Doll hand that grips

dtm1234 · Post by **dtm1234** » Fri Feb 08, 2019 9:01 am

I've been reading Panther's ongoing open hand surgery and it's given me an idea.

The basic premise is a hand that is naturally closed but can be opened with fingers splayed out. When the hand is let go the fingers gradually curl back into a closed position but on a gentle scale instead of a death grip.

Just imagine a doll that gently holds your hand as you hold hers, or spreads her fingers against a wall as you caress her from behind.

The only problem is I have no idea how this would be feasible but I've seen robotic prosthetic hands and a hand that either opens or closes has to be less complex than that.

rubherkitty · Post by **rubherkitty** » Fri Feb 08, 2019 1:09 pm

dtm1234 wrote:I've been reading Panther's ongoing open hand surgery and it's given me an idea.

The basic premise is a hand that is naturally closed but can be opened with fingers splayed out. When the hand is let go the fingers gradually curl back into a closed position but on a gentle scale instead of a death grip.

Just imagine a doll that gently holds your hand as you hold hers, or spreads her fingers against a wall as you caress her from behind.

The only problem is I have no idea how this would be feasible but I've seen robotic prosthetic hands and a hand that either opens or closes has to be less complex than that.

Small cables pulled by coil springs. Each finger joint end slightly beveled so the hands curl.
Would not be pose-able.

Average Joe · Post by **Average Joe** » Wed Feb 20, 2019 10:50 pm

I've been experimenting with shower curtain rings, the metal ones that open and close. They're not much thicker than the finger wire but have hinges and are made of steel. The only issue so far is lateral (side to side) stress, due to the flimsy rivets.
Have faith, a solution shall cometh!

Chris98king · Post by **Chris98king** » Thu Feb 21, 2019 12:40 am

I don't know about grip but I was thinking about trying to print a skeleton hand with actual real joints. Has anyone tried this? If so how long do they hold up?

Technician · Post by **Technician** » Sun Mar 03, 2019 1:03 pm

The simplicity of this idea from dtm1234 has a lot of merit, and if we're not re-inventing the wheel it's stupid easy to accomplish.

Substitute the bendable finger wire with thin spring steel wire that's already curled.

NewFrontiers · Post by **NewFrontiers** » Sun Mar 03, 2019 1:18 pm

Technician wrote:The simplicity of this idea from dtm1234 has a lot of merit, and if we're not re-inventing the wheel it's stupid easy to accomplish.
Substitute the bendable finger wire with thin spring steel wire that's already curled.

I wonder if this would work...
https://www.mcmaster.com/spring-temper-wire

Technician · Post by **Technician** » Tue Mar 05, 2019 11:28 pm

That looks like pretty thin stuff, I was thinking more along the lines of flat spring steel wire. Kind of like the stuff used in a small engine pull starter but a bit stronger maybe. There's probably round stock the same sizeish as the oem finger wire though.

rubherkitty · Post by **rubherkitty** » Wed Mar 06, 2019 1:30 am

#1 Find the type & size of wire you want that you can bend with tools, but won't snap. Then it should be strong enough for doll play.

Annealed wire is too soft. Generally formed into shape then tempered to spring steel.
Some spring steel is tempered so hard it will snap if you try to bend it to some set shape.
I've made springs before by annealing the wire, forming then heat treating.
Heat treating makes it super hard then you have to draw out the temper so it won't be brittle. I dropped a fully tempered .190 wire spring on the concrete floor and it shattered like glass.

Maybe a leaf rake that uses the flat steel tines?

Technician · Post by **Technician** » Wed Mar 06, 2019 9:09 am

That's a thought. Round wire should be easiest to find, most hardware stores sell a variety of springs in different sizes so just form the wire into whatever shape.

kklouzal · Post by **kklouzal** » Wed Mar 06, 2019 1:27 pm

How about a small torsion spring coupled with a joint similar to those used on our ratchet sets to angle the socket?

The universal joint above has two pivot points allowing for rotation on 2 axis however removing one of the pivot points will restrict movement to a single axis like a finger.
You could mill out a small slot in the center to insert the torsion spring and that would give the joint resistance. Just use one or two turns on the spring to keep it thin and also a small gauge to keep the force required to move the joint low. The arms on the spring could be set to the appropriate angles to make the fingers have a default resting position of a closed fist.

I might have over-engineered this though, the proposed flat spring steel wire idea might be the way to go I just feel like it's going to give you curved fingers.

**Now we just gotta cram a motor in there and we can move the fingers with our smartphone**

MannequinFan · Post by **MannequinFan** » Wed Mar 06, 2019 1:29 pm

dtm1234 wrote:I've been reading Panther's ongoing open hand surgery and it's given me an idea.

The basic premise is a hand that is naturally closed but can be opened with fingers splayed out. When the hand is let go the fingers gradually curl back into a closed position but on a gentle scale instead of a death grip.

Just imagine a doll that gently holds your hand as you hold hers, or spreads her fingers against a wall as you caress her from behind.

The only problem is I have no idea how this would be feasible but I've seen robotic prosthetic hands and a hand that either opens or closes has to be less complex than that.

Dtm, The 14 GA wires that were are doing are actually pretty stiff and will hold a "grip" to a certain extent.
Exhibit A...

If you folded the fingers into a loose fist, you could open them around your member and they should exert a slight grip. Not a lot, but enough to perhaps feel some pressure.
I think Panther did a little "bedroom test" for this function. He didn't go into details but from what he said I think it must have worked...
viewtopic.php?p=1464642#p1464642

BuilderOfCastles · Post by **BuilderOfCastles** » Wed Mar 27, 2019 11:34 am

I have given a lot of thought to doll hand mechanics and...

All of my better ideas require casting a new hand, because the finger bones would be much larger than the wire.
(unless one of you out there has figured out how to hollow out TPE hands easily.)

14 gauge spring steel wire is not bendable.
The stuff can put a dent in your vice.
Yes, it is flexible over the length of the finger, but you will never bend its joints.
You will probably need to use a thinner wire. And wrap it out to original size (like using brass tubing K&S)

The guys doing the stranded wire with the brass tubing have many good things going for them.
It can be retrofitted on most dolls easily. (just like replacing wires)
However, the end result will be broken fingers and future replacement.
Its what happens when you bend copper; it gets work hardened, and then it snaps.
I wish i had my tools, then i would machine you all a wrist, instead of trying to 3D print a part that needs to be steel.

My thoughts on doll hands... human hands are cast in a half curled form. Doll hands are cast flat as a pancake because making those molds are EASIER.
Now, would closed hands or open hands be better? Well, for pictures, one or the other is always what you need.
For expression or touching, and open hand.
For holding an object closed.
My feelings are to make a half closed hand with friction joint finger bones. Because the TPE / silicone will try to push the bones back to its cast shape.

MannequinFan · Post by **MannequinFan** » Wed Mar 27, 2019 3:10 pm

BuilderOfCastles wrote:The guys doing the stranded wire with the brass tubing have many good things going for them.
It can be retrofitted on most dolls easily. (just like replacing wires)
However, the end result will be broken fingers and future replacement.
Its what happens when you bend copper; it gets work hardened, and then it snaps.
I wish i had my tools, then i would machine you all a wrist, instead of trying to 3D print a part that needs to be steel.

BOC, the hand plate part does not need to be steel, just the wrist connection. It just needed an eye bolt.

Panther has been testing these for a while now and so far they are holding up just fine...

: IMG_4651.JPG (444.78 KiB) Viewed 3392 times

The problem with friction type joints is that with wear, they will eventually lose their friction.
We see this happening all the time with other hinge type joints in dolls. Eventually they will get loose.
Then you will be looking at replacing, or at a minimum, needing to remove and make adjustments to a much more expensive item.

Not sure what your costs would be, but the two printed palm plates cost less than a dollar for material and the only labor is pressing print and removing some support material when they are done. The eye bolts are a little over a buck for two at Home Depot. Wire is dirt cheap.

The question we have to ask ourselves is how far and to what expense and complexity we want to go for dolls that are only designed to last a few years anyway. It's kind of like putting a Rolls Royce engine in a Ford Pinto and then welding the hood shut. It just doesn't make a lot of sense unless that expensive engine remains serviceable. For more advanced skeletons to be realistic what we need are dolls that are designed to be serviced and maintained just like your car.
Unfortunately we're not there yet - at least not for cheap.

Boobman · Post by **Boobman** » Wed Mar 27, 2019 3:50 pm

A Ford Pinto is a crappy & ugly car just like a AMC Pacer but load them up with my favorite dolls & the car would look instantly a lot better in the interior of the car anyway. :haha4:

Would venture to say these car lots with cars that are not moving well put a hot doll in a bikini in the passenger seat with a notice that says buy the car get the doll for free.

BuilderOfCastles · Post by **BuilderOfCastles** » Wed Mar 27, 2019 3:51 pm

Mannequin Fan

At that size of part, it is all machine time, and no material cost.
If i had my CNC mill, it would be less than a dollar of steel, and press the button and come back later.

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.

But, i am glad to hear that it is holding up.

- - - - - - - -

I have been working on other types of joints to keep tension uniform over the life of the doll.
Things involving springs and machined wearing surfaces.

But, that will require a lot of experimentation.

- - - - - -

What may be really good for doll manufacturers is to change from an outside torque bolt, to an inside one.
Such as cap head screws.

Then, when you need to tighten, you stick a hex wrench through a tiny hole, and tighten.
You may even be able to get away with the hole just squishing itself closed.