Mamiya 645 - extended tube thinner than No. 1

..has anyone's tried making one? I'd like to use my 45mm (the large and underperforming original) at about 0.35 metres. The unaided lens stops at 0.45m and then with tube No1 (and with the lens on infinity) it's far too close. Maybe it's possible to 'thin down' the centre of a No 1. Don't mind if auto aperture is lost. I really don't want to use a CU lens.

In screwing around with stuff fuzzygraphic, I've cobbled together many things including mounts and tubes.
Usually have used PVC or similar plastic pipe and most things "worked" sort of. I guess it's just fiddling about
seeing if things worked or not. Not exactly precision for sure.
If you're looking for something specific, the local machinist is your friend but he's out for your money, get a pre-nup.

You'll need to do the calculations for the extensions and make sure he understands what you want/need. I'd imagine
you could use the mounts from the tube you have and have a tube made. Should be no problem.

Why not simply buy a longer FL lens, to use with the usual extension tube for M645?

The 50mm for the RB has a floating elements that moves for optimization at closer distances, as far as I know, no version of the 45mm has a floating element so I am not sure how well it will perform close up, the #1 tube is about 12mm, right? You might be able to make a shorter tube by using some "JB Weld" to cement a body cap and a rear lens cap together and then Dremel the heck out of the middle. If you have the right machines you could also thin the caps before gluing with a lathe or even cut a #1 tube in two and remove about half the tube.

If there's one thing you can be sure of: the large and underperforming original will only be even more underperforming at close focus distances...it's not too important how it works - a dreamy, abberration-filled image will be just fine.
ps i think both versions the 45mm, the 'C' and the 'S' have floating elements...they just don't need to be set manually as on an RB.
When i use the 45 C lens i remember a quote from a jet-engine designer who was having trouble with the performance of a new engine. His team set out to produce the most poweful engine for the size and bulk - but after a long development period all they could claim to have achieved was 'the size and the bulk'!