Warped Backplate Problem

[Benthoven]

Hi everyone - I hope someone here has successfully dealt with this problem before, and can offer some insights to help me solve this one.
This is actually my own personal instrument (not a customer's), an 1870's German bass with a flat backplate that has developed a nasty warp in the lower bout over the years.  This bass has been here in Las Vegas, in the dry, arid Nevada desert environment since at least the 1960's, and I only acquired it about 3 years ago after it sat warped, seams open, and unplayed for at least 20 years.  We got it closed and reglued in 2012, and since then this bass has performed beautifully and sounds magnificent.  I've been playing it almost daily with no further problem since then.

However, like most of the rest of the US, we experienced a really wicked cold dry weather snap this past weekend.  In addition to that, the bass has for the past 3 weeks been housed 24/7 in a new environment - on the bandstand in one of the major shows on the strip, where it's too hazardous (and scary) to haul it up 10'-12' on and off the raised bandstand every night.   So, as you can see in the pics, over the weekend the bass popped *wide* open on the G side of the lower bout, with the backplate warped back into a fairly severe concave profile.

This backplate is so stiffly warped, I cannot even push it closed with my fingers without creating new cracks in the backplate, so even if I were to just crank it down with clamps and glue, I'd probably just create even worse problems to repair.  Can anyone suggest a strategy as to how this warping can be eased?  My instinct is to come up with a gentle way to re-humidify the backplate while clamping it flat somehow, and have some ideas how this could be done (all without taking the two-piece backplate completely off), but I'd sure like to hear from someone who has done this successfully before.  Any suggestions?

 

Just as a post script here - what I've observed dealing with stringed instruments in this harsh desert environment over the past 10 years has been the biggest challenge of my woodworking career.  The desert just sucks the moisture right out of anything wooden, and I've found that humidifiers of any kind are practically useless here against the forces of mother nature.  It's been better here to just let wooden instruments shrink, acclimate and find their stable new 'normal' here, and just regulate for the environment.  Any attempt to maintain moisture levels in wood beyond what the desert will allow you, is a futile tail-chasing exercise in my experience.  The upside is, that once the new normal is established, it's generally very stable, but getting there can be pretty rough on instruments.

 

 

 

 

Edited January 6, 2015 by Benthoven

[Benthoven]

Well, the bass sorta made its own decision (as they are wont to do).  After about 24 hours of running a humidifier, I was in the adjoining room doing other things and heard an audible "crack".  It started in the middle of the lower C bout running south, directly down the center of the worst warp in the back plate. So I left it alone to observe while working on other things, and it eventually opened itself to about 3/16".  There. Tension released.  I guess sometimes you just have to let it crack, right? It's not like I could have stopped it.  Back plate reglued, crack filled and touched up, action set up, sounding as great and thumping hard with its new wooded end pin, and gig-ready before the deadline to return to the bandstand. 

 

http://i1292.photobucket.com/albums/b580/rblinfo/Finished_zps4d9d0c39.jpg

Edited January 7, 2015 by Benthoven