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I've been using the two-way rods from Allied and LMI. While they work great they are heavy. I think I'm going to go with the Benedetto style with two anchor points with one being a standard thread and one being a left hand thread. My question is: is the placement of the rod in the neck critical with this design? My thinking on this is that it's really more or less the same design as the Allied/LMI with the steel bar welded across the top being replaced by the underside of the fingerboard. Thoughts.

The truss rods I make are similar to the Bennedetto t rod. They are a compression rod and I like to put them below the center line of the neck at the very least. The rod on mine sit 7/16" deep at the nut. The anchor a bit deeper. At the body joint the are deeper at 1/2", + for the anchor.
Because they are a compression rod the risk of blowing out the back of the neck is minimal to nil. At least I've never seen or heard of anyone having that problem with the ones I make.

To clarify I'm not talking about the single-action compression rod that he shows in the book. He uses a different style now. It has two anchor points. The one at the heel end has standard threads and the one on the nut end has reverse threads (it might be the other way around I can't remember) so it's a two way rod but it doesn't have the steel bar welded across the blocks.

A two way truss rod is cool but not often needed on an archtop guitar. Jazz players tend to like heavy strings. For that reason I just get by with a single action truss rod. These are light, reliable and easy to install. I think the best way to anchor one of these is with a simple 90 deg. bend rather than a barrel nut. A nut can fail where the bend cannot. I make my own with some mild steel rod that I got for a song on Ebay but I do use a $4 allen nut from LMII . The use of the allen nut reduces the size of the access hole. So far I have never needed to pull a neck the other way. Just my 2 cents.

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I'm of the opinion that it's better to have it and not need it than to need it and not have it. Besides, the work it would take to install this kind of rod is only marginally more than what it would take to install a regular compression rod. I'm just trying to figure out if the placement is critical. Seems to me that as long as it's off center it would work just like the two-way rods I've been using. I just thought I would ask to see if I wasn't overlooking anything.

I agree the 2 way has advantages. But they usually weigh more and I am trying to lose weight right now. On top of that I don't like the extra cost over a homemade unit ( almost free ) . As a side note, if you induce some back bow then level and crown the frets, you will have a little 2 way ability with a one way truss rod. I have used the 2 ways before and they work great, so I say go for it. Like I said they are cool.

_________________
http://www.cushmanguitars.com/.

A man who carries a cat by the tail learns something he can learn in no other way.
Mark Twain

Mine look like this and are double action.
Left hand thread is on the hex end and the rod is adjustable through the sound hole for a steel string.

If it's like the photo, placement IS critical, the further off the centerline the better. It doesn't work the same as the other two way rods, which curve one way or the other, and take the neck with them. That one works by offsetting the compression caused by string force. If it's above the neutral axis of the neck, making it longer would offset the string force. If it's below the neutral axis, making it shorter would offset the string force, and it would operate as a normal compression rod, with the advantage that it could also be adjusted the other direction to induce relief.

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I have never seen a truss rod like those. How are they installed? What do the anchors attach to? Anyone have a link to installation instructions or a picture of one in a channel on the neck?


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How are they installed?

If you are asking about the ones in my picture the procedure is to rout a sloping 3/16" channel into your neck blank and then rout slots for the anchors. I then backfill the slot with Mahogany leaving only the top of the anchors showing. Some people use a template to rout the anchor slots, some use a CNC. I use a milling machine and I angle the blank to give me a 1/16" drop over the length of the rod. Anchors sit 1/32" lower and the anchor sizes and shapes will vary depending on who is using them.

Tim, yes. That's the kind of truss rod I'm talking about. Benedetto just has the access point at the headstock.

Rodger, that's the information I was looking for. Thanks.