Two Way Trussrod Question

[mandomaniac]

Have a question for those of you who have experience with the two way adjustable trussrods. How do you handle glueing the FB to the neck? Seems like any glue on the top flat surface of the rod(which is flush with the neck's upper surface) would interefere with the action of the rod as it must change position ever so slightly under the FB to adjust relief. Have about decided on using epoxy to glue FB, trying to avoid the midline, and apply release agent to the trussrod. Any help would be appreciated. THANKS! Tom

[sunburst]

Never used a 2 way in a mando, but First Quality uses silicone calk in their banjo necks. A couple of dabs under the rod and a layer spread on top.
If you don't know, they prepare the banjo necks for Gibson. I was just told about the calk by them on the phone a couple of days ago because I'm using one of the rods in a banjo neck.

[Jim Hilburn]

I use a custom order 2-way from LMI. I heard about them from John Garrity. The first ones I used, I left the flat steel upper rod level with the f.b. plane, and glued the f.b. to the remaining surface. The one I'm doing now ended up a little below the surface, so I ca glues a filler to it.
However, this design of rod can apply crazy amounts of force to the neck ,and should never need but the slightest tweak. No glue would stand a chance against it, but you would probably hear some cracking noises that would make you think you had destroyed something as the glue joint was broken. Mandolins tend to amplify any noise the rod makes.

[Lynn Dudenbostel]

I get my 2 way rods from Steve Smith at www.cumberlandacoustic.com. He puts heat shrink tubing on the rods so glue isn't much of a problem. But, I always set mine about 1/16" deeper and put a thin maple filler strip on top of it. Stay away from epoxy and use hot hide glue or titebond to glue the fingerboard on. Epoxy has too much creep over time. I had one epoxied fingerboard joint fail on an early guitar some years ago. Never again! The only place I use epoxy is for inlay work.

Lynn

[Bandersnatch Reverb]

Dunno if this works on mando, but it works on guitar.

If you think about how you route for the two way truss rod... its possible make allowance to remove the rod (with its ends) from the adjustment opening. In that case the glue would not be a problem, but you might want to consider something to pull thru the channel as a "cleaner outer" when the fretboard is applied.

[mandomaniac]

Interesing info....thanks to all. Next one I'll try the deeper approach with thin filler overlay. Still seems like there is some risk of glue interfering with the action if it sneaks past filler.
Lynn, I am making my own with high tech aluminum for the flat 'frame' part and brass rod with RH/LH threaded ends. Very light actually. Does Steve put heatshrink over the ENTIRE assembly or just the round rod portion? BTW...Your warning on epoxy has made me have second thoughts. Do you recall the type you used that failed?
Thanks again...Tom

[sunburst]

A few thoughts.

I once replaced a broken brass truss rod in a mandolin neck for a guy that has an industrial metals business. He could have made a rod out of anything, we talked about titanium, but decided on plain old steel because of the smaller coefficient of expansion. I assume you've done the math and know what will happen with temperature changes using aluminum and brass together. Also, will the threads be reliable in terms of galvanic action? I don't mean to imply that you haven't thought things through, but just in case...

I don't recommend epoxy for the fingerboard joint either, but there's no guarantee it will fail. There are thousands of Stelling banjos doing fine with epoxied on fingerboards.

[mandomaniac]

Sunburst, that's what this forum is for and I appreciate your thoughtful input. I put some thought to it, but maybe missed something. Indeed the coefficient of expansion is greater for both the materials than highcarbon steel, but they are relatively similar to each other. I figure it is an adjustable mechanism anyway....if you fly from Phoenix to Fairbanks...it will change twice as much but can be adjusted. The galvanic action issue is more of a concern...particularly since this prototype mando might be construed as a boat paddle. #http://www.mandolincafe.net/iB_html/non-cgi/emoticons/biggrin.gif #Definitely wouldn't want to build an aluminum boat with brass fasteners, but I felt the trussrod would be likely in a pretty dry environment inside the neck. Hopefully I'll be OK. May have to dig out that titanium, but think I would go back to steel as you did if problems arise. Thanks again. # # Tom

[Michael Lewis]

Both brass and aluminum will expand and contract much more than the wood of the neck, so you might be adjusting it fairly often. The typical truss rod is steel with a brass nut in case it gets stripped. That way you just replace the nut with no damage to the rod. Just a thought. http://www.mandolincafe.net/iB_html/non-cgi/emoticons/wink.gif

[mandomaniac]

Well , now you've got me pondering things a bit more. Seems that if this was a 'traditional' rod the coefficient of expansion would matter a great deal more as you say. I'm trying to figure how this really applies to a 2-way rod...since the mechanism of action within the neck is so different. The LH/RH threads allow one to either push up in the middle of the FB, creating back bow, or push up on each end of the FB, creating relief. If the coefficient of expansion of the lower 'round rod' and the upper 'square frame' piece are equal (or at least close) the tension within the assembly (and thereby the pressures on the FB)should remain the same.
BUT HEY.....I'm not a metallurgist....please set me straight!!! I'm about ready to slap the FB on the neck and then there's no turning back. I can always mill a steel frame and rod ....just was trying to cut down on weight.
I appreciate any and all help...THANKS! # #Tom
BTW....will hopefully finish up this prototype and try to post some pics soon.....it may not be a boat paddle after all! http://www.mandolincafe.net/iB_html/non-cgi/emoticons/laugh.gif

[Dave Wendler]

The double rod doesn't have near the expansion/contraction problems of the traditional Gibson style. I worked with these things for several years; installed thousands of them while I was at PV. The rods there weren't the "double acting" type, more like the old Rickenbacker rods; bowed back only.

With the guitar necks I'm doing now, I use a double acting type and they do adjust rather quickly but are VERY stable once set. Since a mandolin usually has a thicker neck profile than a guitar neck, you shouldn't have any problems with cranking that sucker through the back side of the neck(I've done this a couple of times!!) ...but you need to be careful. The action isn't only in the center of the neck....you will generate tremendous "back" force out at the ends of the rod.

They are heavy....particularly on my VERY lightweight guitars; I've been struggling with a way to use the double rod with the top flat bar being made from carbon fibre and then pinning the threaded blocks to the ends...haven't got it figured out yet, but using 1/8" stainless rod should be possible rather than a 3/16". It just might be possible to do this if I stick to just a "back bow" style...

[mandomaniac]

Hey Dave....That's what I suspected....thanks for the info...encouraging words indeed. I was ready to glue up FB today and now feel better about using this rod. I doubt it will give me any trouble and is indeed much lighter than steel.# #http://www.mandolincafe.net/iB_html/non-cgi/emoticons/biggrin.gif
Thanks... # #Tom