Thread: 30mm MDF sheet on trestles

You have to remember that MDF is a timber product! And consequently will exhibit similar characteristics to solid timber (believe it or not)> Even though it is 32mm thick I think that it will react to humidity variations. Storing it on edge will be a better way to preserve its flatness but I think it will still bow or cup. The addition of steel angles will increase its overall weight no doubt but I would still bet that it won't control the movement of the sheet.
I have seen heavy pyneboard benches sag under their own weight attributed to the moisture in the air and time
A mate of mine has a good welding bench.......it has a top made from 30mm plate.....that stays flat
Another thing using MDF to weld on is....it will burn and smoke from the hot metal and sparks. It won't stay pristine for too long
Thats my 2 bobs worth and you can have the wet blanket for free

Somehow MDF and welding of any kind don't seem to go together all that well to me.

thanks for the input guys- i should clarify, that i'm primarily using the mdf to jig, align and tack weld the components together, not for heavy duty welding purposes- the MDF won't be subjected to excessive heat or sparks as the metal that's actually in contact with the bench won't reach very high temperature with a few tack welds done with the TIG process.

i'd love a 30mm plate bench, but it's not really possible due to space/location, hence the 'foldaway' solution

so do you think there's anything I can do to control movement and keep it flat? how about more steel angle, so I have a few rails running lengthways and a few running widthways, attached to the board with plenty of screws?

like I said, I haven't done much woodwork at all so not quite sure what to expect. i would have thought a decent amount of bracing with steel would resist any warping/bowing pressure exerted by the wood, but maybe those pressures are alot stronger than i'm aware

thanks again
Corgan

Steel bracing will definitely help. To get best bang for your buck on steel, try screwing something like 60mm by 3mm flat plate to the long sides. Not very heavy but the depth of steel rather than the width is what will stiffen it best. A piece of thin tin sheet will help protect the MDF from sparks, etc but it may burn through if it was earthing any steel fabrication being welded on it. Might need to prime the underneath if you cover the top. Or try blackboard paint both sides - good for marking out your fabrications on top when on the trestles and good for doodling on the underside when it's stashed vertically - especially if suspended on a couple of pulleys.

thanks geoff- that was another thing I was considering, sealing the whole board with some kind of paint or epoxy to keep moisture out (it's listed as 'moisture resistant' MDF already, but i dont know how many grains of salt to take that one with)

I like the idea of bracing the sides, I hadn't thought of that. I might just brace the sides with flat bar as you suggested, as well as the bottom with angle (probably a bit less than originally planned to save on weight)

Sounds like you could be on the right track with your bracing. You could even make your trestles fit in-between the braces (or go a bit more complicated and hinge them to the bracing).
I am not sure how moisture resistant 'moisture resistant' MDF is, but normal MDF swells when it absorbs moisture, particularly through the sides; so some sort of protection is important.

I realize you already purchased it but a 30 mm MDF is equivalent in mass/area of 9 mm thick Ally plate. It would still need some bracing and cost more than MDF but would have several advantages over MDF ie no moisture probs, could take more knocks, and zero fire hazard.

i shudder to think of the cost of that much 9mm ally plate! but if the mdf table doesnt end up working out, it's probably the road i'll have to go down. as it stands the MDF cost me $100 cut to size, and I got two smaller offcuts which are useful in their own rights for jigging up smaller fabrications (full sheet size was 2400x1200, would have cost $77 if i didnt need it cut down)

thanks for the tips and suggestions, i will pick up a few bits of steel later in the week and brace it up over the weekend.

any final tips on the best product to seal it with?

A lighter and more stable solution would have been to create a torsion box - two layers of 10mm ply with a simple 80mm thick web framework inside to keep it all flat.

Build a Torsion Box Assembly Table - Fine Woodworking Video

I use 15mm compressed cement sheeting sitting 90x45 framing pine sitting on 4 trestles this stays pretty flat and doesnt burn probably the same weight as the mdf

Originally Posted by fubar

I use 15mm compressed cement sheeting sitting 90x45 framing pine sitting on 4 trestles this stays pretty flat and doesnt burn probably the same weight as the mdf

thats wat i was thinking use cfc

Combine Mastersplinter's and fubar's ideas then some thin steel plate on top for conductivity

thanks for the replies everyone, i will have to build one of those torsion box assemblies when i get some more space for a permanent bench (or even a smaller portable one when my big mdf board is flogged to death)

as it stands, i've bought and drilled 3 lengths of 50x50x5mm steel angle to brace the underside, and 32x3mm flat bar to screw onto the edges of the MDF, with all that steel i'd be quite surprised if it were able to warp.

i will just have to put up with the already existing 1-2mm variation in flatness along the 1800mm length of board, i can always shim the components when assembling for tacking to get them back into flat.

screwed the steel bracing in place this arvo, and it's removed that slight warp so the board is a fair bit flatter now. the angles had a minute bend in them which the board has taken on but i can live with it, as it's probably 0.5mm over an 1800mm span.

i'm quite happy with the ease and simplicity of this workbench and i think i'll get a good amount of use out of it before having to upgrade to something else.

cheers
Corgan