Do CNC guitars dream of electric sheep?

[curtisa]

Been banking this one up for a while, so you'll have to excuse the photodump.

Yet another challenge to set for myself - how much guitar can I make on the CNC? Turns out, quite a lot actually. And even then, I'm not exploiting the machine to its absolute fullest potential. As a side note, the modeling and development time invested in building this on the CNC far outweighs the time it would have otherwise taken me to build this by hand by a good 5-to-1. For one-off builds there's no way doing this on the CNC is faster than using more traditional methods.

Specatronics:

• All native timbers again (my usual) - Redheart Leatherwood body with figured Eucalypt carve top, heavily chambered, 5-piece neck with Leatherwood/Myrtle/Blackwood laminates, Gidgee fretboard
• Headless design
• Absolute no-name, cheap-as-chips pickups from Aliexpress in hum/sing/sing configuration. TBH I've seen several videos floating around where people do various blindfold tests between these kinds of bargain basement pickups and the big guns like Seymour Duncan or Dimarzio, and every time I think, 'actually, those don't sound too bad at all and I think I prefer the sound of them over the premium pickups'.
• Budget headless tremolo, again from Aliexpress. I'm not expecting much from it, and I've also ordered a couple of aftermarket mods for it to help it along, namely a pair of trem stud inserts and a new bar from Schaller. In effect this build is looking ike a sequel to my last documented here, Operation Shoestring.

The willing participants jointed and rough cut on the bandsaw. Yes, I know - I could've done this on the CNC, so I'm already off to a bad start:

 

Here's where the fun really starts. While there's nothing particularly interesting about using the CNC to do the control cavity, where it has been invaluable is that I can mill the interior chambers to take into account 3D features like the belly cut without the fear of accidentally punching through when doing them by hand:

Here's where the interior moulding of the belly cut is starting to appear. The 3D model of this feature is based on a 5mm wall thickness once the matching carve is completed on the reverse side:

The inside is just a series of staircases that approximate the shape of the belly carve. I could spend more time performing more milling operations to smooth out these steps, but this feature will be sealed up and away from prying eyes, so further machining is just wasting time:

Also using the mill to add two locating holes to align the two halves of the body while gluing:

[curtisa]

I'm also milling the interior surfaces of the carve top to match the carve that will eventually be applied to the body, so the interior height of chambers can be maximised and weight reduced even further. Here's the upper chamber being hogged out on the rear surface of the carvetop. Once again I'm shooting for a wall thickness of 5mm once the carve is complete:

Apologies for the washed-out look. In retrospect I shouldn't have bothered with the flash, but hopefully you can just make out the staircase effect of the 'inverse carve':

The finalised interior work. The little chamber at the lower left also has an inverse carve applied to it, even if it's a bit hard to see. The control cavity is deepened to allow for the pot shaft to poke through and an extra ledge added for the 5-way switch. Note also the two locating holes to match the body in the previous post:

[curtisa]

The two mirrored halves ready for a test fit. A couple of 6mm dowels are all that's required to keep things from sliding around once the glue goes down. The pins are positioned such that they either disappear altogether once subsequent routes are added to the body, or they'll be hidden underneath other features. In this case the rear pin gets 'erased' by the tremolo route, and the forward pin is in the middle of the neck pocket:

A quick test fit reveals how close the two halves line up. Here's looking into the control cavity. The line between the pale Eucalyptus and the darker Leatherwood is pretty much non-existent:

Before burying the guitar in clamps and glue there's one more important CNC operation to do - wiring channels!:

Also need to be mindful of where the gluing surfaces are on a guitar with so many hollow parts underneath. With that in mind I'm only clamping around the edges and in a straight line through the middle:

[curtisa]

Next step - make a start on the neck. We start off with nothing much more than 'a plank'. A pretty fancy plank, but a plank nonetheless. This one was a blank I actually glued together several years ago just to use up some leftover laminations, and is only just big enough for this project. I need some way of holding it to the table such that the cutter can get all the way around it without crashing into any clamps. The way I've done it is to screw the blank onto a substrate of MDF from underneath, which itself is screwed to the CNC table at precise a location. The screw holes in the blank are located in the space where the truss rod will be installed, so the temporary holes will  eventually be 'erased'.

At the time I did this work my machine didn't quite have enough travel to do this neck in one go, so you'll notice there are two extra drill holes at the left of the MDF substrate. The intention is to machine the length of the neck in two halves by moving the plate across to the next pair of screw holes halfway through. This kind of work is known as 'tiling'. At this stage all I'm doing is milling the silhouette of the neck:

At the halfway point the neck and MDF plate gets moved along to the second set of holes and the other section of the neck outline gets milled:

[curtisa]

Now I have the outline of a neck complete with the headless 'headstock', I need to flip it over to add the trussrod channel. The trouble is I can no longer use screws to hold it down without leaving behind telltale screw holes that will destroy the appearance, nor can I use hold-down clamps if they get in the way of the cutting head. So one way around it is to mill a temporary holding jig out of MDF to fix the neck in place for the next operation.

A matching 'socket' is milled into a sheet of MDF that the neck plugs into. It's milled to be a tight press fit. There are six screw holes milled into the MDF jig that locate with the same holes used to attach the previous MDF plate, so everything remain inline. The three big holes in the middle are to help me push the neck out of the jig, as there's almost no way to extract it once it's pressed in:

As the truss rod route is a bit shorter than the neck I can fit the whole job into the travel of the mill in one operation without resorting to tiling it:

[curtisa]

Making a start on the fretboard by thinning down a Gidgee blank to 5mm. The sooty skidmarks are probably a good indication that I'm probably overdue to replace the paper on the sanding drum!:

The blank then gets trimmed down to become the target shape and taper before being attached to the neck. This time because the stock is so thin, light and flexible I can just attach it to the CNC table using double-sided tape without worrying about fancy jigs or clamps:

Also taking the opportunity to add a few locating holes to line it up on the neck blank and stop it slipping around under the clamps:

A quick check to see if everything lines up:

Truss rod access has to be added manually on the drill press. Takes a while to line everything up, but only a few seconds to drill:

Then bury the neck in clamps. These particular truss rods are completely sealed except at the access nut, so I'm not worrying about taping over the channel to prevent glue ingress. There's a little bit of tape at the exposed end of the headstock, but that's there more to make it easier to keep that part of the neck clean so I can add a piece of veneer to cover the top of the truss rod channel where it exposes the nut:

[Andyjr1515]

Splendid level of detail here, @curtisa 

Funnily enough, I spent most of yesterday talking to a guy who is designing a semi acoustic bass destined for a CNC router!  My input was about the bass design more than the CNC challenges, but a number of issues you illustrate here came up in conversation - jigging, positioning, clamping.

Following this one

[curtisa]

Yes! Half the challange of doing this on the CNC is working out how exactly I'm going to hold the damn things in place without them either slipping, not being aligned properly or being held in such a way that risks the endmill crashing into the clamps.

It gets better later on. I'll add a few more pics...

[curtisa]

So once the neck comes out of the clamps it's time to focus on the other operations I need to add while the back of the neck is still a flat surface and easy to deal with. The neck get pushed back into the MDF jig and secured to the table. This allows me to add the inlay channels to the fretboard. I'm doing my pseudo-sinusoid dotted pattern on this one, with inlays created from a contrasting piece of timber (again, a Tasmanian native called Cheesewood; very hard, pale and dense):

 

The cutter is a 1mm endmill, at an eventual depth of 2mm. This gives me plenty of leeway when I add the radius without risking exposing all the inlay:

Sadly I don't appear to have a pic of the inbetween stages, but the individual inlay pieces are just milled from the paler piece of timber and then just slot into each of the channels on the fretboard. Sounds easy, but there's a lot of fettling, fine sanding and gnashing of teeth in order to get all these fiddly, fragile bits of wood to go in to each of the recesses properly.

Once the inlay dries it's back to the mill, where the radius can be added. The cutter just zigzags back and forth laterally across the surface of the fretboard inscribing an arc in the Z direction of 16". This is still just a rough radius at this stage, so there'll still be sanding to do to get all the machining marks out of the fret board:

I can also take the opportunity to add the nut slot:

Now this is getting a bit schmancy. Blind fret slots! And cut to match the radius of the board as well. No more grain matching sawdust and CA to hide the fret ends. Oooo, you cheeky devil, you! The cutters that do this are only 0.6mm in diameter, so I have to go slowly and carefully:

A bit hard to see in this photo but I've also added a chamfer to the tops of each slot with a vee bit, which will help each fret sit flush when pressed in. The blind fret slots prevent me from adding this by hand using a needle file, as would otherwise be possible if the slot was cut the full width of the board, so it's the CNC to the rescue again:

[curtisa]

This CNC malarkey means I can do all this stuff bass-ackwards to the way I've been doing it up till now. How about roughing in the neck carve?

I need to hold the neck upside down on the table, but because I've added the radius to the fretboard I no longer have a flat surface to work against, so I need another jig to hold it in place. This one is shaped for the fretboard to plug into it, plus I've added a couple of threaded inserts at each end where I can screw some work holding clamps for added security. The 'Mickey Mouse ears' at each corner of the jig are to allow clearance for the sharp corners of the fretboard to fit into:

This kind of 3D carving results in a pretty rough texture which eventually gets scraped and sanded down by hand. The unfinished neck almost has the appearance of courdroy trousers, as the cutter works up and down the length of the neck to leave behind a surface finish that only approximates the target contour. Obviously I could program up much smaller steps and get a much finer surface finish, but at the unnecessary expense of greatly increased milling time. As it was I think this took about 45-ish minutes. I've also programmed the toolpath to leave behind 0.2mm of material all over, which gives me something to work with when it comes to hand sanding and scraping:

[curtisa]

Time for a wee break from proceedings. The lack of a headstock means any logo I apply needs to go elsewhere on the instrument. The common spot for these headless instruments appears to be just above the neck near the neck pickup and bass-side cutaway. I've seen seen this done as plain engraving (Strandberg) and a decal (Kiesel, Steinberger). I'm going to match this location for the logo, but but I'm going to go for something a bit more wanky in presentation and do some V-carving.

First, some volunteers from the audience. Here's some dark Blackwood and Eucalyptus from the offcuts bin to experiment with a bit:

Step 1 is to engrave the design into the Eucalyptus using a vee bit. It's important that a tapered bit of some kind is used for this operation:

In the Blackwood the mirror image of the design is embossed into the surface with the same vee bit, giving a kind of paper stamp effect. The vee bit ensures that the peaks of the embossing remain crisp and sharp. Each corner of the letters' stroke has a prismatic effect:

After separating the Blackwood mirror from the block the two pieces can be married up:

After a few hours glued up in clamps the excess Blackwood can be planed and sanded down:

Because of the use of prismatic carving, much finer detail can be obtained than by inlaying into channels with vertical sides. With regular engraving the finest detail you can do is limited by the radius of the smallest cutter you have on hand. The only drawback to this technique is that it only works on flat surfaces, If the inlay is sanded back unevenly (eg, on a radiused fret board), the thickness of each of the strokes vary as more or less of the prismatic inlay is exposed.

A bit of danish oil brings out the true effect of the contrast. The whole logo here is only 8mm x 60mm:

 

[mistermikev]

yes dr freud... it says 'aftermarriage'. 

some nice stuff there.  I like the inlay pattern.

[Crusader]

Mind-blowing stuff. I have a brother who does CNC for a cabinetmaking firm. I might have to call round his place with a few beers!

[ScottR]

Did you cnc your electric sheep for the guitar to dream of?

And on a somewhat more serious note, is there, or will there be any camphor left on your fret slots after sanding it smooth?

All in all, this is a fascinating project and excellent display of problem (creating) and solving.

Do carry on and show us more. That fretboard timber looks like it might be a gem in the rough.

SR

[MiKro]

@curtisa

Nice write up. I will say this though, I go about many of the operations that you do in a totally different way. Thanks for sharing, so others may see that CNC is not evil. It is just another tool in the shop, that when utilized can benefit the end result. 

mk

[Norris]

That's fabulous work. It must have taken an age to program. Kudos for such meticulous detail and the well organised logistics to pull it off!

[curtisa]

17 hours ago, Crusader said:

Mind-blowing stuff. I have a brother who does CNC for a cabinetmaking firm. I might have to call round his place with a few beers!

Thanks Based on how long I've spent at the computer setting this up I reckon you'll need a bit more than just a few beers.

[curtisa]

17 hours ago, ScottR said:

And on a somewhat more serious note, is there, or will there be any camphor left on your fret slots after sanding it smooth?

Errrmmm. I'd like to say I planned it perfectly and milled it right the first time, but I may have miscalculated how much chamfer I really needed and sanded all my hard work away and was forced to add it back in by hand by scraping with the corner of a razor blade

[curtisa]

16 hours ago, MiKro said:

Nice write up. I will say this though, I go about many of the operations that you do in a totally different way. Thanks for sharing, so others may see that CNC is not evil. It is just another tool in the shop, that when utilized can benefit the end result. 

Cheers Mike. Yes, I'm sure there are many convoluted ways to skin this computerised cat. I'm largely making this up as I go along and hoping I don't back myself into a corner along the way. So far so good (touch wood).

[curtisa]

13 hours ago, Norris said:

That's fabulous work. It must have taken an age to program. Kudos for such meticulous detail and the well organised logistics to pull it off!

Ta Noz. Modeling and programming this has easily consumed a few  weeks of casual work on the computer. The milling time so far is probably sitting at 5-6 hours (including false starts, tests and making jigs).

[curtisa]

The bridge that's getting fitted to this doesn't come with any suggested routing plans, so I'm having to construct my own as I go. Fortunately it's not too dissimilar in construction to a Floyd Rose, so I can base some of the dimensions on their plans and adjust to suit. This will be a recessed, fully-floating setup. To save me greif I've done a test cut on a bit of scrap pine with the right thickness, plus the neck pocket:

And the spring cavity at the rear:

After refining some of the dimensions and cuts it's time to cross fingers and commit the cavity operation to the body. The leftover slivers of timber at the outer edges of the trem ledge and neck pocket will be milled away once the perimeter is finalised in a separate operation:

The pickup cavities follow, revealing the wiring channels added earlier as they are cut:

Finally, the body gets flipped over and the rear spring cavity can be cut, plus the recess for the spring cavity cover. If I planned this better I would have done the control cavity cover recess at the same time:

[curtisa]

The belly cut is done as a two stage operation - the first just hogs out the excess and leaves behind the staircase approximation of the eventual hape. The second uses a ball endmill to get closer to the final shape while leaving a smoother surface finish that needs a bit of scraping and sanding to smooth out:

Neck screw holes and ferrule counterbores are next. This is getting down to the last couple of operations that I can do while the body still has flat surfaces. The screw holes themselves are only 12mm deep, as the endmill used to create them is too short to do the full depth cut, but with the holes started it's not difficult to finish them off with the drill press:

More crazy-ass jigs. This time I need some way of securing the body to the table that doesn't involve clamps at the edge of the body. This is because for the next couple of operations I need the cutter to have full unfettered access to the entire of the body without clamps getting in the way. The solution I came up with was to secure one end of the body through the neck holes and construct a wooden plug that passes through the trem cavity and screws into the table:

[curtisa]

Starting to get to the pointy end of things now. The top carve adds a cylindrical profile to this build, but the bound edge at the perimeter of the body remains a constant height, so the cyclindrical form constantly changes its radius as the body gets wider and narrower at the extremeties. Once again the carve is roughed out in staircase form before a lateral pass across the full width of the body is added to get rid of the steps:

The perimeter of the body has also been roughed out in the above shots for the top half of the body thickness. I'll then use this cut surface to manually router off the excess for the lower thickness of the body using a regular bearing bit.

 

[curtisa]

Some of the finer details can be added to the top face of the body. Volume pot and controls:

And lastly the body roundover. Because of the constantly changing curved surface of the top, this isn't the sort of feature that could be easily added with a regular roundover bit in a manual router. There simply aren't enough flat surfaces for a router to rest on, and the gently angled surface where the top meets the edge means that a regular roundover bit would leave an ugly gouge around the edge of the body:

With all the chambering and removal of material this body is an absolute feather weight. Out of curiosity I chucked it on the kitchen scales:

That's pretty much bang-on 2.5 of your imperial pounds!

And that gets things pretty much up to date with the progress on this build. That might seem like a pretty quick turnaround on things from start to finish, but the date on the first photo is 1 December 2019, and the last one on the scales was taken yesterday afternoon.

[ScottR]

7 hours ago, curtisa said:

That's pretty much bang-on 2.5 of your imperial pounds!

 

Hold on to it tightly or it might just float away.

SR