SIMPLE radius jig (compound or straight)

I'm not gonna say that I invented this, but I've never seen such a simple approach to this task, and in the slight chance that I might be onto something, I plastered my name and stuff on these images. Just picture homer Simpson yelling "patent pending!" and pointing with a squinty glare...

I've seen compound radius jigs that look like a flying trapeze for a router, and I've seen regular radius jigs that are bulky (involving a sled with a radiused bottom that rides a pair of rails). I was trying to think of the easiest way to manipulate a cutter in the shape of a radiused fretboard, and eventually I wondered if I could suspend an enlarged radius just outside the face of the fretboard, and guide it over a large router table. I sat with a pencil and paper to figure it out. Then I came up with this*
http://photos-h.ak.fbcdn.net/hphotos-ak-ash3/s720x720/549808_183141818471974_100003284720671_311571_2961 01446_n.jpg?dl=1

Which works something like this (shown with neck made of scrap 2x4)
http://photos-f.ak.fbcdn.net/hphotos-ak-prn1/s720x720/552459_183142065138616_100003284720671_311572_1070 156074_n.jpg?dl=1

The radii on these jig ends are 1" larger than my target radius (7.25" to 9.5" compound) because my cutter is raised 1" above the table. The faces of the hardwood mounts on these, which meet the neck's back faces, are exactly 2" above the apex of each arc, so the thickest part of the neck JUST touches the cutter. The result isn't ready to play, but with a little sanding, it's still 10 times faster than using a radius block and sanding the whole radius down! I need to make more necks.*

Enjoy :)

Andrew, I didn't know you posted here also! Good to see you, brother!

Been a member for a long time, but rarely post. It's a different kind of creativity on this forum, but in any case, there are many wise ones here. I come to soak it all up. Sometimes I get to offer tips on what works for me, like with this thread.

Wait, now I'm thinking the over sized radius on the jig might not have been necessary... I'm gonna cut a slice out of this neck to see, but I think I might have made this an 8.25" to 10.5" compound radius... I can't wrap my brain around the mechanics. Can anyone figure this out for me?

I've thought about trying to do a compound radius in the past and could never come up with a simple solution - my own or anyone else's. What you've done here is the simplest approach I've ever seen.

Kudos to you! Can't wait to see how it works out on a real neck.

That will work for sure Andrew but the problem is to control the tracking of the cuts as you move your neck above the cutter. I mean you must have some method of constantly moving the job ( or the router, depending on the design) in regular increments as you slide it across the cutting face of the bit. If you just swoosh it across the cutter in haphazard method you'll find the cuts will be all over the place as well.

How do you propose to advance the cuts? Whats controls the direction of the slide?

If you can do it great, but I think you'll find that you will need more than a steady hand, but a good idea!

Wait, now I'm thinking the over sized radius on the jig might not have been necessary... I'm gonna cut a slice out of this neck to see, but I think I might have made this an 8.25" to 10.5" compound radius... I can't wrap my brain around the mechanics. Can anyone figure this out for me?

Just inspect it with a fretting caul of the size you cut.

I think the oversized radius is necessary, but I don't think I could explain why very well.

That's an interesting take on a radiusing jig. I suppose you could make a similar setup that would hold fretboards as well.

I usually take a little off on a belt sander and finish with a radius block but I have been only making one at a time and I don't use a compound radius.

I mean you must have some method of constantly moving the job ( or the router, depending on the design) in regular increments as you slide it across the cutting face of the bit. If you just swoosh it across the cutter in haphazard method you'll find the cuts will be all over the place as well.

I disagree. I think as long as the bit is sharp and your not taking too much material off in one pass, there should be no problem. The cutter should not remove any more material from any one point on the neck than the jig will allow. A good bit and a smooth technique should produce good results in my opinion. All the same, I'd like to see a finished neck.

Thanks for sharing, Andrew!

I shoulda got a pic of the result. It's clean. I'll post it soon- I live away from my workshop.

Great idea, people do the same thing using their jointers - only issue I can think of is you need to have a dead flat router table if you are going to swing it around. Any varation in the surface will be transfered to the neck. If you follow a straight plane (that's tested flat) I reckon you can get a pretty much finished radius - especially with one of these:

http://www.freudtools.com/images/PRODUCT/medium/181.jpg

No reason why you can't get an almost finished surface with a sharp bit - my jig turns out a surface that just needs a quick wipe with some 220 sandpaper in your hand.

You could make some smaller, tighter radius ones to do the other side of the neck too!

Genius! I've used a router table too, but my jig has rails (and it's sloppy overall)
Maybe people use the railed jigs because it's easier to make the rails flat than the whole table..

The geometry works the same. The resulting radius is the radius of the arc minus router bit cutting length as in every radius jig.

Imagine this: your arcs have a radius of 1", same as the router bit height. You would get a "radius of 0 inches" - the cutter would cut up to the center of the imaginary circle and there would be nothing left of the work piece (you can't really do this, but helps to figure it out)

All these jigs work the same - the difference is what is stationary and what is moving. This must be the simplest around. Good thinking!

That's a pretty good idea. The problem is that I don't have a router table that big and a table big enough to do that most likely wouldn't be flat, so the resulting fretboard wouldn't be either. That's my experience with sheet goods today anyway.
I do think it could be a decent way to rough out a single radius prior to sanding block though.

Andrew,
This is a good idea you have and I think there have been some good comments. Here is a similar concept using a jointer table.
http://www.tdpri.com/forum/tele-home-depot/228113-fingerboard-radius-jig.html
I think it might provide a smoother result, BUt, you can do yours without a jointer, which many folks on the TDPRI lack. Nice idea.
Rex

I wouldn't get too hung up on the table being dead flat. Close just might be good enough considering that the wood is going to move a bit any time you remove material, never mind what happens during fretting, fret levelling, movement under string tension, etc.

But not having a large surface is pretty much a deal breaker.

I would consider a sheet of plywood suspect, but a nice chunck of melamine just might yield acceptable results.

Larger, flatter table? What about getting a large sheet of that PRIMO quality plywood from Rockler, the stuff that is like 37 ply and has a baby smooth surface. I bet that is close to flat. Maybe glue dowels protruding from the bottom of it, to sit in index holes on top of your small router table.

Great idea, can't wait to see how it turns out.

Having a larger radius on the guide legs makes sense to me. Looking at it end-on, you'd have two concentric arcs.

I wonder if I could slap a larger table on top of my router table and still get the bit to protrude enough?

One suggestion I'd make, since you've got so much of the bit exposed and it's not buried in a fence or anything, would be to put a short section of plastic tube in the cutout of the table as a safety guard so only the tip of the bit is exposed. Set the tube just low enough to clear the workpiece blank, then you can take several passes creeping up on the bit height until you're cutting in the middle as well as the edges.

If your table is lower on one side by 1/32" than it is in the middle then you'll end up with a 1/32" dip in the middle of your fretboard - and that won't be fixed by a sanding block - the block will just follow the dip.

The trussrod would be able to fix the dip though, or a heavy fret leveling.

Any wooden table surface might be flat one week, but not the next. You'd really need a large, heavy metal surface or a device that controls the distance between the bit that is right next to the bit.

Well, I guess I could try to find a dead flat stable surface... How about laminated particle board (like Ikea uses to build basically all of their furniture)? I buy piles of it from their As Is section, for like $0.50 per board- makes great scrap for jigs and templates... Or since I don't need width so much as I need length for this jig, how about I track down a slab of flat granite, maybe like 6" or 8" wide and like 30" long... Cut a hole right in the middle for the bit... I do haircuts for a couple of contractors, and I bet I could score some scrap granite, if I tried...

...whoops

Well, I guess I could try to find a dead flat stable surface... How about laminated particle board (like Ikea uses to build basically all of their furniture)? I buy piles of it from their As Is section, for like $0.50 per board- makes great scrap for jigs and templates... Or since I don't need width so much as I need length for this jig, how about I track down a slab of flat granite, maybe like 6" or 8" wide and like 30" long... Cut a hole right in the middle for the bit... I do haircuts for a couple of contractors, and I bet I could score some scrap granite, if I tried...

You could try a slab of solid surface countertop material (Corian equivalent). You might be able to get an offcut large enough free or cheap from a countertop fabricator...maybe one of your clients. It should be flat enough, is completely stable, and a LOT easier to cut for an insert than granite.