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1 3/8" MDO panels

8/1/17       
Tim  Member

Website: eastmanwoodworking.com

We need to build a number of paint grade exterior doors with raised panels. The panels are 25" wide and 1 3/8" thick. I would like to laminate 1" + 3/8" MDO but would welcome any words of caution. Technically it would be an unbalanced panel with the different thicknesses, but in this case I don't think it should be a problem. The edges will get an applied wood edge which will be shaped to the raised panel profile. We would probably use Titebond III, or if that is a terrible idea West System.The glue line will be totally buried and the edges covered with wood edging, so it may be expensive overkill to use West System. We will be vacuum bagging the panels for glue up.

8/1/17       #2: 1 3/8" MDO panels ...
Adam

I like mdo plywood. However, it's not the best choice for your project.

Exterior MDF

8/3/17       #3: 1 3/8" MDO panels ...
David R Sochar Member

We have recently upgraded our exterior panels that are at risk of any exposure to a 7 ply panel, even if they are paint grade.
A center core of 1/4" MDF exterior, then on either side a thick face of solid wood, then a cross band of 1/16" veneer, then face ply of 1/16" veneer. The solid wood is where the raise happens. We might use urethane glue to get the solid plies to width, but everything else is epoxy. These are beautiful panels as the veneer faces give us the opportunity to book match and center grain patterns.

We refer to them as 'bulletproof', though they have not been tested in such a manor. We do have a few samples made up and finished, and sitting out in full sun, in the drip line of the shop roof (R+D testing dept.). They have been out there over a year and show no sign of degradation.

I have an old guy's resistance to MDF, and limit its use to out of sight places where stability is required. It also is not allowed on the edge equipment - joiner, planer, or the shapers. I refuse to accept its wider uses as woodwork. There are no pretty or fanciful shavings, just an abhorrent brown dust that annoys and gets everywhere.

In the past 15 years, we had a series of problems with full thickness, edge joined panels showing a hairline crack on the joint line. We think that may have been dull joiner knives. An easy fix.

Then we had a series of failures on joint lines with East facing and West facing dark finish doors. We even had an East facing veneered core door fail by cracking veneers and then the core underneath failing. That was all due to TBIII's propensity to fail at higher temperatures. Glue techs told us to not use it if the door might get sun, or might get a dark finish. We measured up to 190 degrees on a dark Walnut face facing East. Well above the point where TBIII looses 70% of its strength.

After 45 years of making doors that get weather, I am surprised to realize I am making such a radical change to what I thought was an unquestioned process. I have tried to make "durable" or "split-proof" panels over the years (usually a 3 ply panel), but have gone back to solid panels since we did not seem to get an advantage. Over the years, we have talked about doors 'of no compromise' amongst ourselves and our customers. I think now we truly have no exceptions to the 'no compromise' standard.


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