EIR back and braces lost their arc

Couple of weeks ago I glued up the 4 back braces to the EIR back of a kit I’m working on. Today I was demonstrating to a friend what a 15’ radius is and I discovered the back and braces lost their arc. In fact, they're now somewhat arced in the wrong direction. So, I’ll be removing and replacing the braces but am wondering what could have caused this to happen. My workshop humidity has been between 39% and 42% since I got a new humidifier 2 months ago. As usual, I’m clueless so any help I can get will be appreciated!

-tommy

[johnnparchem]

How long did you have the wood with the humidifier before you started building? The back will shrink and flatten when dry. I would guess that the plate was still drying when you made it, Especially now that it is going in reverse. Bump the humidity up to 50 percent and see what happens. I had it happen once. The arc came back when the relative humidity was higher.

[Darryl Young]

John likely nailed the issue. You either aren't controlling the humidity or the wood wasn't stabilized at that humidty before you glued the braces.

Humidity at a steady 52% for 16 hours. No change so far.............
Give it more time or up the humidity?

-tommy

[darren]

I had it happen too... the arc never came back and I planed the braces off and started fresh with new ones. General rule is don't brace your plates until they are ready to glue to the rim.

The arc didn't come back for me. either so I started to plane off the braces and start fresh. But how was I to know that during the brace removal process that I would crack the back. So, replacement back is on the way. Let's see how I can screw this one up .

-tommy

[Tom West]

Tommy: Hard way to learn about RH and it's effects. For your back to go from a convex to a concave I would suspect your RH changed more than 10 or 15 points. You really need some way to measure RH so your not repeating this one. Also in my book it's far better to brace a bit too dry than a bit too wet. Braced wood that is taking on moisture is pushing itself together. Braced wood that is drying out is trying to pull itself apart.Good luck on the new back.
Tom

[tippie53]

These the the simple how to learn mistakes. Wood can be funny. It takes longer to dry out then to moisten. I also use a heat source before glueing . A cloths iron can help. it is amazing how much water can be pulled out of the plates . Iron for 5 to 10 minutes then glue. You are adding a good bit of water into the plate with the glue so you want this as a dry as you can get it.
I set my Dehumidifier at 35% for 24 hr before glue ups.