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BuilderOfCastles wrote:OK, 3D printing SUCKS!
it is strong only along the direction of the thread.
In between each layer it is actually quite weak.
This is true for FDM printing (filament type used for home printers), but not for all 3d printing methods.
Multi Jet Fusion prints (nylon powder type) are equally strong in each direction and are used for functional parts. I'll be using this for the hand skeleton I've been working on.
Agrees with MannequinFan - also if you want to have a stronger 3D Printed part, you can just create a mold and recast it using a different material. I've done this with very good success.
So, you just take your part, turn it inside out and mill out that shape in aluminum with a CNC router.
If you have a CNC router, why not just machine your part out right. It could be physically smaller, be much stronger, and you wouldn't have to work with melting plastic.
And also, there's an added coolness to having an aluminum skeleton
All this machining may be fine for a $15K robotic doll, but a $3K doll is going to be welded tubing w/ bent strap and nylon joints.
For a simple skeleton, the tube cutting, forming metal straps for joints, drilling the strapping and nylon bushings for the joints, welding and assembly is for sure a 8 hour job + material cost.
Going downtown. Gonna see my gal. Gonna sing her a song. I'm gonna show her my ding dong! C&C
So, you just take your part, turn it inside out and mill out that shape in aluminum with a CNC router.
If you have a CNC router, why not just machine your part out right. It could be physically smaller, be much stronger, and you wouldn't have to work with melting plastic.
And also, there's an added coolness to having an aluminum skeleton
We weren't talking aluminum, we were talking plastic.
And, yes, you can CNC mill aluminum. You just get into an operation that takes the same amount of time for each part. No time or energy savings. 15 separate milled pieces is no joke.
Its a trade off. For one doll, your girl, you can do anything. Doesn't matter if it takes a couple minutes or all weekend.
If you are making them for everyone else, how much is your time worth?
The strength of aluminum is not that great in small parts.
There are many plastics that are stronger in that scale. As in, they will bend back into shape whereas the aluminum will be all bent out of shape.
My personal thoughts right now are grinding finger bones out of spring steel.
I hope this isn't too "spammy". Earlier I talked about a rib approach that used a simple oval. I wanted to show an aluminum bracket I recently made to place left and right oval half at a small angle (about 30 deg.). Right now it's just on 1 rib pair, but I would like to do this to the top 5 rib pairs.
How is it feeling to you?
Wrap it in a roll of foam rubber and give it a hug.
Tell us how it is.
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The reason i do not do similar is that i immediately discard the idea.
All those joints (as you have made) are fragile and can't work for long in a sealed doll.
So, until i got ideas of how to attach it all together in a way that will stay together for at least five years of a guy laying on top of it, well, i just keep churning ideas.
Someday, i (or someone else) will hit on an idea that is manufacturingly good and usably good.
I'm buying one of these plastic Pose -N- Stay Halloween skeletons. I know it will need some re-inforcement and better joints made. These are 5' tall so it will work for my bubble butt skinny chick.
Body will be comprised of various densities of foam w/ some air chambers in torso for weight reduction and flex allowance. Bone, I want to feel, will be covered w/ thin EVA foam. Then the whole works covered w/a silicone coated catsuit.
Attachments
doll skeleton pose n stay.jpg (9.09 KiB) Viewed 1737 times
Going downtown. Gonna see my gal. Gonna sing her a song. I'm gonna show her my ding dong! C&C
The ribs are angled downward, and when you push on them from the front
they tend to sway downward with some give. The lowest 3 pairs of ribs are not
connect rigidly so they move freely in any direction. For the top 5 pairs of ribs
I'm planning on connecting left and right rigidly, and they are very still stiff if squeezed
from the sides, but still sway downward. I'm only connecting them so they hold their shape
from the muscles
I attach. If you're not attaching individual muscles, you may be able to get away with
seperate left and right ribs and then they squeeze pretty good.
SeanSteel wrote:The ribs are angled downward, and when you push on them from the front
they tend to sway downward with some give. The lowest 3 pairs of ribs are not
connect rigidly so they move freely in any direction. For the top 5 pairs of ribs
I'm planning on connecting left and right rigidly, and they are very still stiff if squeezed
from the sides, but still sway downward. I'm only connecting them so they hold their shape
from the muscles
I attach. If you're not attaching individual muscles, you may be able to get away with
seperate left and right ribs and then they squeeze pretty good.
Does this help?
They absolutely have to be connected.
And in such a way as they have some squishiness to them.
Finding a replacement for muscle and tendons is really a pain in the ass.
My best plans, right now, are to injection mold the whole thing in one piece of plastic.
and cheating a lot with connections on the inside.
i could probably make a prototype with a large 3D printer,
but it will probably be easier to cut it out of a thick sheet of HDPE and the form it with heat.
This way, the rib cage is all one big piece with no mechanical fasteners.
The problem with this comes when you try to integrate it into the spine of your doll skeleton.
But, you could just ignore that, as the spine of a doll skeleton is much closer to the middle of the body. (in other words it goes through the middle of the rib cage
Another way of connecting ribs would be a thick, cast, rubber band.
A thick piece of rubber with holes in it where the rib bones go through.
High molecular weight (or ultra high) PVC. Feels like wax, can be bent to extreme ranges, and has very high yield points as far as tensile and shear strength. Self lubricating too during machining process....
Interesting. In my opinion, the current skeletons are generally weak. One always thinks, metal will be strong and able to resist, but it always depends on how it is made. How the joints are welded onto the tube and also what hardware they use. The Chinese tend to use cheap grade bolts in many applications. For example a 4.8 bolt is weaker than a 8.8. And who knows if they use a 8.8, that it is indeed a true 8.8?
I think water cut profiles made out of aluminum would be a good alternative for skeletons. They can be made by pretty much any shop and can be assembled without special equipment. No welding necessary. No bad welding joints that can crack. Especially on that thin tube wall thickness. The weight would remain pretty much the same, but it allows more flexibility with other ideas to get rid of unnecessary silicone or tpe.
