Prevent warping but allow planing

Question

I'm getting ready to make a desktop by gluing up thirty 72"H x 1.5"W x .75"D boards of alternating Maple and Mahogany. I'll be gluing the boards on there faces for a final desktop that's ~6' wide and ~1.5" thick.

My original thought was to alternate the direction of the face grain as I glued them up to help prevent warping. Once I get ~12" (16 boards) glued up I want to run it through my planer to level it up perfectly. My concern is that I had a friend tell me to take care when running a board through a planer to take note of the direction of the grain and to make sure the blades were removing material like so:

O -> /////////

Instead of like so:

O -> \\\\\\\\\\

Well if I alternate my grain, I'll have every other board going the wrong way. So do I protect against warp, or use proper planing technicque?

Answer 1

I have glued up similar wood slabs without being overly concerned about grain direction. Regardless of grain direction the individual boards will control the tendency to warp of adjacent boards to the point where warping should not be a problem in a desk application. If you had a condition where either the top or bottom was regularly exposed to more humidity and temperature differences than the other then it might be possible that the slab would warp as a whole.

The reason for running the grain through a planer in the direction your friend suggested was to avoid tear out where wood fiber deeper from the surface is pulled out by the planer knives. The risk of this occurring is greater near knots or in patterned wood grain specimens such as with curly maple where the grain directions may be more vertical to the flow of the material through the planer. It is a good idea to align the boards to flow as suggested, but when that is not possible then resort to very shallow plane settings so that the knives cannot get a grip on the poorly aligned wood fibers. This means more passes, but it will usually work just fine.

Answer 2

Very smart to glue this thing in stages. Clamping up 30 of those wet noodles at once would be an adventure.

As far as warping goes, this grain orientation thing is worth a discussion, but the real culprit is moisture, and the balanced (or un-) transfer of it from the wood into the air, as has already been discussed. You've got more sq footage face-glued here than I can figure in my head, and no single board will be able to force the rest of that thing out of alignment. As long as you don't try to fasten that thing down too tight you should be ok. If you would like to discuss fastening strategies, let me know.

Ditto on tear out and lots of passes.

Many cabinet shops these days have wide belt sanders, and often they will do some sanding for a fee. I'd check it out, because then you can plane to within a 1/32 or so (hopefully your tearout wont exceed that) and they can have that pretty slick for you. Around here guys charge anywhere from 100 - 175 an hour for that kind of thing, billable by the hour, and/or maybe buy them a belt. Figure on paying one hour.

I am, however, a little concerned about the size of this thing. I’m not sure about your math, as far as the number of staves you are gluing up, but I might be missing something. More important is your expected finished top size.

A glue-up using the materials you list above will not give you a top that is 1 ½ thick or 72 long. I would consider myself doing exceedingly well if I got 1 5/16 and 71. I might be assuming too little, and if I am I apologize, but I thought I should mention it.