# Question on how to make a part - ( very small splines )



## DHarris (Jul 3, 2017)

Ok, the part in the photo is a Servo Horn for "giant scale" rc aircraft (80" wing span and up).  I need to make some "unique" configurations to fit into planes that the stock ones (or even after market ones) just won't fit.  So, here's the question:  as close as I can measure, the id of the spline hole is ~ .215".  I can't measure the depth of the spline for major diameter.  There are 25 splines in that little bugger.  (edit: material is aluminum)

So, how do I make splines that small?  ( I have a Sherline lathe & mill available).

thanks for reading and any / all suggestions.


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## francist (Jul 3, 2017)

Material is aluminum or steel?

-frank


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## DHarris (Jul 3, 2017)

Hi Frank,  It's aluminum - I've edited the post to include that data now - -


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## francist (Jul 3, 2017)

Cool, thanks.

Couple thoughts come to mind right off the bat:

One is broaching on the lathe using a smallish HSS cutter much like doing had wheel graduations, except this would be in an inside diameter instead of a handwheel's OD. 3/16 cutter maybe get in there but still be rigid enough to push in as a broach. 

Second thought is if it's aluminum, could you make a male version with splines and broach it in one shot? Not much material to move, really. Got a shaft to try one with?

Looking forward to seeing some of the other suggestions as they come in.

-frank


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## DHarris (Jul 3, 2017)

Hi Frank,
Would love to have a steel shaft to use as a broach, unfortunately, the mating part is typically a small brass gear on the Servo output shaft. maybe someone will be able to tell me how to make a steel "broach" to push thru the aluminum!  (I just can't think of any way to cut "teeth" that fine!
Dave


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## mikey (Jul 3, 2017)

I would imagine the easiest way would be a splined rotary broach. It's going to be expensive - you need to drive head and then you'll probably need a custom broach. It would work fine but its going to cost you.


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## kd4gij (Jul 3, 2017)

If you can tig weld or know someone that can. Cut the hub out and weld it in the new part.


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## DHarris (Jul 3, 2017)

Thanks everyone;

Mikey, yea - knew it would not be cheap to buy something, just hoping there was a "hobby" way to do it!

kd4gij, Yes, I've had friends tig up parts for me in the past, just galls me to have to destroy a perfectly good part to create another.

will keep digging to see what I can come up with!

Dave


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## kd4gij (Jul 3, 2017)

If you have a hobby shop near you. They might have a hub. Another thought look for the local flying clubs.


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## Jimsehr (Jul 3, 2017)

Call Westco broach in El Monte Ca and ask Tony . If anyone knows he will .All he does it internal blind broaching and he makes his own tools.
Jimsehr


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## rrjohnso2000 (Jul 3, 2017)

I see two issues. How to reverse engineer what you have and then how to make it. 

Optical comparator would be an easy way to measure. Microscopes can be adapted for measurement as well. Even the inexpensive digital microscopes. All of these would be helpful in creating any tooling as well. 

Or you can just canablalize parts are rework them. This seems easier but less fun.  You have good tools to do it if you want


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## mksj (Jul 3, 2017)

It would seem that this is a Futaba 25T 4F spine for direct connection to a (large) servo, if so the specs should be standardized and available from Futaba or you can buy a spline coupler to send  to have a broach made? Have you looked for servo extension arms, or servo arm insert.  Google Servo Arm Insert 25T Futaba.  With an insert, you could drill out the center and press in an arm with some red loctite. 

Otherwise I would grind a HSS or tool steel cutter, put the shaft in a rotary table and cut the teeth indexing at 14.4 degree increments.  I build a degree chart in excel, and just advance the rotary table and hold the cutter statically in my mill using the spindle to cut the splines. The other option would be to fabricate a rotary spinning spline cutter out of tool steel,  chuck the cutter in the mill, use a rotary table in the horizontal plane and index the shaft cutting each spline in the shaft with the mill.   Not sure what you can do on the Sherline, these approaches require a rotary table with some accuracy.

Custom broach would be expensive, but is an option. http://www.polygonsolutions.com/rotary-broaches/special-form-rotary-broaches/


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## mikey (Jul 3, 2017)

I wonder if you could make a single tooth cutter in the form you need and stick it into the end of a bar, then drive the bar down with the quill of your drill press to cut one tooth at a time. You can't do it  with the Sherline mill but you might be able to do it with your drill press and a rotary table. Just brainstorming here.


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## tq60 (Jul 3, 2017)

Here is a way to cut splines on a shaft but you need to determine how to index.

Place shaft in chuck of lathe with minimum stickout.

Next cut a tool to same shape as the spline and place it in the tool post sideways facing chuck and place dead center.

Use hand wheel on carriage to move carriage making lathe into a shaper.

Cut one tooth at a time then rotate to next position.

Once you have it figured out you can make a broach.

Sent from my SAMSUNG-SGH-I337Z using Tapatalk


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## DHarris (Jul 4, 2017)

Wow, some great ideas everyone!!  Will look into them all.

mksj - They are for the High tech servos - (basically the Futaba equivalent spline).  had not thought of a servo arm insert - great idea!

Thanks everyone,

Dave


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## DHarris (Jul 4, 2017)

Just Googled the servo arm inserts and they look to be the way to go for what I need to do!  They work similar to a "blind nut" or "pem nut" and can be pressed into the aluminum arm. 

Just because I'm a glutton for punishment, I'm still going to try to make a broach to do this with - should be a fun experiment! (and excuse to buy some new tools too! - must feed the addiction)


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## joshua43214 (Jul 4, 2017)

This would a simple project, and yes your Sherline can do it.
You can groove steel with hand tools (called gravers), grooving brass or aluminum is even easier.
I would use the mill with a rotary table myself. Plenty of good suggestions on using a single edge broach already, so I wont repeat them.

Search YouTube for "broaching on the lathe." You will get good examples of it. I have broached keyways several times, it is really a trivial thing, but it is really cool.
If I had to make several, I would cut the matching splined shaft from O1 or similar, harden it, then just drive it into the aluminum with a press. This is a tiny little part, no need for special tooling.


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## DHarris (Jul 5, 2017)

Thanks Joshua43214 - yea, will be doing a lot of Google searching for this one - I think it will be a fun project to try to make something for the small Sherline equipment!  Had not thought of using some type of Graver to make the broach itself.


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## 4GSR (Jul 5, 2017)

There are several different types of splines.  Look in your Machinerys Handbook.  As one post suggested, put it under a comparator to get a better picture of the spline.  A couple of things that will be needed when requesting a broach or any other tooling, is the pressure angle of the tooth profile as well as the diametrical pitch of the tooth profile, just like a gear.  Looks like a fun project.  
Another source that you may look at is Stock Drive Components.  (I think that is the name of the outfit.)


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## DHarris (Jul 6, 2017)

Thanks Ken - there is soooooo much for me to learn about this subject (just a beginning Noob at this - was an electronics engineer for career - machinists would not even let us walk thru "their" shop - and rightfully so).


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## rgray (Jul 6, 2017)

4gsr said:


> Another source that you may look at is Stock Drive Components. (I think that is the name of the outfit.)



http://www.sdp-si.com/
Lots of good stuff from them.


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## 4GSR (Jul 6, 2017)

Here's some spline shafts and hubs sold by SDP.  They are in the diameter range but not fine enough to match that in your picture.

https://shop.sdp-si.com/catalog/?brand=sdp&cid=p206

Thanks Russ for the link.


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