That’s a great idea. It would certainly save time.
Also, your point about differing woods has illustrated itself even further this morning. When I came out to my office/workshop this morning, the 2x6 had moved that it was actually a snug fit. There weren’t any major shifts in temp or humidity, so best I can figure is movement of the wood after it was cut and “relaxed”.
So I think the next piece will need to be in hardwood regardless.
Yahtzee!
I had a piece of darnifiknow (though I think it’s maple) that I just got in a lot of hardwoods and exotic smalls and so I set that piece up so I could test fit the neck.
I had to use a little force but not really mash it, and it squeaked its way in. So with that I think the pocket is all set!
I have a bit more design work to do - bosses for the retainers for the back covers (I think that’s what they are called?) a truss rod access route, etc. but after that I think it will be time for a pink foam test. 
I’d like to thank you again for the pink foam suggestion. After trying to figure out the right feeds and speeds, it really goes fast! And a much better way to make mistakes….like……this one:
It’s left handed and I’m not! lol.
Oh and this one:
I got the flip wrong!
It’s ok, though, lessons were learned, and it still has value from a sizing and test bed perspective.
How are you aligning your workpiece after the flip?
Because the only thing being cutout on the back is the cavities, and they don’t have to be perfectly inline to the top, I elected to use centerlines on the waste board
And registration lines for the edges of the slab.
Edit: I should mention here I’m open to suggestions on that too. Obviously this is a big learning process, and while it might not be critical for placement in this build (unless I cut the f holes from both sides to ensure a clean edge), other things in the future probably will. I had looked at doing registration pins or fence but ultimately didnt want to get caught up in analysis paralysis, which I am prone to.
I updated my back and front side files to be right handed and oriented correctly. 
more cutting tomorrow!
I like to leave some of the stock attached with tabs and bore locating holes all the way through so lining up the flip is easy.
Let us know if you’d like suggestions on process for flipping…
So if I setup these hole, and they are equidistant from the center line:
Then I could even tap in dowels before my flip, and that would take care of alignment and flip confirmation, right? And since the holes will already be there, i don’t need to add anything to my corrected, right hand body?
Yes, that’s one valid approach to a two-sided job — the problem is, using center doubles any error, but if the dowels are accurately sized to the holes it should work.
Yep as Will says, it’s all about trying to get the errors to cancel out rather than compound. I might go for a third dowel pin on the centerline above the neck cutout.
This might be more complicated than what you need right now, so pick and choose useful nuggets, what I like to do is
Attach an additional piece of 9 or 12mm MDF as a fixture to work on, check I have a nice solid location to get a repeatable zero at the front left top corner of that fixture board, surface it if necessary. I have a few of these in the offcuts rack which are slowly becoming European cheeses.
Run Job 1 which bores the dowel pin holes into the fixture board, this is run from the fixture board Front, Left, Top Zero, all jobs run from this X, Y zero, if you can all from this Z zero too.
Clamp your stock in position, measured by human, onto the fixture board. Run Job 2 which bores the dowel pin holes into the Stock. Stick the dowels through (no need to move the stock, same zero) and you’re now located and zeroed for your first side op.
Run the rest of the first side toolpaths. If you need to move clamps to make areas available for machining, the dowels will help the stock not move.
Unclamp and flip the part along whichever axis you told the CAD, place it back on the dowels and clamp it down.
Still using the same X, Y (and pref. Z) zero of the fixture board, run the second side toolpaths.
This approach cancels out some of the accuraccy issues that might otherwise occur, we don’t need to know the exact dimensions of the blank, and any small machine calibration errors don’t count. The only error that doesn’t get cancelled here is if the X rail is not fully square with the Y you’ll get errors in the flip. There’s a long post somewhere about squaring and calibrating your machine 
Edit - as you’re working on chunky bits of wood then either short steel dowel pins or wooden dowels would allow you to surface the full blank to correct thickness during your first side ops, to ensure that when you flip all the rear features are correct depth compared to the front.
HTH
I have done several doubke sided items and use the dowel method easy use place on material then when i am ready to flip I zero to wasteboard and put holes directly into my sacrificial wasteboard. One method i will say is i stagger the dowel holes i.e. bottom left top right this also helps placement and less movement.
I just used an angle the last time I tried it and no dowel holes. But I was about 1/64” off in my measurement of the width the material so my sides were off about 1/32”. It took some sanding.
I may try dowels next time.
Hey,
First off… I’m curious! The drawings at the start of this post seem to be for a right handed bass… any idea how it got reversed?
Also, it looks to me like the back is cut for a right handed bass…so the flip might be correct but the front drawing somehow got reversed? (I’m doing mental flipping and may be wrong on that)!
I personally use 2 dowel pins for orientation, both on the centerline…1 above and 1 below the guitar itself.
I also use the center of the work piece as my zero. I only do this when
CNCing guitars. The reason, which I think is very important, is that the body is usually made up of 2 pieces of wood glued together and that seem should be in the center of the gutter/bass (unless the instrument will be painted and the grain completely covered).
So I draw the centerlines on the instrument blank and use a V-bit to get the most accurate alignment over that point. I then jog the machine along the seem and make sure the the seem is still centered at both ends to confirm the seem is square to the machine.
Once that is done, I clamp the blank down and cut all the top cuts including the referencing dowel holes. After that I remove the blank and reset Z-zero only and cut the reference holes in the waste board. Then flip it using dowel pins to reference and cut the back.
Regards,
Lou
Appreciate the thoughts there! There are definitely some bits ill take away from that.
A couple of questions, though.
Is there a reason to bore the holes in place before putting the stock in position? Seems like you would have an even more accurate placement if they were done at the same time? Unless I’m missing something.
yeeeaaah…clamps. I have been avoiding upgrading my work holding to something that isn’t tape and superglue, and its holding me back. I mean so far its worked great, and I haven’t really needed to address that, but it is becoming clear that especially with 2 sided stuff, I need to finally go ahead and bore threaded nuts, or try to get a t-track or similar system going.
Yeah, I know right where it happened. As I have been adding to and modifying the designs, I have moved a lot of things around. And in this case, carelessly. I just started flipping orientations for convenience and didn’t realize the implication.
I really like how this looks, and it really makes sense in my brain, too! I am shifting my wood plan a little bit, thinking more of a bookmatched box elder top over ash slab, so that centerline is going to be super important as you indicated!
Right now im working on figuring out how to shape a forearm contour (not found on the original bass) in the software too, similar to your tummy cut and heel contour. Extending beyond the actual workpiece hadn’t occurred to me yet, so thanks for sharing those images! Gives me another couple of thigns to try.
Edit: Oh, that isn’t CC, is it? Maybe VCarve?
If you want to do that sort of thing in Carbide Create (w/o Pro) see:
I actually picked up pro. I am still going through the vids on the 3d shaping. I figure I will use this until I shift my whole workflow out to something like fusion 6-8 months down the road.
I tend to bore the holes first to avoid having a really deep bore through the whole stock and then into the fixture board. It doesn’t really impact accuracy as your zero is from the fixture board not the stock, so it doesn’t matter when you bore, the holes will be in the same place, or the whole trick doesn’t work
As mentioned above though, you might have some feature of the stock you really want to align, in those cases I tend to use a V bit to score a centerline or other marker on the fixture board to help me place the stock exactly where I want it.
Well, yes and no, you can tape and glue down to the fixture board, just leave gaps for the dowel pins and it’s fine. If you bore a nice tight fit for the dowels they’ll actually do most of the job of holding the workpiece anyway, you just need to keep it down.
On these two part table legs I didn’t use any hold-down clamps at all, just rubber malleted them onto the four pins and used low helix cutters.
In this case there’s no ‘flip’ per se, I machine two halves of the ellipsoid leg separately and use the dowel holes to join them once machined, so I definitely don’t want to bore the whole hole from the top
One handy trick for MDF fixture boards is bore out the holes, wet the inside of the holes with CA glue, set it with accellerant, re-bore the hole, I do this on the reference zero corner too and it leaves a really hard solid fibre-acrylic composite that survives through a few workpieces.
Correct, I’m using VCarve Pro on this.
A couple of other thoughts that may be helpful…
I did program the CNC to do the arm bevel and the body round over but decided to do those by hand. I have a jig I made to cut the arm bevel on my bandsaw and I used my router table to cut the round over. The program showed those 2 tasks taking over 5 hours… by hand it took me an hour.
Any profiles you do on the CNC consider doing them at less than optimum quality, ie higher stepover and less passes. Then sanding out the ridges. On the guitar I’ve showed, earlier the 2 profile cuts, the belly cut and back side of the neck pocket, were done at different stepovers. The neck area would be more difficult to sand so I did it more precisely on the CNC… On the belly cut I did the opposite.
Saves time and wear & tear on the machine.
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