Louie Atienza's semi-automatic proportional archtop jig

[Nelson Palen]

Wait, we want to go too!
Read "would be good if you can post the new thread here"
Thanks guys, I enjoy reading your posts.

[Greg Robinson]

Mike and Louie, please don't take it offline, keep it here!
There are many members interested in CNC, it's implementation and applications, and I'm sure everyone would appreciate seeing what the two of you have done with it. A new thread would be the best place for the new topic.
Thanks!

[Louie Atienza]

I guess we're staring a new thread then! Coming up...

[Steve Senseney]

Good!!

[Greg Robinson]

Thanks Louie!

[Mario Proulx]

I'm not into CNC, but damn, I'd sure like to understand what this thing here does. Sorry, but I still don't get it. A video would surely set off the "ah-ha!" light, but maybe just a few better pictures and captions? I have no clue what is following what, where, and how. What's that frame thing above the router for?? What defines the arch? Where the missing axis?

I'm the guy that typically sees one photo of a tool or jig and understands it completely and almost always can see an improvement right away, then heads out and builds his own version. The fact that you've totally stumped me with this one says a lot!!!

[Louie Atienza]

Mario, I'm in negotiation for a Les Paul inspired guitar, so I might do a video then. In the mean time, I hope can explain more.

The jig works like a Duplicarver, in that a guide, which are the two long straight edges at the front bottom of the carriage, follows the arch templates, which are the two ipe pieces. The templates are shaped in the cross section of a cycloidal arch. These templates angle variably, according to the position of the follower. The follower's location is determined by the position of the top, which is attached to a matching tempate, and rotates center on a pin.

To operate the jig, you'd set the depth of cut, push the follower into the top template, and move the carriage back and forth. Rotate the top a small amount, and repeat till done. Since the carriage can only move back and forth, on center relative to the body, when the follower 'sweeps' the arch templates closer to parallel with the carriage guides, in the 'eyes' of the carriage it 'sees' the arch as foreshortened. Conversely, when the follower is pulled toward you, the arch templates become more perpendicular to the carriage guides, and 'elongates' the arch in the 'view' of the carriage. So, think of it as an infinitely variable radial duplicarver!

The bar on top is strictly for reinforcing the long carriage, as to not make it bulky and heavy, looks and weight...

[Mario Proulx]

Now I get it. Your photo sequence is confusing, and not clear at all, so I wasn't "seeing" what moved and didn't move, and how.

What's the advantage over a typical duplicarver, other than not requiring a "master" plate?

BTW, you'd gain a lot more stiffness if you triangulated the uprights; even a small cable or wire would suffice.

Oh, and how did you decide where the "center" of the plate would be? Appears to be right in the waist, but that isn't the lengthwise center, is it?

[Louie Atienza]

I tried to explain it the best I could, really! Sometimes it's crystal clear in my ming, but conveying to text can be tough...

I did include a sequence of photos that show how it operates step by step. But obviously, to do this without a wing man can be tough, and subjecting my camera's shutter and lens to wood dust may not be the best idea. I guess the pics were more for posterity's sake, but decided to share them, as I thought it could be of benefit to others. I am the originator of the concept, but I don't mind sharing it either.

The triangulation was supposed to happen. I could have used wood, but I wanted to do pipe, and there was no other arvhtop projects coming up, so you could figure out how that goes! But I like your idea of using cable; easy to implement, lighte than pipe or wood, and the option of making the tension adjustable!

The "pivot point" of the plate is dead center lengthwise, along the center seam. This pushes it away from the waist. However, it can be placed wherever one wishes; I think it might be of benefit to have the pivot center of the waist, which would make the upper bout a bit 'tighter' and the lower bout by the bridge a bit 'looser', which might be good soundwise...

[Nelson Palen]

Louie, it took me a while to understand this one also but now I see it as sheer brilliance. Some of the greatest inventions, I believe, start out as less than fancy construction and leave room for plenty of improvements. The brilliance, however, lies in the underlying concept and the "out of the box thinking" that goes into that concept. You're probably going to tell us that this design started taking shape on a napkin?

[Louie Atienza]

Nelson, your complements make me blush! But really, I had a couple ideas. Originally there was only one template and guide, but it would have been mechanically complex, and not reproduceable by someone with modest means. Adding the second guide made it so simple it was almost trivial.

I think the ironic thing about it is that I've built the jig about a hundred times in my mind before making it (without any drawings), and only made two tops with it since introducing it in the previous forum almost a year-and-a-half ago. What I DID write on a napkin were the dimensions I needed so the arch templates still clear the body template when swung to their max. That gave me the width I needed for the jig to ensure the arch templaes were fully supported by the tabletop.

In hindsight, I think I built this more to humor myself, that what I thought of in my head could become something simple, yet functional. I did use it for the last electric instrument challenge we had. Going from flat to arched and sanded took about an hour. I still have the first top, which was for a revisit of a nylon string archtop, this time non-cutaway, what I was to started to concentrate more on the care of my mom before she passed. I want to explore the use of the jig for carving the inside.

The big downside to it is just that - it's big! Though, for someone whose shop does many archtops that wouldn't be too much an issue. I keep mine leaned against a wall. The small downside is that it'll create some chips. But interestingly, I'd estimate about 60-70% of it would pool toward one area, so drilling a hole or two on the table surface itself for dust collection would be a huge improvement.

[Samuel Hartpence]

It took me a while to understand it as well, but after looking at the photos and description while thinking about the application I got it. Basically the best way I could describe it is that the two vertical or slope guides are coupled to each other and the "pointer" that traces the outline of the body in a similar fashion as front wheels in a car are coupled together. As the pointer moves towards the waist, it steepens the gradient of the of the two slope guides by decreasing the "run" while keeping the rise constant.

Absolutely brilliant!

I have a strong technical background (engineer), but wasn't raised making a lot of saw-dust so I've been intimidated to try any carved tops. This is a jig I could actually see me trying out.

[Louie Atienza]

It took me a while to understand it as well, but after looking at the photos and description while thinking about the application I got it. Basically the best way I could describe it is that the two vertical or slope guides are coupled to each other and the "pointer" that traces the outline of the body in a similar fashion as front wheels in a car are coupled together. As the pointer moves towards the waist, it steepens the gradient of the of the two slope guides by decreasing the "run" while keeping the rise constant.

Absolutely brilliant!

I have a strong technical background (engineer), but wasn't raised making a lot of saw-dust so I've been intimidated to try any carved tops. This is a jig I could actually see me trying out.

Thanks, Sam!

Your engineering background has made your explanation more concise and elegant than I could have possibly explained! In the same way that the wheel when pointed straight would look like a rectangle, as the wheel turns toward 90 degrees it starts looking more like a circle. As a former cabinetmaker, stairmaker, and framer, I cant believev I never thought about using "rise" and "run" to describe this!

I think the great part about this jig is, that if your pointer is small enough, the jig works regardless of body shape, and even cutaway. On my first archtop acoustic I drew curves in CAD and shrunk and stretched them to get them all proportional at each octant. This gets tedoious and not as accurate as the curves "in between" are just averaged out.

[Harmon Gladding]

I am amazed to find this discussion.
After a couple years of thought experiments, I have been planning to post a design for semi-automated top, back, and neck carving with a homemade duplicating router stand for my first instrument, an A-style mandocello. A cam in the shape of a curtate cycloid profile will swing according to the body radius presented by a rotating internal body form. The duplicating router with a 3/4" hemispherical core box bit, moving in a plane radial to the axis of rotation of the form, will follow the profile cam with a horizontal rod which can engage the cam as the router and cam move. The carving blank will be attached to the top of the form. For the area between bridge and neck heel, the form will slide in a direction parallel to its midline to engage a different profile cam gradually by means of ramps. I hope this arrangement will also be able to match the top or back edges to the shape of the internal form. The sides will be formed of bent veneers glued to the outside edges ala Martin Jacobson.
For the neck, a pattern is made using simple geometric solids, a cone for the tapering neck, a segment of cone bent into a torus for the heel, and a ramp for the head. The cone and torus translate into a proper neck cross section when the pattern follower is in the shape of the desired cross section and the small (nut) end of the cone has the same diameter as the router bit. For my follower, I duplicated the small end of a hen's egg, which provides just the right aspect ratio and profile for the mandocello neck.
A fingerboard blank will rotate about an axis whose distance from the blank will be greater at the bridge end than at the nut end, generating a conical surface having a larger radius at the bridge end, when the router slides linearly. Is this a correct definition of compound radius?
I was motivated by a fear of handcarving.

[Randolph Rhett]

I guess I have to wait for the movie version to come out, the book version is just too hard to follow.