How to increase friction in metal ball+plates joints?
January 7, 2012 7:24 PM   Subscribe

Chemists, Engineers, Tinkerers, and Adhesion experts of MeFi: Is there some sticky substance I can put in these metal ball+plates joints that will do the opposite of lubricating them -- increasing the friction between the surfaces? This is for a slightly nicer (chrome) version of this lamp that I just got (new in box) at a flea market.

The thing is mainly metal rods (the robot limb sections) with small metal balls on the ends. These ends are joined by having pairs - the ends of adjacent sections - sandwiched between two small metal plates, which are then held together by means of a single screw per joint (tension adjustable with an allen wrench).

So, it works better than I'd think, but I'd like it to be a little stiffer. I think it's higher quality than Amazon's Holmes model is (mine is Portfolio brand), but I can still see a lot of potential for improvement.

My question is this: is there some kind of sticky substance I can use that will make the interface between the metal balls and the plates have a higher coefficient of friction, so that the screws don't have to be quite so tight, but the whole thing will still keep its form?

I want to re-position it at will, too, so just using some kind of glue or epoxy doesn't seem a good alternative.

I know that if this were plumbing joints, I could use something like teflon tape; is there a coating I can put on the metal balls and/or plates to make them more grippy? Post-it-note-type adhesive?

I believe I can completely disassemble the joints if necessary to mess with the metal. However, I can't find any other lamps like this one after searching for the model number, so I can't afford to experiment too much.

I tried looking up info about adhesives, and re-discovered the "how to stick X to Y" web site, but since I want to re-position stuff, this doesn't quite fit. I'm not sure how even to search for what I want.

Any ideas, engineers of Metafilter?
posted by amtho to Science & Nature (16 answers total) 1 user marked this as a favorite
I can't think of an adhesive off hand, but I'm sure there's a chemical you could use to etch the metal joints to increase their friction. That said, it would probably be easier to rough up the edges with a bit of sandpaper.
posted by stuboo at 7:41 PM on January 7, 2012

Well, on stringed instruments with tuning pegs, you use peg dope, as a stick or as peg drops when your pegs slip. This increases the friction so the pegs won't slip but they can still be turned as needed. I have no idea if this would work on metal, though. Just the first thing that came to mind.
posted by cabingirl at 7:43 PM on January 7, 2012

Wow, peg drops look interesting! I know it's intended for wood, not metal, but it might be worth trying if nothing else turns up.

This makes me wonder whether dancer's resin (rosin) would be something to consider. Maybe I could melt it and apply it to metal.

Also: if anyone has ideas about how to test this extra-lamp, I'd love suggestions. My only idea is testing a smooth-headed nail against maybe a hinge plate.
posted by amtho at 8:03 PM on January 7, 2012

Little shards of rubber from a thin bicycle tube.
posted by rhizome at 8:32 PM on January 7, 2012

posted by gyusan at 8:43 PM on January 7, 2012

Sex Wax

Or sand applied directly inside the joints.
posted by the man of twists and turns at 8:46 PM on January 7, 2012

Loctite threadlockers might work for this. They're basically adhesives that seal threaded fasteners, but only semi-permanently. Different strengths come in different colors; you can find them at hardware and auto parts stores. Ask the staff which color they recommend for your needs. I think that once you break the bond you may have to reapply the stuff, though.
posted by Quietgal at 8:48 PM on January 7, 2012

There's no "anti-lubricant," but the traditional ways to increase friction in a joint are, in order of easiest to hardest:
* remove any lubricants
* rough the surfaces
* increase normal force
* more surface area (usually requires a re-design)

If cleaning with a solvent (check to make sure it won't eat the paint / plastic first) doesn't help, you can try to pull the joints apart and rough up the facing surfaces. If you flush all the lubricant, make sure the joints won't rust. (Are they steel or aluminum? If steel, you'll want some sort of film lubricant, just very little of it.) If you end up roughing them up, make sure to clean them well before re-assembling lest you end up with gritty-feeling joint movements.
posted by introp at 9:17 PM on January 7, 2012 [3 favorites]

Sugru? I don't know how well it sticks on metal. "It forms a strong bond to aluminium, steel, ceramics, glass, wood and other materials including some plastics like perspex and ABS and rubbers like silicone and butyl rubber."
posted by bread-eater at 9:30 PM on January 7, 2012

2nding Introp's post above. A Dremel tool would be an asset here, for roughing the contact surfaces and/or increasing the surface area.
posted by drhydro at 9:42 PM on January 7, 2012

I'd take it apart (one joint at a time) and visit the metal balls and plates a little with some 400 grit sandpaper. It would seem like if they were smooth it would slip more, but if you have a slight burr in there it's going to be like trying to balance something on a knife edge or needle point.

If that doesn't work and the screws aren't counter bored (a little socket cut in the metal so the screw head and sit down into it flush with the surface) I'd look at getting some hex head screws from McMaster Carr with the same diameter and pitch and a tiny little wrench to tighten them with. A screw pitch gauge would help with this.
posted by Kid Charlemagne at 12:56 AM on January 8, 2012

Thanks for the suggestions so far! Loctite sounds promising; I thought I'd heard of something like it, but, you're right, there's no guarantee it will work in this case.

Re: mechanical solutions. I'm pretty sure there aren't any lubricants present, and, believe it or not, the metal balls are already pretty rough; I haven't checked the plate surfaces and divots, though. The normal force is limited to what can be achieved by tightening the screws, and by the strength of the metal plates (and the durability of the allen-type hex hole for tightening), and the fact that one screw tightens plates for two ball joints at once.

Unfortunately, the joints are pretty open, so adding sand doesn't seem like an option. It's really like a sandwich. The close-up of the Amazon image kind of shows the joints.

I've never used Sugru, but I've been intrigued. It doesn't look like I could easily achieve a thin enough coat to allow the joints to still stick together well (plus, well, chrome robot + bright blue hand-molded rubber... I'm not sure I want to go there). Any experience with this? I don't have a lot of play w.r.t. the length of the screws.

Maybe I'll examine a plate surface to see if I can make it rougher.

I think the metal is all steel; I don't think it's as soft as aluminum. Mr. Robot Lamp is pretty heavy, also.
posted by amtho at 4:46 AM on January 8, 2012

pine sap
posted by orme at 6:26 AM on January 8, 2012

Carbon assembly paste. Available at higher-end bike shops. You could ask the tech to just sell you a tiny dab of it, even.
posted by drmarcj at 9:55 AM on January 8, 2012

Re: Sugru, you can get it in black, and you could probably just use a little dot of it where each screw makes contact.
posted by limeonaire at 10:57 AM on January 8, 2012

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