# Making internal splines



## Maplehead (Aug 28, 2017)

Hi All

I want to make 6mm wide by 18 teeth internal splines in c360 brass for guitar knobs.
Any ideas on how?
I'm imagining some sort of male spline bit that I punch into a hole size below the teeth diameter.
Alternatively, if I could just by plastic 18-spline inserts I'd do that but they appear to be non-existent on the Web.


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## francist (Aug 28, 2017)

You're right, there appears to be precious little out there or at least I'm not having much luck finding anything. I know "someone" makes brass inserts like what you want, but where to find those I don't know. I measured some plumbing stuff (some of the older toilet shut-off handles and such used spline shafts) but they seem to be too large a diameter (around 8mm). There are some places that will sell you the tool, but be prepared for $$. Search for "spline broach" without the quotes and you should find some sources.

If I was making custom knobs and wanted to do that I would probably just buy the cheapest knobs I could find and then turn the outside part off it to make my own inserts. Depends on how many you need though, might be cost prohibitive that way. 

-frank


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## DAT510 (Aug 28, 2017)

Rotary Broach?






There are kits/plans available and there have been some treads about them on HM.  

http://www.hobby-machinist.com/threads/shop-made-rotary-broach-down-and-dirty.48805/


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## British Steel (Aug 28, 2017)

The tool in question is a rotary broach, making the splined broaching tool would be the hard part, but doable if you have a number of splined holes to broach...

OR you could buy decent quality pots with 1/4" and flat shafts?

Dave H.(the other one)


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## whitmore (Aug 28, 2017)

Maplehead said:


> H
> I want to make 6mm wide by 18 teeth internal splines in c360 brass for guitar knobs.


This outfit <http://www.sturdybroaching.com/contact-us-2>  seems to offer sleeves that
you could fit into a brass knob (glue or knurl-and-press), and in a variety of materials.
Probably the 18-spline and mild steel for an insert would be an easy task for them...

For mass production, one would usually cast (Zamak?) the spline in a knob, but through-hole
with a broach is fairly fast, and blind-hole with a rotary broach is ... possible, but
tooling cost might be considerable.   What exactly is your shaft specification that
the knob engages?   Eighteen flutes, and 6.0mm diameter, would seem to
imply circa 0.45mm tooth width?  Seems rather fine....


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## Maplehead (Aug 29, 2017)

Thanks for the replies All. I guess I have some research to do.
I'm not too big on the solid shaft approach because I don't like the set screw look on these knobs.
My shaft specs are the standard metric split shaft pots.


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## seasicksteve (Aug 29, 2017)

Just a thought. This doesnt appear to be a highly stressed part. You could try to form the internal feature with and epoxy. Use the male spline as a mold just use a liberal amount of release agent on the splines. Make the hole in the knob a bit oversized or even cone shaped to create a mechanical lock. Just make sure its clean and a bit roughed up where you want it to stick and used release agent where you dont want to stick. I would use a metal fillled epoxy like devcon plastic steel.


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## seasicksteve (Aug 29, 2017)

You could do it with a small single point tool and a dividing head. It would be a slow and tedious process. You would need a relief cut for chip release at the bottom of the hole. A single point tool would need to be ground that creates the desired groove profile. Use a shaper, slotting head, lathe ect to do the actual cutting.


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## Maplehead (Aug 29, 2017)

seasicksteve said:


> Just a thought. This doesnt appear to be a highly stressed part. You could try to form the internal feature with and epoxy. Use the male spline as a mold just use a liberal amount of release agent on the splines. Make the hole in the knob a bit oversized or even cone shaped to create a mechanical lock. Just make sure its clean and a bit roughed up where you want it to stick and used release agent where you dont want to stick. I would use a metal fillled epoxy like devcon plastic steel.



Interesting idea. If I use the male splined shaft as a mold, wouldn't that make the internal splined hole easily slide on and off of the shaft?
For the long run I'd love to go the rotary broach approach, but man that tool holder is expensive. Also, I can't find the 6mm 18-spline rotary broach anywhere.


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## Karl_T (Aug 29, 2017)

This is an easy job to burn on a sinker EDM. Farm it out to somebody that has one if you need a bunch.

For one or two, I'd use the single point cutter idea. A mill with rotary table would work well. So would a lathe but accurate rotation of the chuck would need to be addressed.  This goes fast once you get it figured out.


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## rgray (Aug 29, 2017)

Maplehead said:


> For the long run I'd love to go the rotary broach approach, but man that tool holder is expensive. Also, I can't find the 6mm 18-spline rotary broach anywhere.



I think you would have to make both. Question becomes whether time allows that.
Link to homemade: http://www.hobby-machinist.com/threads/shop-made-rotary-broach-down-and-dirty.48805/

Many more threads on here for both broachs (cutting tool) and the rotary broach (that holds the cutting tool)


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## mcostello (Aug 29, 2017)

Here's a picture of some parts I made.


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## whitmore (Aug 29, 2017)

Maplehead said:


> I don't like the set screw look on these knobs.
> My shaft specs are the standard metric split shaft pots.


I've seen knobs, with cylindrical bores, and an S spring insert, that bites into the hole.  The bar of the "S" engages
the slot in a split shaft.   There might be a dimple in the bar, because it made a good tight friction fit to the shaft.
It might have been a D shaft, such as on my electric oven knobs (plastic knob, steel spring insert, onto
a D shaft).

Alas, don't know a supplier for such.   Maybe a manufacturer of the pots can connect you, though.


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## tq60 (Aug 29, 2017)

Many options are about.

First question to ponder is the user and operation.

If the user "eats bananas and walks on their knuckles" it requires a different design that that of a gentle touch.

Contact the manufacturer of the pot and ask them where one gets the knob to fit.

Simply put they build them for some need as someone wanted them at some point in time.

Likely the knows will be plastic but material does not matter.

You can get a plastic knob and machine it to form an insert that can be epoxied in or the knob manufacturer may have the inserts.

If torque is not much the knob could just slip on.

Or creative idea would be to cross drill a hole in the hole.

Imagine looking into the hole and shifting it at an angle to where you could drill a tiny hole into the side of the hole.

In this you slide in a chunk of wire to act as a key to prevent rotation.

Bend it then it adds holding power to help keep knob in place.

Sent from my SAMSUNG-SGH-I337Z using Tapatalk


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## Wreck™Wreck (Aug 29, 2017)

Maplehead said:


> Hi All
> 
> I want to make 6mm wide by 18 teeth internal splines in c360 brass for guitar knobs.
> Any ideas on how?
> ...


You have not supplied the single most important bit if information which is How Many Parts?


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