Replies

1. 
   Jamie_Buxton | Apr 10, 2003 06:27pm | #1

   Could we have a little more detail?

   • What are the dimensions of the warping board?
   • Approximately how much is it warped?
   • Are the six components sitting on it or below it?
   • If you play the stereo at your usual levels for an hour or two, and then feel the surface of the board closest to the components, does the surface feel hot, or just a little warm?
   • How much access do you have to the warping board?  For instance, can you just turn it over so the warp goes up instead of down?
1. 
   SThomas | Apr 10, 2003 06:43pm | #2

   off the top of my head (going over to look at the problem more closely)-- maple is 24" X 72", the components sit beneath, behind doors with what I thought was acceptable ventilation, I cannot simply flip the top, unfortunately, and at this moment, I don't know the severity of the problem. I fear I am going to have build new, even better ventilated doors...

   Stephen

1. 
   HowardAcheson | Apr 10, 2003 07:18pm | #3

   When I build entertainment centers I try to use veneered composite tops just for that reason. If I have to use solid wood, I put a plywood panel just below the top to act as a separator and use "buttons" in slots to attach the top firmly to each upright panel. The plywood panel is designed to isolate the top and to have cross ventilation. I also use a "Whisper Fan" to force ventilate the component area.

2. 
   Jamie_Buxton | Apr 10, 2003 08:18pm | #5

   Stephen --

      While more ventilation couldn't hurt, my guess is that heat from the stereo really isn't the issue.   Modern solid-state components just don't generate a great deal of heat.  My guess is that you'll find that the warping board is barely warm to the touch.  That is, the warping is coming from some other cause.  Perhaps an individual board in the glue-up was still a little wet when you machined it, or something like that.  You can attach straightening bars to the underside of the warped one -- although you have to design them to allow the maple to do its normal expansion and contraction due to humidity changes.  And, of course, you have to be willing to look at the straighening bars, too.   Another approach would be to rebuild the warped board with veneered plywood, which can be more stable than solid lumber.

            Jamie

2. 
   RoyinMD | Apr 10, 2003 07:51pm | #4

   Can you modify the back and/or bottom with ventilation slots or holes. A chimmey effect might do the trick, colder air in low and warmer air out high.

   Enjoy, Roy

3. 
   rmcjh | Apr 10, 2003 08:38pm | #6

   Stephen:

   I agree with Howie in that a small fan moving air within the enclosure will be of benefit.  You can most likely get everything you need from Radio Shack.

   Roger

1. 
   SThomas | Apr 10, 2003 08:49pm | #7

   People: Thanks much -- good suggestions, all.

   I think I will attack the problem thusly: drill holes in bottom and shelves, hopeful that the chimney effect will work. I will likley also attach straightening bars (any advice on how to construct to allow for wood expansion -- as simple as lengthy and wide slots for the screws?) to the underside, as they will not be visible. As for attaching plywood to the underside, not possible, short of major, major work. Perhaps that becomes necessary, but in the meantime...

   Am I to infer that had I constructed the top of veneered plywood with edging, I wouldn't be confronted by this problem? Yet another in the endless line of lessons learned...

   Lastly, can someone tell me what the appropriate moisture content is for wood before working??

   Thanks again.

   Stephen

1. 
   Kell | Apr 10, 2003 11:00pm | #8

   I am fascinated by this having built four or five entertainment centers over the years and about to build another one.  All the ones I've built have utilized veneered plywood for the spans and have never experienced the warp. 

   Your question about moisture content is no more than 6 - 8 %.  Kiln dried maple should easily be in that vicinity.

   I seriously doubt it's the electronic components that are causing this.  I can't imagine that they could generate that much heat to dry out one side of a board enough to cause warp.  I've worked in electronics retail for over 20 years and unless you're running tube amps at a volume level that is likely to make you wish you're in the next county or a very poorly engineered Class A solid state amp at the same volume, they just don't produce that much heat.

   Is the cabinet sealed in some way to reduce dust collection and therefore increasing the effect of the electronics?  If so the fix you've suggested may help to resolve it although I don't know if what's already happened can be fixed.

   Kell

1. 
   SThomas | Apr 10, 2003 11:50pm | #9

   Kell--I'm not sure what to say in response to the issue of heat-generation of the components. God knows, I will defer on the issue, however, I have to tell you, when I put my hand on the maple (on the side of the unit that houses the six pieces), that puppy was WARM. I'm thinking that it might be wise to ask the homeowners to spread out the components, moving some to the other side of the unit that is, currently, completely empty. And the answer is yes, I did seal the underside of the maple -- let me guess, another in the long list of 'things Stephen learns the hard way?'

   Lastly, thanks for the info. on moisture content; now, for another follow-up, stupid question: is ALL lumber kiln-dried or is that another issue I need to be aware of??

   Thanks again.

   Stephen

1. 
   Kell | Apr 11, 2003 12:42am | #10

   stephen,

   Sealing the wood was the right thing to do.  My question is whether or not the cabinet is sealed as in air tight or close to it.  If it is, and there is that much heat generated, then my guess is that that is the cause of it.  Wow!  We've both learned something on this one; guess I've been fortunate so far!

   Lumber can be either kiln dried or air dried.  I'm no expert on either of these but a number of folks on this forum are and will correct me if I misspeak here.  Kiln drying involves placing the freshly cut lumber in a hot environment, a large, low temperature oven actually, for a relatively short period of time (< 30 days?).  At the end of this cycle, steam is injected into the kiln for a brief period of time to help stabilize the wood and reduce case hardening.  (Do a search of the forum for several threads on this topic.)  Case hardening will have frustrate you when you see a beautiful piece of wood that you've lovingly jonted and planed, turn into a helicopter blade!

   Air drying involves stacking the lumber in such a manner that allows the flow of air around each board.  This is done typically outside with lumber being covered with a tarp or small overhang to reduce the amount of direct moisture coming in contact with it.  The wood is separated by small piecesof lumber of the same species called stickers to help in the drying.  Every so often, the wood is restacked to allow each board to get adequate ventilation.  The drying time in this process is usually referred to by the rule of thumb, one year per inch of thickness.  (4/4 lumber needs one year., 8/4 needs 2 years, etc.)

   Others far more informed on the subject have written threads here that I recommend reading but this should give you a brief idea of what's involved.  Welcome to the I learn-it-the-hard-way club!

   Kell

2. 
   SThomas | Apr 11, 2003 03:24am | #11

   Kell--"Welcome to the I-learn-it-the-hard-way club?" WELCOME? While membership was a privilege I believe I was granted at birth, it's an honor I think I could just as easily have missed...oh, well. Perhaps one of these days I'll find come to accept my membership...nah, who am I kidding?

   And in answer to your question, no, the cabinet isn't air tight. Indeed, I THOUGHT I had made necessary concessions to the components. again, oh, well. And thanks much for the primer on lumber. I was vaguely aware of the different methods, it simply never occurred to me if one method is preferable to another or to ask at the lumber yard.

   Continued thanks for the dialogue.

   Stephen

3. 
   HowardAcheson | Apr 11, 2003 08:10pm | #12

   No, not all furniture lumber is kiln dried. Some is air dried and many woodworkers prefer it as the color seems to be better.

   As to the kiln drying. Most furniture wood that is kiln dried is dried to about 5-6%. However, wood will begin to acclimate itself to its envirnment as soon as it leaves the oven. It the environment has a higher relative humidity than 20%, it will begin to take on moisture until it is in equilibrium with the air. If the environment is 75% for example, the moisture content of the wood will move to about 10-12%. As the RH changes, the wood will pickup or lose moisture to equalize and when this happens, the wood will expand and contract. If one side of a panel changes in moisture content and the other one doesn't, warping will result.

   In answer to another question, moisture content changes in composites and plywood have almost no affect on the stability of the wood. That's why a veneered composite or plywood top would be most unlikely to be affected by moisture content changes.

4. 
   clampman2 | Apr 12, 2003 08:42am | #13

   Stephen,

   I assume your problem is "cupping", that the temperature within the unit is causing the bottom side of the top to shrink resulting in a top that is humped up in the middle.

   Two feet is a very wide glue up without solid fastening from beneath. By solid fastening I mean screws with washers through slotted, slippery, hardwood blocking. Or use double holed washers sold specifically for that purpose .

   The other thing you can do in the future {in like situations) is to rout 1/4" coves in the bottom of the top to relieve the stress and allow your fasteners to work more easily. I try to shy away from saw kerfs, as they create stress risers and can cause splits in the top.

   Good luck.

   Clampman

1. 
   SThomas | Apr 12, 2003 04:27pm | #14

   Clampman--Thanks very much for the lesson. Next time, I'll be sure to take these steps BEFORE I've finished. Regardless, could you further edify me -- what type of screws should I use, wood or drywall or fundamentally immaterial? Secondly, as for the slippery strut, can I simply mill some excess maple, cut some notches into it, wax or soap the piece and then attach it to the underside of the top?

   Thanks again.

   Stephen

1. 
   clampman2 | Apr 13, 2003 08:50am | #15

   Stephen,

   Maple is a good choice. Rather than wax it, I would sand it well and spray on some sanding sealer or zinzer white pigmented shellac. They do not evaporate or mysteriously vanish like wax does, and are very slippery as well. I don't like to use soap around wood as it attracts moisture, and I think it is harsh on wood.

   I like to use large diameter (like a # 12) pan head screws as opposed to drywall screws on the theory that they are more rigid than drywall screws and less likely to bend, possibly causing the washer they are going through to bind on the wood. Also, they have a large flat head which is easier to use with washers. The downside is that they are usually slotted screws which are always a pain.

   Does anyone else out there have other methods?

   Good Luck Stephen.

   Clampman