Pull Release Knife Edge Changer Design

[Tim Toberer]

I found a few pictures of Blanton and Fender knife edge changers, but can't find any of the individual finger. I know the Jackson Maverick is a pull release with a knife head changer. If anyone has any design considerations, or a picture of what an individual finger looks like I would love to get some help. The head looks kind of like pac man. I know the materials are important, because you want the knife edge to wear, not the changer finger.

14199_663462403E9B45EC8CC7ADD8F29C764D_1.jpg

[Jerry Overstreet]

viewtopic.php?t=356353&highlight=fender+artist

This is for the all pull knife edge design but perhaps it will help.

[Tim Toberer]

Thanks Jerry, that is helpful. I haven't seen that. I maybe can get the angle of the Pac man mouth from that.
Here is a video description of making an all pull changer, that has a unique design in that it doesn't use a bar axle. The axle rod is mounted to a plate like a knife edge changer. I haven't seen a design like this before, not sure if it is original? https://www.youtube.com/watch?v=wpRPyxuv42s

Not sure if this is worth pursuing, but I like the idea of a being able to easily remove the changer fingers for cleaning and maintenance. Also this would reduce the amount of friction, which is a big problem in pull release.

[Ian Worley]

The changer finger design in the vid is the same as early Sho-Bud all-pull changers. His benchtop demo at the beginning is basically a Fingertip setup, but the general concept was the same for subsequent iterations up through early '70s Professional. ZB and others of that era used similar designs. It's mechanically more simple than a more modern two piece scissor design but it's more limiting in terms of leverage and range.

You might want to check out a Carter Starter changer, it's basically the same. They have a round axle, but the fingers have the "Pacman mouth" open side. It's bit like the fingers in the vid, but they don't have to be slid on from the end of the pivot axle.

[Ian Worley]

Here is a Carter Starter changer

[Tim Toberer]

Here is a Carter Starter changer

That is pretty close to what I was envisioning. Interesting how they use the comb to support using such a small axle. Looks like 3/16. I know most people aren't looking to the Carter Starter for inspiration, but I really like this. Thanks again Ian!

[Ian Worley]

BMI changers use an even smaller axle, 1/8" Ø I believe. According to Don Fritsche, the theory was that the smaller axle has less surface area, therefore less friction, which is the same general concept as with a knife-edge pivot. The changer mount is constructed in a similar way, with slots in a block of aluminum forming a solid support "comb" between each finger. The small diameter axle can easily accommodate the force applied by the tension on the finger at each short axle segment.

BMI finger.jpg

[Ian Worley]

Here are some fingers from an early (~'64-'65) Fender 800. The base plate with the knife edge pivot surface is ~0.109" or 7/64" thick. The radius of the mouth in the fingers is about 0.055", so basically also 0.109" diameter. Notice also that the top surface on these old Fender fingers is not concentric with the pivot point.

800 fingers.jpg

[Tim Toberer]

Those are really helpful pictures. Much food for thought. There is a solution in here somewhere for me. I have pretty much stopped building new because I just feel there is no point until I figure out the mechanics of these things a bit better. I feel like I am getting closer.

[John Hyland]

So the burning question is why aren’t knife edge fingers more common.
What appeals to me is the ability to remove a finger for repair or replacement without removing an axle and upsetting the other fingers.
Also flat bar will be stronger than a round bar

[Jerry Overstreet]

Good Question John. Maybe some of the experienced builders can give us some insight.

Another feature of the knife edge changer is less string breakage, at least in my case with the Fender Artist. I have not broken any strings on either neck. The strings are the ones that was on it when I got it in Oct. '23 and I've played a lot including a few outings of several sets.

I'm not smart enough to know the reason. Maybe because the string loads from the back side and wraps all the way around the finger...radius...movement?

I guess I'm just lazy but also I wanted to test string breakage by not changing any of them right now. Some of them are rusty and grungy but still alive. It's just sometimes I am curious concerning operation and longevity of things, but now the experiment has pretty much run it's course and it's time for some new wires.

[Tim Toberer]

So the burning question is why aren’t knife edge fingers more common.
What appeals to me is the ability to remove a finger for repair or replacement without removing an axle and upsetting the other fingers.
Also flat bar will be stronger than a round bar

This is a great question! I really like the idea of using a narrow axle and a comb with a finger similar to the Carter. This would be an extremely low friction setup. A proper comb looks fairly difficult (for me) to make. This is the downside, but the fingers would be easier to machine, being thinner with less materiel to remove. I like 3/8 finger spacing so with a 1/4 finger, that leaves an 1/8 comb tine. Seems doable. The plate axle is a cool idea, but seems like it could be more problematic to design correctly. No spacers and 3/8 thick fingers. I can't quite wrap my head around it.

[John Hyland]

So the burning question is why aren’t knife edge fingers more common.
What appeals to me is the ability to remove a finger for repair or replacement without removing an axle and upsetting the other fingers.
Also flat bar will be stronger than a round bar

For info I started thread in the pedal steel section as I think it will get more interest in the larger forum.

viewtopic.php?t=407338

[J D Sauser]

I am very much considering a knife edge changer for my future all-pull guitars with 4R/3L... for the more "meat" it leaves on top of the finger (for wich I have use for something I will disclose later) and also less friction and wear issue (yes, I will wear too, but it will NOT affect function as much as it does with a 360 degree encapsulation as when on a fully surrounded shaft), and finally, because it allow to completely eliminate any suspicion of change axle deflection affecting the tuning.

... J-D.