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I put a couple engelmann spruce tops in the oven for an hour last night at 180 deg F. They warped and cupped. I've had them for a year they've been sitting on a self in my basement in Alberta in a house with forced air heat, they should be dry. Should I have clamped them between something first? Did this occur from uneven heat? Is there a way to straighten them out or are they pooched?

Either way no big deal, I have more of these tops and they aren't very stiff. I can always use them for other experiments. I was going to build guitars 3 & 4 with these tops mostly to try and get better at building, doing binding and finishing. The guitars would never be sold.

I think that clamping them or weighing them down flat (with spacers) is the way to go.
Pics would help to see how badly they're warped and cupped - I've ironed backs flat (wrapped in aluminium foil)

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

+1 to what Colin said.

I weight mine and keep them weighted until completely cooled for a spell. I've been wanting to make a fixture or "carriage" that is oven proof just for this task but have not gotten around to it yet.

Depending on how thick or thin you like your tops, some builders go for uber stiffness and others end up with tops that they can shake out like a blanket... the warpage may not be an issue once braced.

You can also manipulate some warpage with strategically applied moisture and weights.

Or you can join them so that the cupping is in the same direction as the top radius, then it becomes a good thing.

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A man hears what he wants to hear, and disreguards the rest. Paul Simon

I use 3 of these , set up like this . Don't tighten the wing-nuts to tight or it leaves a dowel impression in the top. 200F for 1 hour, let cool in the oven then repeat.


Bob

Great idea Bob!

Love the dog !!! Airedale? And I love that baking setup !!!

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Joe Beaver
Maker of Sawdust

I have setup like Bobs, but mine is made up of some flat maple pieces, about 1/2 inch wide by maybe 1/4 tall, threaded rod and wing nuts holds it all together .. I can get about a dozen tops at a time into the oven, 2 hours at 195F, convection fan on, then complete cool down overnight in the oven .. wing nuts are snug when they go in, and are about two revolutions loose once the tops are done ... everything except sinker redwood gets done, I had a couple of those crack on me first time I did them ..

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Tony Karol
www.karol-guitars.com
"let my passion .. fulfill yours"

I often ponder the benefits of doing this.

I noticed a pretty reliable 15% drop in density by baking, coupled with a pretty reliable 15% corresponding drop in stiffness.

Seemed like kind of a wash...

Ed, check out Brian Burns data on backing tops. His data shows stiffness increases.

Bob

Joe, yep he is a 'Dale

Thanks Bob,

I've been trying to remember who's site that was for a long time.

My data does not track his data, though I'd have to say that it's more than possible his testing etiquette was better.

His numbers are so minimal IMO to go straight into the meh bin, save for the 21% increase in Q, which I think is a big enough change to warrant attention.

I just don't know how to test for Q...

Though it's probably in the Gore/Gilet books in the parts that I can't understand...

I'll have to give it another gander...

hmmmm. we usually bake cookies during Christmas...

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Tony Flippo

Mm mm....lutzcake!

Time for another trial just for kicks...

I use a similar set up like Bob, only I used cut offs from metal closet rods.

Don't forget the added benefit of the top being less likely to crack down the road if it has been baked. After the top is baked, it will not return to it's original size when re acclimated to shop humidity, therefore less likely to crack when/if exposed to low humidity by the perspective client.

Chuck

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Maybe a few spring washers under the nuts if it annoys you?

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

Doesnt annoy me at all Colin, just stating that the tops do shrink minimally ... its not enough to let them warp

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Tony Karol
www.karol-guitars.com
"let my passion .. fulfill yours"

Even those numbers would indicate an improvement because stiffness is a cube function of top thickness, so you could "buy back" the stiffness with a little top thickness and still wind up with a lighter top of equal thickness,
Mike