Thread: Making a very flat surface.

Personally, I’d avoid the MDF as imo it’ll warp and/or swell over time, with moisture, glue, humidity etc.

I’m on the verge of fixing my table top and I’m going for 2 layers of 17mm formply from the Big B. $55 per sheet 1800x1200, then some tassie oak trim around the edge to cover up the 2 layers. Screwed from underneath.
These would be super flat


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I had to build a 3.6 metre long torsion box and did not have a flat enough area to do it on. In the end DaveTTC helped me make four flat beams from MDF. We basically made I beams with the two flat faces being separated by MDF separators. I will take a photo later and post it as I am using two of them to build my router table on.

All the work benches at my old work are 32mm MDF, no sagging or swelling to be seen.

I recently made a MDF assembly table but used 18 mm with bracing Wireliner.

It becomes effectively a torsion box, and I have to say it is as solid as!!! You wouldn't go pounding stuff on it, need solid wood for that, but for a base for doing glue-ups, epoxy pours flattening slabs and so on, it's the ants pants.

Not only that but the base I put it on wasn't flat as it turns out. I noticed after assembly that it was fixed on one side and the middle only, so hanging in space for half of it. In four months now it is still as flat as it ever was and still hanging in space. It it is flat you want, I reckon that's the answer. Will add a few pics of the progress and finished product

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Originally Posted by elanjacobs

All the work benches at my old work are 32mm MDF, no sagging or swelling to be seen.

Elan. Are they treated/sealed in any way?
My MDF sheets in the shed tend to swell with the humidity, I’m in SEQld!


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Originally Posted by Runningman

I’m going for 2 layers of 17mm formply from the Big B. $55 per sheet 1800x1200

Check Gumtree. I got 1800x1200 for $30 in Sydney. If anything it should be even a little cheaper for you, being 1000km closer to the source.

Formply is a very good surface, and nothing will stick to it (if someone knows of something that will then I'd like to know what it is.....), but be aware that being black or near to it makes it a tricky colour to have as a workbench. Virtually waterproof too, until you have a cut edge (which can be waterproofed with Sikaflex Pro).

My bench top is 19 mm MDF Torsion Box Design
The rips were 19/42 mm from the Big B.

Still flat if this helps

An i never got around to finishing it [emoji849].

Cheers Matt

Originally Posted by Runningman

Elan. Are they treated/sealed in any way?
My MDF sheets in the shed tend to swell with the humidity, I’m in SEQld!

Nope, but Melbourne is a bit drier than QLD...

This is it
IMAG2882.jpg

70*70 Beech legs, 145*35 apron with 3x 70*35 stretchers at the top, one between each pair of legs and a 100*22 board at the bottom, all in Vic Ash and dowelled together. The top is screwed straight through with 70mm screws and covered with a sacrificial sheet of 3mm MDF that's flipped/replaced as needed.

The MDF was originally smaller, but got bumped up to a full sheet to suit the work I was doing. The overhang is too big for that frame and it does droop a couple of mm, but a properly sized frame with about 100mm overhang would be fine.

I have got a mdf bench top, 2 x 3/4” sheets glued together, about 900 x 2400mm with timber edging and a heavy timber base. I coated it with Cabot’s CFP, have recoated it twice in 16 years . It has lasted very well, and still looks good.

At my local Men’s Shed our benches are all topped with 32mm MDF then a sheet of Masonite on top - all sitting in a 35mm pine frame. The Masonite can be replaced easily when damaged - our Shed members are sometimes a bit enthusiastic Works really well.

Regards,

Brian

Originally Posted by FenceFurniture

Formply is a very good surface, and nothing will stick to it (if someone knows of something that will then I'd like to know what it is.....).

Spray on contact adhesive. Ruins the smooth surface of your form ply benchtop also. Don't ask me how I know.




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I made a model aircraft building table from 32mm MDF 25 years ago. One sheet of 2400x1200 for the top, with 200mm wide 32mm MDF rails inset 200mm from the edges all round. It stayed in one place for 20yrs, once leveled and flattened there was no obvious or measurable movement during that 20 yrs. I still have it, currently in vertical storage with the legs removed, but may not be as pristine now as I know that the storage area has had standing water on the floor a couple of times so suspect it might have gotten wet along at least one end.

MDF is fairly good in regard to flatness, but not perfect, a typical 2400x1800x18 sheet can have 0.5mm variation over the surface, I used to operate a cabinet makers CNC using sheets that size for the vacuum diffuser/spoil board. This involves skimming 0.5mm of both sides of a board to remove the skin and get the board porous for the vacuum clamping, then reskimming as required through the life of the board. Quite often the initial 0.5mm skim would clear about 80% of the skin and leave up to 20% with some skin remaining requiring a second skim to clear the surface.

I've used 25mm MDF for the tops of rolling cabinets. One has a grinder and the other has my thicknesser/planer on it. No issues with distortion or sagging but the top is supported on 3 sides and the planer top is only about 900mm long. Other bits of MDF stored loose in the garage are fine as well, including a large 19mm (~2mx1.2m) sheet used as the base for my router flattening jig. It's flat enough for woodwork. If you need an extremely flat surface, you could do a torsion box style workbench top, quite a few resources on the web on how to make one. If your workbench is still useable and the top is flat, maybe get a 12mm board of some sort and screw that down on it?

MDF makes a good top, provided it is kept dry. I have it on most of my benches and they have given less trouble than the timber ones.