I am kind of curious to see what others have to say on their experience or opinion on mixing metal types of their ball and socket joints. What I mean by this is that the metal types of the plates and the balls are not the same. Things like steel or aluminum plates with brass balls but all combinations are fair game. I know what my experience has been to some degree on this but I like to see what others have to say. The sort sort of discussion I would like to stir up is listed below but is by no means exhaustive.

1. This works in a pinch but runs into issues quick

2. Works great for this situation

3. Cost is good but the life is short

4. It has or doesn't have complications when used with these items (i.e. chemical reactions)

5. Good if you are starting out but poor in intensive shoots

6. The common issues with this setup could be helped if it was done differently (i.e. design tweaks)

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To add a note to this that I am aware of galvanic corrosion between aluminum and brass under specific conditions.

I hadn't heard of the reaction between aluminum and brass. Would you explain?

GALVANIC CORROSION:

DO NOT worry about it. Armature not 'electrified or immersed in electrolytic solution' (do Wiki lookup). Natural galvanic corrosion in dissimilar metals can occur, as an example ... in house piping plumbing it may sometimes be an issue (e.g. water lines). For us in this extreme micro-niche of the stop motion animation arts ... it's a non-issue.

Using brass balls within sandwiched plates is advantageous in a few ways - The materials are easier to work with (for the non-hardcore metal worker) AND brass balls within the sandwich plates follows the principle of having the balls slightly harder than than the compressing plates. You want the balls to wear-in & seat (with use) into the sockets or hole-type sockets. Whatever metals used for balls and plates, you do not want the balls to be softer than the plates. The balls might get  scored & scratched and/or go out of round because the harder plate would be causing an abrasive type wear on balls. Again, the rule: Hard Balls wearing-in against the Softer (less hard) Plates.

Of course, before embedding armatures in molds (if you're using casting rubber method), you protect the skeletal jointed armature by wrapping it with some protective material or a spray sealant of some sort. For those really hardcore eclectic & dexteritous Stop Motionists .... steel material components (e.g. steel plates, steel balls, etc) can offer more options in designing & fabricating a more delicate armature with  thinner/narrow joints (depending on puppet character concept) but still be strong/sturdy armature. With brass & aluminum, the joints,they usually need to be bigger/bulkier to get the same strength factor as steel joints.

I understand that 1018 steel plates and 302 stainless balls is a nice combo because each alloy is the softest in its family. Looking at hardness charts, I assume folks using O1 tool steel need to go with 440 balls?

I guess it is a mater of what stock you start with and how much or little machining you are wanting to do along with how you are doing it. 1008/1018 cold rolled has good machinability and can already be close to the thickness you are wanting.

Sven, do you know of anyone who uses O1/440 and why?  I can image it being desirable for a puppet that's to have a long life with little maintenance, but I don't know what kind of facility/expense would be involved trying to machine it. It must be really hard on tooling.


I use mostly 1018/302, with some 2024 thrown in now and then on swivel and hinge joints.  I used to use more 2024, but it kinda sticks to the ball when allowed to sit in one position for a while.  Then you need to "break" it free, which is distracting.

I've used brass on fingers (http://hettmerfx.com/stopmo/wendigo_hand.jpg), but mostly because K&S had nice shapes that made it easy to assemble.

Good to know about 2024 sticking since I was going to try that soon. Kind of makes sense now that I think about it. 2024 is more susceptible to corrosion do to its copper content as its surface is usually clad in one fashion to prevent this. Machining would indeed remove a good amount of this clad for the socket plates and in general copper reduces corrosion resistance more than anything else. So even in great conditions this is going to corrode/oxidize and eventually make the balls stick.

Jeremy Spake recommended I take a look at O1. I know Merrick Cheney's using it for some of his parts, like in his hinged toes. Based on those two names, I can guess that it's pretty common in Laika armatures... Jeremy's likely the only one using the stuff without CNC — and I'm not sure if he uses it at all for commissions... But he's in the top of the field, so I'm all ears if he says it deserves attention.

I think Patrick Zung may have also talked about using O1 a couple of years back.

Talking about CNC, well to a degree, I am trying out getting some part "blanks" printed out in 3D. They are a 420 stainless steel powder that is later infused with bronze. I will oviously be doing work by hand before they are usable but I am interested in seeing how it turns out as an option.

I'm using 303 stainless balls and brass plates for my B&S armatures. Don't have enough time with them yet to say how well they'll hold up over a longer shoot though. Initially the movement is very smooth and I can tighten them up to a reasonable degree. I did ruin one set of sockets when I really clamped down hard to see how tight I could make them. If I were looking for more compact size, I'd go with 1018 steel or similar socket pieces and the 303 balls. I tried 440 stainless balls before and found them difficult to work with.

I generally used 2024 aluminum and steel balls (not stainless). Only one was precision steel with steel balls. My feeling was always that the all-steel had something better about the movement of a joint. Not that the steel/aluminum had any issues, just that the all-steel one had a different feel that I liked.

However, as I said, most were aluminum plates and blocks because it is much faster to tool.

Best,

Rick

I generally use a buffet of 510 phosphor bronze for clamping plates (superior strength, and bearing quality), brass for connector ends/clamp bases (ease of machining/superior solderability), 302 SS balls (because they are hard enough, yet still machinable with HSS tooling) and low-carbon steel for connecting rods (because it is impossible to accidentally harden it; a primary weak point where the ball is soldered on).  If they get molded I coat them with Sprayon 322 silver vinyl coating (because it is cheap, effective, and ridiculously easy).

I have some armatures almost 20 years old that are still working great, and currently proving themselves in the toughest of conditions; with my toddler son...

Best,

Ted 

http://trikfx.com/

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