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Christmas eve for me meant that I had about 8 hours of relatively un-inturrupted time to do what I wanted. Namely, finally machine a bandura neck.

This is try two in poplar and I still haven't got all the bugs worked out but I'm getting closer. I probably got within around 5 thou-ish alignment between the 4 sides.

I have christmasy stuff to do now so I'm not going to go into great detail right now but perhaps tomorrow when I have more time.

Enjoy....

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

That's impressive! Nice work.

What are the long tapered pockets under the fingerboard for?

I figured that thing would be four setups minimum. That's no small accomplishment in the short time you've had the cnc stuff, Andy. Nice work.

The vaccum will have varied effectivness with different species....and the holding power is based upon species permeability, surface area, and vacuum cfm. Could be that you're getting marginal on several of those factors. I've never tried to use Poplar but Maple, for instance, because of its lack of pores in the grain, might fool you into thinking it is non-porous yet it is quite permeatble with respect to liquids. Check a 1/4" plate of poplar by soaking one side with water. If within a minute the water seeps through the back it won't hold vacuum very well without a high cfm pump.

If the two-sided tape is effective to hold a part in a given scenario....then another option is to simply apply one-sided packaging tape to the part, blocking all permeability, and then use the vacuum fixture as designed. Accomodate the tape thickness in the program.

Let me spend a minute on this.....using my method, 10-20 hg with almost no cfm WILL pull the tape away from the surface so I use very thin tape and design the vacuum grooves so that there is only .03" depth, an 1/8" or 3/16" groove width, and a constant grid that usually has about 1" spacing. Applying vacuum to the thin tape pulls the tape into the grooves, BY STRETCHING THE TAPE, this is important because doing this locks the whole part onto the vacuum plate, preventing XY movement in some pretty dicey setups. Thin, colored packaging tape is super cheap and works well for this.

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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

That looks fantastic! Nice work. What Stuart said is probably right on. Sometimes it can be hard to pull a vacuum tight when it's sucking right through the wood.

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"I want to know what kind of pickups Vince Gill uses in his Tele, because if I had those, as good of a player as I am, I'm sure I could make it sound like that.
Only badly."

Thanks guys.

The pockets under the fingerboard are there simply to gut some weight. The actual neck will be in hard maple and it gets dang heavy with a chunk of maple that size. I'm just doing poplar for now to test my program. As to the effect on sound - who knows?

It's funny how that machine will do exactly what you tell it to. After spending about 4 hours of toolpathing, fatigue was setting in and didn't realize that somehow my CAM software pulled a spindle speed of 1500 with about a .5" DOC (My hand was pretty quick with the e-stop luckily) and another path where my initial DOC was again around .5" which accounts for the massive tearout in the one section.

I too agree that it's probably that my pump is too low a volume (a bit above 1cfm) for airy woods. I have the same problem with MDF. The other 3 sides worked fine but they were also 2"+ in thickness.

I'll definitely try the thing you recommended Stuart, but I'm not going to re-do my vacuum fixture at the moment as this experience is making me consider pretty seriously a 4th axis and, I'm not sure how many instruments I'll make with this exact neck design. I'll definitely at least try some packing tape with what I have now to see if it will work with the setup I have.

Because this is a 4 sided setup, I zero'd at the table top (fixture top actually) so when I added the carpet tape, I also added some to the bottom of my zero plate. Kind of obvious now after the fact that the zero plate would be stuck to the table and hard to get off in time while the machine zooms to my fixed plate to measure the tool offset.

This has definitely been interesting. I think my alignment would have been even better had I remembered to clamp as well as vacuum when I was drilling the initial alignment holes on my stock. As it was, I was drilling strictly with vacuum clamping and in spite of a low feed rate, you could tell that the stock was moving during that process. Those first holes are my key to accurate alignment for the 4 sides.

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

P.S. - I had a moment and some of that cheap brown packing tape sitting around so I tried it. It worked - sort of. Because of the big open spaces in my vacuum fixture, the tape cracked on me! I tried on the back of a piece of MDF and it sucked it off just like you said it would Stuart.

Perhaps I will re-make my fixture with a tighter grid pattern. Just money right?

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

Yep...it'll pull it right off if the depths are too deep...but trust me...if you get the depths shallow on the vacuum channels I think you'll be pretty happy with the general idea. It lends quite a bit more utility to the standard vacuum plate concept and is particularly useful for highly porous woods.

_________________
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

Andy,

I have to commend you and congratulate you on the great work!!

This looks awesome!

You relatively have had your CNC machine for a short time, and you are now getting great results! You took the plunge, created great looking solidworks models, and now you are making great looking parts!



Aren't you glad you went down the path of CNC machining?

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-CyborgCNC
http://www.cncguitar.com
https://www.facebook.com/CncGuitar

Thanks Cyborg,

I am pretty happy I went to the dark side. The biggest rub is that it re-calibrated what I consider an "expensive" tool

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

...For better and / or for worse. I know what you mean. If you accidentally tell it to mill through a clamp, or plunge full speed into some unsuspecting area of the stock, it will be more than happy to oblige.



This is something I try to keep an eye on. As tempting as it is to sometimes run "just one operation" in the evening, I know I'm less on-the-ball in the evening, than earlier in the day.



Beauteous work by the way.
Keep up the good work!

Nice job Andy! It looks like you were able to get the model worked out and the results are impressive.

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Brad
Avon, OH

Programming that scroll alone was no small task, I'm sure.
Andy, you mentioned 4th axis and I've always wondered if that wouldn't be the best way to approach neck machining.
I use a "pseudo" 4th axis for fret board machining which is basically a trunnion type fixture which allows tilting for inlay angles.
The same could possibly be used in lieu of a 4th axis by manual indexing to 90 degree intervals.
My concern is how the part could be fixtured to allow access to all four sides without repositioning on the trunnion fixture.
Any thoughts on that issue?
Nelson

Essentially, that's what I did. If you look at the shots I posted, you can see I machine the "right" side, then the "left side", then the "Front side" and finally the "Back side", all 90 degrees apart.

It seems that for a guitar neck though that a 2 sided setup plus something for the head stock (if it's angled) should be good enough but, it sounds like you're doing some inlay that's not on the front or back planes eh?

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

http://trunniontable.com/stallion-trunnion-p-1.html

Andy, this is kind of what I had in mind when mentioning the trunnion table method.
The idea would be to machine the neck on all sides with one clamping setup.
Problem is...it doesn't address the headstock angle on a guitar neck.
Nelson

Yes, I've seen but haven't used trunnion tables.

I really think that the headstock angle thing really puts a 4th axis in the realm of 3rd or 4th place for CNC-ing a neck. I still think that a 2 or 3 setup type of thing would be easiest and fastest.

I think the way to do it would be to make an indexed fixture with a spot for the front and a spot for the back that uses indexing pins to keep the alignment right. I'm not really seeing what 4th axis would bring to the table for a guitar neck. With indexing pins and vacuum, you could change sides pretty quickly.

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

I agree with you, Andy. Even the big boys like Taylor fixture their necks similar to what you're doing.
I use a clamp fixture for CNC'ing the headstock tuner holes, outside profile and binding ledges.
It clamps first on excess material at the tail end and also just ahead of the nut location.
The tuner holes are done first and then clamp bolts go down thru a couple of them before removing the first clamps.

Adding to all the comments above, you've come a long way in a short time.
Keep up the good work!
Nelson

If you count the first process as happening on a squared up blank, then you can have a three sided fixture and hit all four sides. My production neck fixture has three setups, and both the front and back sides of the neck are done on the top side of the fixture. Pins are used on all three sides.

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Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

Did I say something wrong?

It's a solid brick of aluminum 4 x 4 x 30" on a big riser plate, the thing weighs 60-70 lbs. Getting it in and out of the machine tends to increase my drive to finally build my 4th axis.

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Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

No, just head slap brilliant.

So Bob I guess you're saying that you would rather use a 4th axis for machining a neck?
Any thoughts on how the neck would be held in the 4th axis?
I assume you would use a trunnion type fixture or maybe just a headstock and tailstock type fixture with nothing connecting them except the neck itself.
Nelson

I still don't get it. What's the brilliant part?

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

I suspect Bob means that he rotates the neck blank among the three faces of the jig for machining but only has to index his router to the jig once.

What BobK said: I only have to index the fixture once, all three setups are on one solid piece, and I machine three at a time so there'd be no benefit to using a 4th axis.

When I looked into using a 4th axis, the elevation required would reduce throughput since I couldn't mount three or four necks on it and still hit all sides without the 'bottom' neck hitting the table. It could possibly be faster if using true 4-axis toolpaths to cut the neck and thus reducing machining time. With the current system I could have six necks in process on my table at once, and my secret sauce techniques only need access to those three sides to work.

Back when I thought there might be a customer for such a thing, I had some special tooling made and coded software to make toolpaths for it. It was stupid fast. Hard lessons about market research.

If I were using a 4th axis, I'd use a trunnion table if I were strapped for vertical clearance. If I had enough clearance to get one neck on top, I'd use a square profile long block vacuum fixture with a different fixture on each of the 4 sides. Either way, I'd make them modular.

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Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

Ok, I guess I did get it as that's how my fixture for this neck is designed. I use G59P8 for the Front/Back part and G59P9 for the Left/Right part.

The fixture itself is indexed to a fence I have mounted to my machine although, something is funky on my because the origin is off by about 10 thou from when I cut it but, I changed my "permanent" fence after I machined the fixture so it could be that my old fence was off by a bit. Too late to check unfortunately.

I've actually been also thinking that if I start getting a reasonable fretboard volume down the road I'll probably make a 3 or 4 up fixture for that as well.

If I do go 4th axis for this I'll probably just hold the stock as I have a lot of machining on all 4 sides. My CAM software will do some basic 4th axis tool pathing as well. I'm going to finish the instrument I'm working on currently first though so probably in the summer some time.

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