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I have a CNC Shark Pro Plus and I have been messing around with "slab" bodies (No contours/carving) and was looking at the time involved in machining and it is far greater than the time involved in making a template and cutting it out by hand. My question is this has anybody else had this dilema? I understand that the attraction with the CNC is that you program it and all you have to do is baby sit the thing and it should be the same every time, but on something like this is it worth the wear and tear on the machine?

Thanks in advance!

David Maulik

Well, it never took me long to cut out the profile of a body with a saw and then shape it with a four-in-hand rasp, file, and then sandpaper.

However.... the point of using CNC is that it is repeatable within the dimensions you wanted. Plus, you make one setup to cut the profile, pickups, and other hardware - knowing that they are all perpendicular and parallel to the world. Adding any rounding over or carving via kellering techniques is just icing on the cake.

So, don't limit yourself - or sell the machinery, and use the money for more tools, supplies, and materials. (or put the money in your pocket)

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"Act your age, not your shoe size" - Prince

A Les Paul has a 42 inch perimeter. At 200 IPM, 1.5" DOC, you're looking at 24 seconds plus 5 seconds each for the spindle spin up and down on the plunge and retract. If you have a hobby machine and need to baby it then you're still only looking at 2-3 minutes on a machine that'll do 200 IPM.

What's the rush? I can't put blanks together with double stick tape fast enough to a feed a machine at that rate! Add that to consistent feed rates, and no human error even at 2AM and you're golden.

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Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

A couple of thoughts here. First, one of the biggest advantages to CNC over my old jigs has been space--those jigs can get big and my shop is small. With CNC what used to take up a couple of big shelf units now fits on a thumb drive. Plus if I want to make a change, it's easy--I don't have to make yet another template.

Bob brings up the second point--you can cut solid bodies in that amount of time IF you have a heavy duty machine that will cut at those speeds. For that kind of machine, you pay the price. The Shark works fine when used within its limits, but that means running shallow passes and slow feed rates to avoid having probleme due to flex of the frame and unsupported rails. Rapids on a Shark are slower than the feedrate through material that Bob based his calculations on. The Shark will get the job done and done well, but it requires more patience.

So I think it's a tradeoff--pick and choose what you want to do with he CNC and what could more practically be done the old way.

I've made a lot of slab bodies with my CNC machines. What I see as the beauty of CNC is that you can "customize" things so easily. For instance, I have a tele and strat Gcode file for the perimeter and neck cut. I have modular Gcode files for various pickup routs and control cavity options. It is just a matter of mixing and matching options into a new word file to get a tele with a strat neck and trem rout.... Yes you could make templates for all that, but that is where the advantage of CNC comes into play. I've done some carved top LP std bodies and corresponding necks as well. I believe if you want to speed up things, use 2d drawings and gcode for simple tasks and save the 3d for the carving. I have an archiac version of Bobcad to generate 2d g code and I will generate a file to do one depth and then copy and paste that file multiple times and change the depths of the cutter in the Z....it is really not the modern way to do it, but it works for simple stuff. I can have a body ready for drilling,sanding, and roundover in a half hour or so at 50 ipm

To me a real benefit using cnc comes when making holding fixtures. As often as possible I will design a multi-purpose function into the fixture. For instance, The fixture I use to hold necks during the top opertaions on the necks also doubles as a half of my fretboard gluing caul. Then, the fixture that holds the headstocks for one operation also doubles as a drilling jig for a later operation...ect.

I developed a vacuum plate that functions for ten discreet body operations....everything from planing the raw, flat panels that comprise my bodies all the way through to the final placement of drill holes for the bridge....done after finsihing. Once all the neck operations are done this plate is set up on the machine and often stays there until the entire guitar is complete.

Body operations on the plate:

1. Several joined, bookmatched panels are planed prior to gluing.
2. The back outside panel is cut to produce the edge profile.
3. The front outside panel is cut to produce the edge profile.
4. The back inside panel is cut to produce the chambers, wiring channels, and registration features.
5. The front inside panel is cut to produce the chambers, wiring channels, and registration features.
6. After the two-halves are glued the back gets its finishing operation.
7. The front gets its finshining operation....neck fitting occurs here.
8. After the finish is applied the back gets a few cuts to open the electronics cavity and create a fit for the string block.
9. The front gets the bridge mounting holes drilled and the fit to my pickup rings is established.
10. The nut is fitted.

This is all done in one setup with the exception of having to set tool heights for these various operations. The plate is made with several registration features that allow the body to be held in place by removable blocks which constrain the outside perimeter. Then, after finishing, a different set of blocks is used which account for the added finish thickness.

Anyway...the idea is to cram as many operations into one fixture as you can.

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I read Emerson on the can. A foolish consistency is the hobgoblin of little minds...true...but a consistent reading of Emerson has its uses nevertheless.

StuMusic

It said 200 IPM on the ad I looked at, maybe I was looking at a different machine? My second calculation (3 minutes) was at 200 IPM with a 1/4" DOC. You can scale to taste, but I'd rather have the machine spend ten minutes on something than me spend two. It never complains, or gets tired...it's the perfect apprentice.

A neck or an LP carve would be quite the operation on a 50 IPM machine- that has 'go have a nap and come back later' written all over it. I have a webcam and remote desktop software on my control PC, so I can watch it on my phone if I'm feeling paranoid. Design 'watch the machine run' out of your workflow for any toolpath you've run before.

And, Stuart, you are such a tooling nerd. You probably get more excited about your new fixture or process than you do about the end result. I know the feeling. We would have the longest talks if you lived here.

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Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

I think that 200 IPM is probably pretty close on the rapids on the Shark Pro Plus, but it's not stiff enough to cut at this speed. It doesn't like to cut as deep as 1/4" in a pass either for the same reason. Cutting something like the perimeter of a solid body in wood as hard as say poplar, from the experience I had with the machine with a 1/4" cutter, running at 50 IPM or so at 1/8" DOC would be more like it. Might be able to do 75 IPM.

It cuts fine if you take shallow passes and a slow feed rate, but the combination of unsupported rails and plastic construction make it a fairly un-stiff machine. It's really designed for making signs in softwood, and it is very well suited for that task. I've used one for making fingerboards and things like that in ebony, and it also worked fine. You just have to take it slow.

I have a heavier machine now and can push it pretty hard...

Dave

I just took a peek at the machine on the rockler website. That machine looks similar to my k2 2514 only obviously with a wider work area. 200 ipm sounds a bit fishy with what appears to be lead screw drive and those smaller steppers. I'd be afraid of losing steps at that rate even on a rapid. The construction of it looks like there is some plastic sheet involved too, which between that and the unsupported rails, makes a slower cutting pace necessary to achieve some accuracy.... It's a hobby machine and would make most general woodworkers envious. That said, you (like myself) will have to pick and choose what your machine can do well. Mine has close enough tolerances for bolt on guitars but it isn't as easy to try and make set neck tenons fit bodies like a $50,000 machine might. Again I'd suggest you try more 2D stuff, as it will be less time consuming and save the 3D for other things that might not take as long.