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I had some pretty good cupping on this set of EIRW. I'm in the process of truing up the sides for binding, but the cupping is too severe to try and sand out, to me. One builder I know and respect suggested using epoxy to level out the sides. Seems like it would work. Anybody ever tried that?

I also wonder just how noticeable it would be if I just blended it in and finished it. Would it be a mistake?

Here's a shot.

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Wes McMillian
Santo, TX
http://www.wesmcmillian.com

blend it with a scraper

I woudl try to use the scraper for each binding + 30-40% of the side width (avoid digging the corner in the cup) and then finish with fine sandpaper (paper only, no pad/block).

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Build log

I agree with Michael and Alex. I'd go ahead and do the binding, then use a scraper wider than the width of the sides, and bend it as you scrape, so that you get a full width, continuous concave curve from back to soundboard- or very close.

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Gene

Politicians and diapers must be changed often, and for the same reason- Mark Twain

Unless I misunderstand the proposed solution, if you bind before leveling the side with a scraper, you will end up with a binding that is thinner in that area. I think you should level the side before you put on the binding.

Also, I wouldn't level all the way down if I were you: I think you'll end up with really thin sides towards the top and bottom of the box (unless you made them really thick in the first place...). Maybe leave some cupping there. It shouldn't be the end of the world. I've made guitars with cupping and the owners never saw it (yet!).

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Alain Moisan
Former full time builder of Acoustics, Classicals and Flamencos.
(Now building just for fun!)

I agree with Alain - this can snowball in to very thin bindings if you install the bindings first.

If it were me I would scrape some but accept that scraping it all out will make the sides dangerously thin unless you bend your sides unusually thick. I also would not attempt to fill the dip with epoxy - that is a LOT of epoxy and I would be concerned about the stability of that much epoxy.

I am wondering what caused this much cupping - Wes buddy were the sides pretty wet when bent?

have you put side braces on yet?

if not make up some quite tall side braces out of mahogany and the find a large peice of flat metal bar about 15mm x 15mm square.
this need to be longer than the width of the side.

now when you clamp in the side brace place the bar on the outside of the rib and clamp the brace on with a g clamp pulling the side flat against mettal bar.
leave this on over night and will be alot flatter in the morning.
you caan do all the braces in one go if you have enough clamps.

i used this technique on a m,blackwood guitar (about my third guitar) that had worse cupping than that and it worked very very well.

it still had some cup after but it scraped out pretty well before i did my binding.

try to get it flat before you do your binding if you can or else you will an under cut ledge at the waist.

I hope you understood that,
Joel.

Thanks, guys. My gut was pretty well telling me it would blend in OK. It originally looked worse than this, I took it down about as much as I cared to for the pics while truing up the edges for my binding rig to reference off of. I think it's good enough now that it will blend in OK. And I do intend to go ahead and prep the sides all the way before binding. All I'm worried about getting prepped flat is where the cutter bearing is gonna ride, kinda like the picture shows.

Hesh, actually these sides were bent pretty dry, very lightly spritzed, wrapped, sandwiched tightly with a heat blanket on top. Both sides cupped in pretty well the same area of the lower bout. Upper bout came out pretty good. Beats me. One of the mysteries of life.

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Wes McMillian
Santo, TX
http://www.wesmcmillian.com

Missed your post, Joel. Yes, the side braces are in, as this is a closed box. Otherwise, your idea would work great. As I stated in the last post, I'm going to flatten a good area at the edges that the binding rig can reference off of.

Thanks for everybody's input!

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Wes McMillian
Santo, TX
http://www.wesmcmillian.com

I had this problem on a maple guitar I built, I don't what the cause of cupping is but I've done some thinking about this, here's one of my untested theories..

it may occur when the sides have to be forced a little too far into a mold after bending (clamps, spreaders, etc.) then the linnings glued, when the clamps are released the linnings hold the edges and the internal stresses results in some cupping

Folks, this is a rather common problem. It is not unusual. It happens with every species, and is particularly problematic with beeswing figure and similar where the sides tend to warp with the moisture. It is why many of us bend our sides thicker, more like 3/32, so we have room to flatten the sides. The proper resolution is to flat sand the sides, then rout and install the bindings. This is why Taylor's new side benders are so fantastic, because all the bends happen under high tension, and without water (except cutaways), there isn't as much of a problem with cupping.

David D. Berkowitz
Berkowitz Guitars

This is why Taylor's new side benders are so fantastic,

What does this mean? What are Taylor's new side benders...?

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Steve Sollod (pronounced sorta like "Solid")
www.swiftcreekguitars.com

Steve,

Watch and be amazed:

Factory Fridays Side Bending Part 1

Factory Fridays Side Bending Part 2

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Dave White
De Faoite Stringed Instruments
". . . the one thing a machine just can't do is give you character and personalities and sometimes that comes with flaws, but it always comes with humanity" Monty Don talking about hand weaving, "Mastercrafts", Weaving, BBC March 2010

Put the wood in, press a button....

I've watched most of the Taylor vids. Interesting stuff. The CNC neck carving one is amazing.

BTW, the EIR...I find the stuff cups like mad. After bending, I sometimes clamp the ends using flat pieces of wood before I am ready to glue on the blocks...might only be a day or two, but they can cup pretty quicky.

With outfits such as Taylor, I bet the wood doesn't have time to cup....

I think that Bob Taylor might have gotten the idea from the George Foreskin grill that you see advertised on TV.......

Man, I'd like one of those Taylor benders... Amazing they can bend 75 sets in 3.5 hours.. I wonder if they let me come in for about a half hour?

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Steve Sollod (pronounced sorta like "Solid")
www.swiftcreekguitars.com

Ever since I started using SuperSoft 2 on my sides before bending, plus a lot less water, I have had far less scraping on highly figured Waterfall Bubinga as well as straight-grained EIR. I typically thin my sides from .080" to .090". Six sets of problem free sides so far!

I spray SS2 onto the sides and let it sit over night as a minimum. I wrap in craft paper and spray very lightly before bending in a Fox bender with bulbs and a blanket. I firmly believe that the grain relaxer whips all of those feisty fibers into shape and forces them to stay in the desired configuration and forget their former alignment.

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JJ
Napa, CA
http://www.DonohueGuitars.com

Amazing, but the worker is so awkward. He just sort've stands there and nods his head while Bob Taylor is actually doing all of the actual explaining. ^^;;

They pay him for his mechanical skills, not his presentation skills.