If nothing else will work, you could use pop rivets. Drill completely through both plates. Find a steel pop rivet that 3/4 of the length of the 2 plates together. Push the pop rivet in and pull the trigger. The friction of the "ball" portion of the pop rivet will hold them together. Do this several times across the face of the two plate and you will be hard presseed to get the plates apart without drill the rivets out. I use this method to hold plastic and a different material together with the ball portion being in the plastic. R. Wink
A lot of creative answers to your question; but everyone seems to have overlooked the most obvious, AND most effective way to solve the problem - a set screw that DOES pull the plates together, and with at least as much force as a cap screw could, but without the cap. And you probably already own dozens of them.
Grab just about any standard insert-type turning tool in your shop, unscrew the clamp that clamps down on top of the insert, and you'll find that the screw inside it is exactly what you're looking for. It's a differential screw - with right hand threads at one end, left hand threads on the other, and a bit of a reduced diameter neck in between. When the screw is turned, it pulls the pieces together with BOTH ends of the thread. And, like any ordinary screw, it locks when it gets tight. No partial threads, interference, or anything like that is required.
Just look in a good tooling catalog to find the size you need. The most common ones are around 1/4" diameter; but they come a lot smaller if you hunt a bit. Then get a left-handed tap to use on one plate, a right handed tap for the other, and you're in business. Stick 'em together and go. And then take 'em apart again with a simple twist of yer favorite allen wrench.
If you look carefully for the right screw, you won't even have to worry about it being the right length. (They'll probably mostly be too long for your 1/2" thick assembly.) Since many of them have wrench hexes that go clean through, you can grind some thread length off either end (or both), and the silly things will still work!
That sounds real good. I wonder how much fun it might be to get 4 or more of them to engage and tighten, especially since the phasing of the threads would vary. It seems that a little extra looseness might be helpful in that case.
Adjust the level. Seriously. Screw what the way overpriced POS Starrett 199 level says. Put an indicator in the machine and adjust the bolts under the sub spindle side until it comes in. (lower the bolts toward the floor to raise the sub spindle up) It probably won't take much more than a small tweak or two on the bolts.
I'm still hoping that someday I'll find a service tech that can properly set up a sub spindle lathe. The guys that are too lazy to indicate the machine during installation are usually the same ones who scramble around the machine like a monkey trying to level it using all six (or more) bolts.
Instead of the easy way which is to use the two outboard screws on one side and the center screw on the other. Then, once level, bring the rest down until they bear some weight. Then indicate the freaking thing, and adjust as needed.
A good question. I can envision it working; but I can't swear that you're wrong. I'm fairly sure, though, that if just a bit of looseness let them all get engaged, then they'd remain in phase after that. They'd need to be tightened simultaneously, of course, in a continous sequence of small increments.
If you want to get fancy, you could make the screws yourself, and be sure the two theads are in phase. A machining center with good rigid tapping could phase the tapped holes perfectly.
I wonder what would happen if one end of the differential screw had a slightly different pitch from the other end. Start by engaging the finer end, use it to adjust the screws individually so that the coarser ends could come into engagement at the same time. Then tighten sequentially.
I hate good questions. My brain starts to smoke after thinking about them for too long.
PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.