How are these little internal gear teeth made?

In summary, the conversation discusses the process of making a servo horn, specifically the internal gears or splines that are used. The suggested methods include powder metallurgy or metal injection molding, drop forging, injection molding, and 3D printing. The use of Kevlar for reinforcement is also mentioned. The conversation also touches on the importance of considering the size and forces involved in the application, as well as the potential issues with directly transmitting torque through a small diameter coupler. Finally, the conversation mentions the possibility of using a square fitting for better force transmission and suggests looking into other arms available from the servo manufacturer.
  • #1
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This is a servo horn. I'd like to make my own if possible, but I have a hard time figuring out how in the world they make the teeth inside these parts. I'm not really sure what to ask in google.
 

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  • #2
In the piece shown the teeth were probably cast in .

Higher precision internal gears can be cut by a multitude of processes .

Search on ' Internal gear cutting ' . Look at the images and videos rather than written descriptions .
 
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  • #3
My guess is that most likely that part is made with a powder metallurgy or Metal Injection Molding (MIM) process.
 
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  • #4
That looks more like a spline to prevent rotation than gear teeth.
It is difficult to cut internal splines in blind holds. The above two answers are both good.

In the unlikely event of the material being very hard and electrically conductive, it could be done with Ram EDM.
For softer materials I would expect it to be drop forged in a press, the same way spanners and sockets are made.
Plastic would be injection molded.

What is the material ?
 
  • #5
The material is anodized aluminum
 
  • #6
How many do you need? If only a few, you might consider making a mould from that one with modelling clay. Modify the mould to suit your needs. Then cast one in the mould with a two part epoxy, include short fibres of something like Kevlar for reinforcing if needed.
 
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  • #7
Search on ' 3D printing ' and ' 3D printed gears ' .

Best again to look at the pictures before reading the text .
 
  • #8
Baluncore said:
How many do you need? If only a few, you might consider making a mould from that one with modelling clay. Modify the mould to suit your needs. Then cast one in the mould with a two part epoxy, include short fibres of something like Kevlar for reinforcing if needed.
Just a few. How would Kevlar compare to aluminum in this case?
 
  • #9
Nidum said:
Search on ' 3D printing ' and ' 3D printed gears ' .

Best again to look at the pictures before reading the text .
It would be ideal to have these printed out but the many companies I've ordered prints from were not too good at fine detail
 
  • #10
kolleamm said:
How would Kevlar compare to aluminum in this case?
That depends on the size and the forces involved in your application, which you have not yet identified.

A coupling like that will tend to be expanded when torque is applied. That is because of the tooth face contact angle.
If made from something like epoxy, then winding a Kevlar thread many times around the outside will counter that expansion.
 
  • #11
Baluncore said:
That depends on the size and the forces involved in your application, which you have not yet identified.

A coupling like that will tend to be expanded when torque is applied. That is because of the tooth face contact angle.
If made from something like epoxy, then winding a Kevlar thread many times around the outside will counter that expansion.
This is basically attached to a high torque servo that will act as the shoulder for a robotic arm which weighs about 3 pounds. It's goal will be to raise a robotic arm that's about the length of a human arm.
 
  • #12
Consider the human arm. It has three major bones with ball joints, hanging from the shoulder with several muscles that change length. The geometry of the linkage has evolved into an optimised solution.
It is a mistake to transmit the full torque through a small diameter coupler directly from a servo motor. How will you link the servo to the arm and how many turns will the servo make to swing the arm through 90° ? Is it geared?
 
  • #13
Baluncore said:
Consider the human arm. It has three major bones with ball joints, hanging from the shoulder with several muscles that change length. The geometry of the linkage has evolved into an optimised solution.
It is a mistake to transmit the full torque through a small diameter coupler directly from a servo motor. How will you link the servo to the arm and how many turns will the servo make to swing the arm through 90° ? Is it geared?
The servo is attached both front and back to the shoulder. Front being the part where the piece above attaches, and back being the opposite side on the back of the motor. The only gears are inside the servo itself. This is a very high torque servo and not a standard one. The arm itself is also very optimized for weight, the heavier parts being closer to the motor while the parts more outward are lighter, such as carbon fiber. I've tested it, it works.
 
  • #14
If this joint is just a coupling link, why not make it a square fitting to ensure robust force transmission?
As is, it does not seem part of a moving linkage.
 
  • #15
Who makes the servo? Perhaps see if they have other arms available?
 
  • #16
CWatters said:
Who makes the servo? Perhaps see if they have other arms available?
The part works fine it never gave me any issues I was just curious if I ever wanted to make one
 

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