arrangement relies on the top surface of the top slide to lock the tool in place, consequently when you tighten the bolts to lock the tool in position then the top of the 4 way is tilting away because of the slack fit on the central stud. I would think that the only safe way to use this configuration is to have a corresponding block on the opposite side and clamp down equally on both, that should stabilise the setup and keep the the top of the 4 way level. Using this type of tool clamping you will always get movement and twisting because of the free play on the central mounting bolt, the only way to eliminate it would be for the mounting stud and hole to be a very close fit.

Dave

First question, have you measured how far above the face of the top slide the lathe centre is?

You may not need to mill anything off, if the QCTP holders take the tooling you want, and they can be set on centre.

EDIT – I was still typing my reply whilst you were editing in the second part of your post above

Edited By David Standing 1 on 12/10/2017 15:03:07

And following on from your edit, unless the bore of your mini lathe QCTP is a snug fit on your toolpost stud, this idea will be plagued with issues of the QCTP block moving around on the studding.

So, again, it will come back to getting rid of the studding, and having a plain shank tool post stud that is a snug fit in the QCTP block.

I took mine from a 12.7mm distance to 20mm distance. That gives a 4mm toolpost base and room for a 16mm tool. Potentially overkill but I wanted to be able to have cheap second hand industrial insert tooling that could fit.

I have a different topslide to yours, mine was very thick and somewhat primitive. Not currently near the lathe to measure how much meat is left though.

It is?