Les Paul CNC Build

Discussion in 'Luthier's Corner' started by Tweaker, Jan 9, 2019.

  1. Tweaker

    Tweaker Senior Member

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    I've been wanting to build a Les Paul for the longest time and I've had this chunk of 8/4 flamed maple sitting around my house just waiting to become a guitar so it's finally time. I know to you purists, CNC doesn't count as built by hand, but CNC is what I do so I want to utilize the machine as much as possible with this build. To those who drop in and take a look, please be aware...I have about a million questions so please be patient with me as I ask them and seek answers!

    I am pretty close to done with modeling the body. Everything is roughly based off the '59 Les Paul drawings that around floating around. I imported a lot of DXF files and retraced all the contours to hopefully get smoother machining. Lots of the DXF files appear to have curves that aren't all that curved...just a bunch of lines. Which is what a curve really is, but these lines are all 1/4" long, which will make for pretty ragged contours. The top carve isn't perfect and will require some hand sanding to fine tune, but the bulk of it should be taken care of by the machine. So for those CAD and 3D modeling junkies out there, here are a few pics:

    [​IMG]

    [​IMG]

    This next pic is interesting, and all credit goes to @pshupe for the idea. I took the top carve, offset it by 7/32" and made the bottom of the control cavity match the curvature of the top carve:

    [​IMG]

    Clearly, this isn't going to be a 59' replica...but I'm not interested in the replica build, I just want to build something rad.

    So onto some specs...I'm planning on using a 4.4 degree neck angle, which supposedly equates to a 1.2 degree pickup plane angle. The problem I'm having here is that when I draw a line representing the pickup plane, it terminates right around the bridge pickup area, not where the bridge is. From what I've read, the bridge region is supposed to be where that angled plane ends. I guess this is my first question...should I increase that pickup plane angle or decrease the neck angle, or is it OK? When I draw a line representing the top of the fretboard, I'm getting a height somewhere between 5/8" and 7/8" above where the bridge should sit on the body. Here's a picture to show what I'm talking about, it's actually a really bad drawing and will probably confuse you more. But the pickup plane angle is represented by the line right about the bridge pickup pocket. (The line up above is just to close a profile to allow for 3D manipulation):

    [​IMG]

    I went down to Tropical Exotic Hardwoods last week and bought some African Mahogany (not interested in spending 3x as much for Honduran) and unfortunately, I'm having some problems. They sell it really rough sawn, but their 8/4 stuff is closer to 2.175" instead of 1.75" and I figured I'd leave a bit of stock on it so after I planed it, if it moved, I could get it flat without issue. After cutting a neck blank and two pieces for the body, I planed them up and was pretty disappointed to see some fractures that were not visible before planing. First off, the neck blank is almost perfectly quartersawn:

    [​IMG]

    But here you can see the fractures that go fairly deep into the wood:

    [​IMG]

    This is the headstock end of the board, flipped on it's side. I think I will be able to pull off a one piece neck from this one, with a 12-14 degree headstock angle. It looks like those fractures will be carved out, and only good wood will remain. But if I want to do a 17 degree headstock, I wouldn't have enough wood. Which leads me to my next question...could I just glue a piece of mahogany onto the headstock area (much like the construction of the heel of a classical guitar neck) to get the extra depth I'd need? I know a scarf joint makes more sense, but I get a kick out of the CNC doing everything. Would that be an acceptable method to make the neck blank thick enough in the headstock region?

    OK, onto the body wood...same piece as the neck blank, but I only managed to get one half that doesn't have fractures in it. Check these out:

    [​IMG]

    [​IMG]

    What you're seeing is the front and back of one of the sides for the guitar back. Obviously those fractures go all the way through, and it's pretty obvious that isn't OK for guitar use. So, next question...is there something I can do about these cracks that will make this wood acceptable for guitar use, or should I just bite the bullet and buy another piece? I was pretty upset when I saw the fractures but since it's already been milled, I can't return it.

    And while we're on the topic of wood, take a look at the maple top to be:

    [​IMG]

    This was a fairly easy bookmatch...sometimes I have a hard time with the saw blade wavering, but not this time. Very happy about it. I have no idea what kind of maple this even is...it was sold as rock maple. Which could mean any number of things, I guess. I know you guys are all against this, but my plan is to use yellow and brown leather dyes to get a honeyburst-ish color eventually. We'll see. I'm planning on using rattle can lacquer (the good stuff, not the home depot special) or maybe some 2K. I don't care about checking, so maybe the 2K would be better because it would cure faster. That's a ways off so we'll discuss that later.

    Anyways, any advice and patience regarding my questions would be greatly appreciated...there will surely be more questions so stay tuned!
     
  2. Shadow Explorer

    Shadow Explorer Senior Member

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    Great start, cannot wait to see how it will turn out!!!

    You could glue a piece at the end, it wouldn't look nice from the rear though. Some epis have their headtock glued in (not the scarf joint),
     
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  3. jkes01

    jkes01 Senior Member

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    Man, those checks suck. Yeah would be impossible to know they were there in rough sawn lumber. Can’t wait to see more, especially interested in the finish. :)
     
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  4. Tweaker

    Tweaker Senior Member

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    I'm still uncertain about the headstock...I've been trying to find the correct thickness, it seems to be in the 14-15mm range, including the veneer. So I'm thinking if I cut the headstock to 0.5", I should be pretty good once I glue a veneer on. With a 0.5" thick headstock, a one piece neck shouldn't be a problem and I won't need to glue additional stock onto the blank.

    The neck/pickup angles are still confusing me...ultimately I suppose it will depend on how high the bridge can be set up. Maybe I just cut the body out on the machine and if I need to adjust the pickup plane angle I can do it by hand.

    I've been giving more thought on the finish...still planning on leather dyes for the psuedo burst, but I'm torn between classic nitro, polyester resin, or 2k urethane. I like the polyester resin because I can get UV resin (no need for MEKP) but I'm not sure how well it bonds to wood. I found some stuff that is supposed to be formulated for grain filling/sealing: https://www.solarez.com/product/polyester-uv-cure-grain-sealer/

    The stuff builds so fast as well...a pint for $20 should handle one guitar easily. Maybe two, depending on how much of a build you want.

    I use Solarez all the time with my surfboards...I'm pretty comfortable with polyester resin, but the times I've used it on wood, it hasn't made much of a bond. Flakes off pretty easily. I'm wondering if I need some kind of sealer under the resin...maybe something as simple as shellac. But the idea of applying the finish and buffing it out in the same day, without needing to mix in catalyst...it sounds pretty good.
     
  5. DaveR

    DaveR Senior Member

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    Double check that pickup plane angle. 1.2 doesn’t sound right, but it’s been a while since I looked into the specs. Something looks off in the drawing. Pickup routes should be at the same 4.4 angle as the neck I believe. I’ll try to check my notes and plans tomorrow to confirm these numbers.

    I also don’t think the precise angle of the pickup plane is super critical if you’re just trying to build a rad guitar. Draw a line between the end of the fretboard and around the bridge area. That’s your pickup plane. If I remember right that’s kind of how I set the angle on my router planing sled. I’m sure it’s trickier to eyeball something with a CNC...

    I recently made a double cut guitar with a 3 degree neck angle, 12 degree headstock and no pickup plane at all. Gibson scale length, tune o magic bridge and the guitar plays great.

    From personal experience I don’t think I would risk using that wood. If you’re not happy with the mahogany, bite the bullet and find another piece. I deeply regret forging ahead with a substandard piece of African Mahogany on my double cut build because the rest of the guitar turned out so well. By the time I was done, I had so much time and money invested that the wood was just a small portion of the overall price.
     
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  6. bluesriffdev

    bluesriffdev Senior Member

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    Looks great. I know the top isn't meant to be an exact replica, but it doesn't seem quite right. Flattens out way too early + the actual bursts (unlike current USA Gibsons) had an arch that actually went concave slightly and then back up level with the binding. I think this slight concaveness occurs outside of the control cavity area... if that makes sense.

    What program are you using to get such nice wood renders for the two different materials?
     
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  7. DaveR

    DaveR Senior Member

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    You were right about 1.2 degrees for the pickup plane, but the pickup routes should match the neck angle. I measured the bridge height on mine and the strings sit right at about 5/8" above the body, so I think you're gonna be way too high if the top of the fretboard is already higher than that. Something doesn't look right in the side view drawing. Like either the neck angle is too steep or just not deep enough in the body? I would go back and reconfirm all those dimensions before committing to cutting.
     
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  8. ARandall

    ARandall Senior Member

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    Neck angle and pickup plane are dependent on the guitar.....but anywhere from 4-4.5 deg will work. You just have to sit the bridge at 15mm off the top give or take and work with the actual thickness of top wood you have. Of course you can manipulate the angle a bit to get the bridge to sit much lower on the body should you choose.
    The pickup plane is based on cutting from about the bridge line to where the fretboard end is. That will depend on the neck angle and top thickness, so it is done secon.....and it is what it is for the guitar.
     
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  9. valvetoneman

    valvetoneman Senior Member

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    if you aim for 8mm above the bridge with a straight edge on the neck with no fretboard you'll be fine and have a nice neck angle, i don't like really high bridges personally

    I also don't think the pickup plane is 1.2 but more like around 1 or slightly under, i use a copy carver with a top mapped from a 56 and tweak to taste, i think my neck angle is around 4 degrees but that's not important the bridge height is which i physically measure anyway, as mine is all by hand nothing is really set in stone

    The thickest part of the cap is under the tailpiece i think which i aim for around 60mm to start before sanding
     
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  10. Tweaker

    Tweaker Senior Member

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    So, the top will only be roughed out on the machine. My plan is to fine tune the carve, especially closer to the binding with the subtle concave. It is all based on the carve templates from ExNihilo that are floating around. Each step is 1/16" above the previous, leaving 3/16" of uncarved maple at the bottom. I am using Fusion 360 for everything...modeling, rendering, and eventually CAM. I just use the maple and mahogany materials that already exist within Fusion.

    So this brings up a question...how deep should the neck pocket actually be? I've been reading that 1.5" deep is the generally accepted depth, but where is that measurement taken? It seems like if the pickup plane angle doesn't match the neck pocket angle, I'll have a pocket that is 1.5" deep in one area, but deeper/shallower in other areas.

    I'll mess around with the pocket depth and shoot for that 8mm figure at the bridge. Should be easy to model in Fusion...keep making the pocket deeper until my line representing a continuation of the fretboard meets a point that is 8mm above where the bridge will sit.

    Work is keeping me pretty busy lately so I haven't had much time to get into the model and make changes. I'll update when I have changes that seem to make more sense. I also need to buy a new piece of mahogany for the back. Once I get the body modeled correctly, I'll model the neck, and actually cut the neck before I cut the body. Then when I go to cut the body, I will cut the neck pocket just a hair too small, and check the neck fit. I can then run the neck pocket operation again, but offset by a thousandth of an inch, and keep doing this until the neck pocket is big enough for a perfect fit.

    This way I can't really screw up setting the neck. That's my biggest concern of the entire process, to be honest.
     
    Last edited: Jan 14, 2019
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  11. DaveR

    DaveR Senior Member

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    The bottom of the pocket sits at that same 4.4 degree angle of the neck plane. The bottom of the pocket is parallel to the top of the neck (picture this without a fretboard). The pocket is 1.5" deep (measured from the maple top). The top of the neck surface should be flush with the maple cap in the area where the fretboard is going to sit (meaning the tenon is also 1.5" tall.

    You are correct that the pocket depth (measured from the top) won't be consistent for the full length of the tenon, but only at the very end of the tenon, under the neck pickup. Since the pickup plane starts at the end of the fretboard, the pocket will technically be shallower where the neck pickup sits, but this doesn't matter because you notch the tenon for the pickup anyway. The depth of the pocket should be a consistent 1.5" from the front end of the body to approximately the front of the neck pickup route. The maple cap needs to be good and flat where the fretboard overlaps it or you could have gaps.

    I think most of the hobby builders around here cut the neck plane first and then the pickup plane. If you think of this as sequential operations, it might be easier to understand. Trying to picture how all these angle relate to each other on a finished guitar is a bit mind blowing.
     
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  12. fretman_2

    fretman_2 Senior Member

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    Got a model of the neck?? I've got a model more or less built, but am struggling with the CAM part of Fusion 360. Onward and upward!
     
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  13. Tweaker

    Tweaker Senior Member

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    OK I think I have a better grasp of how the top carve works now, thanks Dave. If I'm understanding correctly, and if I'm simplifying the carve correctly for the sake of explanation...the tailpiece sits on a flat plane (maybe not flat due to top carve, but for all intents and purposes, its flat for now) and the bridge might sit on a flat plane, or it might barely just sit on the edge of the pickup plane. From the bridge, the slope is 1.2 degrees down...a subtle slope, until it hits the end of the fretboard, where the slope becomes steeper at 4.4 degrees.

    And if I'm understanding this all correctly, and in order for the binding to be consistent, the 4.4 degree slope terminates at the point that will leave 3/16" of maple behind, where the neck meets the body (16th fret, I believe). So the neck pocket should sit 1.5" lower than that point on the maple cap. Am I close?

    Regarding the neck model...not quite there yet. Haven't had as much time as I'd like to mess around with it. I'm still debating on what headstock angle I want to use, as well as the headstock thickness. I don't want to go any thinner than 1/2" I think..

    My thoughts on the headstock angle are leaning towards something in the 12-14 degree range, as it'll be a one-piece neck and I want to minimize any weak spots in that area. I'm also planning on including some kind of volute, though I'm not sure how extreme I want to make it. Maybe with a shallower headstock angle I don't need to worry about a volute?
     
    Last edited: Jan 15, 2019
  14. pshupe

    pshupe Senior Member

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    Exactly. Think of it the other way though. Start your neck plane at 3/16" above the top and route at 4.4 degrees until it exits the top. Mark out where your fret board ends, from the edge of the body (16th fret) toward the bridge. Start your PUP plane a little beyond that line and it also exits the top at a certain point, usually around the bridge location. The tailpiece generally sits on the flat portion which is at the top full thickness of 5/8" above the body joint.

    This is where I used to use a box jig. I set the angles on the box jig then the starting points mentioned above.
    box-jig side elev.jpg

    I just finished up a neck model for my SG, with a friend's help. Let me know if you want some help with tool paths. I have that worked out as well and could send you the

    The head stock angle is probably great at that 12 - 14 degrees. I would go closer to 12 personally. Too shallow and I find the string pressure at the nut not that great. I used 11 degrees for my Firebird and, although I haven't tested, it's seems pretty good.

    Capture2.JPG

    Capture.JPG

    I doubt you would "need" a volute. They would be handy for the vintage truss rods because of the big access route. I would suggest using a double action truss rod with a allen key adjuster. That way the access route can be very shallow. Strength of the neck also depends on neck thickness / profile at that location as that is the thinnest part of the neck and the deepest route for the rod.

    Cheers Peter.
     
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  15. DaveR

    DaveR Senior Member

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    Sound right. Keep in mind if you cut your binding channel the same way the as vintage LP's, you'll have a little sliver of maple cap visible BELOW the binding in the deepest part of the cutaway. There are tons of pics of that all over this sub-forum.

    Figure out what tuners you want to use. There is some range of adjustment, but not a whole lot.

    I just finished an LP build with 17 degree headstock and another guitar with 12 degrees and a volute. Both had 3 piece necks and probably didn't NEED to have a volute. Even with a 1 piece neck, I really don't think a 12 degree headstock needs a volute, and while it could be beneficial to have on a 17 degree, it's obviously not necessary. I added one for kicks, and like the way it feels, but it's not needed. I'm glad I didn't add a volute on my LP build because it would not have fit in the LP case that I bought for it. Another minor thing to think about.

    Keep in mind the access hole for a traditional truss rod gets bigger the shallower your headstock angle is. From 17 to 12 the access route is almost twice as long, and requires a custom fabricated truss rod cover in my case. While I've never used one, I think @pshupe is right about minimizing the size of the access with a 2 way rod, plus I wish I had used two way rods on my builds.
     
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  16. cmjohnson

    cmjohnson Senior Member

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    Since you're not going for replica level authenticity, consider a few changes. For one, the 17 degree headstock angle is the reason why Gibson headstocks break so much. If the guitar falls over the back of the headstock is going to strike hard. Ease off on the angle somewhat if that idea appeals to you. I've done as light an angle as 11 degrees and it comes out great. It also looks more elegant to my eye. No issues with sustain or string pressure across the nut. In fact it seems that the slightly reduced pressure helps the string to not bind in the nut slot, improving tuning stability.

    I've never done a neck tilt angle as steep as 4.4 degrees. I think the most I ever did was 3.5. Since most of my builds are more PRS-ish, a 2.5 degree angle is my standard angle.

    I also cut my cavities perpendicular to the top plane, so there's no skew between the pickup hardware going into the body and the pickup cavity. This requires me to set up the body on the mill table with the body supported at a 2.5 degree angle.

    If I were to CNC my tops I'd leave them pretty rough because I want some room to make adjustments when I do my final shaping with a random orbital sander.
     
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  17. Tweaker

    Tweaker Senior Member

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    Right, so some progress on the neck. Got it modeled, not perfectly, but naturally I want to leave some room for hand sanding :laugh2: I ended up modeling a 12 degree headstock. After reading through a million posts and especially what's been posted here, 12 seems to be a good number. I left room for a 3/16" nut (apparently that's the Gibson size? Not sure why Epi is 1/4" but whatever) and I'm going with a true 24.75" scale length. I don't care about the rule of 18 or 24.625" or whatever...not going for vintage accurate!

    [​IMG]

    As you can see below, the headstock transition is fairly sharp, but I expect to smooth that off with some sanding.

    [​IMG]

    Here's the real money shot of how not-sexy the transition is. Pretty clunky, but room for fine tuning by hand. I hope.

    [​IMG]

    You can also see, I didn't model in a volute...having never played a guitar with one, I thought it best to build a guitar after the manner in which I'm used to playing. So no volute. The neck isn't going to explode on its own, and I've never dropped a guitar so I think I was overthinking the neck break scenario...more than likely not going to happen, so why complicate the build. Now, regarding headstock thickness. I think I'm going to go with the Golden Age keystone style tuners: https://www.stewmac.com/Hardware_an...e_Keystone-style_3_and_3_Tuning_Machines.html

    I think these will look nice and I don't care about brand names anyways. The headstock is 0.55" thick, so then with some kind of 2-3mm veneer, I think that should be about right for these tuners.

    So, with all this neck business, I'm about ready to go back and mess around with the neck pocket and change any angles there. I haven't done much research regarding the neck angle and what impact it has on the guitar. All I know is the neck is angled because the top is carved. I chose 4.4 degrees because that's what I see floating around the web as a common angle...sounds like maybe it isn't the best option.

    @cmjohnson I think you have a pretty good grasp of what I'm up to...the CNC is doing the bulk of the work, but leaving a lot to be fine tuned by hand. The top is for sure not going to be right coming off the machine, but it'll get me close enough and prevent me from making any tragic mistakes!

    Also...I still haven't picked up any new mahogany. I might have time tomorrow to get some.
     
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  18. pshupe

    pshupe Senior Member

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    About neck angle - all you are really concerned about is bridge height. Check the section in Fusion and draw a line along where the string path would be then mark out the bridge location and height and that is what determines neck angle. Here is a example for a flat top but it is the same principle for a carved top.

    [​IMG]

    Cheers Peter.
     
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  19. fretman_2

    fretman_2 Senior Member

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    Transitions between the headstock and profile, and profile and heel give me problems in Fusion 360 too. I too just made them sharp and I'll scrape and sand them to a curve.
     
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  20. Tweaker

    Tweaker Senior Member

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    I use pretty much only the loft and combine features in Fusion. The actual neck profile is the easiest part...draw an ellipse, rotate it 90 degrees, and loft it to the next profile. The heel was a little more tricky but I really like how it turned out...shouldn't need much fine tuning, to be honest. It's mainly the headstock transition that will need the most work.

    Didn't have much time to work on the body tonight, I'm hoping to get pretty close to done with the body tomorrow though. If it all looks good, I can probably cut the neck this weekend. I'm always a little hesitant to cut the neck because with several ukes I've done, the neck would warp a bit after being cut and I'd have to cut a new one. I suppose I may as well just cut the neck...if it's gonna warp, it's gonna warp.
     

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