Double Top, Quilted Sapelle.

[Nick O]

Hi Todd, A man after my own heart! I'm doing the double back that Dennis linked to. It's spooky to see somebody thinking down the same lines as myself (almost at the same time and on different sides of the globe) but coming at the problem from two different directions. I'd love to hear or compare the end results although the two will sound differently anyway being different styles of axe I love your extra 'touches' too, such as your using different woods when laminating head and tailblocks! and congratulate you on them. Even if they aren't seen I like to add these little classy touches because,even if nobody else does, I know they're there!
I shall continue to watch your build with interest.

[tlguitars]

Hey Darryl,

I'm thinking of this as a tone-braced back. You just have to forget about the 2nd back (and subsequent air chamber) and think of a normal guitars back that's braced stiff and heavy(-er normally), but is now a thinned out and lightly braced Sitka back. The key is thinking about it as it relates to putting your hand over a sound port. If you've ever done it you know there's movement and the air inside the guitar will move regardless of having a sound hole; and it's large, connected movement. I'm not worried about the backtop "not" being able to "sound." To me it's mainly just a reflector. I've seen the other chamber build (Nick O's build) referenced earlier in this post and I dig the idea, it's just not where my mind or experience is at for this build.

While there is a second chamber of air hiding behind my second top, I don't want to loose any pressure (possible tone) during the exchange from front to back (top chamber to bottom chamber). I'm hoping that if nothing else that hidden chamber of pent up air will boost the force that my flexibly topped 2nd back air chamber will push (reflect) the air out of my primary sound hole. I'm not looking for "blend" or "total guitar vibration" tone, I'm looking to allow the box to resonate without my chest and arms stopping the vibration of half the reflective surface. This is (based on) the Contreras take of a double back, and his guitar has no chamber... I'm worried enough about controlling the movement in the air chamber I have (and think that I'm just starting to know) to add another unknown to it.

Limit or inhibit, mmm.... I don't think so. Trying to remember my college musical acoustics class... Whether there's a second air chamber behind the top (or a large beer gut) I think the result will be the same if not better. There's no braces on the top of the back to limit or get in the way of the air flow, so it's basically just an open chamber; and the back that's now on (in it) is substantially more flexible then a standard back and braced to possibly tone. Which should be a plus. I don't think I'm limiting anything at all.

Hey Nick,
Yeah, I dig your build too. Looks waaaay cool. And many thanks for the nod on the insides of my boxes. When trying to design my own take on the standard shapes I thought, "I can't do anything new to the outside of the bock that hasn't been done, so why not use my scraps and other ideas in a design related way and "cool out" the rest of my guitar (inside and out), so long as what I add doesn't add to the box in a non controllable or sonically appropriate way: Weight, Flex, Stiffness, or Strength wise?" And that's where I'm at. It's funny to see others now using my ideas. Strange. And I always look inside the box when I find a new builder or makers guitar in a store, at a show, or at the camp fire. Construction and design as a whole impresses me, not just some top purfling and a cool inlay, you gotta look at the whole thing.

Thanks guys. I hope I did justice to my justification. Todd

[tlguitars]

So I've been asked to show how I do my bevel insert in detail by one of the members here. Problem is I do this free hand-ish to getting the compound profile is tricky but whatever here's who I do it. I start by laying out my inside the side profile and my top plate location on the top of my cut out. I'll then add under a 1/4 of an inch to act as a kerfing reference. I transfered my drawing to a jig (board) and I manually draw the reference lines.


I'll then do the same thing on my side drawing 3 lines. Normal Kerfing. Bottom Bevel. Finished Kerfing. That way my side profile will be flat and uniform.


Then I'll joint off the side waste and start to pre-route my profiles with a 45 degree bevel bit on my router table.




Then I'm over to my edge sander where I have shape the compound profile to my insert. I cut my belly carves on my electrics the same way and after doing as many as I have I've "figure it out" in that I can usually correct "all" of my mistakes instead of "some!!"




Now the part of the sander to use is the supported flat part just where gap of the tension drum and the back meet. Basically just below the screw visible on the top.


Once the outside is done I start the inside.


Then I sand with 120 grit and flat block, and file if needed.



I'm sure there's a way to get the bevel preset with jigs but I dig the free hand (for now) and feel that as long as I pay attention to my lines everything should be just fine.

[Chris Paulick]

Thanks Todd, I got the idea now of your layout. The only thing I'm lacking is an edge sander but I think I can make it by laying my 6" X 24" belt sander horizontal and get it or I have a pnumatic hand held drum sander from Grizzly that might also do the trick. I really appreciate you taking the time to explain and take the pictures. It's a great help. You're the man .

[tlguitars]

Hey Chris,

Files!!! You can do it with files and be just as clean. It just takes more pulling work (manual labor) then the sander. If you lay it all out and can route the bulk with a router like I did on my table, you'll be half way there. If you have a table vice you can clamp it in and route bulk. Then you can go back with files and take it to the finish level. Just use Mahogany, Spanish Cedar, Walnut, or something similar that won't pull out in chunks when you file. You'll be fine. If your belt sander has a disc on the side that'd work too. The vertical belt should be cool too. Just do a 2 X 4 tester to get the balance of pressure from your finger tips and the cut of the sand paper in your fingers before you try and actual one. It'll cut a little faster but it'll get you close to the actual feeling. Filing works too and can be just as fast. I'm to the point now where I don't have to file hardly anything but early on I's sand 2/3rds and file the rest. Hog the bulk and finesse the rest.

[Chris Paulick]

Yeah, I have all that stuff no problem. I just used some rasps and files and sander when I bellied out and carved the arm rest on a Tele I made. I have the router bit from when I did the Laskin armrest and ribrest on my lasted build.
http://www.luthiersforum.com/forum/view ... 01&t=22386" onclick="window.open(this.href);return false;
I like this method of shaping the insert first. On the Laskin it was cut the block and route it after the top was on and guess how much to take off the back of the block( I used some cherry I had). At least that's how it was shown in the tutorial I read. I didn't care for that so I'm glad to see your method. You have also inspired me to start fancying up my insides.

[tlguitars]

Yeup, the tutorial you read was correct on the Laskin method. Super smart and a lot simpler then this method. This is waaaay more crafty. Most of the guys I know doing Kevin's way have it all programmed out on a CNC and get the final insert by cutting it out of the perfectly routed block. That'll be nice... someday, but for now I craft and shape. I do leave the middle of the insert slightly thicker to support the weight or pressure of the playing arm. But it's slight. I think it's fun to shape the compound radii. Makes think about what I'm doing, which is cool.

There was a bevel Tutorial that was just going up on this site. viewtopic.php?f=32&t=1092 It shows a great idea for clamping it in.

If you need any more Lemme know but I'll keep this on up to date and check my other bevel build posted here if you wanna work ahead.
viewtopic.php?f=72&t=114

[Chris Paulick]

Sure thing I appeciate it. I saw your Italian bevel some time ago and that's where you showed the bevel but didn't get into it's layout. I have to get some printer ink tomorrow and print these out. Lot's good stuff in them.