My Curved Truss Rod Channel Jig

IceGator8

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The thing I've been worried about the most in my build is cutting a curved truss rod channel. I've considered using a dual action rod which is much easier to install but I wanted to have a go at a carving the channel for a vintage rod. Keep in mind there are folks on here who have used a vintage truss rod with straight channels with success.

I got the idea for the jig from this thread on TGP:
Calling Out to Builders…Favorite Jigs, Templates, Tips & Techniques - Page 5 - The Gear Page

Our own Roman Rist and Jack Briggs participated in the thread. The thread is full of all kinds of great tips and examples of jigs. I modeled my jig off pic Scott Lentz posted about halfway down page five. Thanks to Scott for the pics.

Also Roman gave me the idea about bowing the truss rod to trace the template in an older thread about this very subject. Thanks to Roman and also BCR Greg who have given tips along the way.

So here's the jig:
Les&


The construction is simple. You need a planed board about 30" long, 8-10" wide, and about 3/4" thick. I found some poplar at my local hardwoods store that fit the bill nicely. You mark where a few frets are for reference points. Then you take your truss rod and bend it a bit while you trace the shape of the bent rod into one side of the wood.

To shape the curve of the rod into the board you could use a band saw but I chose to use my oscillating spindle sander. It took me about ten minutes to rough out the curve with the spindle sander. I then finished it off sanding by hand.

The other piece of wood you need is something to mount the hold-down clamps. In this case I found some scrap maple at the wood store. It's perfect for the job. I got the clamps for five bucks each from Harbor Freight. I'm not a fan of Harbor Freight but for things like the clamps it's good. I screwed the maple onto the poplar like this:
DSC00802.jpg


I put the neck on the jig and used it to help place the clamps. I made it so the clamps touch the neck on parts that will eventually be cut away. I screwed the clamps into the maple and the jig was done.

Here's a good top view where you can see the curve in the board in relation to the neck:
DSC00793.jpg


One of the biggest pains of this project was finding an arbor long enough to mount a 3/16" slot cutter at the proper height. Most arbors are 3" long which isn't long enough. While I was at the tool store I eyeballed a router bit that was a little over four inches long and had room for two cutters separated by a bunch of spacers. I think these types of bits are used on moldings or something like that. I asked the salesperson the price of the bit and he told me it ran around $160. Yeeeech. It turns out I was able to buy the just the arbor and a bunch of spacers for around $30.

I bought a 3/16" slot cutter with the arbor and used the 7/8" bearing that came with it for the new arbor. When I set up the new arbor I found I didn't have enough spacers to reach the threads at the top of the arbor. Without more spacers there would be no way to tighten the locking nut of the cutter. I ended up buying another 7/8" bearing as a cheap way to add another spacer. Here's what the cutter looked like when I finished putting it together:
DSC00804.jpg


Here's how the whole thing works. The 3/16" slot cutter/arbor is mounted in the router table. The bearings follow along the edge of the jig that has the curve of the rod. As I get into the middle of the jig the curve of the jig gets deeper. At it's deepest point this setup should cut a channel of 1/2". I can manipulate the depth a bit by pulling the neck closer to the edge of the jig or pusing it back. you set the height of the cutter so that it hits the centerline of the neck.
DSC00806.jpg


I did some preliminary testing today on some scrap before I had to go do Christmas eve stuff. It cut the channel great but burned the wood a bit in the process. I'll fine tune the speed of the router to get rid of the burning. Another slight problem is that I either didn't get the clamps tight enough or I need another clamp because the test piece drifted backwards a tad. This is a minor problem that I'll get fixed in the next day or two. Oh the 3/16" slot cutter didn't cut the channel wide enough. I can either buy a 1/4" slot cutter or I can widen the channel a bit by cutting the center and then raising the router bit a little and cutting again. Of course you would then need to take the same amount off the bottom of the channel.

That's it. I hope this helps anyone who is struggling with the mystery of the curved truss rod channel. Feel free to ask any questions that you have.
 

pvt

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I think that if you used your table saw to first cut a 1/8" straight slot with a depth slightly shallower than the final desired depth, it would help with the burning, as well as the problem of the neck tilting back while making the cut. Maybe double-side tape the neck to the jig in addition fo the clamps for some extra insurance.
 

IceGator8

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I think that if you used your table saw to first cut a 1/8" straight slot with a depth slightly shallower than the final desired depth, it would help with the burning, as well as the problem of the neck tilting back while making the cut. Maybe double-side tape the neck to the jig in addition fo the clamps for some extra insurance.

Two very good ideas! I will experiment with the speed of the router first to see if I can eliminate the burning but if not I think the table saw would be a great way to start.
 

IceGator8

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So I had a chance to test the jig. Above I think I mentioned that I was experiencing burning when cutting the channel. Well I'm here today to take my lumps. Why? I had the cutter facing the wrong direction. No wonder there was smoke in the garage.:applause:

Today I figured it out, turned the cutter over, and tested again. Perfect.

Here are some pics:
DSC00812.jpg

DSC00818.jpg

DSC00819.jpg


The deepest part of the channel is exactly 1/2".
DSC00823.jpg


The truss rod fit in the 3/16" channel perfectly:
DSC00828.jpg


DSC00833.jpg

DSC00834.jpg


My only question is if I got the channel deep enough on the headstock end. When I measured it's slightly deeper than 3/8"

DSC00830.jpg


Now I'm going to make a maple fillet that follows the exact curve of the channel.

Well there you have it. Hopefully this helps others who want to use a curved truss rod channel on their build. Please feel free to ask questions or give feedback.
 

pinefd

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Great job! And yes, having the cutter facing in the wrong direction can indeed be a problem (lol).
 

lexluthier72

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Hey I saw this on your Blog! I was wondering what spacers you used on the router bit. I located the arbor, but what width spacers are you using to "stack" the bit. Do you have the amana part number for the spacers? I'll be building one of these shortly....Also, any idea on the depth of the slot on each end of the neck?
-Erin
 

monsterwalley

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Hey I saw this on your Blog! I was wondering what spacers you used on the router bit. I located the arbor, but what width spacers are you using to "stack" the bit. Do you have the amana part number for the spacers? I'll be building one of these shortly....Also, any idea on the depth of the slot on each end of the neck?
-Erin

My first time with the same set up I stacked washers as spacers. I knew better but was in a hurry and it was late. I got the nut good and tight. I knew I would have a little vibration and was taking a chance but did it anyway. It worked fine until I measured the slot. As I started the cut, the nut got tighter and consequently my slot ran out a good sixteenth of an inch off center. I ended up gluing a filler strip in and redoing it after I had my local machine shop make me a spacer.

If you have a machine shop local, that'd be my answer.
 

lexluthier72

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I found the spacers through Amana. 1/4 wide steel...They are on order. Now, I just need to know how deep the slot is supposed to be at both ends, and in the middle.
 

IceGator8

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Looks like you answered your own question. Yep, the spacers are Ammana. I have no problem with the setup. It cuts a perfect slot.
 

lexluthier72

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Hey IceGator....Do you know off hand what the depth of your slot was when finished (at the ends, and at the middle)? If I get those measurements, I can use the "bent rod" method of layout. =)
 

IceGator8

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I simply don't remember! Sorry about that. I would go measure off the jig but I'm currently in the process of buying a house and all that stuff is in storage.
 

lexluthier72

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Cool. No Worries. Hopefully someone else chimes in. =) There has got to be other folks on this forum who have done this.
-E.
 

lexluthier72

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So...I found this drawing, and printed it, and measured it. (it printed full size!) At the nut 3/8ths, at the 7th fret 1/2", at the 19th fret (end of truss rod) 1/4". Hopefully this helps the next guy!
-Erin

LesPaul-styletrussrod1copy.jpg
 

scott lentz

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I see you have your fixture up and running! I have used this set up since the early '80s. The first depth mesurements I took off a 1969 L.P. when I replaced the neck. Over the many years I made several changes. I've taken several different gibson necks apart and found the dimensions vary from model to model. The important thing to remember is the the filler must fit exactly to the rod and the slot and filler width must not be to tight as to remove the glue when installing or to loose as to not hold the rod in.
 
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captcoolaid

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Okay total newb question why the curved rout as opposed to a straight rout.
 

LC100

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Okay total newb question why the curved rout as opposed to a straight rout.
Pretty reasonable explanation on the differences here. Can use that as a baseline for digging up more on the pros and cons of each.
 

bruce bennett

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very nice jig, and very well made.
heres my down and dirty cheap version of routing a curved bottom slot

DSC00757.jpg

DSC00756.jpg

DSC00750.jpg

DSC00761.jpg
 

Bob1

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Oh I like that version Bruce!

I think I will try to make one similar to that when I have time.
 

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