The New Fingerboard Compound Radius Jig

[LedBelli Bass]

A couple of months ago I had a thread up discussing my current fingerboard compound radius jig and looking to brainstorm a new, improved version. That thread generated a lot of discussion, but little in the way of new ideas. Here is my own design that is the product of my day-dreaming since then.

The idea is to have as few moving parts as necessary. The old jig always left me feeling insecure, like I was always on the verge of an accident. On this jig, the only thing moving on each pass of the router IS the router. Much more secure and much more repeatable.

Accurate and repeatable . . . that's paramount.

This jig will radius a fingerboard up to 36" long (for concept basses with full-length fingerboards).

There are still a couple of bugs to work out, and I have not tested it yet . . . probably tomorrow.

The fingerboard carriage is made from 3/4" quartersawn Oak. The "twist" of a compound radius is induced . . .

The sled is removable for access to the carriage. It sets on the guide pins pictured:

 

[Beej]

I can't wrap my mind around this, but I get the feeling the answer's obvious. How exactly does it work to produce the compound radius?

 

[tdogg]

that thing is spectacular. i was thinking of something like that to radius a bass body (a la Warwick). it would be cool if you could make interchangable side plates so you could do different radii

 

[tdogg]

ok silly question: what is holding the fingerboard down? double sided tape? magnets? magic?

 

[LedBelli Bass]

ok silly question: what is holding the fingerboard down? double sided tape? magnets? magic?

Magic . . . double-sided magic tape!

 

[LedBelli Bass]

I can't wrap my mind around this, but I get the feeling the answer's obvious. How exactly does it work to produce the compound radius?

In much the same way as my former jig, only on this one the carriage twist is induced by the carriage bolts guided in the radius channels. The Oak carriage "twists" as it is guided left or right.

The radii on each end are different. On this jig it is 15" to 23" compound. One end of the jig is channeled to a 15" radius, while the other end of the jig is channeled to a 23" radius.

Keep in mind, I have not tested this yet. This may be a perfectly good piece of firewood before we are done!

 

[tdogg]

sounds like a feasable idea. what are some manufacturers that use compound radii?

 

[JC Basses]

A piece of art! Are the end radius templates able to be taken off and changed for different sizes? That would be sweet because you can do any compound radius or just a regular radius.

 

[DBC]

Of the top of my head, Nordstrand, Lakland and others but I won't say if I am not sure and of course "LeBelli (ha ha)!!" I can't pop off the others You would be suprised of who does and some that you would think would and don't. I think the major part is the production mode. I trickles down to the fret and leveling process also.

To get low action a awsome playing bass it is all worth it !!!!

Thank you LedBelli, You're too COOL!!!!


Dino

 

[LedBelli Bass]

sounds like a feasable idea. what are some manufacturers that use compound radii?

On wider fingerboards a compound radius is almost compulsory if one is wanting a fingerboard with a radius of <15" at the nut. The wider the fingerboard at the 24th fret, the more necessary it becomes to flatten the radius so as not to feather the edge of the fingerboard.

 

[LedBelli Bass]

A piece of art! Are the end radius templates able to be taken off and changed for different sizes? That would be sweet because you can do any compound radius or just a regular radius.

If this prototype works, then I will do exactly that, Jared. For this one, I glued the end-caps into place. that can be easily undone if I wanted to.

For now, I'm setting up for a test piece tonight. Stay tuned!

 

[Jonny B]

subscribed.

 

[LedBelli Bass]

Okay, I did a 16" long test piece and things did not go so well.

One issue I anticipated (earlier reference to bugs to be worked out): the weight of the router creates too much deflection when passing over the center span. The milling showed clear evidence of this. Worse, the deflection varied with each pass, creating "grooves" of varying depths, depending on how much of my own arm weight I rest on the router. Clearly, this will need some major attention.

One issue I did not anticipate and that I'm still looking for the source of: the test piece tapered in thickness, getting thinner as I milled toward the smaller radius. I thought I designed an allowance into the radius crown heights to take care of this; will need to double check.

Will be doing some more tinkering, but I think I'm on the right track. As far as the "security" of using something that is locked down and lacks all the moving pieces of the old jig, this is a vast improvement.

 

[LedBelli Bass]

I've determined that all of the issues described above are the result of the deflection of the carriage under the load of the router plus arm weight. In other words, the bed of the router "floats" up and down to a much greater degree than I originally took into account. With the right amount of arm weight, as much as a 1/32" !!!!

So, tomorrow . . .

 

[praisegig]

I've determined that all of the issues described above are the result of the deflection of the carriage under the load of the router plus arm weight. In other words, the bed of the router "floats" up and down to a much greater degree than I originally took into account. With the right amount of arm weight, as much as a 1/32" !!!!

So, tomorrow . . .

Couldn't you put 2 saw kerfs into the rail and mount w/screws pieces of 1/2" aluminum/mild steel angle, to stiffen the rail? Might be an option...........

 

[stoo]

Gotta love simple solutions to complex problems!


How many different positions do you have to move the fingerboard carriage round to get a smooth curve to the radius?

 

[LedBelli Bass]

Couldn't you put 2 saw kerfs into the rail and mount w/screws pieces of 1/2" aluminum/mild steel angle, to stiffen the rail? Might be an option...........

yes, that is one of the things I'm considering. Whatever I do, it needs to be zero deflection, <.005", preferably better than that.

Gotta love simple solutions to complex problems!


How many different positions do you have to move the fingerboard carriage round to get a smooth curve to the radius?

^^ Each pass is about 5/8" wide, so depending on the fingerboard width you can figure around 6 positions total.

 

[stoo]

^^ Each pass is about 5/8" wide, so depending on the fingerboard width you can figure around 6 positions total.

Won't that leave "corners" though? Or is there a fair bit of further finishing done afterwards?

 

[Stone Age]

That is genius!

 

[Eublet]

Of the top of my head, Nordstrand, Lakland and others but I won't say if I am not sure and of course "LeBelli (ha ha)!!" I can't pop off the others You would be suprised of who does and some that you would think would and don't. I think the major part is the production mode. I trickles down to the fret and leveling process also.

To get low action a awsome playing bass it is all worth it !!!!

Thank you LedBelli, You're too COOL!!!!


Dino

Pete Skjold uses a compound radius on his boards. From memory it's 12" to 18", so it's fairly subtle. I asked about the jig he used around a year ago in one of the Skjold mega-threads, and one of his fans posted some pictures of it there in response. I would imagine they are still out there somewhere if you are looking for ideas.