FB Radius Jig

[DJ Parker]

Hello To All,

I'm finally getting back into the build and wanted to share my version of a new FB radius jig although I cannot lay claim to these inventions, rather more so my version. The last time I posted I had just constructed the sanding beam track type radius jig. A simple jig that takes a lot of elbow grease and even though I am not high production it still was a pain. After looking at several router based versions I simply built one of my own. Using the melamine parts from an old office desk, the overall 'sled' just slides back and forth with ease. The router is on a plexi-glass base that I draw out on AutoCAD and then a friend cut it on his CNC. This one has a 20" radius.

It works great however on the next cut I think I'll run the thing along the length of the board instead of perpendicular to it just to compare router lines. After this it still goes into the beam track but the amount of sanding is cut way down. I've seen a couple of variations on YouTube as well.

Thanks for looking!

[David King]

Looking good! I see you are equipped for some very wide fingerboards.

[Jason Rodgers]

I dig. A better solution for radiusing is on my list.

So, the 20" radius rails run on bearings?

[Pete Halliday]

Are you just using tape to hold down the fingerboard? Any issues with movement if so?

[DJ Parker]

Thank you all.

The center strip (Maple) that the FB sits on is 3" wide so there is a little room to work with as the widest FB ends up being around 2-3/8" at one end. I use double stick tape and it is very secure. I buy it from Grainger (#9579) and it is about an inch wide and is quite thin.

The Plexi rails do ride on small bearings, cheapies from Home Depot but they work great. The rails which have the radius are bolted together and hold the router base in place that way I can loosen the bolts and use the same base on another set of radius rails.

Regards

[David King]

Ideally you'd be able to radius the fingerboard after it's been glued to the mostly shaped neck.

[Barry Daniels]

Running the router parallel to the neck will leave a much smoother surface than routing side to side. It also takes less time and effort.

[Gordon Bellerose]

Running the router parallel to the neck will leave a much smoother surface than routing side to side. It also takes less time and effort.

+1.
I have a radius jig that works in a similar manner. Mine is certainly not as professional, but gets the job done anyway.
I find routing down the length of the finger board, moving the router a bit to the side, and routing back down the finger board, the easiest and most accurate.

[DJ Parker]

Thank you both!

Yes, I am in 100% agreement with the longitudal option as I sand on this FB. Going across perpendicular left very small ridges but ridges nonetheless. I suppose I will create some incremental stops or use a clamp to simply hold it in place so I can slide it along the length.

I have seen some great ideas about radiusing the FB on YouTube. I like the one where a stationary belt sander is used with a thin radiused block below the belt albeit it looked a little unsafe.

I think that if a person had a shaper that could be an option. A while back, I had a router bit made for the sole purpose of hollowing out the bridge on a gypsy guitar. I sent my CAD plan to this company and for $130 they sent me a professionally made router bit which had bearings and was safe to use provided you used it safely.

I wonder if a shaper bit, and I say shaper because it would be a long bit maybe 3" or more, were to be designed to have a radius on it and have two or three blades it would be just like a heavy-duty moulding making bit. It would cut the radius just like a planer cuts a flat surface. Hmmm, sounds like another jig for future research

Well, anyway...Regards!

[David King]

DJ Parker,
I visited the Ken Smith factory in 1988 in Nazareth, PA. They were using a 12" radius shaper cutter to do all their fingerboards at that time. I first saw the concave radius belt sander in 1986 at Johnny Mørch's shop though I think it's use was already discontinued at that time because it wasn't accurate enough. With so many of us looking towards a conical fingerboard profile it makes sense to research what you really want before you invest heavily in a system that doesn't deliver everything you might need up front. What you have now clearly works well and will continue to do so.

[Eric Baack]

Yeah, the side to side motion leaves some annoying grooves. I did that using my router and a 3/8" box core bit and it took a bit of time to sand that out with a flat beam. I cut it using back and forth cuts because I was hand programming the code.

[Greg Martin]

What a great jig,seems simplified compared to other versions. Ive wanted to build one for some time,but the math to figure the different radiuses etc make my brain hurt. Could you go over the concept and formulas needed? not so much the step by step build but formulas for a 12" radius. maybe it could become a sticky for the math challenged.

[Barry Daniels]

You don't need formulas. Just get a stick, put a nail in one end and a pencil through a hole 12" away and draw the arc. It is really that simple.

[Todd Stock]

Good riff on Marty McClary's radiusing jig - you'll still need separate carriages for each radius to be milled, but def a little less fabrication and good visibility. A few things:

- The nominal radius is NOT the radius of the guide...do the full sized layout of the bearings, fretboard platform, and upper surface of fretboard to get the right radius - it will be larger than the nominal.

- A lengthwise climb cut will do less damage to the edge of the board and leave a much more consistent surface; use a 3/4" bit with a 1/2" shaft for smoothest cut...which means you'll want to use a PC-890 or similar to get the speed and power right for the job. If going to a full sized router, beef up the guides to 3/4" ply and platform to same...the frame of the router will provide a lot of resistance to flex of the router platform.

Attached are .jpg's of the plans I did for Marty's jig back in 2008 or so, plus shot of a board fresh off the 3/4" Whiteside bit. PM with email address if you want the full sized pdf files, but everything is dimensioned in the jpg's for 16" radius.

[DJ Parker]

Thank you Greg, Barry, & Todd,

I appreciate the interest, comments and advice. I am lucky in the sense that I have access to AutoCAD in order to lay out the radius, bearings, router and all the parts to have an accurate sideview of the jig. I understand that any radius is only that particular radius and any movement outward or inward changes the radius. With that said, the radius that I am actually cutting has ended up being 19.578" which for me is fine. Even though the difference in radius on paper is almost 1/2", the actual difference in the cut on the edge of the FB between the two radius's is the size of a hair. After a few swipes on the 20" sanding beam we are right back on track.

Hmmm, I guess really do use math later in life!

Regards.

[Marty McClary]

Hey All, Glad to see my design is still relevant and useful. I made a smaller version to do a whole neck instead of just a fretboard with a harbor freight laminate trimmer. It's a little lighter duty but really does the same kind of job. I've found that if you radius before you taper the fretboard, any tear out will be on the other edges that get removed. Todd did a nice job on those drawings and thanks for sharing those again.