Official Luthiers Forum!

I'm about half way through my first figured redwood guitar. This one will be a baritone. I was more than a little nervous about using figured redwood, so I'm doing an experimental build. I'm hoping that others have done this and can talk about their experience.
I looked into Nomex and while others are very happy with it, I'm not at all enthusiastic about building with it. (No offense intended, I just don't care to do that right now.) I have seen others work out a nice method of making a special shape for the inside piece to make it light and have strength in the right place. That is also a nice approach that I'm not interested in.

There are many ways to approach this, we all have to decide what will work for our skill set and understanding. I decided to laminated a piece of lutz to the redwood with epoxy. No, nothing not fancy. I thought I'd give it a try and if at some point along the way I was not satisfied, I'd just stop and use a different top. (I have a wonderful customer that has agreed to all of this.)
I build my tops to a deflection value, not thickness, so I figured that if I got it to deflect and it was still light weight, it might work out. The trouble with that is - I never weigh my tops. Dooh!
So here are some pictures of the process.

Spreading the slow cure System 3 epoxy on the figured redwood -



The glue went through the plate. If you try this - use wax paper or do as I did. That white plastic sheet underneath is HMWPE.


Now for the Lutz top.


Place a sheet of UHMWPE over the top piece and clamp.


Wait over night and remove. You can see how the epoxy penetrated the redwood.



A word of caution - I was trying to be careful with the epoxy because I did not want it be too heavy. When I cut the perimeter, it was obvious that I had some dry spots so I needed to sand off the Lutz and try again.





I ended up with a total thickness of about .095" with the lutz being only .025". I'm not finished, but I can say that I am very please with it after voicing. With it the body assembled, it has one of the deepest resonating tap tones I've heard. Based on that, I fully expect it to be one of my best sounding guitars yet. Of course I won't know for sure until another month.



So - Who's has tried something similar? How did it work out?


Yes - That's bubinga on the back/sides.

_________________
"An adventure is only an inconvenience rightly considered. An inconvenience is an adventure wrongly considered." G. K. Chesterton.

Very interesting. I got a top just like that from eBay, but crashed and burned when it kept cracking. I decided to try soaking with CA glue--a big bottle I got from McBeath Hardwoods, but that turned out to be a waste of time too. The wood had no stability, even though it looked stunning. Luckily I didn't pay much for it. I'll never try CA glue like that again. Epoxy sounds like the ticket. I ended up using small pieces of those boards for inlays on boxes I made. Live and learn.

_________________
"Preoccupation with an effect gives it power and enhances the error"
from "Your Owner's Manual" by Burt Hotchkiss.

Steve,
I double my redwood tops but not quite the same way. Only thing I'd suggest is to use a vacuum bag to glue the tops together since it will even gluing pressure. If you don't have one you are welcome to use mine.

_________________
Peter M.
Cornerstone Guitars
http://www.cornerstoneukes.com

Peter,
I thought a bit about that before I started this. The great thing about epoxy is that it does not require the even pressure you want with a typical water based wood glue. With epoxy, you just need to hold the parts together. I have the two plates held between two 1/8" thick HMWPE sheets which served to spread out the forces. With the clamps, go bars and bag of lead, it was held together.

Thanks! That is a very nice offer and I'd love to try it sometime.
I just don't want anyone thinking that they have to use vacuum clamping to try this. It would make it an easier job.
Would you need to run the pump for several hours while the epoxy cured?

_________________
"An adventure is only an inconvenience rightly considered. An inconvenience is an adventure wrongly considered." G. K. Chesterton.

Steve,
Did you weigh the epoxy before applying it? Basically you are adding about 20 - 50 grams of dead weight to the top using a ply process. It would stand to reason that the lower frequencies could be enhanced since you have added mass to the top. On the other hand when you use Nomex you are cutting the total plate mass anywhere from 30% - 50% and glue weight is in the 5 - 7 gram range. No doubt that your stiffness ratio will be up exponentially with the overall all weight of the plate. This process is opposite of the targeted goal of the Nomex sandwich method of a higher stiffness to lower weight ratio.

The epoxy permeability is due to the localized run-out of the curly grain which is running 90* to the surface plane.

_________________
tim...
http://www.mcknightguitars.com

Tim,
Numbers aside, have you or anyone you know tried this method? I'm curious how they liked the sound. The tap tone on this guitar is wonderful. I can't wait to get strings on it.

OK - now for the numbers. I used 20 grams of epoxy. Some was cut off, so I'd guess that I have 16 grams of epoxy in this top. That's about the weight 4 sheets of paper. Not insignificant, but not a lot either. With the added stiffness of the plate, I was able to remove more from the braces when voicing, so I might not have any extra weight.

_________________
"An adventure is only an inconvenience rightly considered. An inconvenience is an adventure wrongly considered." G. K. Chesterton.

Just because an epoxy joint is less likely to fail under incomplete clamping doesn't mean it's no longer of benefit to clamp it right. Clamping with any adhesive (gap filling or not) still serves to evacuate the extra adhesive from the joint, and in a composite structure that means less dead weight.

_________________
Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

Bob,
That's exactly right!


I'm not getting any replies from people saying they have done this.
Has any tried this? Does anyone know someone that has done this?
I can't be the first.

_________________
"An adventure is only an inconvenience rightly considered. An inconvenience is an adventure wrongly considered." G. K. Chesterton.

Steve,
I have done two Curly Redwood tops in a similar fashion. I use a proprietary design which I call "semi-double" which eliminates some of the extra weight while strengthening the weak areas on the figured top. My semi-double tops are stable and sound great but they are not match for a true double top or even a straight grained redwood top..... I guess beauty comes at a price.

_________________
Peter M.
Cornerstone Guitars
http://www.cornerstoneukes.com

Nice looking guitar there Peter. All I can think of when I see those curly redwood tops is how floppy they feel. After your description though I do see you have fixed that problem.

I make laminated tops for archtops. I made some with curly redwood that turned out too floppy across the grain and didn't use them. I did not experiment any further but could have stiffened it up by adding another layer (or two) running crosswise to the top faces. But this is a whole nuther thing obviously.

So I have no direct experience with making a flat top but would probably try to match the face piece with one or two laminations that beef up the crosswise stiffness. I would use urea formaldehyde glue since it dries glass hard and is light.

I would only suggest next time that apply better pressure next time. Put it between 3/4 plywood and park a car on it. Or plenty of clamps or better yet vacuum.

Let me know how it sounds, I am interested.

_________________
Ken

Funny you should say that. At one time, I did the calculations. Lets try that again.

Take a typical top - 22 X16 =352 square inches.
Vacuum will give you about 14 PSI of force.
A typical car weighs about 3500 lbs, so lets take 1/4, or 875 and divide it into that top's 352 square inches. 875/352=2.5 PSI

Now let's take a look at that go bar deck in the picture above. 16 go bar rods
17 clamps and one 25 lbs bag of shot. I don't know how much force the rods give, but let's say they do 10 lbs, and the cam clamps I'll estimate at 25. ( I think these are low. Does anyone have a better idea on these forces?)

The rods, clamps and bag add up to 160+425+25 =610 lbs or 1.7 PSI

So the clear winner is the vacuum clamp. That being said, when I cut the profile of the top and the sound hole out, I checked for a good bond, and it was good. My suspicion is that for epoxy bonding, 1.7 PSI is acceptable.



Will do!

_________________
"An adventure is only an inconvenience rightly considered. An inconvenience is an adventure wrongly considered." G. K. Chesterton.

Very true because epoxy is one of the few glues that like a fairly thick glue line.
I would recomend a urea formeldhyde glue and a vacumm bag for this. Thinner glue line, harder more ridgid glue than epoxy, less chance of voids and better aproximation of the wood with a bag. It would make for a lighter, stiffer top which I would assume is what everyone is after. If not using a bag I would want more cauls and pressure than a go deck, and few clamps and a sand bag. I like your idea but I think you could really improve the technique for accomplishing it. Simple press could be made if you don't have a bag. You could made sandwitch starting from the center and working out you would have glue, wood, thin non-corrugated cardboard, 1 or 2 pieces of 3/4 ply or mdf, (might use 1 piece of mdf on the inside and ply out side of that.) and a series of cauls. I will post a picture of a simple set up for this later today.

Link

_________________
Cut to size.....Beat to fit.....Paint to match.

I was actually going to mention the car VS vacuum thing, but I'm glad you did instead. I'd say the go bar number is high (probably closer to 5lbs) and the cam clamp number might be low depending on how the clamps were applied. One of the nice things about vacuum with slow-curing glues is that it's really tenacious and tends to want to pull every last drop of excess glue out of a joint (it's also one of the messy things about vacuum with slow-curing glues!)

I don't believe in thick glue lines, for any glue, ever. My general method these days (and I always have perfect joints now: thanks Fadal!) is to clamp to substrate failure, even with a perfect joint, just to leave the minimum amount of glue possible in a joint. That's not always possible, of course, but I think it's a good thing to aim for.

_________________
Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

Go-bar rod clamp force. My 5/16" fiberglass rods measure 7lbs and I think that is fairly typical. It does not matter how much they (or any gobar rod) are flexed.

_________________
Steve Smith
"Music is what feelings sound like"

Steve another method of clamping that I have used on various projects is to get 2 pieces of MDF. I use the shelving material that has a vinyl film on both sides. A couple of good coats of paste wax on the vinyl will make for easy release. Them make up some clamping cauls out of oak or maple. 1" x 2" seems to work well. Plane a curvature on the top edge of of the cauls leaving the center alone and tapering about 1/16 or so towards each edge. Then place 3 cauls on top with 3 corresponding cauls below. Clamping the ends of the tapered cauls will cause the clamps to exert pressure in the center as well thus eliminating the need for long clamps. Works like a charm. I agree with Bob Garrish regarding thick or gap filling glues.

_________________
Beautiful and unusual tone woods at a reasonable price.
http://www.rctonewoods.com/RCT_Store
The Zootman
1109 Military Rd.
Kenmore, NY 14217
(716) 874-1498

Just for the record - this method worked very nicely. The client was very pleased.
He said the guitar exceeded his expectations.
I'll definitely do it again.

_________________
"An adventure is only an inconvenience rightly considered. An inconvenience is an adventure wrongly considered." G. K. Chesterton.