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  Topic Review (Newest First)
05-18-2014 03:36 PM
Bedis I would go with the phenolic coated plywood. I made an out feed table for my table saw with 3/4" baltic birch coated with black phenolic, and had no issues cutting it. I have had it for about 6 years now and still flat and true. Bill
05-18-2014 02:47 PM
Salty Dawg Ok, just finished up my bookcase project & I used MDF lite for the raised panels on the doors & sides of the cabinets, I have leftovers of the MDF lite & Oak plywood, enough to make another table, I measured the MDF on the end that I had cut & the opposite end I have not cut & has been in the garage for 4 months now & both ends measured the same. On the other hand, my wife's boss has a half sheet of some high dollar phenotic plywood that is coated on both sides that he said he would give me but he said it was extremely hard to cut. Which one would you guys & gals go with? The phenolic with the oak plywood on bottom or the mdf lite with oak plywood on bottom? I already have an oak frame for the top to sit on.
05-05-2014 12:01 AM
Peter M Rout out the rebate for the router a bit deeper and use the leveling screws to adjust for any movement. That said, movement in changing (circum-ambient) environment is impossible to suppress. Metals and water-impervious materials respond primarily to changes in temperature; organic materials (e.g. wood and wood fiber constructs such as MDF) respond primarily to changes in humidity. The only solution I have found is temperature control for the former, and thorough sealing [multiple coats] of the entire structure with a water-impervious material for the later. Temperatures where I live ranges from below zero to about 130F; humidity from 0 to 100%. I build with dry wood( about 17% water content) and use either a clear polyurethane (catalyzed) or epoxy paint sealant on furniture and have had no significant movement/dimension problems. And . . . I try not expose the work to either of those temperature extremes.

Good luck, let us know when you find a solution.
05-04-2014 04:05 PM
DoItMyselfToo Don - on the underside of the table I recommend using a solid frame around the perimeter and cross braces across from side to side. Steel angle iron that's painted makes sense to me. As for the top, perhaps going with a moisture stable material, such as solid phenolic, would eliminate future issues. From what I hear solid phenolic would last forever.
05-04-2014 12:55 PM
DaninVan I just checked our local weather...9C and 92% relative humidity.
If I left a piece of unsealed MDF outside, but under shelter, I'd expect it to absorb a lot of that moisture, as the norm from the lumberyard would likely be between 10% and 20%, depending on how long it'd been sitting in storage.
High relative humidity is normal here on the West Coast, but nobody complains because the temperature is usually very pleasant (not too hot; not too cold).
I've had the same problem as you experienced, on my RAS MDF table, when I left it out in the unheated garage. I just avoid MDF.
05-04-2014 12:30 PM
Marco Like others stated a flat frame underneath is needed no matte rmost material
05-04-2014 10:31 AM
Cherryville Chuck
Originally Posted by DesertRatTom View Post
If you're going to put in miter slots, you should add a second layer, at least half an inch to retain the strength.

I guess my wife is right about me getting nit picky about things.
My last top was only 5/8" melamine coated particle board and it had slots for t-track cut into it but I did try and keep them close to the frame members underneath. It's still flat after 4 years and it stays outside from -45C to +40C so thicker isn't even necessarily needed since mine was only 1/4" thick in spots.

BTW, I used biscuits to attach my top. Just one more way to skin the cat.
05-04-2014 10:18 AM
DesertRatTom When I want a top to be and remain perfectly flat, I make a framework of 3/4"x2" hardwood that has had the edge jointered dead flat. I then run it through a table saw to make the width the same all round. Drill oversized holes, larger than a wood screw head to leave 3/4 inch of wood at the bottom. I do this every 6 inches or so, then attach the whole thing to a 3/4" ply top with 1 1/4 wood screws.

I use a long bit in a countersink to drill completely through the last 3/4 inch of the frame. That allows the screws to get a half inch grip in the top, but doesn't go through far enough to raise a bump on the top side while avoiding any splitting. If using mdf, you have to predrill the screw holes for the MDF. I then start two screws through the framework to hold it the frame place while I double check the fit, then screw the whole thing in place. Nothing I make this way ever warps. I bet this would work on Corian as well but I'm sure you would have to pre drill the holes or risk damaging it. Some sort of top laminate material might make workpieces slide smoother, but make sure you apply it so it is perfectly flat. If you're going to put in miter slots, you should add a second layer, at least half an inch to retain the strength.

I guess my wife is right about me getting nit picky about things.
05-04-2014 08:40 AM
Selwyn Senior Greetings Don. My table has two pieces of angle iron, one on each side, that strengthens the table. I wonder if something like that would help?
05-03-2014 08:32 PM
jw2170 It almost sounds like the edges around the plate have got wet, somehow.

I have used MDF for other projects and the humidity has not caused that much swelling.

Even for items stored out in the car port......

If the edges continue to curl up, I would bite the bullet and make a new top from birch play.
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