Making internal splines

Maplehead

Registered
Registered
Joined
Feb 20, 2017
Messages
437
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.
 
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
 
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)
 
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....
 
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.

IMG_0469.JPG
 
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.
 
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.
 
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.
 
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.
 
Back
Top