back breaking work

[Darren Molnar]

Hey all,
Does any one have experience putting a break in a carved back? Tips, warnings? Any volunteers

[ctregan]

http://www.bryantbasses.com/basses.p...rmo+model+Bass

It looks like a difficult break with the back swell.

Would it help if the back flattens out just before the break? or does it look better if the swell rolls into the break?

I am trying to do the same thing on my project, at this time, all I have is some test samples on small pieces of wood.

How do you avoid the black line on a break joint?

[arnoldschnitzer]

First, cut a groove all the way across the inside of back 2/3 of the way through. Then, use heat and water to soften the area. Bend it slowly while applying the heat. Keep the water and heat off the center seam. Many makers construct a beam to support the back just below the bend; this beam is fitted and clamped in place. Then you place the back, outside surface up, at the end of your bench and bend the upper section down against the support of the beam. Keep a bucket handy to puke in just in case it breaks in half.

I don't do breaks on my roundbacks anymore. Not enough hair left to give up any more...

[1st Bass]

I bent mine full-thickness-- not having cut the groove. I did pretty much as Arnold says, using wet dish-towels and a clothes iron on high to keep the heat and moisture up .

I took a long time with it, and used bar clamps to apply the pressure. Poured boiling water on the cloths to start with, and let it sit a while, then began applying a little pressure, and ironing the whole bend area, maybe 6" wide (I made a more gradual break).

Kept applying more heat, more moisture, more pressure, until it was completely bent. It took me about 2-1/2 hours, but it worked. I was really afraid I might break it. I could probably have gone a little faster.

I posted pictures before on the thread titled "progress report", but only of the finished product-- I didn't have a camera available when I was building it.

I completed the purfling after the back was bent.

Chet

[Darren Molnar]

Thanks all, I think I got just enough spare hairs to try this once in my life. Just once, mind you. I'm glad Arnold mentioned the support beam, I was thinking of it, but wasn't sure.I'll make one today.
I also put some temporary cleats along the center line, on both sides of the plate, just in case.
I'm going to try one more thing, also. Let me know if you think this is crazy. I was thnking that it would be nice to have a backing strap, like when the ribs are bent, to help prevent breaking on the outside. So I think today I'm going to glue a strip of cloth, over where the break is going to be, to act as a temporary backing strap. It only has to hold for as long as it takes for the bend to establish.

I already had a puke bucket for the rib bending, Arnold. But I'm thinking of upgrading to a puke trough! This point is stressfull!

[dennis duvall]

when i cut my groove on the panormo pattern it was a bit narrow,and the edges met befor the bend arch completed. adjusting that "faux pas" with the steamed half bent back bend was a b**ch at that stressful time (the puke bucket was kicked and bent also) duvall

[james condino]

Darren:

I did a break with a very deep bend on a new carved back a couple of months ago at full thickness without removing the big channel of wood like the Chandler book instructs or as Arnold mentioned. The results were very pleasing. PM me and I'll send a few images if you'd like.

I tried this in the past with just mediocre results using a simple center support beam. I originally bent the break on this back about 18 months ago in Portland, Oregon in the spring. I had a couple of things going on in life that year and knew that the bass would be in storage in the high desert for about six months and then there was a good chance that it would be moving with me to North Carolina. Because of those things, I chose not to join the back or top to the ribs during that period for fear of them splitting.

A year later, my hunch was correct and the seam from the bend to the button split open and the break bend had relaxed to almost nothing. Time for some majic and to rebend the entire thing. The center seam support is a good idea, but since I realized I only had one good shot to get it perfect on this one, I went a lot further.

I made a complete mockup of the desired finished back curvature out of MDF (medium density fiberboard) glued up in 3/4" layers until I had a giant, 70 lb., 24" x 30" by 8" thick block. I cut out a slightly oversized shape of my ribs (don't forget to add the back button!), and then spend about two hours with a large plane and carved out a mock up of my finished back with a slightly larger bend than I was after, to compensate for some springback.

I screwed the whole beast down to my workbench and starting at the button, I clamped my unbent carved back to the end of the "mold". If I was to clamp the back to the mold near the c-bouts and go the other direction, I would have a lot of tension to deal with; working from the button back, a gentle downward push allowed gravity to do it's thing.

Using the standard wet cloth over the top of the maple, I used a clothes iron on the steam setting and worked the entire piece for about 25 minutes, doing my best to minimize the area over the joint. As the back would gradually bend into position, I clamped the perimeter down to the mold. I let the entire setup cool completely overnight and then repeated the process two more times, but never removed the back from the mold until it was finished.

The results were just what I was hoping for. I started out with the carved part of the beack ending right where the bend begins. The finished effect visually appears as though the two morph together. The bend goes from right about 8" rib thickness at the upper corners down to 4.75" at the button / heel junction. Pretty extreme, but that is what I was after. The bass has a few other fun things going on also. I'll post images of it next month.

After all of that, I'm glad I did it and have sweet bragging rights when I show it off, but I have to agree with Arnold in that I probably won't do another one. Getting that done was a major crux and stressor for me, even after having built 157 instruments over the years (this was the first complete carved bass). All things considered though, it was sooooo much easier than doing a difficult restoration when somone brings their bass in to me in pieces stuffed in a large hockey gymbag....

I don't have any more need for the mold I used, so it is available if anyone is interested.

j.
www.condino.com

[james condino]

Here are a couple of other images of the back and ribs.

j.

[Darren Molnar]

James, that bass look hot! I'd love to see more! Thanks for sharing you're method. And every one else, once more.
My bend went ok this weekend, nothing broke, at least. I'm going to iron out a warp at the back button area today, to get the back sitting comfortably with the ribs.

[toman]

I've often wondered about this, especially with round backs and thought "why not just cut the back, mitre it, and join it back together". (before carving, obviously) It seems to me like that would be a whole lot less stressful and time consuming, and would eliminate the risk of breakage. Maybe even pose less chance of introducing stress into the finished instrument, as the back wouldn't try to revert to its original flatness.

Anyone think that would really have much effect on the tone, or any structural issues? I've seen old flatbacks that look to have been either made or repaired basically in four pieces like that; what's the story there?

[Matthew Tucker]

I have some Australian cedar (recycled tabletop) that I want to use for a flat-back bass. It isn't quite long enough for a complete back, so I am planning on doing just what you said; make a scarf joint at the break, and reinforce behind with stout cleats.

[arnoldschnitzer]

Originally Posted by toman

I've often wondered about this, especially with round backs and thought "why not just cut the back, mitre it, and join it back together". (before carving, obviously) It seems to me like that would be a whole lot less stressful and time consuming, and would eliminate the risk of breakage. Maybe even pose less chance of introducing stress into the finished instrument, as the back wouldn't try to revert to its original flatness.

Anyone think that would really have much effect on the tone, or any structural issues? I've seen old flatbacks that look to have been either made or repaired basically in four pieces like that; what's the story there?

It's an end-grain to end-grain joint, which is inherently much weaker than a regular joint.

[toman]

Originally Posted by arnoldschnitzer

It's an end-grain to end-grain joint, which is inherently much weaker than a regular joint.

That stands to reason, but is there really enough stress there to be a problem, especially if, say, it was cleated?

[arnoldschnitzer]

Yes. Have you ever seen a flat-back bass in the Winter? The back has a tendency to curve inward due to shrinkage. A joint at the break is a bad idea, although I have seen it done.

[toman]

Yes, I actually have a flatback that's quite sunken, although it's stable throughout the year and has yet to crack. Do you think the same amount of concern would apply to a roundback as well, like is being discussed here?

(I'm not advocating this or anything, just curious...)

[Matthew Tucker]

You would do it I imagine if the upper part of the back were badly damaged; there is ample scope for bracing and reinforcing at that point. I would likely build in a slight outward curve in the back at the break, as I would at all the bracing points, to compensate for any tendency for shrinkage across the grain, and cleat with stout cleats rather than a solid brace, to allow the wood to move a bit.

I have seen a break done with a series of dovetails. Looks pretty but i don't imagine it would be much stronger.

[toman]

Dovetailed would be interesting, no doubt. I just wonder about this every time I see a guitar with a nice scarf joint headstock. Though granted, that's thicker and much narrower, so less seasonal movement. The back could be braced directly below the joint though...