Prs Style Control 'dents'

[ArieBombarie]

Hi there, I'm buidling my first guitar (LP-style, mahogany body and neck, Zebrawood carved top)

I want to add 'dents' around the controls like on PRS and (some) ESP guitars.

here are some pics to show you what I mean by 'dents'

My question is simple: what's the best way to make these dents? any ideas?

Grz Arjan

[Acousticraft]

The easiest way to achieve those counter sunk hollows is to grind a spade tip wood drill of the correct diameter so the corners are radiused evenly. Mount in a drill press and drill them at a slow speed.

Practise on some off cuts before you try it on your 59 Les Paul.

[hooglebug]

or a cove router bit.

[Prostheta]

To make a recess with a radiused inner edge, and a flat base to seat the nut/washer/bushing, you can rout it out a number of ways.

One process is to work out the overall diameter, base diameter, and the radius of the inner edge. A 1" diameter recess with a 1/2" flat base would need a 1/4" radius (or greater...see below) round-nosed bit, and a few Forstner bits.

Firstly mark up a cross with a central point. Use a Forstner bit to cut to the base of the recess (in this example to a depth of 1/4"). Take a piece of thick clear Perspex and do the same - etch in a cross and cut it with a larger sized Forstner to the outer radius. With the etched reference marks on the bottom face of the template, align this onto the workpiece and use the round-nose bit with a (in this example) 1/2" bearing to follow the inside of the template, and work the radius down until the nose of the bit reaches the depth of the first hole you sunk with the Forstner.

This would leave you with a recess which enters the body perpendicular to the face of the workpiece however. You can use a round-nose bit with a radius larger than the depth of the recess so the edge isn't at 90° to the face although you will need to create a larger diameter hole in the template, a larger corresponding bearing and the template may need to be thicker or to sit further off the face of the workpiece.

Another method is to drill the holes for the controls that are going into the recess and use a coving cutter router bit with a bearing on the bottom (the same size as the drilled hole) in a drill press. Slowly lower the bit until the bearing enters the drilled hole and very very slowly allow the coving bit to create a dish. The slower speed of a drill press compared to a router means that advancing the depth slowly is the name of the game. Clamp your workpiece securely. I wouldn't use a router for this, as it's asking for trouble having both cutting edges are engaged in the workpiece with a fairly large bit. Having a guitar spin around and whomping you in the stomach or having the bit's shank break at high speed is bad news.

Just my take on this.

[avengers63]

Having a guitar spin around and whomping you in the stomach....

That gave me a great visual - like something straight out of The Three Stooges. Good chuckle to start the day with.

That 'cove bit in the drill press' is a good idea. I'll have to give it a try.

Edited June 24, 2008 by avengers63

[Prostheta]

That wasn't my idea originally however, so i'm not taking credit for yacks due to whomped stomachs!

[madawgony]

The method I have used on two builds was the cove bit in a drill press. Although the cove bit does not work well with the relatively slow drill press speed; it tends to tear instead of cut. Alot of sanding was inlvolved to finish them out.

I achieved a decent result but I am going to try other methods.

Using a forstner bit to hog out the depth and then followed by a radius bit to roll the top over works, but it leaves you with the sharp transition at the bottom of the cavity.

Grinding/sharpening a spade bit sounds interesting, I think I will try that method.

[CrazyManAndy]

There is a video on the net showing a guy using the cove bit/drill press combo. It's been posted here a couple of times, you might be able to find it with the search function.

CMA

[ArieBombarie]

Thanx for all the suggestions, I'll be testing them out on a piece of scrap wood....

If search the forum again and came across some earlier posts on the same subject (funny thing is, I couldn't find them before as there is no agreed upon term for these dents/holes/thingies, I've search for "cove bit" and they poped up!?) They all seem to agree upon the methods used. Couldn't find the video though :-(

thanx again,

Grz Arjan

[Blackdog]

I tried the cove-bit-on-drill-press method, but it has a tendency to tear a lot (it's a big bit at low speed) as was mentioned. Another problem with this method is that you're limited to the size of the bit: speed knobs are 1" diameter, a cove bit of 1 1/4 leaves a barely noticeable effect with the knob in place, and that's a big bit already.

The method of cutting the flat bottom with a forstner and then use a roundnose-top-bearing bit with a template works best for me. The cut is much cleaner and with the proper template you can make dishings of virtually any size or shape. Not exactly like the PRS but still a very nice effect.

[SwedishLuthier]

A template on top of the guitar works but only if you haven't started to arc the top. I prefer to arc first, I then use a cove bit with beatrign in my pillar dril/mill combo. Works nice with some minor tearing.

[Mattia]

I've done it by hand/freehand before, and it's OK, but I think I'd be tempted to get one of those 'drill router rasp' type bits, ball shaped, and rough it out with that. Clean up with sandpaper. Might be worth a shot; the bigger issue with router bits in a drill press is that a drill press is too darn slow. Clamping a plunge router in place in a 'router thicknesser' type jig might work too.

[Blackdog]

A template on top of the guitar works but only if you haven't started to arc the top. I prefer to arc first, I then use a cove bit with beatrign in my pillar dril/mill combo. Works nice with some minor tearing.

That is true.

But you can always suspend the template over the body, there are many ways for this, like with thicknessing jigs as Mattia mentions.

In my carvings I leave a flat area at the center of the top. My template is long and has the hole for the dishing at the end, so I clamp it to the center of the top and leave it suspended over the controls' holes. Works well for me.

I might still try the grinding and sharpening of a spade bit, though.