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Burns Gear-O-Matic Truss Rod

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Burns Gear-O-Matic Truss Rod

Postby Barry Daniels » Sun Jul 30, 2017 5:01 pm

Here was something I had never seen or heard of before. Its a truss rod installed in some Gretsch archtops in the 1970s that uses a geared adjustment system. I have read that they were problematic. This one, which was installed in a 7-string guitar, was frozen and the adjustment nut was completely stripped. I had to pull the fretboard and pull the rod out after removing the wood spline and some wood in front of the end support to take the pressure off the rod. During removal it bent on me due to the very soft metal rod. This rod is considered a dual action rod.

I am going to replace it with a Blanchard rod, after filling in some of the rather large holes left in the neck.
Attachments
Geared truss rod.jpg
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Re: Burns Gear-O-Matic Truss Rod

Postby Barry Daniels » Sun Jul 30, 2017 5:03 pm

The truss rod adjuster was accessed through a hole in the back. It is the lower hole and the adjustment nut was several inches deep into the hole. I can't figure out what the second hole is for.
Attachments
back access.jpg
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Re: Burns Gear-O-Matic Truss Rod

Postby Barry Daniels » Sun Jul 30, 2017 5:04 pm

Here is the gear box on the end of the rod. And the stripped adjustment nut is on top. The nut appeared to be made out of a metal as soft as lead. The adjustment knob looks like it is engaged with a reverse slotted screw driver. But it is so worn I can't be certain of the original configuration of the nut.
Attachments
gear box.jpg
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Re: Burns Gear-O-Matic Truss Rod

Postby Barry Daniels » Sun Jul 30, 2017 5:07 pm

And here is the gear box opened. I could not get the gear to turn on the rod, even when it was removed and accessible.
Attachments
open gear box.jpg
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Re: Burns Gear-O-Matic Truss Rod

Postby Peter Wilcox » Sun Jul 30, 2017 7:08 pm

So it seems the worm gear is a threaded nut, that is supposed to loosen or tighten the rod as the adjusting nut (on the end of the worm) is turned. Assuming the worm turns OK, I'd say the threads on the rod and the worm gear are frozen tight to each other, not surprising if the metal is soft.
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Re: Burns Gear-O-Matic Truss Rod

Postby Barry Daniels » Sun Jul 30, 2017 9:07 pm

The round gear on the rod is internally threaded and it turns on the threads on the rod. It turns about one half turn in either direction before it freezes up. The gears and the box don't seem all that soft, but the rod and especially the adjuster on the end of the cylindrical gear are very soft. I don't see any stripping of the gears or thread rods, but they are unusually sharp and appear to just dig into each other creating a lot of interference. Pretty weird. Also, the hardened grease doesn't help any. I am certainly NOT going to rebuild the rod and re-install it. The owner wants to modernize the guitar.
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Re: Burns Gear-O-Matic Truss Rod

Postby Peter Wilcox » Sun Jul 30, 2017 10:19 pm

If the worm gear (the name of the gear with the internal threads) is hard, and the rod is a lot softer, then I'd guess the gear's threads have bunged up the rod's threads, and that's why it won't turn properly, akin to using a steel nut instead of a brass one on a normal truss rod. Looks like an attempt to adjust the truss rod other than from the ends of the neck - guess it wasn't very well implemented.
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Re: Burns Gear-O-Matic Truss Rod

Postby Barry Daniels » Mon Jul 31, 2017 10:31 am

I think the design of this rod is over complicated and places a couple of small engaged gear teeth under a lot of stress for a long period of time. That combined with questionable metallurgy is probably what lead to this one freezing up.
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Re: Burns Gear-O-Matic Truss Rod

Postby Bill Raymond » Mon Jul 31, 2017 6:34 pm

Those were put in Baldwin-era Gretsches, and as you have concluded, more complicated than is necessary.
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Re: Burns Gear-O-Matic Truss Rod

Postby David King » Sat Aug 05, 2017 2:02 am

I have one of these rods someone gave me. They were fraught and overwrought to say the least. They came with a zither pin key or perhaps a drum key to adjust them and it looks like someone along the way went at this one with a pair of vice-grips or a pipe wrench. It's not the strangest truss rod out there but it's one of them.
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Re: Burns Gear-O-Matic Truss Rod

Postby Barry Daniels » Sat Aug 05, 2017 9:25 am

Yeah, the adjustment nut was completely worn smooth. But it was deep in a hole so there was no way to get a normal wrench or driver on it.
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Re: Burns Gear-O-Matic Truss Rod

Postby Gordon Bellerose » Sat Aug 05, 2017 11:04 am

Thanks for this post Barry. In the repair business a person can run into a lot of different things.
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Re: Burns Gear-O-Matic Truss Rod

Postby Barry Daniels » Sun Aug 06, 2017 10:15 am

I don't know if anyone is interested but here are some more photos of the Gretsch repair. I filled in the holes left from removal of the geared truss rod, including the 1/2" diameter access hole through the head block. I am currently building a new fretboard and will also be replacing the wiring harness and the pickups. The next step will be re-routing the truss rod slot because the new rod requires a 1/4" wide, flat bottomed slot whereas the old rod was in a 3/16" curved bottom slot.
Attachments
IMG_0562.jpg
IMG_0561.jpg
IMG_0560.jpg
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Re: Burns Gear-O-Matic Truss Rod

Postby Gordon Bellerose » Sun Aug 06, 2017 11:21 pm

Barry, this may be out of bounds, but I am wondering what you would charge for a repair of this nature?
Removal of the fret board, removal of the old truss rod, filling in the holes, re-routing the truss rod channel including drilling it out for the adjustment end, installing a new rod, having to rebuild and install the fret board and then a fret level and set up. I haven't mentioned the rewire job either.

Quite a list, and a fair amount of time involved in this.

If you're not comfortable publishing this on the forum, would you consider PM'ing me?
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Re: Burns Gear-O-Matic Truss Rod

Postby Barry Daniels » Mon Aug 07, 2017 11:27 am

I'll take this off-line.
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Re: Burns Gear-O-Matic Truss Rod

Postby David King » Tue Aug 08, 2017 4:19 pm

Test the Allied lutherie rod in a mockup of a neck to make sure that the threaded end blocks are correctly aligned and it doesn't bind up under tension. Testing the rod out of a simulated neck won't tell you much unfortunately.
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Re: Burns Gear-O-Matic Truss Rod

Postby Barry Daniels » Tue Aug 08, 2017 8:12 pm

David, actually Allied Lutherie doesn't supply the rod anymore due to reported problems with their supplier. I bought the rod directly from Mark Blanchard. I will take your recommendations in mind. I didn't realize that binding was an issue. Is that specific to the Allied Lutherie rod or to others also?
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Re: Burns Gear-O-Matic Truss Rod

Postby David King » Wed Aug 09, 2017 11:48 am

Hi Barry, it's a potential problem with any rod that has a threaded block welded at either end. Getting those tiny welds right is a difficult matter and when the price point is less than a buck you can see how expediency might win out over perfection. Mark is silver soldering each rod himself and doing his own quality control so I expect that perfection is the rule. He's charging what it actually costs. I've seen the Asian 2 way rods selling in bulk for $1.25 each. There are a lot of middlemen between the factory and our domestic suppliers and none of them seems interested in testing or adding value in any way.
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Re: Burns Gear-O-Matic Truss Rod

Postby Barry Daniels » Wed Aug 09, 2017 3:26 pm

Thanks David. I may make a quick simulated neck and test it out. I definitely need a functioning rod in this guitar.

So if I understand you correctly, upon adjustment the blocks on either end of the rod can get out of alignment with each other so that they would lock up in the neck slot, preventing further adjustment?

I have occasionally taken a dremel cutoff disc and eased the edges of the blocks on truss rods. Or even some emory paper will round over the steel blocks. Even though this might be a useful thing, it probably wouldn't prevent the issue you are talking about.
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Re: Burns Gear-O-Matic Truss Rod

Postby David King » Wed Aug 09, 2017 7:47 pm

Hi Barry,
In this case one of the threaded blocks was welded on askew so that as the adjusting rod advanced into the block at the far end of the neck it met with more and more mechanical resistance until it simply wouldn't turn any further and this happened before the neck could be flattened. I should probably state that this was a sample rod provided free of charge by Allied as part of a comprehensive test of many of the most popular rods on the market that I conducted for a 2014 GAL presentation. Of the eight rods and rod systems I tested in eight identical bass necks it was the only one that failed to get the neck flat under string tension.
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