Emergency fret bender

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Trevor Gore
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Emergency fret bender

Post by Trevor Gore » Thu Nov 19, 2015 6:46 pm

Every now again one gets caught short. :shock:

Normally, I use fret wire from a coil which is already bent to a tighter radius than any fretboard I use and just cut 'em and press 'em in. Then someone orders "odd" fretwire, a whole coil isn't needed and the fret wire comes in straight lengths. Then you're left with straight wire and a curved board and you get caught short because you didn't plan ahead.

Rather than waiting 7-10 days for a bender to turn up from the USA (I didn't fancy my chances of getting smooth curves bending by hand), of course I did what every good shed-dweller would do and knocked one up out of bits and pieces that were lying around in my "spares" boxes. It took about 20 minutes to "design" (find bits that would work and figure out where to put the centres) and about 40 minutes to make. After I'd finished the bending I took it apart and painted it. If I hadn't, where I live it would have rusted solid by the time I got around to using it again. All the pics are "after the fact", so no progress shots. They weren't a priority at the time.

The starting point was 3 socket head cap screws, 10mm x 50mm, a bunch of washers and an old credit card (actually a hotel room pass key which somehow never got returned).
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The smaller washers are 3/8", the large washers are 5/16" id, 1 1/2" od, which I drilled out to 10mm, the pass card (0.8mm thick, about the thickness of a fret tang and barbs) has had a disc cut out using a 1 1/2 inch hole saw and is used as a spacer between the two large washers. This is the center "drive" wheel.

The other two wheels I cut from scraps of 10mm polycarbonate (from jig making) using the same hole saw.
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The groove in the od was made by chucking up the socket head cap screw with the polycarbonate disc on it (held with a nut, of course) in the drill press, spinning it up and scratching out the groove using the end of the broken file. The white plastic washers are what separate neodymium magnets (ex magnetic arm rests) which happen to be 10mm id.

The base plate was a bit of rusty steel (ex some concrete shuttering, I think) which happened to be about the right size. This piece is 90 x 130 x 8mm. A piece of decent quality ply would work just as well.
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With this type of bending device, where the bends are always going to be much larger radius than the wheel sizes, the wheel sizes are largely irrelevant. What matters is the distance the outside two wheels are apart and the penetration of the middle one - i.e. how much lower the circumference of the middle wheel is below the line joining the circumferences of the two outer wheels. As the finished wire radius is not critical (I've never had to modify the curve of coiled wire irrespective of the fretboard radius) the penetration is not super critical. The governing equation is the radius of curvature through three points of known separation which can be found on numerous luthier sites usually with respect to making radius dishes. For this fret bender, the separation of the centers of the two outer wheels is is 60mm and the penetration is 2mm, which gives a curve radius of 225mm, which results in about 300mm wire radius with a bit of spring back of the wire. I slotted one of the holes with a file so I could make a one-time adjustment to get exactly what I wanted.

Here's the finished gadget, which looks like it will roll miles more fret wire than I'm ever likely to. Drive is provided by the hex wrench applied to the rear of the center wheel. Use whatever washers you need in whatever places in order to get all the grooves to line up. I left the non-adjustable lower wheel with some end float on it so it self aligns.
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kiwigeo
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Re: Emergency fret bender

Post by kiwigeo » Thu Nov 19, 2015 7:51 pm

Stewmac buster!!!!
Martin

routout
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Joined: Mon Jun 15, 2015 7:34 am

Re: Emergency fret bender

Post by routout » Mon Nov 23, 2015 8:27 am

Very innovative that's for sure and it does the job. :D
John ,of way too many things to do.

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Trevor Gore
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Posts: 1313
Joined: Mon Jun 20, 2011 8:11 pm

Re: Emergency fret bender

Post by Trevor Gore » Wed Jul 26, 2017 9:26 am

If you want to un-bend fret wire, check out this thread.

Kamusur
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Joined: Thu Dec 30, 2010 10:08 pm

Re: Emergency fret bender

Post by Kamusur » Wed Jul 26, 2017 7:04 pm

Very nice Trevor.

Steve

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