Doll hand that grips

[MannequinFan]

The thing i really do not like about the eyebolt is the wearing surfaces not being ground flat. So, the pressure from tightening is only on the most raised edge, which is easily worn down.

I'm not sure it will be an issue with normal use, but that's a good point.
Panther just used a flat washer on each side of the eye bolt and it seemed to work fine.
I guess a small rod end could also be used in lieu of the eye bolt. Don't think you'll find these at your local hardware store though and they're a bit pricey...

https://www.mcmaster.com/3798k35

[BuilderOfCastles]

I guess a small rod end could also be used in lieu of the eye bolt. Don't think you'll find these at your local hardware store though and they're a bit pricey...

https://www.mcmaster.com/3798k35

Yes, that thing is very pricey and completely not worth it.
you can just take a file to the faces of the eye bolts, but like you said, it will probably be just fine.

The problem would probably only ever show itself if you use the wrist to support doggy-style.
(and i have other features of a palm plate that will help there.)

- - - - - - -

So, what do you think about joints being made with cap head screws (that have a hex hole drive) instead of the hex bolts?
Of course you would need to solder or tack weld on the nut.

But then, when you wanted to adjust the tension, you make one small round hole, push in the allen wrench and tighten.

- - - - - - -

Have you ever though of a way to easily core out the fingers for a bigger wire thingy?

[MannequinFan]

So, what do you think about joints being made with cap head screws (that have a hex hole drive) instead of the hex bolts?
Of course you would need to solder or tack weld on the nut.

But then, when you wanted to adjust the tension, you make one small round hole, push in the allen wrench and tighten.

Have you ever though of a way to easily core out the fingers for a bigger wire thingy?

I think using the allen head screws for adjustment is a great idea. It makes me wonder why they haven't done that.
I guess you'd have to find a way to seal around the hole inside though so water doesn't get in and cause mold growth.

I really don't know how you would core the fingers out though- that would be a tough one.
I just sent a new version to Panther for testing that uses printed fingers instead of brass tubes. They are bigger than the tubing (5.25mm square) so we'll see how well they fit without any coring.

[-Ragnar66-]

though not entirely related I did think about a fixable glove, possibly in flesh tone that leaves the palm and parts of the fingers free. That not just for griping purposes, but also for protection on the dolls hands/fingers if additionally fastening a ~2" soft material cylinder to the palm. Sort of exoskeleton so to say. Does that make sense anyhow?

A basic design item like this to work from, yet not that rugged. (edit: also found some interesting to work on archery glove and surf rubber hand glove designs)

[Technician]

Last night I laid in bed, mind racing so I decided to give it a direction to race in. This topic came up so I imagined a simple articulated finger with no hinges or moving parts. The whole finger would be 5 pieces total.
I made an image of one segment, please forgive my inability to use CAD, learning it is on my to-do list, this was done in GIMP.
So the main body of the segment is blue, white represents a hole down the center of it and red represents a channel cut along the top.
My thought is simple, each segment floats on a piece of spring steel flat wire that is already bent and influenced into a fist. Affixed to the tip segment is a cable that runs the length of all of the grooves cut along the top back to the back of the hand.
Pull the cable with an air muscle or whatever and it opens. I believe nylon would be strong enough for the segments, she's not an industrial robot, she's most likely a jerk off machine or posing for a picture holding a beer or umbrella or some damn thing.
The steel spring would wear the nylon, but a little doll-safe Vaseline as grease should ensure like 1000 cycles before the square hole becomes oblong enough to allow a segment to cock onto it's side.
Once again, apologies for the horrific visual.
It should go without saying that the tip segment should be a modified version of this with the hole stopping short and a catch for a ball at the end of the cable like a bicycle brake cable may have.

Finger.png (4.68 KiB) Viewed 1998 times

[Technician]

Here's a terrible rendering of my vision for the accompanying fingertip.
Same visual rules apply, white is a hole or absence, red is a recess, darker blue shading is rounded.
So now there's a small hole entering the top and opening larger in the bottom to hold a something on the end of the cable. The white hash marks on the bottom photo signify how deep I would expect the tunnel for the spring to ride in to be.
I wish I had a 3d printer, lol.

FingerTip.png (4.77 KiB) Viewed 1992 times

[BuilderOfCastles]

Here's a terrible rendering of my vision for the accompanying fingertip.
Same visual rules apply, white is a hole or absence, red is a recess, darker blue shading is rounded.
So now there's a small hole entering the top and opening larger in the bottom to hold a something on the end of the cable. The white hash marks on the bottom photo signify how deep I would expect the tunnel for the spring to ride in to be.
I wish I had a 3d printer, lol.

FingerTip.png

i suggest you skip learning CAD, and just go to 3D modelling. Like FreeCAD.

What you are missing is drafting knowledge. You know, what becomes a hidden line, how to make just enough views so that people can understand... those things.

And, you said you wanted a 3D printer, and you will need something like FreeCad to use that.

There are two positions that we normally see women's hands in. Fully open, or fully closed.
The half closed position is saved for times when they are alone and not expressing anything.

So, your idea would work ok for one extreme, and be almost incapable of the other.
Yes, this is the problem with many great ideas.

Your idea may make several people happy. And it really will only take a lot of trial and error to get it right.
* What size of spring steel applies the correct force.
* How big do the plastic pieces have to be to hold that?
* Can we get it all together and inside a dolls hand?

[Technician]

Amazon sells 3/8" nylon rods and flat springs for small engine starters. I may order some stuff in and prototype a finger by hand. Not looking forward to filing a square hole down the middle of them because nylon it tough stuff. The cable groove should be easy to file in with a rough file and rounding out the ends should be easy on a bench grinder.
This would possibly be easier with steel tubing, maybe I'll try to make a conceptual finger that way since I've got four different sizes here of brake line and fuel line. That would mean doing something to keep it from cocking sideways on the spring but if I dent the groove in for the cable that may do it, and I can always solder guides in I suppose.

[BuilderOfCastles]

i suggest cutting the groove with a back saw.

just build a miter box / clamp thing that will allow you to slice each side fairly straight. Then nibble out the middle.

There was a guy who made a setup with a dremel tool and just cut a slot in the entire length of the stock.

You can also try forming the slot with heat.
Heat up nylon pieces to somewhere near plastic point.
Then take a piece of metal, the size of the slot, heat it up higher, and press it into each piece.

[slvstake]

The only issue I see with this is that unless the mechanism is controlled externally, or remotely to place the doll's in a relaxed/unstressed posture, then any internal mechanism would have to maintain a constant spring tension/compression, holding the fingers in a closed position. That would mean that manufacturers would have to mold the fingers in that position, so that becomes the new relaxed posture. Otherwise the material will always be stressed, and would crack in no time.

Unless of course, they made the digits individually articulated, and just provided you with a replaceable silicone/TPE textured glove to place over the robotic hand.

[rubherkitty]

Good point slvstake
You almost need a spring loaded group of finger cables that you can adjust tension on via a screw.
Maybe have one coil spring that provides some spring tension to fingers, but the spring would also be housed in a gear rack that can but adjusted forward and back via a pinion screw. You could then adjust the fingers to 99% loose to full close grip.

[Technician]

I had considered the cables joining and going to a mechanism. Something of a toothed rack with a reversible powl of sorts to where queezing one part of her wrist would advance it a click, and squeezing another would release the powl and retract it one click.
Opening and closing her hand would be a matter of squeezing her wrist 10 - 15 times in the right spot. Something like that also would mean the hand could be ratcheted to it's midway point to go in the mold.
Such a mechanism could potentially be drum based so the cable wound around the drum directly.

[Technician]

I got some 3/8" nylon rod, a coiled spring, and a thin cable. Before cutting into the rod I did a prototype (of a prototype ironically) out of nylon tubing.
Mixed emotions about the results, it works but this particular spring is a bit too malleable and once straightened does not return to a full fist. Where it's at in the picture is where it stays after repeated straightening though so this concept does indeed work.
Now I'm thinking there's more to learn about spring steel and the proper spring for the application is just knowledge away.
At some point I'll finish crafting the segments for the prototype and research springs in general.
Were this 1/2" tubing I feel there would be enough room inside for the spring to not straighten so much but then that would constitute man-hands, ick.

20200213_105526.jpg (1.15 MiB) Viewed 1865 times

[doll-o-grapher]

Gents, if I may, you're all trying to re-invent something that already exists.

"Rose" or "Heim" joints.

https://en.wikipedia.org/wiki/Rod_end_bearing

These are commonly found on race cars and helicopters, and in miniature form, on model aircraft, especially the swash-plate mechanism of scale RC helicopters.
Example - Slightly oversize for use in fingers - https://store.rc4wd.com/Aluminum-Black- ... _4462.html

A U-shaped Clevis connector on one threaded rod, with a bolt through the leaves of the U and the center ball of the Heim joint, champing the U to the ball,... with the ball then stiffly moving inside the socket.

In a sealed environment, such as inside a Silicone or TPE casting, these would be exceptionally hard wearing.

Each knuckle bone would be the Clevis at one end, threaded rod in the middle, and Heim joint at the other end.

Many, many edits later,.... http://www.zedjet.com/m3-aluminium-clevis-pkt-2.html
Clevis sample - https://www.gravesrc.com/great-planes-s ... 40-12.html

Threaded rods for the bones already exist too - https://www.integy.com/st_prod.html?p_p ... _catid=323

And from the same site, a potential cheaper option that has no sideways play, so would be a little more fragile then true Heim joint.
https://www.integy.com/st_prod.html?p_p ... p_catid=91

The finger tip bone would replace the U shaped Clevis connector with a flattened pad under the fingerprints.

There would need to be a limiting mechanisim to stop the fingers bending more then a few degrees backwards along the knuckles, but to allow slightly more movement at the base of the finger. This could be achieved by taking a washer type electrical connection, removing the sharp edges, and bending the washer over to slide on to one of the threaded sections and be secured with a pair of nuts.
Example, minus the plastic sheath - https://www.jaycar.com.au/red-black-gol ... 2/p/PT4560

The combination of the Heim joint and this limiting mechanism, could very well feel like a bone under the TPE skin.

Adjusting the locking nuts for the Heim joints and screwing them further along the threaded rod, allows changes in lengths of fingers and joints, to match the mold for the different model dolls.

The only parts I haven't been able to find in RC Catalogs or electronic stores, is the U-shaped Clevis connectors in a size small enough.

Many, many edits later,.... http://www.zedjet.com/m3-aluminium-clevis-pkt-2.html

[rubherkitty]

but this thread isn't just about finger joints. It's about how to make the fingers have a spring loaded grip.
Free moving joints will just make floppy fingers and are no better than just using finger wires w/ tube segments if you want the hand to pose or grip objects.

Doll joints as a whole are easy. It's getting the proper tension for posing or sex play and the longevity of those tensions over the lifetime of the doll.