Louie Atienza's semi-automatic proportional archtop jig

[Louie Atienza]

I originally posted this on the old forum. I wanted to come up with a way to shape an archtop plate, that took into account the actual shape of the top and adjusted the arch proportionately at each section. So at the waist, the arch would be tighter, and behind the bridge, wider, yet the two areas would be shaped proportionally to each other (which I think is most pleasing to look at...)

I've seen router jigs that created "steps", but that requires a lot of post-shaping, and the ledges by nature of the jig are evevnly spaced, which makes the top look like it could have been done with a panel bit, which is OK by me for a solidbody, but not an acoustic.

There is the Duplicarver, but still, the first one has to be carved. Cutting out cardboard gauges is another way, but then you need to make new ones if you make a different shape. I wanted to make this ig universal, meaning it can work with amy shape, electric or acoustic.

Here's what I ended up with:

[Louie Atienza]

The router is affixed to a carriage that pivots, and slides back and forth. I use ACCURIDE drawer slides for the front to back movement. The bars above are for reinforcement.

The two "sweepers" are my arch templates. They are linked together so they move synchronously. They pivot on the same line as the guitar top. The linkage passes through a follower, which lets the linkage slide freely, and the follower rides in a slot to constrain its movement. Shown is my small bodied template and blank.

The idea behind this jig is, as you turn the top/template a certain increment, you push the follower against the template. This causes the arch templates to pivot. From the side view, this would "shrink" or "expand" the arch template to "fit" each section. So you'd het a more sweeping arch at the wider sections, and a more pronounced arch at the waist.

The back view shows the pivots, two simple door hinges, and the linear system which are the drawer slides.

[Louie Atienza]

Closeup of the pointer mechanism. In hindsight, making this actually come to a point would aid in accuracy.

[Louie Atienza]

The 3/4 view shows the concept at work. You simply turn the top template a little, push the follower against the jig, and move the carriage back and forth. Goes by a lot quicker than you'd think, maybe 10 minutes per pass, and two passes.

[Louie Atienza]

Here's the bottom of the follower; a guide made out of HDPE, to allow it to glide easily in it's groove.

[Louie Atienza]

Here's a shot of the first pass. You can go pretty deep with softwoods, and the carriage aborbs the torque of the router. The bit height should be the same line as the rails on the carriage.

[Louie Atienza]

Closeup. You'll see I pre-routed a rabbet beforehand. This denotes the thickness I want at the edge. You can also see the arch tightening toward the waist.

[Louie Atienza]

The first pass all done. I removed lots of material in a short time. Starting to take shape. I had made improvements to this jig since, by thinning the pointer, and using round guiderails and a ballnose bit, to remove some of the stairstepping.

You can see I started the second pass, and the router barely touches the rabbet.

I made an error in the previous post. For the first pass, the bit is slightly higher than the guide rails, and level with them for the second pass.

[Louie Atienza]

The second pass all done. About 20 minutes elapsed time from start to finish. You can see the stairstepping at the waist.

[Louie Atienza]

Some quick sanding...

In theory this would also work for the INSIDE carve as well, though I have not tested this yet. In that case it would be easier to carve the inside first and outside last.

[JC Whitney]

Sooo... the pivot points for the arch templates/sweepers are aligned with the "center" point of the top? That's clever! I'm tring to picture how the setup would be modified for an inside carve... would the only difference be concave vs convex templates? If the profiles of the inner and outer templates matched, would the result be a consistant thickness throughout the top? That's fun, thanks for sharing.

[Louie Atienza]

Sooo... the pivot points for the arch templates/sweepers are aligned with the "center" point of the top? That's clever! I'm tring to picture how the setup would be modified for an inside carve... would the only difference be concave vs convex templates? If the profiles of the inner and outer templates matched, would the result be a consistant thickness throughout the top? That's fun, thanks for sharing.

Yes! And, yes! In fact you could theoretically make the inside template such that you had, say 3/16" in the center and 1/8" at the edge, which would eliminate a lot of tedious hand work... Of course, there is some final shaping, and the recarve should be done by hand (preferably after binding) but it's nice to spend time on final shaping and tuning, instead of roughing!

[Samuel Hartpence]

I link to a video would be worth so many words...

[Louie Atienza]

I wanted to do that, Sam, but was waiting for a specific job that would require it, rather than cut something out. But since I've had ideas on doing another archtop Strat body, I might just have a go at this soon...

[Jason Rodgers]

When you first posted this I TOTALLY did not get it. Now it makes sense! I think I couldn't see the plexi linkages between the following point and the ramps.

The only thing I have questions about are the ramps that attach to the following point: are they anchored, and why are they angled like that? Shouldn't they be straight and in slots to move in and out with the pointer, thus raising and lower the slope?

[Louie Atienza]

When you first posted this I TOTALLY did not get it. Now it makes sense! I think I couldn't see the plexi linkages between the following point and the ramps.

The only thing I have questions about are the ramps that attach to the following point: are they anchored, and why are they angled like that? Shouldn't they be straight and in slots to move in and out with the pointer, thus raising and lower the slope?

Aaaahhh, that's the 'beauty' of this design, Jason, and the limitations of others. If the ramps (or I should say, templates) move in and out parallel to the pointer, that in essence would make the profile exactly the same all around. In that case, one could just use a wide panel bit, or some of the other router jigs out there. So they're only anchored at one point, and allowed to pivot, as the pointer moves.

With this jig, that angle always changes according to where the pointer is, thus "tightening" the arch in the eyes of the router guides. If you imagine yourself on the side of this jig, with your eyes level to the table, you'll see as the angle of the templates change, the arch changes as well. You can do this with your hand. Hold one hand in front of you, perpendicular to your face, then slowly rotate your palm and fingers away from you, keeping your wrist in the same place. While we are aware that our fingers moved away, in a a 2D world the hand appears to get shorter. Same thing with the letterings painted on the road. From a distance, the font looks normal. But as you approach, you realize that the letters get more and more elongated.

To me, the arch looks better, and would be a more "mathematically correct" way of doing it. Of course I could just throw a blank on the CNC and press "GO" but where's the fun in that? But in fact, if you had to draw the archtop surface in CAD it would do exactly this. You would draw one 'drive' curve, which would be the template in my case, and 'sweep' it around the outline shape from the center. The CAD will proportinaltely shrink or stretch the curve to "fit".

[Pete Halliday]

First off, this is a very clever jig you've come up with and I intend to copy with pride. I am curious if you've used this on a a top with a cutaway. Do you end up with a good arch shape to the inside of the cutaway?

[Mike Sandor]

Louie,
I am most impressed with your designs. Very ingenious. I too have made a duplicator and used the "ramp" idea to make radius sanding disc's.
You should post some of your CNC projects.
Mike

[Louie Atienza]

Thanks Mike... The feeling's mutual, as I've always been inpressed with your designs, especially your custom hardware. I'm in the process of designing and building a CNC specifically for that purpose.

I developed an adjustable dish radius jig, that I posted a while back in the old forum; I might have to repost the pics here...

Pete, I'd be honored if others used this method for making arched tops! The last guitar I made with this was for the last electric guitar challenge (which I was disqualified for posting pics 4 minutes too late HAHAHAHA! I have the pics on my other computer so I'll post it later, but it has a Florentine? (pointed) cutaway, like a LP, and the curve still came out well...

Maybe, since we're moving the MIMF into the 21st century, we could have a separate forum for the duiscussion of CNC and instrument building?

[Mike Sandor]

Louie,
would realy like to see where you are with the CNC project. I don't know if this is the place, start a new thread, maby take it off line? I am getting real close to purchasing the servos and drives and would be interested in what direction you went.
Maby we could share some idea.
Mike