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A working on a couple of Ike’s. The backs have been joined for some time
And when I went to brace them up I noticed some cupping.

I plan to brace them up and wonder if should stretch across the cup () or with the cup ((

Please lend some help this way
Thanks
dave

Well, I have no scientific proof hat this is a reasonable thing to do, but most cases if there's a bit of cupping, I'll brace into the cupped side, since the wood is trending that way anyway...

I would hang them on a clothes hanger with a spring clip so the air can circulate on both sides for a day to see if some of the cup goes away. Like Ed, I would brace with the cup.

Bracing against the cup would look more like this: )(

I can’t see any benefit to doing that, so I would brace with the curves all going the same way: ((

But what do I know? I submit to a wiser builder, if there is some good reason to bend the warped back in a direction it doesn’t want to go.

I tried some damage control
Spritzed the cupped side with a little warer
Set some stickers on a radius dish
Then pressed the cupped side (facing down) into the dish and let it dry over night.
It is now dried and set into a perfect 15’ radius.

I would put it up where it gets good air circulation for a week or two and watch it.

If it moves around in a smooth uniform way - brace with the cup.

If it picks up any lumps or humps that come and go with humidity - scrap it. This sort will forever eternally be a problem.

been doing this for 20 yrs and ran into this a few times. There are a few reasons that this happened so there is no one correct answer.
A Know why it cupped
was it RH poor storage etc. So wetting and allowing good air circulation is not a bad thing to do.
B Dampening and clamping flat or radiused as mentioned is also a good option.
C One option that I found to be helpful was to heat the plate , I have used cloths irons where I used steam heat and then clamped flat, I used heat lamps and now I have a heat blanket that is 18 by 24 so I can control the heat.

heat seems to be the most reliable option for me. In all cases, if it was RH imbalance they flattened out pretty quick. If it was caused by runout in the tree there will always be residual warpage and it is often shown on both plates. In that case I would joint the edges by clamping a straight edge on the plates , glue them pressed flat , then sand to thickness ( .095) get the iron out and heat them and press them in the go deck to my back radius dish and glue in the braces. This worked and I have a few guitars that are out there over 10 years and help perfectly and no cracks.

so as you can see there are many options , the best advice is to ID why it warped. A cloths iron can be your friend in many cases.

_________________
John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

As John mentions - ironing out a chronically warped back works really well.