MDF for Workbench Top?

[bp122]

Hi all

I haven't really bothered with building a new workbench from scratch, as I cannot really justify the cost and time at this stage, where I have a few small scale projects coming up (shoe cabinet, closed computer cabinet, picture frames, shelves and draws for various parts of the house etc)

So, I came across a solid pine dining table which someone was selling on the popular sticky tree website for £20 delivered. It has a heavy 50mm thick top and round legs, hasn't got a brilliant apron, but is quite stable once the top is screwed on. It is the right size for my work area in the garage but just over an inch lower than I'd like. The top itself is heavily varnished but I can't find a spot which is flat for longer than 3 inches I have also trimmed the edges which had a fancy routing on it (but was uneven) with my track saw, so it is uniform and straight.

I am thinking of attaching an old record face vise to it (which I restored myself to an operable condition) and to give the table a bit of height and heft at the top, putting two sheets of 18mm MDF glued together and screwed on top of it. It will give it a flat surface and the fact that two MDF sheets are glued, it might keep it flat for a while.

Down the line, I'd like to create a tool draw, a couple of cabinets under it to aid the storage of all frequently used bits and bobs.

1. Is this a good idea, and has anyone else done this?
2. If yes, what sort of finish should I apply on it?
3. Or would it be a better idea to stick one MDF sheet to a melamine faced chipboard
4. same question as #3, but use a flat hardwood table top from a different table instead of the melamine?
5. Also, instead of fitting a vise, for my application, would a bench bull be a better solution?

I won't be banging a lot on this table, ex: chisel work or carving etc. I just need a reliably flat table for assembly and planing

I also plan to drill a few holes for dogs / holdfasts, later on of course, as there isn't a great deal of room to attach clamps on this.

Please share your thoughts and experiences.

Best regards
B

 

[gmgmgm]

I have an 18mm thick MDF sheet as my workbench top. It's great - nice and smooth, and looks even better whenever I dry Osmo brushes by giving it another coat. And it's easy to replace (in fact I have the next sheet ready underneath), and I don't worry about putting a screw into it at any time.

But don't just assume it will be flat if you have 2 sheets stuck together. MDF will mould itself to the underlying shape fairly easily, so it needs strong support.

 

[bp122]

Ah, interesting. What do you coat it with? Some sort of poly?

 

[lurker]

Just a thought, make sure it's heigh enough. I am a short @£se but I reckon a diner table would be a good 4 inch too low for me.
You could do as you Plan with two sheets of mdf but put 3 inch battens between the current top and the new one
The resultant gap would be a handy shelf for tools.
Also think about ensuring there is no leg rack, although you could fix that as you go along

 

[bp122]

Just a thought, make sure it's heigh enough. I am a short @£se but I reckon a diner table would be a good 4 inch too low for me.
You could do as you Plan with two sheets of mdf but put 3 inch battens between the current top and the new one
The resultant gap would be a handy shelf for tools.
Also think about ensuring there is no leg rack, although you could fix that as you go along

See, I like this idea. But I do have a question. What is racking?

 

[ED65]

1. MDF as a workbench surface? Loads. Screwed directly to solid wood though, not so much. No reason it can't be done if you attach the disparate materials correctly, to allow for seasonal movement in the pine.

2. Nowt? You can seal MDF quite well with any common varnish or clear coating, or shellac if you have enough of it. I think some use a wax or oil&wax finish on theirs, but plenty of MDF benches have tops that are left unfinished. One further option is to skin it with hardboard, the idea being this is a sacrificial layer that can be replaced in due course if it becomes to chewed up or dirty (after flipping once to double its useful lifespan).

Just one further thing to note since you mention holdfasts are a possible future addition, some holdfasts don't work on excessively thick tops and 18x2 + 50 is getting towards the upper limit of what may allow the shaft of the holdfast to cant over far enough to lock. There are workarounds for this, as there are for tops that are too thin, but something to bear in mind.

 

[MikeG.]

......... What is racking?

Parallelagramming. I just invented a word. :lol:

 

[bp122]

1. MDF as a workbench surface? Loads. Screwed directly to solid wood though, not so much. No reason it can't be done if you attach the disparate materials correctly, to allow for seasonal movement in the pine.

2. Nowt? You can seal MDF quite well with any common varnish or clear coating, or shellac if you have enough of it. I think some use a wax or oil&wax finish on theirs, but plenty of MDF benches have tops that are left unfinished. One further option is to skin it with hardboard, the idea being this is a sacrificial layer that can be replaced in due course if it becomes to chewed up or dirty (after flipping once to double its useful lifespan).

Just one further thing to note since you mention holdfasts are a possible future addition, some holdfasts don't work on excessively thick tops and 18x2 + 50 is getting towards the upper limit of what may allow the shaft of the holdfast to cant over far enough to lock. There are workarounds for this, as there are for tops that are too thin, but something to bear in mind.

That seems all well, then. I like the hardboard idea. And regarding holdfast and table top depth, I thought I had to have them deeper, but I'm glad to have learnt it isn't true.

......... What is racking?

Parallelagramming. I just invented a word. :lol:

Now I get it, the misalignment effect when something is clamped at one end of the vise.

 

[Ttrees]

Racking as in the legs getting forced and snapping the joints apart from planing. Maybe try finding an old solid core or composite door instead as it will be long enough to go against the wall instead of needing a pretty heavy bench for working on comfortably rather than something that you will be fighting with. Make some sawhorses for it and call it a job done

 

[bp122]

On Sunday, I got the two sheets of MDF and cut them to size (plus a few mm on all sides) and glued them to each other - which was mu first glue up of anything that size. I left it to set on the workbench and couldn't get back to it until last night.

When I came to see how it went, I removed all the clamps to find out that because I had spaced the MDF off the table top using scrap pieces of MDF and were unevenly distributed, and I had placed weights on it to help with the clamping force, there is a huge bow in it now. The bow deviation measures about 12 mm in the middle, over a length of 1400 mm.

So last night, I cleared the table, placed the glued up top on two scraps of MDF placed at the ends and put some weights in the middle - see if it improves this - fingers crossed.

 

[ED65]

Ouch! I fear you may have glued in that shape but fingers crossed.

If you have to do this again, instead of weight or clamps you can use a rake of screws interspersed around the sheets instead. These can be removed after the glue has set or left in if they won't potentially get in the way of future dog holes.

When I glued up my benchtops (MDF x 2 and one layer of ply) I put them on the floor as it was the largest flattest surface I had available.

 

[bp122]

That is a good idea with the screws, and the floor.
But I don't have a non-carpeted floor area that big which is flat. The garage floor is really wavy and ridged concrete

But it has given me an idea though. If the weights don't help straighten the sheet and if it is indeed irreversible, I was thinking of cutting the sheet length into parts and place the sections individually on the bench top and use another top layer to cover up the creases and screw them all through to the Pine base.

I mean, technically, if I cut the bowed top in half, the error must also be halved, so if I do four parts, the error will be only a quarter of what it is - again, in theory.

Option two was to screw the full bowed top to the base along the middle (where the error is maximum when kept convex side up) whilst using some wedges on the sides to really get it down?

None of these sound like great options, but they are nevertheless options I am left with, I feel.

 

[MusicMan]

Cutting up and regluing should help with the bow as you say. But the stiffness will suffer considerably, as it will be limited by the stiffness of the sheet that you glue it to. If your bench supports are flat and stiff this may not matter too much. And also the resulting bow (up to 7.5 mm!) and wavy surface will still be bad, unless you can really pull the top down onto the stretchers. As it is MDF you can't plane it flat, either (indeed this is the big disadvantage of an MDF top).

I think you'll find yourself redoing it. Next time, get a long spirit level and be sure that the supports for the spacers are level in both directions, and don't put any weight in between them.

 

[ED65]

That is a good idea with the screws, and the floor.
But I don't have a non-carpeted floor area that big which is flat. The garage floor is really wavy and ridged concrete

I was going to add this above, I did it in the sitting room on the carpet.

I put down newspapers of course and did it when SWMBO wasn't home. I'm not suicidal after all :lol:

 

[bp122]

That is a good idea with the screws, and the floor.
But I don't have a non-carpeted floor area that big which is flat. The garage floor is really wavy and ridged concrete

I was going to add this above, I did it in the sitting room on the carpet.

I put down newspapers of course and did it when SWMBO wasn't home. I'm not suicidal after all :lol:

Ha ha Fair enough!

Cutting up and regluing should help with the bow as you say. But the stiffness will suffer considerably, as it will be limited by the stiffness of the sheet that you glue it to. If your bench supports are flat and stiff this may not matter too much. And also the resulting bow (up to 7.5 mm!) and wavy surface will still be bad, unless you can really pull the top down onto the stretchers. As it is MDF you can't plane it flat, either (indeed this is the big disadvantage of an MDF top).

I think you'll find yourself redoing it. Next time, get a long spirit level and be sure that the supports for the spacers are level in both directions, and don't put any weight in between them.

I think you are right about a redo. I'll still try to botch it and see if it works. If not, I can use the pieces for another project that requires 36mm MDF pieces!! Bloody hell, this is turning out to be more work than doing a proper glue up with proper wood! - Someone once said, shortcuts often take one longer to reach the same place!