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Well, I've been making banjo parts on the CNC for a little over a year now. It's been working out really well, and I've learned a lot about CNC, Rhino and MadCAM in the process. Many thanks to the folks on this board as well as over on the CNC forum for the assistance--I don't know how I got by in the pre-Internet days! Anyway, I've built some archtops in the past "the old time way," with lots of elbow grease involved. Tendonitis in my elbow has kept me from doing much of that kind of heavy carving in recent years, so I decided to try it out on the CNC.

I modeled a 17 inch archtop guitar in Rhino and wanted to do a proof of concept on the CNC to make sure that my MadCAM tool paths worked out like I thought they would. For my test top, I scaled the entire model down to tenor uke size--I've always wanted to build an archtop uke. I did my toolpaths in MadCAM, and today I did a couple of test runs on some cheap pine. I'm quite pleased with the results. Once I sand the surfaces down, I'll be darned near right on final thickness. I'll still have final plate tuning, recurve scraping etc. to do, but it's darned good right off the machine. I'll try it in real wood in the next week or so.

On other fronts, I've been making a lot of custom banjo bridges--the CNC sure makes cutting those out a lot easier! Still quite a bit of handwork to get them where I like them, but I've worked up some new designs that let me do a lot of EQ on the tone fairly easily. They've even been selling well, and that's always a good thing! I've also added a 4th axis to my XZero Raptor machine--I hope to be able to do things like tailpieces using MadCAM's 4th axis capabilities.

Anyway, here's a picture of today's experiment. The tap tone is actually pretty good, especially considering it's "shelf wood" status....

Looks excellent, Dave. What sorts of tool paths are you using? Raster type of thing or a morph thingy?

How about some pics and info on your 4th axis? I want to add one after I'm done with my current instruments, probably late summer. I was planning on using a sherline 4th with a tail stock for Bandura necks.

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Thanks Andy! I'm using a facing type tool path for roughing out, and then an X axis raster for a clean up cut. I've attached a picture of the first time around--I've cleaned up the tool paths since then and taken care of the rough edge--a little boo boo in my measurements....

I'll try to get some pics of the 4th axis in the next day or two. It's a really simple one--a stepper with toothed pulleys driving a Taig mill headstock. It has a 2:1 ratio between the stepper and the axis--not nearly as fine a ratio as something like a rotary table arrangement, but plenty fine enough for what I'm doing. Plus there's no backlash at all. Mainly though, it was simple and cheap. If I end up using it enough and find it wanting, I might upgrade sometime but for what I'm doing with it, I think it will be fine.

Dave

That sounds like an interesting idea for a 4th. If you grab the headstock and try and rotate it wi the stepper powered up, are you getting any movement from the belt?

I'm thinking that I'll be able to do the sherline 4th for under $600 since my g540 already has the spare driver. Don't know how bad e backlash is but I've heard from a couple sources that the Sherline rotary table is a really good value.

_________________
http://www.birkonium.com CNC Products for Luthiers
http://banduramaker.blogspot.com

If I grab the headstock with the stepper powered up but at idle, yep I can move it fairly easily. The 2 to 1 advantage quickly overcomes the idle current holding power of the motor, especially when coupled with a 4 inch chuck. But, when the motor is moving, I can't stop it or make it miss steps by grabbing the headstock. I'm not sure how it will do if I use it for indexed work, but it seems to be fine for simultaneous 4 axis. Time will tell. The Sherline would do better in holding without a doubt.

I have read on other boards that the newer Sherline rotary tables have not been up to the quality of earlier ones, but I don't know whether or not that's the case, but might be worth taking into consideration....

Dave

Eeeenteresting on the Sherline quality. A buddy is a long time dealer and I think he has some that he's had for a couple years. I'll have to buy one soon.

I am planning on using my 4th for indexed work so your plan might not fly for me. Perhaps with a bigger ratio though?

_________________
http://www.birkonium.com CNC Products for Luthiers
http://banduramaker.blogspot.com

ball, just wanted to let you know to get ready to upgrade to Rhino 5.....so you can soon use madcam 5! I talked with Joakim today and I will be getting my beta version soon to wring out to try to find bugs. Hopefully of course I will find none but that is why we do beta testing. You can hear the excitement in Joakims voice when talking about all the differences between v4.3 and v5 of madcam.

When the v 5 comes out, I hope to do a little guitar parts demo. Hopefully by then I will have a machine worthy of a video!

Mike

Shoot, I'm just now finally getting halfway decent at V4! I'll be interested in reports on the differences--that'll be up to you turmite! In the meantime, here are a couple of links to super exciting videos I made yesterday after work. Mahogany plate being cut....
http://youtu.be/LLG_c8XVS-Q
http://youtu.be/TTSWnX6oKsk

Dave

Do not worry,
everything you know about V4 will apply to V5,
only you will have a lot more!
It is easy to go from V4 to V5 but if you have to go back from V5 to V4,
it almost makes one cry!
I use V5 daily, but teach V4 once a week, and that makes me really wish that
McNeel would publish the V5 officially really soon!

Guess I'd better start saving my pennies!

Rhino 5 beta is free for all V4 license folders,
just use your serial to download it from Mcneel site.
You can have both at the same time on one computer, they are independent that way.
It is Very stable and totally usable, only it has to be re-installed every month.
It cannot be bought actually before it is officially out.

Well in the past couple of days, I've cut a real back out of super hard old mahogany and then hand graduated it. I've also cut a real top out of Englemann Spruce--I'll graduate it sometime later in the week. The toolpaths are working out great, and the plates come off the machine requiring very little hand work prior to assembly--just enough to take out tool marks and tune. I've left enough wood in my model to allow for quite a bit of variation in wood--there will always be plenty of hand carving before it's ready to go. Anyway, here are a couple of pics of the effort to date.

Dave

Looks great Dave. I have a question for you. How did you fixture the top when you machined the inside of the plate as I can see it has already been carved? Did you build a vee for it to sit in, or did you use some sort of risers? I ask because I have to highly figured bearclaw tops to machine in the not too distant future, and that of course will be after some tests!

Mike

ps what step over did you use for your finish pass?

Thanks Mike! On this one, I fixtured using wedge shaped blocks on the underside, then made sure I had everything leveled up good before I cut. For my full size guitar design, I have things arranged to cut pockets on the top in the corners, the ends and outside the waist that leave .25 inches of material at the bottom. Then I can flip the material over, block the plate up using the pockets I just cut and know that the flat back surface is going to be level and well supported. Then I can flip it back over and machine the outside surface. I think that's the way to go since it makes cutting the inside a self-leveled operation. . I like doing the outside surface last so that I can cut F holes from the top without removing the top from the machine after doing the top surface.

I used .0631 for stepover on the finish pass--it's what madCAM defaulted to with a .5 cutter, so I tried it and it worked fine.

Dave

Nice job on the contouring. You've got a great eye.

What steps did you take when drawing that up. Or where did you learn the process?

Thanks! When I drew this up, I drew up a 17 inch guitar. I decided that to test my processes out, I'd shrink the 17 inch model down to a 10 inch wide tenor uke or tiple body. So with the exception of the height of the plate and thicknesses, the whole thing is 10/17 scale. I left a bit more height than that, but not a whole lot. I scaled 2D, then scaled Z separately.

For drawing, I did what I guess is the "usual" thing and built a wireframe with contours that basically came from the Benedetto book. A little different, but close anyway. Then I started applying surfaces, tweeking the wireframe and reapplying surfaces. Most of my modeling techniques on this one came from a video I got from guitar3dcad.com. Good video. Past that point it's been good old handwork the way I've always done things.

Got the X brace glued and shaped yesterday. I just glued the back to the sides earlier today. The first CNC-started archtop is well on its way. Considering that the body that I'm gluing up today was a stack of lumber on Tuesday and that I only get to work in the evenings is pretty amazing to me. Without the CNC roughout, this would have taken me weeks. The handwork goes pretty quickly when the bulk of the hogging out is done.

Dave

Another couple of progress pictures. The second one shows a different use for the CNC machine--manual binding machine. In this picture, I'm just using a flush trim bit, but for instruments like archtops where the sides are the same height all the way around, using the CNC as a good solid overhead router with micro adjusting depth control is pretty sweet.

The first picture shows the assembled uke body. Not bad for 5 days worth of evenings I think. Time now to cut binding channels and scrape the recurve. Then it's time to model and cut a neck and fingerboard....

Dave

Nice work, Dave!
Interesting idea on using the CNC for binding rabbets.
Do you feel that the guitar body can be leveled well enough to ensure consistent binding rabbet height?
Regards
Nelson

Thanks! I haven't had any problems leveling the body (I level to the seam between the plate and the sides). But, as in the case of any fixed overarm router, the downside is that if for some reason you slip, the only direction the cutter can go is farther into the material instead of having the cutter move away from the cut. I guess I could work out some kind of stop that would keep this from happening, but it's pretty much the same deal as with a Safety Planer on a drill press--hold that wood down tight to the table!

Dave

Here's a link to the update/finale' of the archtop uke project: http://luthiersforum.com/forum/viewtopic.php?f=10101&t=36414

I am happy with the results.

Dave