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I know it’s not as accurate as a table, but I use a trim router with an edge guide for truss rod slots. The problem is it’s just not super accurate as far as lining up. Anyone know of a good accurate guide I can get for my colt?


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Do you have the plunge base? You can attach two edge guides to the same rods; one on each side of the neck. In other words, one pair of rods in the base, but two edge guides attached to that pair of rods, one flush (but not too tight) to each side of the neck. The router will only be able to move in a linear fashion, up and down the neck shaft.

I use a Rockler Trim Router table ($70) with my Colt for truss rod slots. And many other applications. It's accurate and versatile -- and not that expensive. It bolts to my workbench when I need it and stores on a shelf when I don't.

most time the accuracy is in the hands of the operator.
when feeding the machine in what direction are you moving it? This matters a great deal. It has to do with the cut and feed direction. If you guide is on the right hand side , you look about the direction the bit will pull. So if you guide is on the left you feed left to right that way the bit pulls against the guide if you go the other way you have to hold it against the guide and that is dangerous and the bit can run on you.

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John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

It would easy to mount it to a piece of plywood and clamp a board to it for the fence. Clamp the plywood to your workbench. Crude but effective.

_________________
Jim Watts
http://jameswattsguitars.com

All great comments.
My main issue isn’t controlling the cutter, but instead lining thing is accurately. I guess I need to carefully do some measurements and such and scribe some lines on the router base.

This is all coming from wanting my slot to be exactly in the middle of the blank, which is where it should be of course


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Routing the slot is among the first operation I do. I then use the slot to determine the center line of the neck.

_________________
Jim Watts
http://jameswattsguitars.com

FWIW, I use a dado set in the tablesaw. The small blades cut the right shape radius at the nut end as a bonus. I have a saw with the dado permanently in which does nothing but the truss rod slot and and x brace laps...

Use the colt or any other router in a router table with a simple fence. Much more accurate than using a hand held router against a fence.

Another option is a sled using a commercial guide and rail. I made this one for retrofits.

At the risk of sounding like a Captain Obvious type smarty pants, there is some layout math that can help you do the job without buying anything, assuming you don't have a router control problem, but rather have a layout accuracy problem.

1. Take the diameter of the router bit you are using and determine what half that diameter is. Assuming a 1/4" router bit, half would be 1/8", or 0.125".

2. Accurately measure the distance from the centerline of the neck to the edge of the neck that you will use to guide the router's edge guide. For giggles, let's say your neck blank is 3" wide. The distance from the edge of the neck that will guide the edge guide to the centerline should be 1 1/2", or 1.5". Note that your centerline needs to really be an accurate centerline for this to work well.

3. The distance from the inside face of the edge guide of the router to the closest side of the router bit should be 1 1/2" or 1.5" minus 1/8" or 0.125". That comes out to 1 3/8" or 1.375".

4. With the router unplugged, turn it upside down and do whatever you have to do to set the distance from the inside of the edge guide to the closest side of the router bit to 1 3/8" or 1.375". I find that a dial caliper does the trick for me. If I try to use other things, it is not as precise. You will be using the jaws that measure inside dimensions, not outside dimensions. They are the sharp, pointy jaws on the back of the caliper head.

I use this method to lay out and route rosette channels with my Bosch Colt, and it always goes well if I am careful.

Good luck!

Addendum to the above: If your neck blank is of uniform width all the way from end to end, you don't even need an accurate centerline. Just use the dial caliper to measure the width of the neck blank at a few spots, average those readings out, cut the average in half, and use that number for the starting measurement in step 2 above. Subtract from that measurement half the width of the router bit, and that is the distance between the edge guide and the closest side of the router bit.