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the following query is only peripherally associated with lutherie in that truss rods are certainly essential to guitar building they aren't used in door slabs...

point being my predicted nightmare has occurred on a (really, really) hidden door system I built (but didn't spec) and has brought to the forefront of my mind a prior mad scientist idea of a dual action truss rod buried in both sides of a door slab (typically 8' for what I normally deal with and 1 3/4" thick)...the solution to my current situation is only going to be achieved by adding in carbon fiber bars (which I haven't sourced yet) on each edge, but in the future...

reason for this post is to ask if any of you all know of a person who fabricates truss rods and would be willing to totally custom make something along the lines of what I'm describing...thicker parts would of course be required to overcome the force a slab as described could potentially generate when it wants to bow for whatever reason it decides to bow.

Mark Blanchard makes them to order. http://www.blanchardguitars.com/guitarp ... _rods.html
What you want seems a little large but you might contact him and see what he says. Beyond that, you could take his design to a local welding shop and have them make you the super version that you need.

I think if you show a D/A truss rod to any machine/fab shop they could scale it up and make one any size you want. Whether they would be effective in a door slab is another question.

If it were my problem I'd consider inserting some aluminum T-Bar stock into the door edges. Sizing and effectiveness would be trial and error without a lot of testing but I think it would be easier and less expensive than CF bars big enough to flatten a slab.

Something like - Thicker T-Bar like 2x2x0.25 would be better but would need to be cut down to fit inside the door edge and you can cut aluminum with a carbide circular saw blade.

Just ideas/suggestions.

_________________
Brian R, Wood Mechanic
N8ZED

I knew I once found a custom fabricator of truss rods, thx bobgramann, I'm pretty sure that was the source I located ages ago (but didn't find today)

rbuddy, I've had basically no luck whatsoever with aluminum, steel, or other forms of attempted reinforcement when dealing with solid woods and while I thank you for the suggestion, I'm not feeling it in this application even though it's an engineered slab with wood only on the perimeters...what I've found is that when wood wants to move, it moves. I once tried (was basically forced to) to straighten out a 3/4" thick piece of bowed MDO plywood with 1" bar stock and it had very little effect...in the end I was supplied a new piece...I have enough experience with milling aluminum that I have PTSD on the subject...cut it, track sawn it, routed it in various fashions, drilled and tapped it, etc...nothing like finding aluminum flakes still floating around months after the last project

as far as carbon fiber, I've never used it before, but so many people seem to think it's the bee's knees for strength I'm thinking of trying it and considering I'm going to have to remove this thing without damaging it in any fashion, put it on horses to get it to flatten out, perhaps modify it slightly to at least get it to close, I might as well mortise in a 1" square rod to both edges and hope it keeps it stable enough. and no, replacement of the slab is out of question as that would for all intensive purposes require redoing the whole wall it resides in. one side of me says "yeah, you called this one correctly, never do it again", the other says "the pivot system allows for a completely hidden system and figuring out how to keep the slab under control is worth the effort"

any real world knowledge of strength of carbon fiber vs. aluminum would be greatly appreciated, as if I'm going to suggest this course of action I'd like to feel I know what I'm talking about...while it has a Young's modulus 2x that of aluminum I don't know if that means 2x as stiff...either way, it's a stronger product for sure and considering the client well worth any cost differential...while NDA's don't allow me to post an image, I can say this door hides a blast resistant door that's behind it and making the access disappear is rather important

Perhaps a design akin to a raised panel door where the wood can move without causing distortion might be more suitable? When the humidity changes, someone will have to adjust the truss rod.

Since you know what direction it wants to bow, you could use single compression rods which are easy to make yourself.

What would be the feasibility of taking it apart, slicing each board down the middle, flipping one half and gluing them all back together like a laminated neck? It should cancel out its own bowing tendencies then. Either that or change to twisting, which is even worse... Maybe slice it up thin and rebuild it hollow with cardboard honeycomb core?

Carbon reinforcing beams won't do any better than steel since the Young's modulus is similar. It's just lighter weight and higher strength, but strength is not really relevant in this case. Coating the whole thing with a carbon fabric skin would be more effective, but would be expensive to get enough thickness to overpower a 1 3/4" board, and bad for stealth unless you add wood veneer on top of it.

serious thanks for all the replies...

the door in question is as follows:

~36" wide by 96" tall 1 3/8" thick "engineered" (e.g. solid wood perimeter of about 3/4" thick with particle board interior with thin layer of MDF faces)

on this base 3/4" MDF core plywood was attached with screws (I was afraid of any distortion caused by glue) and covering the screws and part of the general layout were 1/2" thick and 1 1/2" wide battens running vertically...the "look" is rift grain white oak plywood running from floor to ceiling with white oak battens spaced 1 1/2" apart...this is all grain matched material running floor to ceiling, and details in the design make the door completely disappear except under scrutiny from very close. I can only assume that the house now having the HVAC in use as opposed to commercial units outside pumping in conditioned air is the issue here...either way, specific causality is now out of my control and the only thing I can think of to save the day is reinforcement of the edges on either side, and that's only plausible by routing a slot and inserting something that will at the very least add strength to resist bowing...taking the door apart would result in required replacement of at least the battens from floor to ceiling and if removal resulted in destruction of the seen veneer because of the glue used to attach them then it's game completely over

the truss rod idea is something I thought of ages ago as a concept for what I see far too often and is always an issue when architects have the unrealistic specs of 1/8" air gaps on either side of a pocket door , so that concept is a for the future project if I even live long enough to do this general design parameter again. or do something similar which would justify the expense (funny thing about the uber rich...they are very rarely interested in spending what's required to pull off some of the outlandish things their architects and designers come up with...those that do are treasures to deal with)...the best lesson I've learned from this is to get REALLY firm about "if you choose this path of completely hidden for an outswing door (which requires a pivot system as opposed to hidden hinges (which lock it in place on the hinged side)) then it's going to cost not only an arm and a leg but also the soul of your first born to boot"...as a note I've done this basic design detail 2x before this with hidden hinges and have heard of no issues that required any attention (though I did worry about issues when doing those projects)...similar thoughts of different humidity levels on either sides of the doors, same thoughts of any error of alignments being tilted towards small gap at top which the force of the door closer would pull tight, etc...this is the first one that's bowed afaik

oh well, many thanks again for the replies...if nothing else it's helping me brainstorm (unbilled) for a solution to this issue with the owner staying the night for the first time in 8 days..."luckily" he's only in town for the night (he owns God only knows how many properties across the world) and I'm pretty sure I can at least temporarily stabilize the door over the next week (stick it on protected saw horses with the bow up) and reswing it the day before he arrives and have time for a more permanent solution after he departs...if I'm lucky I can source carbon fiber reinforcement very quickly and try that, though from quick looking that in of itself won't be cheap

Oh, I didn't catch that it was only solid wood on the edges. Particle board should already be largely homogeneous, so the slicing and flipping idea is out. Sounds like simple humidity expansion then... no other solution than to equalize it on both sides. Even if the edge reinforcements remain straight, the middle of the door will bow and reveal itself.

The real question is why didn't the others have the same problem? Better ventilation behind them?

indeed...why the problem?

I completed this door around 8 months ago and it was stable when I transferred to another site 6 months ago...since then it got finished, etc...

I transferred back to this site 3 weeks ago for hardware details and I did check on it and noted nothing that raised my eyebrows, then got notified by the superintendent and owner's rep that there was an issue 2 days ago...3 weeks ago the HVAC wasn't in service...now it is...if anything the central air covers more of the house than the temp system...go figure...current humidity in the house is real low at around 25% and if anything the area behind the door should be "wetter" which implies to me the slab should have bowed in...that thought brings up the idea of putting a like hygrometer on both sides of the door the at least have that info...there are fine details to all of this as far as paths of air to both sides that I haven't paid any full attention to being that my scope of labor isn't in this area and this issue was just brought up to me and I'm still in the panic mode of trying to solve it let alone quantify it! I do walk pretty much the whole site day to day as a normal course of work and do notice some things, but I haven't bent my full attention to it all as of yet being that I have a lot of other things to do to get the house ready to live in

Another idea (without seeing the door, so my understanding maybe non-existent): Can the wood on each side be firmly attached on only one end with screws and the screws ride in slots for the rest of the length?

Trying to picture the layers of the door panel sandwich and having trouble with that.

From back side of panel to front I'm picturing a "thin layer MDF face(s)" on X/X" thick particle board, then the second thin layer MDF face.

Screwed to that is 3/4" MDF core ply, I'm guessing with an oak veneer.

And then the vertical solid oak (?) battens, screwed or glued to the 3/4" MDF.

If I have that right, the only way to keep the panel flat is to keep it in a climate controlled environment that is close to the same conditions in which it was assembled. That means both sides of the door.

If that is the case and the space behind the door isn't under the influence of some other humidity source you may find that after the door has time to reach equilibrium that it flattens back out to the form it had when assembled. To speed that along you might suggest leaving the door partially open for a couple weeks to speed that process up and see what happens. I wouldn't change anything for 2-3 weeks.

If the door is going to be under changing climate conditions, especially variable RH, your door will warp and I don't think any edge treatment will cure it though it could help.

If your battens are solid oak they are not going to change in length appreciably as a result of temp or RH but the panels will so the problem is somewhat built in.

It sounds like you can take the door out by reference to putting it on saw horses if I got that right. If so, and if the back side of the door will not be seen in use you could try and reduce the stress the panels are inducing to the assembly. You might consider routing or sawing some horizontal slots thru the panels from the back side maybe 1/4" shy of going thru the ply core panel. Kind of like expansion joints in concrete. Maybe a slot every foot of height. It would make it a lot harder for the panel's swelling to warp the door out of flat.

You could do more too but since I'm just guessing at the construction details I'll leave it there for now.

Good luck.

_________________
Brian R, Wood Mechanic
N8ZED