Here's a shot of a joint I made recently. It's OK, but I'm looking to make it better.
The lower pivot can be tightened to the point where the gap is closed but the joint isn't as tight as I'd like. I'm wondering if it's my relief slot pattern or the metal or both or something else.
The slots are all 0.020”. I’ve made joints where lack of relief prevented me from tightening the joint enough. This pattern seemed OK based on pictures I’ve seen of armatures made by people more skilled than I am.
The material is 1018. I’m considering getting some O1 and trying that in case the 1018 is too soft, but I thought I’d post here to see what folks think about that or if there are other suggestions.
That looks pretty similar to the relief slots on the Tom Brierton armature I have, and they work. But I wonder if that vertical slot on the bottom goes far enough past the rod that is being gripped, on the side away from the tension screw? I see it couldn't go much further before getting too close to that other slot coming in sideways (don't get what that one is for).
Also, if you are using similar or identical materials in your joints (clamps and pins, in this case), you may never achieve smooth movement. Smooth movement in a joint relies as much on parallel surfaces and even tension as it does on dissimilar metals (or hardness). In your case the pin should be significantly harder than the clamp. Lubricants can help a bit (as a band aid), but best to simply use materials that will cooperate as you wish them to. Your tolerance with this type of joint is critical as well; if you are oversize (even by a few thousandth's) on the clamp, the single screw to one side will bias tension towards its side of the clamp (pinching and choppier movement). A harder pin will help offset that as well. That other clamp above it will be operating more smoothly, because you are free to adjust tension evenly across the face of the clamped area.
Movement on these joints is nice and smooth. The pins are O1 tight tolerance, which now are clamped in1018. I have joints in this puppet that are O1 on O1, and those are smooth as well.
I suspect one element of the problem is that the puppet is large, so I want to tighten this more than I might otherwise. These are essentially hip joints of a mechanical quadriped, and the large pin (3/16" diameter) is the front/back rotation. (The horizontal pin provides in/out; by design there is no third axis.) The legs are about a foot from table to hip. The joints held better before I cleaned off the scaling from brazing the pin to the thigh, but then after the pins became smooth again I had to tighten them more, and that's when I noticed I could squeeze the clamp shut.
looking at this joint a little more, why not just go with a separate plate (instead of slot and single screw) and do a double tension screw setup? You can save space and maximize grip by...
1) opposing the direction of the two tension screws (those allen screw heads can be obtrusive, especially when you want each to have a clean counterbore) and..
2) by notching (same diameter as tension screw through-hole) the rod (not more then 20% total diameter) and laying out the joint so that the rod-notch is aligned with the through holes of the two, now closely set tension screws, you can capture the rod in the joint (otherwise they tend to drift over time as you move them) while ensuring you have gotten as on top of the rod with the tension screws as humanly possible. That should solve both your tension and flex issues.
I'll try opposing screws for the single plate. Most of the other joints in this thing are plate hinges like that, except they don't have the opposing screws.
I've seen a lot of single-screw hinges like this so I thought I'd try it here, but perhaps this puppet is just to heavy for that to work.
As for the notch, I chose not to do that because they're going to add some stuff to the side of the puppet and it's not clear how thick that layer will be. So I left it adjustable since I couldn't make it right.
Also, the puppet is in England and I'm in Michigan, so the notch boat has sailed. :) But I can send revised hip plates.
the kind of joint you have there needs a metal with low ductility so that it doesn't stretch out from tensioning. i think 1018 might be an easily cold formed metal and not ideal in your current use. try the o1 instead or use a bigger piece of the 1018 leaving more depth of metal over your rod so that the hinging part of the metal has more cross section to resist stretching.