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I know there are saveral "swing arm" machines out there that use large bed sanders, routers, even tablesaws to cut a compound radius.

I have a small shop(don't want to store a big fixture, and don't have a big enough sander), I like the idea of compound radius fretboards, and I do not wan't to sand them by hand with radius blocks.

I came up with this idea: It basically uses to radiused end pieces. When pushed across a router table(at the right angle) it will create a perfect section of a cone.

I also have the fixture tapered, to cut the f/b taper w/o needing to do doublestick tape twice.

The inspiration for this was reading that double bass makers do this by hand with a plane. This is basically the "handplane" way to do it on a router table.

The downside is that is is a little prone to user error. The way I see it if the bit is set to the correct depth(there will be a go-no-go gage built in) there will be no way to bite too much, but if used at the wrong angle a little too much meat could be left on.

If needed I have a touch up sanding block designed.(transparent grey in pic)

Don't know if this explains it easier, but I will basically need to move it across the router bit parallel to each string(which aren't parallel with each other) not an exact science. When doing the middle pass I will move it along the center line, and the outside passes will move along the line of the taper rather than parallel to the centerline.

I'm wanting input. Will this work? Has this idea already been done? If you were building it, how would you improve it?

I also made an excell spreadsheet, based on the stewmac formulas for conical fretboards if that would help anybody.

The spreadsheet was helpful to create the "ideal" radiusses for a given taper--> if you select the correct ratio between radius and taper your fingerboard will have the same hight in the middle and edges of the f/b all along it's length.

Edited by Mike Herr
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So the little red thing is the router bit sticking up from the table?

Looks like it should work just fine - I've seen a similar jig turned on edge and used on a long edge belt sander. If your beam is rigid enough, then the radius "gauges" at each end should only touch the table at one point - like rolling a cone (on its edge) on a table. Yeah you can get the angle wrong as you slide it over the bit, but just take multiple passes and it should even out.

The trick here is designing the end gauges so that the jig can accommodate different fretboard thicknesses while still keeping the beam parallel to the table - you almost want a separate jig just to set the end gauges correctly. Also, a router bit will tend to chip out brittle woods and tear out figured woods unless you're taking very small bites (bit height).

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Thanks for the reply, yes the red thing is the bit.

At first, I planned on being able to swap out the end radiuses, but I think it would be easier to build a seperate jig rather than fussing with alignment/indexing them.

The trick here is designing the end gauges so that the jig can accommodate different fretboard thicknesses while still keeping the beam parallel to the table

Unless, I'm missing something, I don't think that would be a concern. I have it desiged to where the bit potrudes 1/4" out of the table. My fingerboards could be up to .4" think and still work. Yes it would change the radius, but not much, for (extreme)example if you were cutting a 16" radius on a 1/4" thick f/b then changed to a 1/2" thick f/b the radius would just change to 15.75" radius.

Am I missing something? I've built one guitar a couple years ago(not in my shop), and I'm in the tooling/set up phase of my own shop.

I just remember a pain in my shoulder and black boogers from hand sanding a radius into an ebony f/b for the one I built.

Thanks for the chipout warning, I won't go full depth right away.

For those of you doing compound radius' for acoustics what are you using?

Martin does 16" and Gibson does 12", is that correct?

My fixture as designed would produce a fingerboard that transitions from 12"rad at the nut to 16.70" at the 20th fret.

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I have it desiged to where the bit potrudes 1/4" out of the table. My fingerboards could be up to .4" think and still work.

You should be good then.

You could certainly set this up for different radii at the ends, you just need to make sure the end gauges are the same distance above the beam surface along the centerline.

The amount of radius change is variable - I think 10" or 12" at the nut to 14-16" at #20 is a pretty "average" amount of compensation.

This could work really nicely with a vacuum clamping arrangement as well.

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I would make sure make those radiuses end pieces very wide. That way you don't risk cutting too deep on the sides.

If you make them 8" wide, it won't be too big and it'll make the whole process easier.

Personally, I working on plans for a swing arm jig right now. I think your method should work out great as long as you set it up right.

Make sure to upload some pictures.

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Mike,

I have been thinking about a similar process for compound radius. At first I started making a jig to fit around my small belt sander and then I found this planing bit. I figure the radius of the guide needs to be 1/4" greater than the desired radius with the bit 1/4" above the table. Do multiple passes starting with the bit a hair above the table, and gradually increase each pass until you get to the 1/4". I intend to put slots in the guides with bolts holding them to the horizontal board to allow for different fretboard thicknesses, and to allow swapping different guides. It would be pretty easy to make any radius guide you wanted for any compound radius or even any cylindrical radius (using the same size guide on each end). I would like to get that excel spreadsheet Mike, to work out the desired radius at the -1 and 28 fret positions, as that is where the guides will actually be. Could you PM me with it?

Cheers,

Brian.

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I made a quick and easy jig a while back which can be used to make a compound radius as well. Uses a router table. I scrapped it when I moved a year ago I may make another..

This is a very rough sketch.

I am not going to get into details as it would be a lenghty post, but it gives you something to think about. It did work.

The pendulum had a long slot not shown.

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I made a quick and easy jig a while back which can be used to make a compound radius as well. Uses a router table. I scrapped it when I moved a year ago I may make another..

This is a very rough sketch.

I am not going to get into details as it would be a lenghty post, but it gives you something to think about. It did work.

The pendulum had a long slot not shown.

That's a great idea. I was about to make a jig where the router moved over the fretboard, but I this makes much more sense. It'll be a smaller jig too and should be easier to set up. I'm not sure why it didn't occur to me when planning the other one.

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That's a great idea. I was about to make a jig where the router moved over the fretboard, but I this makes much more sense. It'll be a smaller jig too and should be easier to set up. I'm not sure why it didn't occur to me when planning the other one.

Seems simple enough, you have to fiddle with the height if you are changing radius. The pendulum swings inside the box. A miter slot is best as it allows you to easy slide the box back and forth as well as swing. Wedging the box against the fence is less than ideal. I guess you can clamp two boards to the table as guides.

As long as you dont do really flat radius like 16" the box should only be about 14-15" tall.

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That's a great idea. I was about to make a jig where the router moved over the fretboard, but I this makes much more sense. It'll be a smaller jig too and should be easier to set up. I'm not sure why it didn't occur to me when planning the other one.

Seems simple enough, you have to fiddle with the height if you are changing radius. The pendulum swings inside the box. A miter slot is best as it allows you to easy slide the box back and forth as well as swing. Wedging the box against the fence is less than ideal. I guess you can clamp two boards to the table as guides.

As long as you dont do really flat radius like 16" the box should only be about 14-15" tall.

I'm definitely going to be doing this. I'll post pictures when I'm done.

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The swing arm type machines seem to be what everybody uses.

Probably work a little better on a gib sander than a router, but I've heard plenty of people who use router both by swinging the router or swinging the fretboard.

It would have the advantage of being able to easily and accurately change radius.

For me the major disadvantage is having a fairly large thing to store.

Make sure to show us pics when you build it.

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Make sure to show us pics when you build it.

Make a good one so I dont have to redesign another one, LOL

Would like to see what you come up with. I guess after you move your shop and after you build a million other things now that you are going pro.

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Make sure to show us pics when you build it.

Make a good one so I dont have to redesign another one, LOL

It's not going to be pretty, that's for sure.

I have it about half finished now. This is pretty much a rough design to see how it works. I'm making sure everything is precise, but I'm just using scrap wood and table legs to construct it. When I know it works, I'll build a proper one.

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It's not going to be pretty, that's for sure.

I've never built any tool jig or fixture that looked good.

Edited by Mike Herr
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I made a quick and easy jig a while back which can be used to make a compound radius as well. Uses a router table. I scrapped it when I moved a year ago I may make another..

This is a very rough sketch.

I am not going to get into details as it would be a lenghty post, but it gives you something to think about. It did work.

The pendulum had a long slot not shown.

I guess no one searched for this one I made? It will do compound radius as well.

MK

Edited by MiKro
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Interesting the way you adapted the sander style swing arm to the box.

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Interesting the way you adapted the sander style swing arm to the box.
Thanks Spoke

mk

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Thats a great jig there Mikro, wish I had the shop space to build one of these. I still use my radius router jig but it can only do straight radiuses and if I want a compound the board its by hand a horrible and innacurate way but I have no other choice.

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I was thinking about the original post on this thread, and here is some info i went over in my head.

If you slot each radius block this will allow you to lower the fretboard right to the top of the router bit.

In order to slide the piece across a router table you would have to build an aux base to support the jig so you can push it past the limits of the table or the blocks will drop off the edge. This could be based on the swing arm sled where the sled moves as part of the assembly.

The other design aspect is allowing the jig to swing freely. Unlike the swing arm this is not an easy task. My solution would be to incorporate 4 bearings into the sled, 2 attached on each edge. The radius blocks swing on the bearings. You would have to make it so the bearing could be adjusted in or out in relationship to the size of the radius block. My initial thought is to place a spacer under each block then adjust the bearings to the block. That way each block will be an equal height off the table, or sled. The blocks would also have to be aligned to the center of the jig as well during this adjustment.

Here is a rough sketch.

As far as storage the design would be modular. The T which holds the fingerboard is one piece, radius blocks another and the sled another. The difficulty of this design is adjusting the bearrings properly. The positive is it is easy to adjust the fretboard to the router bit. My other idea is to add a long tall bar above the radius blocks which can be used to swing the jig, like the swing arm style only in reverse. Again another modular piece.

Every design has it's limitations as does this one. I think by not having a center piviot point the jig though less complicated would be more difficult to control. adding some type of complicated bottom guide could work to offset this limitation.

It could work.

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Thats a great jig there Mikro, wish I had the shop space to build one of these. I still use my radius router jig but it can only do straight radiuses and if I want a compound the board its by hand a horrible and innacurate way but I have no other choice.

Storage is not really an issue with mine as it is only takes up about a 30"x20"x6" space when disassembled. it easily stores in a top shelf or other upper location out of the way.

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• 2 weeks later...

It does look like a good jig, and I looked at this thread in case there was actually a machine method that would convince me to change from my hand plane. Nope, I'm sticking with my method. The easiest, and I'm certain the most accurate, method of making a compound radius FB is with a hand plane. I wouldn't even think of using a radiused sanding block, as a matter of fact, I avoid sanding in general on guitars. Even on a block, sandpaper is vastly inaccurate compared to a scraper blade or plane when it comes to leveling surfaces. In fact, it really surprises me that a reputable supply house like Stewmac sells so many of them. Not only is shaping a compound radius with a handplane easy and almost mistake proof, it's fast too. William Cumpiano outlines the method in his exellent book. No, for me to change to a machine method, it would have to make a more level, smooth FB than my handplane, and I just can't see (or feel) that happening soon.

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It does look like a good jig, and I looked at this thread in case there was actually a machine method that would convince me to change from my hand plane. Nope, I'm sticking with my method. The easiest, and I'm certain the most accurate, method of making a compound radius FB is with a hand plane. I wouldn't even think of using a radiused sanding block, as a matter of fact, I avoid sanding in general on guitars. Even on a block, sandpaper is vastly inaccurate compared to a scraper blade or plane when it comes to leveling surfaces. In fact, it really surprises me that a reputable supply house like Stewmac sells so many of them. Not only is shaping a compound radius with a handplane easy and almost mistake proof, it's fast too. William Cumpiano outlines the method in his exellent book. No, for me to change to a machine method, it would have to make a more level, smooth FB than my handplane, and I just can't see (or feel) that happening soon.

I like scrapers too. They're also good for shaping when you only need to take off a little bit.

Radius sanding blocks are a nightmare to use, IMO. I never tried using a plane for radiusing. I just figured it wouldn't work. I'll give it a try on a scrap piece. I think a spokeshave would good too.

When you use a plane to radius, do you slot after you do it?

I'm still working on my jig that I mentioned before. I haven't touched it since that last post, but I'll be on it again soon.

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from Brunner guitars was posted recently on MIMF. With the right (simpler) end templates it coud be used for straight or compound radius fretboards (The radius of the template needs to be the desired radius at that end plus the distance from the back of the jig- where the template rides on- and the cutting surface of the router bit.

I think that this design is flexible enough to make it worth the effort building it.

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No no no no no no no.

No!

The Brunner jig will NOT allow you to cut a compound radius, because the swivel axis is not the same as the axis of the cone whose section you are trying to mill. The geometry is all wrong.

It is a fine jig for roughing out the back of a neck, but even trying to mill a constant 12" radius on that thing you would need an arm with 12" of throw, and a really tall bit on your shaper.

EDIT: My bad - I did not catch this the first time around, that the pins around which the arm rotates are not fixed, they are actually allowed to slide.

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Hi Erik,

The throw arm is only a handle - it doesn't determine the radius. The radius is determined by the shape of the end templates. Look at about 28-32 seconds into the video on the top right.

Here are a couple of quick and nasty diagrams which might explain it better - or might not.

Basically, just add the distance "x" evenly around whatever shape you want for each end and that will be the final shape of your neck or fretboard.

If one end template has a radius of 7.5"+x, and the other has say 20"+x, you will get a compound radius. As long as the distance from the edge of the template to the face of the support board is the same on both sides, you'll get even thickness of board along its length.

With correctly designed end templates as it is used in the video for neck profiles, this jig will even do the neck taper, though I imagine very difficult to do fretboard taper.

In my diagrams I have more than 1/2 the circle, but you only need as much of the circle as needed for the fretboard. (If my diagram was to scale, the fretboard would be about 8" wide - the diagram was more for the concept - I did say it was quick and nasty)

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