Blockboard as replacement for MDF - Torsion Box

[paulc]

Hello,

I want to make an assembly table and would like to base it on designs I've come accross which use a torsion gridwork of 2x4 sandwiched between 2 sheets of mdf.

However I'm reluctant to use mdf as I hate it as a material and I'm not confident that it would hold bench dogs etc. well

I've come accross this stuff which is nice and cheap , but will it do the job as a replacement for mdf in torsion box, cheers

http://www.woodworkers.ie/sheet_materia ... ls/99/109/

I would be putting a removable top of veneered ply on top

Paul

 

[jasonB]

I would think the fact its a lightweight blockboard will mean that the core is relatively soft so unlikely to be any better than MR MDF. If it were a birch faced blockboard with redwood core then it would be about teh same as MDF.

J

 

[Jacob]

Hello,

I want to make an assembly table and would like to base it on designs I've come accross which use a torsion gridwork of 2x4 sandwiched between 2 sheets of mdf.

However I'm reluctant to use mdf as I hate it as a material and I'm not confident that it would hold bench dogs etc. well

I've come accross this stuff which is nice and cheap , but will it do the job as a replacement for mdf in torsion box, cheers

http://www.woodworkers.ie/sheet_materia ... ls/99/109/

I would be putting a removable top of veneered ply on top

Paul

I reckon for an assembly table you are better off without the sheet and just have an open frame of 2x4" joists (or smaller) at say 6" centres. Makes handling, clamping, cleaning, etc easier. Debris and glue drops through. You can always drop on a sheet if you really need to.

 

[marcus]

I'm making a torsion box at the moment for a similar-ish purpose and have decided on good quality ply for the skins. Certainly better wearing and stiffer than mdf. Will probably coat with epoxy paint. Another option is formica (as a protective layer on top of the ply), or a sacrificial layer of thin hardboard, though that might be a bit tricky as you would have to somehow make holes in it that would line up with the dog holes in the ply if and when you replaced the hardboard.

I wanted to use thick hardboard (12mm) which I had seen recommended, which would be absolutely ideal but isn't available in the UK :-(

I'm also planning on drilling a grid of 8mm holes all over one side at 50mm centres, which can be used to make forms for all sorts of bent shapes by attaching templates to them using metal pins....

 

[twothumbs]

Jacobs suggestion is an interesting one and worth thinking about. Steel fabrication firms use very large flat bed tables to set up assemblies and are made out of a grid of large RSJ's set just off floor level. These can take very heavy loads of course but are set leveol and true. The principle is right. Open grid would allow wedging, packing, clamping, get your fingers underneath, and so on. Depends on wht you see as most suitable to you. Laminaboard would be a better option for sheeting but dont know if it is available nowadays. Would save a lot of dog hole cutting or whatever. The more I write the more I like it! Best wishes.

 

[marcus]

Yes it's not a bad idea at all, so long as it is built in and able to take rigidity from walls and floor. If it's to be moved about then a grid without skins won't stay flat. Also with an un-skinned grid it would be more important that the material it is made from is totally stable if you really need it to remain dead flat, ie not solid timber.

BTW re. your core material if you go the torsion box route, I would have thought that 2x4 would be a lot thicker than necessary

 

[Jacob]

Yes it's not a bad idea at all, so long as it is built in and able to take rigidity from walls and floor. If it's to be moved about then a grid without skins won't stay flat.

Why not? It will if you make it properly. It's up to you.

The assumption that you need something dead flat and super rigid is wrong anyway. If you apply clamps to sides of your chest of drawers or whatever it'll spring in and out of shape quite independently of the surface it's sitting on. If you were to force it down on to a flat surface, against it's will, it'd spring back as soon as the clamps were removed.
You don't really need anything that special for assembly but an open frame is fairly traditional, and very useful.

 

[marcus]

I've always found that reliably flat surfaces are very useful in a workshop, and the larger the better, not least as a point of reference. It's not essential, but it makes life easier.

I do see some advantages to an open grid, and perhaps it would be possible to make one from softwood that was strong, portable, resistant to racking, and genuinely flat and stable, but I can't see a way of doing this that would be as compact, cheap, and quick to make as a torsion box.

I've experienced complex glue ups, particularly chairs (especially when repairing antique chairs which were often not put together that well in the first place) gluing up skew when done on wonky surfaces. To my cost....

 

[twothumbs]

OK So how abouit a door blank as a ready made box. You could choose the construction for weight and puttuing dog holes through. Just a thought. Best wishes.

 

[Jacob]

...
I've experienced complex glue ups, particularly chairs (especially when repairing antique chairs which were often not put together that well in the first place) gluing up skew when done on wonky surfaces. .......

Instead of relying on a surface you'd do much better to rely on your eyeballs and if necessary put in packing, wedges etc to level things. Then you can glue up absolutely anywhere!

 

[marcus]

You do that then.