Veneer press platten question

[marcus]

I'm making the platten for my new veneer press. It is essentially going to be a large torsion box. I'm wondering what to make it out of...

I am basing the torsion box on Ian Kirby's design. he suggests using MDF for the core and 12mm HDF for the skin. Only trouble is I don't think you can get 12mm HDF in the UK.

So I need some ideas about what to use instead. Needs to be hard wearing 'cause I want it to last. Needs to be very stiff to help distribute the pressure. Needs to be stable to help the whole thing stay flat. Also some degree of moisture resistance would be helpful as there will be lots of hide glue involved.

Also I'm thinking about covering the finished face with formica to make cleaning easy. Presumably I would need to do both sides to avoid warping, or does this not happen as it does with veneer? But then if I put formica on the back as well them how will I glue it to the core? Any other suggestions to make the face waterproof and wipeable?

It's going to be fairly large – 3' x 6', and I'm thinking about 6" thick for absolute rigidity. It is going to double as a reference and assembly table.

Lots of questions (lots more in my head!). I've wanted this press for five years and I want to make a good job of it! Any suggestions appreciated.

Thanks

Marcus

 

[o0dunk0o]

what about the melamine faced moisture resistant mdf used or bar carcassing? It comes 18mm thick and is slightly stiffer than standard 18mm mdf.

I've glued this stuff together fairly successfully with sticks like sh*t and pocket hole screws, alternately you could router rebates in the face for the longitudinal braces and glue with pva or titebond

 

[marcus]

Thanks for this. A good idea, though I'm a bit worried that the construction adhesive needs a certain amount of 'bulk' to work properly, and wonder if this would interfere with the flatness.... Not sure.

I think I may go with 18mm MR mdf, and put formica on both sides of the torsion box, which should then be stable I think....

 

[Mike.S]

How is the pressure to be applied to the platten e.g. hydraulic, hand screws etc and at how many points? Just that 6' x 3' is pretty big and the type/number of pressure points will impact on the materials and thickness necessary.

In case they might be of interest The WoodWhisperer has two videos on the subject:

Torsion Box Assembly and

My New Assembly Table

 

[marcus]

It's going to be hand screws (21) which will be braced across the underside of the torsion box by square section steel tubing.

Had a bit more of a think over night about the torsion box itself. Current plan is core made from 18m mdf, probably 4" deep, and 1/2" birch ply for the faces, finished with epoxy paint on both sides....

Thanks for the links, will have a look!

 

[Mike.S]

Marcus

I did a reasonable amount of research into Torsion Boxes before my recent project (posted separately) and would just make the following observations:

- the thickness of the core members makes little difference to the strength of the box; it's the depth of the core that is key. The deeper the core, the stiffer the box - double the depth and the stiffness increases by a multiple of eight (i.e. cubed).

- the skin thickness is important - thicker is stronger.

- Given the above, I'd be inclined to go for 18mm skins and thinner core. I used thick paper cores (honeycomb with 28mm cell size) and 6mm mdf skins and can stand on it (14 stones+) without crushing it!

- Not sure from your post whether you're planning to use just one skin. That may be OK for an assembly table but for a platten two skins (i.e. top and bottom) will increase its strength considerably.

- As you've got multiple screw points, deflection should be less of an issue.

- A strong bond between the skins and the core is important. Lateral forces need to be resisted i.e. tendency for skin to slide off of the core, so a good non-creep glue is best e.g. cascamite and not glues such as hot melt, contact adhesive etc.

If you want more in-depth information, including calculating deflection, strength using different thickness skins etc, then I recommend Ken Horner's More Woodworker's Essential Facts, Formula's & Short-Cuts. It has a whole chapter devoted to Torsion Boxes.

HTH

Mike

 

[marcus]

Thanks Mike, very helpful, have ordered the book!

The intention is to have skins both sides. Originally I was going to use the torsion box on its own to anchor the posts for the hand screws, but I figured that the edges of the box would then be under huge pressure, which even with a torsion box might be asking for trouble, hence the steel cross brace idea. It will be helpful to ge the book and have some figures to go on rather than just guessing!

I'm also thinking of drilling the bottom skin in a grid (like peg board) so I can use it to anchor jigs for steam bending if I turn the box over. I don't have a huge workshop, so am hoping to get as many functions out of it as possible. Hopefully this won't affect the strength or stability....

Marcus

 

[Mike.S]

Glad to have helped.

As it's going to be multi-function, with steel support you may want to view another Utuber's production of a multifunction table (18mm top; melamine/formica applied; dog-holes; steel support etc): Allan Little (aka AskWoodman) is a Texan who enjoys using several words when one would do but I quite like his style. The full video is in 47 parts :shock: , but part 1 is here How To Make The Ultimate Work Table.