device to press R/C servo spline grooves into a hole ?

Anybody know of a mechanical device to "carve" or press the spline grooves into a hole so we can use custom components
on a R/C servo ? I know there are several alternatives such as those gears and hubs offered by ServoCity but it might nice sometimes to mount a part directly to a servo without going through all the adapting.
Thanks ! JCD
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pogo wrote:

A motivated hobbyist might go to a machine shop and have a punch made that could then be used to produce the serrated splines. It would work in materials like plastic and wood, but not metal -- and least not as long.
-- Gordon
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might
Actually, I just got a new Sherline mill, so this sounds like an "educational" first project for me. I see a box full of "not quite right" spline punches in my future ! :-)
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pogo wrote:

If you can swing for the gear cutting rig they sell for it that will make your life easier.
You can try one in aluminum to see how it works but for something production oriented you'll probably want steel. You can read up on how to case harden steel. You could also adapt John's comments re: heating, which would be necessary if you're using a plastic like acrylic that can crack.
-- Gordon
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full of

Yep - that gear cutting rig may be a little while down the road ... :-)
It should be a good exercise, none the less. I may decide that a steam engine is easier !
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pogo wrote:

Never thought about it much before but ... are they mostly the same? That is - are the output shafts of most or all servos following some kind of agreed standard? I would expect micro servos to be different from standard sized but it would be interesting to know.
Pete Harrison
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Peter Harrison wrote:

I don't know how to cut them out, but I think one of the videos at FreemanSupply showed how to cast plastic parts with the shaft adapter built in.

There are basically two camps. Hobbico and Futaba, if memory serves. Wherever you buy a servo, they usually specify which type of attachment the servo was designed for (if its not obvious from the brand). These standards came from the compatibility attempts of smaller vendors -- no committee needed.
- Daniel
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Hitec, not Hobbico. :)
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I remember a while back I saw a webpage where the guy was casting plastic parts (his own wheel hubs i think..) to match the grooves on a servo motor axle. it was fairly labor intensive though: - take mold of axle - make mold of the part you want to make - fill w/ epoxy or resin of some sort - wait, etc
pogo wrote:

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pogo wrote:

If you just need to put a spline pattern into a thermoplastic like nylon, you can use a heated tool. Get some pinion wire which matches your spline from Stock Drive Products; they have a big selection. Buy the steel wire, not the brass. Cut off a few inches. Clamp it in a drill press. Use a file to file the wire to a point. Now you have the tool.
Heat up the tool to the point that it will soften the plastic you're using. Various ways of heating the tool will work; one of the neatest would be to find a soldering iron that will hold it like a soldering tip. Practice on some scrap plastic. Drill a round hole smaller than the tool, then push the heated tool through the hole to form the desired spline.
This isn't a precision technique, but may be good enough for your application.
If you're working with metal or a thermosetting plastic, you'll need a real "spline broach", which can cut a spline.
                John Nagle
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John Nagle wrote:

Great if it were true. Futaba servo spines have 25 teeth; Hitec 24. Not saying there aren't pre-made spline wires made with this many teeth, but Stock Drive doesn't have them.
-- Gordon
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Thanks Gordon. Exactly the kind of info I needed since I have an idea for a hobbyist product that, of course, spawned the need to cut spline patterns into a hole.
JCD
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Cool. I didn't know there was such a thing, but knowing this helps!
Actually, I have an idea for a product, which of course spurred the need to cut spline patterns into metal (possibly plastic).
Thanks !
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I found this in the specs for some spline wire at Boston Gear. Do you know what the PA and DP means ?
a.. Pinion wire teeth are drawn, not machined, for great cost-efficiency. a.. It offers a smaller number of teeth as compared to cut gears. a.. Pinion wire is ideal for the development of prototype gears for new applications. a.. It's available in both brass and steel, to meet a variety of needs. a.. 14 1/2 PA, 24, 32 & 48 DP satisfy diverse engineering requirements
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PA - pressure angle - 14.5 degree -most involute cut teeth_Pressure Angle (theta) -the angle that determines the pressure angle between contacting teeth. Also determines the size of the base circle.
DP - Diametral Pitch (P)- A ratio equal to the number of teeth on the gear per inch(or cm) of pitch diameter

grooves into a hole so we can use custom

gears and hubs offered by ServoCity but it

through all the adapting.

nylon, you

from
what the PA and DP means ?

applications.
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been there, done that. :)
what _I_ did, was to take a chunk of one of the harder steels (round stock) turned it down a bit on both ends, one end was a 'shoulder' that would allow it to shore up against the bottom of the chuck in my drill press, the other end was narrowed down before tapering out to the end (punch end). The punch end it drilled out so that a pin could be used as a guide for centering. The teeth were made on a lathe not by having it running, but by using the threading gearbox as a divider head and using the carridge to 'scrape' grooves along it. (V tip sideways).
conclusion: mediocre success, I was a little short on time, so the work was a bit sloppy, you also need to get the angle on teh V just right for the tooths depth to lign up with its width.
it worked great on plastic (I was pre-drilling the holes and using the punch to spline them) but when I tied aluminum I lost a tooth (serves me right)
I'll see if I can remember to take a picture some time
dan
pogo wrote:

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pictures!
http://eds.dyndns.org:81/~ircjunk/dscn8315.jpg
http://eds.dyndns.org:81/~ircjunk/dscn8316.jpg
dan
rue_mohr wrote:

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rue_mohr wrote:

Looks good.
Folks without a machine shop can somewhat duplicate this by purchasing a metal gear set of whatever servo type they want to use -- Futaba or Hitec. It helps to attach the gear to a longer post with a blunt end for hammering, though for some work I did I didn't bother with this step. You can use a similar setup if you wanted to cast some of your pieces, too.
I've found that it helps to drill a pilot hole only slightly smaller than the inside pitch of the spline. Heating the metal does help with some plastics. Acrylic will just crack.
-- Gordon
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and from experience, let me say that the gear trick is atleast worth a try. I think all in all, that thing took 8 hrs to make up ( I think it took about 3 seconds of me trying to push it through aluminum to rip a tooth off)
dan
Gordon McComb wrote:

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rue_mohr wrote:

But the problem with the metal gearsets is that they tend to be made out of soft metal -- brass or aluminum. I suppose someone somewhere makes them out of steel, but those aren't normal hobby store finds.
So, one must limit the use of the metal gearset idea to softer materials, such as expanded PVC, maybe nylon, or polycarb or acrylic if the metal has been heated up. For plastic it definitely helps to drill that pilot hole for heated stamping so that there's no flash left over to carefully clean up. The trick is not removing the spline too soon, or else the plastic contracts too much when it cools.
-- Gordon
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