Motion in vacuum - wiggle stick

How to get to vacuum, what the classes are, and what is needed for what job.

Motion in vacuum - wiggle stick

Postby Doug Coulter » Sat Jun 11, 2011 2:29 pm

Sometimes you wish you could move things in a vacuum without opening a seal, in fact, pretty often. Sometimes you can find the right kind of wiggle stick or fixture surplus, and sometimes not, and the new ones are expensive to say the least. I needed a push-pull and twist for the new beam device, didn't have the right thing -- the O ring versions leak too much, and the price of a new one, well, wow comes to mind.

So, I'm making one, which will be magnetically coupled, out of junkbox stocks here. The idea is you have a tube sticking out from the tank, sealed, inside is vacuum, with a magnet in it attached to the actuator rod for whatever you want moved in there, and make a magnetic yoke to move the inner magnet from outside. Just getting started on this today. Here's what I have so far.
FlangeWeld.jpg
Reused flange and SS tubing welded in

Not the prettiest weld I've ever done (or seen) but good enough. I had some thickwall SS tubing in the junkpile and this flange that had a 3/8" hole in it off center. I put a 1/2" mill in the lathe tailstock to clear up the off center hole, then drilled it for real to fit the tube. The trick here is to not drill quite all the way through, leaving a thin bit left. This gives a flat shoulder to make the tube align straight, and a little extra material as filler - automatically the correct alloy too. This cleaned up nice on the lathe and with some grinding and steel wool on the inside.

Tube.jpg
All welded up

I cut a piece of 1/8" SS plate to weld over the other end. Ugly but tight, and it also cleaned up nice on the lathe after. I should remember to do a practice weld first - it always takes me a minute to remember the technique.

Magnet.jpg
Magnet and rod holder

For various reasons, I wanted an insulated actuator, both electrically and thermally. The thing is, ceramic is not your easiest to work with material. I had a grade 50 NeFeB magnet that fit in the tube nicely (this piece of tube was wierdly sized), but didn't trust gluing the rod right to the magnet, so I made a rod holder with a setscrew to glue to the magnet. In the picture, the magnet poles are left and right, so a single yoke can do all the required motions -- push pull and rotation. I used brass at this end as it's a non galling material against SS. I'm still thinking about options for the other end at the moment...probably I'll make a few different ones for different jobs.

More when I finish and test this thing. It has plenty of strength out in the lab air, a little sticktion, but should do for target positioning. One reason to insulate this is to have a wire off the target holder for diagnostics -- measuring net current and so on, or biasing the target. Or faraday probe -- whatever.
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
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Doug Coulter
 
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Re: Motion in vacuum - wiggle stick

Postby Doug Coulter » Sun Jun 12, 2011 8:23 pm

Another day, another little bit of progress. I made the magnet and yoke for the outside, and a viton gasket as this might be the main port that gets opened on the new system. Yet to do are cut the ceramic to the right length, and make a holder for the end for whatever it might wind up holding. Pretty much anything I can devise that will take a 1/4" rod in one end.
No claims on the magnetic design here - I just needed a handy way to hold the outside magnets, with a side of keeping the stray fields down a bit. These grade 50 magnets are way overkill for this - several kg of force at least, but I had them and they're the right size for this. I'd originally bought them for the cyclotron project, but found it more or less impossible to gang up without things flying apart - even with some special tools made to make that attempt.
Stick.jpg
The stick, almost ready to install


I also painted the outside of the SS tubing with graphite dry film lube so it's easy to slide without a lot of stiction.
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
User avatar
Doug Coulter
 
Posts: 3515
Joined: Wed Jul 14, 2010 7:05 pm
Location: Floyd county, VA, USA


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