Double ball joint design

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hobgobbln
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Double ball joint design

Post by hobgobbln »

I saw something someone had made and I want to make my own but I'm not sure about the details.

I'm not sure what those joints are actually called so I'm not able to find info on the proper way to build them. The main thing I'm not sure about is where the holes come in contact with the ball. Simply drilled? Countersunk? Stepped? A negative hemisphere for more surface contact? It looks like he simply drilled the holes but my main focus is rigidity when locked down as opposed to smooth motion. I plan to use steel balls with aluminum plates.

Griz

https://youtube.com/watch?v=OnpOa9WtF7o ... IECMiOmarE
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Charles T. McCullough
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Re: Double ball joint design

Post by Charles T. McCullough »

Micromark sells a similar item for miniature work. It is called a "third hand". (Not the name for the joint used.)
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https://www.micromark.com/Triple-Grip-Third-Hand
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They also sell one with a magnifying glass and LED light.
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Obviously not big enough for anything more than tiny stuff that does not have to be held rigidly (barely good enough for holding wire in place, but invaluable when needed!). But similar to what you describe.
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I don't think there are any specs for building what the video shows... it is all sort of personal preference for materials and sizes.

I like the one in the video... big, hefty and rigid! Vice-grips are a lot better than the alligator clips on the small commercial one. One of the comments on the video considered using threaded connections for the rod to ball connecting using different lengths of rods. I can see making different end devices for the business end clamping. Vise-grips, welding clamps, magnets, lights, torches, magnifying glasses... all sorts of things could be substituted, whether threaded onto a ball or each with their own permanent ball.
hobgobbln
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Re: Double ball joint design

Post by hobgobbln »

I used to have one of the third hands with the magnifying glass and alligator clips for soldering.

I’m not looking for specs as much as the design practices. I’m trying to figure out what the strongest way would be. If I just drilled and lightly deburred it, all of the clamping force gets exerted on a small contact area so the friction would be high. But if it was a hemisphere it would have much more contact area but the same clamping force would be spread out. I’m not sure which would be better for holding as rigidly as possible.

It’s a really cool design and I can see all sorts of uses for my shop.
earlgo
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Re: Double ball joint design

Post by earlgo »

The third hand that I bought when my son was in high school and making circuit boards for robotics is just like the one shown in the Micromark catalog picture but the cast base on mine has XACTO in cast letters on it. I probably bought this 35 years ago, and I'd bet it was from Radio Shack, remember them?
Xacto third hand.jpg
Xacto third hand.jpg (93.29 KiB) Viewed 1398 times
--earlgo
Before you do anything, you must do something else first. - Washington's principle.
hobgobbln
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Re: Double ball joint design

Post by hobgobbln »

earlgo wrote: Wed Feb 15, 2023 3:25 pm I'd bet it was from Radio Shack, remember them?
Remember them? I was crushed when the last one near me closed. That's where the one third hand I had came from too. And about 35 years ago haha

What I'm looking to make is similar in scale to the one in the video I linked to. I do a lot of fabricating for a guy on the side and am constantly trying to hold things in weird positions in 3d space. Something like this would be a godsend. I'm actually prepping for another project right now that this would be used for. I just need to figure out how to make it first.

I remembered a video Tom Lipton did about making a "dog meat" single ball swivel base. I put that in quotes because it was beautiful when he was done.
He used a flat 24 degree included angle on one half and made a 90 with a countersink on the other. It looked like it held really well, but before I go making a dozen of these things I'd like to try to find a tried and true design if at all posible.

Griz
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Bill Shields
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Re: Double ball joint design

Post by Bill Shields »

Drill the hole then chamfer it at 45 degrees for ball contact area.

When you have the ball and plates, squeeze them in a vise..or mash lightly in a press
Too many things going on to bother listing them.
jcfx
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Re: Double ball joint design

Post by jcfx »

I know those joints from stop motion animation, the skeletons for the puppets are called ball & socket armatures
that type of joint has been around since the 1920's ( The Lost World silent film and in King Kong 1931 ) don't
know who first came up with it, but I guess it might have been Willis O'Brien.

I don't think there is is a proper name for the actual joint, like the third hand soldering aids they're meant to be adjustable
on the fly since in animation you need to move the puppet ( and tighten if it gets too loose )
What he's showing in video looks like he copied a stop motion armature joint, I suppose it would lock down tight with
no movement with a single screw, but I think if it had a double screw with longer plates he could have used much thinner plates.
He also seems to gloss over that you would need soft steel balls, ball bearings would need to annealed so that you can drill
a hole in them on a lathe. Silver solder is also an option to attach the rod to the ball, for puppet sized joints that's how
it's done.

Those joints are not hard to make in Lazze's scale, a little more difficult for a puppet because of the size.
Google for ball and socket animation armatures, there's tons of info out there...

This video may help - https://www.youtube.com/watch?v=UwBrTLCOE9A

I also miss Radio Shack, it was a great place in it's hey day, I stumbled onto their going out of business sale
and bought whatever I could, switches, resistors, diodes, the receipt was over 12 ft long !
During the lock down I rebuilt my third hand soldering aids I hated the formed ball ends, now much smoother
with a real sphere on the ends.
third hand ball and socket joint.jpg
third hand ball and socket joint.jpg (74.34 KiB) Viewed 1371 times
hobgobbln
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Re: Double ball joint design

Post by hobgobbln »

Bill Shields wrote: Wed Feb 15, 2023 5:00 pm Drill the hole then chamfer it at 45 degrees for ball contact area.
I'll plan on making them like this. I guess I can always try a different seat later on.
jcfx wrote: Wed Feb 15, 2023 6:40 pm This video may help
It did. Other than thinking about his mill's poor dovetails, seeing him stand on those with just the drilled hole makes me believe I'm over analyzing this.

Thanks everybody. I think I've got a game plan now. Though if anyone does have more info I'd love to hear it for future uses.

Griz
jcfx
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Re: Double ball joint design

Post by jcfx »

You can chamfer the holes or not either way the ball is still riding on a narrow contact area.
As far as I know those ball joints move, as they're meant to be from an animation standpoint
but for work holding I would double bolt it and possibly use a ball end mill or core box router bit
to get more surface area grip on the ball.
Ball socket.jpg
Ball socket.jpg (36.46 KiB) Viewed 1338 times
I don't know what the large balls he used are made of, they both have a metal skin but one
had what looked like a wood core, the other may have been cement ( he called it sand :roll: )

Robin Renzetti did some similar joints for a camera mount arm - https://www.youtube.com/watch?v=LWUHlyi-8Mc
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Bill Shields
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Re: Double ball joint design

Post by Bill Shields »

Your point above regarding line contact is absolutely correct

This is why, if read fully, I suggested chamfer the hole and press the ball bearing down into the hole ..this deforms the aluminum around the hole and creates surface area contact

It has worked well for me for several decades.
Too many things going on to bother listing them.
hobgobbln
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Re: Double ball joint design

Post by hobgobbln »

jcfx wrote: Wed Feb 15, 2023 11:34 pm but for work holding I would double bolt it
For an animation setup or camera arm like what Rob made I can see how the double bolt would be beneficial. In my head it would let you adjust the grip of each ball separately within reason. For what I'm doing I think I'll stick to a single large bolt in the center with thick plates to make clamping easier since I'll be holding the far end in my other hand. I will give it a try if the single doesn't grab hard enough though.
Bill Shields wrote: Thu Feb 16, 2023 5:51 am This is why, if read fully, I suggested chamfer the hole
That's how I'm going to make them. I drew them up in Fusion this morning. If I use 1" steel balls, drill 1/2" holes in the plates and chamfer them an 1/8" deep, it puts the contact area roughly where the points of an inscribed square would fall.
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Bill Shields
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Re: Double ball joint design

Post by Bill Shields »

That's how I'm going to make them. I drew them up in Fusion this morning. If I use 1" steel balls, drill 1/2" holes in the plates and chamfer them an 1/8" deep, it puts the contact area roughly where the points of an inscribed square would fall.

then give them a good squeeze in a hyd press or large bench vice...to 'spread out' the contact area.... :D
Too many things going on to bother listing them.
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