Enclosed Scissor Fingers

[Les Ford]

This is a changer for a new project. The finger assemblies hang from both sides so that they won't easily swing out of aliginment and there is no need for a comb below. Instead of a rivet I have used a 3/8 inch delrin axle which is fixed in position with a set screw in the lowering finger. The string spacing will be 3/8".

I was hoping to fix some of the issues I have had with scissor fingers and make something that was more reliable and required less adjustment. It looks like it should work but I won't really know until they are all in the guitar.

[Ross Shafer]

Those look great, nice work Les!

[Rich Cottle]

Not bad , it looks like you got a hold of a milling machine , I'd like to.see a picture of just one finger assimbly with short pull rods , tuners and a return spring , showing how the three parts are interconnected

[John Hyland]

I like this concept but wonder about the side to side friction where metal can build up a bit of corrosion. That said this is a very similar concept to my 3d printed finger set which like yours relies on concentric pull loads to minimise twist. So far side to side friction hasn’t been an issue with the plastic.
I’m planning on pulling out the changer set soon so I will be able to see how the fingers are holding up.

IMG_6593.jpeg

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[Les Ford]

I made extras so that I can swap some out if there are issues with friction. I'm finding the delrin axle to be a little tight in some cases but I am hoping it will loosen up with use. If not I will ream them a little.
I am hoping that having the loads equal on both sides like this will prevent the binding that comes up in some poorly adjusted scissor fingers that tend to twist because of the lopsided forces in the setup. Having said that, other people seem to be able to get them to work properly so they can't be all that bad.

[John Hyland]

I’m not sure if the fingers will be as close together insitu as they appear in the photograph but be aware you might get thermal expansion or a slight twist from an eccentric belt crank.

[J D Sauser]

It's a subject I am mauling in my head for decades. I don't like anything which is off-center.
The problem with the proposed very nice design, besides it's parts' complexities, may be mass. Because we move these things and moving means acceleration, and mass needs energy to be accelerated.
Will this little more mass really be noticeable in our application? I doubt it, but it's a good one to look up my technical formula handbook.

Friction, is as we know a problem too. We like aluminum, because it's light and easy to machine. I frankly, the only changer I built had a mix of steel and brass.... because of my concern about friction and wear. Aluminum does not "run" well on anything, not even... actually even worse against itself (Aluminum against Aluminum).

But brass has even more mass.
And steel rusts.

Thanks to the OP for sharing!... J-D.

[John Hyland]

It's a subject I am mauling in my head for decades. I don't like anything which is off-center.
The problem with the proposed very nice design, besides it's parts' complexities, may be mass. Because we move these things and moving means acceleration, and mass needs energy to be accelerated.
Will this little more mass really be noticeable in our application? I doubt it, but it's a good one to look up my technical formula handbook.

Friction, is as we know a problem too. We like aluminum, because it's light and easy to machine. I frankly, the only changer I built had a mix of steel and brass.... because of my concern about friction and wear. Aluminum does not "run" well on anything, not even... actually even worse against itself (Aluminum against Aluminum).

But brass has even more mass.
And steel rusts.

Thanks to the OP for sharing!... J-D.

Plastic addresses all those concerns

[Les Ford]

Hey JD, The total weight for the whole enclosed finger assembly is 36 grams. The weight of the same thing in the traditional bent steel side-hanger configuration is 52 grams. This gives a thirty percent reduction in mass over the traditional side hanger.

It is worth bearing in mind that this is a 3/8 inch wide assembly which gives enough meat to cut out for the 1/4 inch center finger while still allowing 1/16 for each side. A 3/8 inch spacing works well up to 10 strings but it gets wide and might catch the bar when you go up to twelve or more strings. I suspect that the major wear will be in the two axle holes in the 3/8" wide outer finger. The lower finger axle is a piece of 3/8" Delrin rod to try to avoid galling and to avoid the axle sliding out if the set screw loosens.

I really won't be able to report on how well this setup works until I get the guitar finished, which will be a while yet.

I'm also trying a similar concept for a "linear" pull finger assembly, which is attractive to me because it has fewer components to interact with each other.