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Old 13th Oct 2020, 11:36 am   #1
PsychMan
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Default Presses / Clamps etc

I tend to do a lot of woodworking nowadays. One issue I have is where I need to press a sheet of veneer onto a panel, or in the case of a restoration I'm doing, a motorboard has some delaminated ply that needs gluing and clamping.

The pieces are too big to get my F clamps onto the area, so I need something firm and very flat I can place onto the piece and clamp at the edges. I've tried a few things, but often find DIY store ply is warped and therefore it becomes impossible to clamp or weigh it down consistently across the piece...Finding something perfectly flat, that doesn't bend or flex with clamps is a challenge.

I'm considering asking a local metal fabricator to cut me some very thick steel sheet. But is there anything else I should be looking at instead?

Best wishes
Adam
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Old 13th Oct 2020, 11:40 am   #2
Station X
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Default Re: Presses / Clamps etc

A sheet of say 10mm MDF weighted down with bricks?
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Old 13th Oct 2020, 11:59 am   #3
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Default Re: Presses / Clamps etc

Quote:
Originally Posted by Station X View Post
A sheet of say 10mm MDF weighted down with bricks?
A piece of marine ply the thicker the better, I have a piece thats been outdoors 18 years and its not deteriorated at all.
or a book press

Last edited by BRASSBITS; 13th Oct 2020 at 12:06 pm.
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Old 13th Oct 2020, 12:03 pm   #4
ex seismic
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Default Re: Presses / Clamps etc

Kitchen worktop?
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Old 13th Oct 2020, 12:07 pm   #5
emeritus
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Default Re: Presses / Clamps etc

A proper wood yard might be a better source of flat ply. You would probably need to go to one to get marine ply anyway. The 1/2" marine ply backboard to the basketball net that is bolted to the top of a piece of 1" iron pipe in an exposed position in our garden is still in excellent condition after more than 25 years' neglect.
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Old 13th Oct 2020, 12:12 pm   #6
PsychMan
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Default Re: Presses / Clamps etc

I did try MDF, but with a big piece, I find it starts bending and rising up in the middle when clamped at the edges.

Maybe 19mm marine ply is worth a try. I could do with finding some decent wood sources
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Old 13th Oct 2020, 12:24 pm   #7
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Default Re: Presses / Clamps etc

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I did try MDF, but with a big piece, I find it starts bending and rising up in the middle when clamped at the edges.
That's why I suggested weighting it down with bricks. Everything will bend if you apply unevenly distributed forces.
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Old 13th Oct 2020, 12:27 pm   #8
John M0GLN
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Default Re: Presses / Clamps etc

Quote:
Originally Posted by PsychMan View Post
The pieces are too big to get my F clamps onto the area,
What actual size of flat material are you looking for?
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Old 13th Oct 2020, 12:49 pm   #9
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Default Re: Presses / Clamps etc

If you want something big, heavy and flat look out for a "Surface Plate" like these. Note the webs on the underside to give them rigidity:-

https://www.ebay.co.uk/itm/Large-Win...MAAOSw7j5ff2rO

https://www.ebay.co.uk/itm/Engineers...IAAOSwTNFfdjYr
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Old 13th Oct 2020, 2:52 pm   #10
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Default Re: Presses / Clamps etc

I'm building a house at the moment, and have found Wickes's 18mm plywood to be the most consistently flat and of the best grade. Of the DIY shops, that is, as our usual woodyard has been closed for a while. A woodyard will be able to supply something like 22mm B/B where the faces are sound and the inner plies are gap-free. As ever, let it acclimatise to where you're going to use it, as any natural material will have some variation with humidity. If you are having difficulty with a large area, perhaps the aforementioned plywood with an amendment from Station X's surface plates - screw some angle-iron to the top to act as a bend-resistant web. A steel fabricator will be able to sell you some for a few pounds cut to length.
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Old 13th Oct 2020, 4:17 pm   #11
M0FYA Andy
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Default Re: Presses / Clamps etc

I would agree with post 4, an offcut of kitchen worktop is flatter, thicker and therefore stiffer, than a piece of plywood or MDF.

Andy
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Old 13th Oct 2020, 7:18 pm   #12
John M0GLN
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Default Re: Presses / Clamps etc

Quote:
Originally Posted by M0FYA Andy View Post
I would agree with post 4, an offcut of kitchen worktop is flatter, thicker and therefore stiffer, than a piece of plywood or MDF.

Andy
My thoughts as well, that's why I asked about the size, there must be countless pieces cut out from the worktops to suit the kitchen sinks bowls, and granite ones as well.

John
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Old 13th Oct 2020, 10:29 pm   #13
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Default Re: Presses / Clamps etc

Paving slab might be flat, heavy, cheap and available I like the surface plate idea; for something a bit lighter and more flexible maybe you could make a wooden one (stiffen a piece of ply with bracing at the rear) and then add bricks to it for as much weight as you need.
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Old 13th Oct 2020, 10:30 pm   #14
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Default Re: Presses / Clamps etc

What about making something like this? My luthiers used to swear by it.

https://www.stewmac.com/luthier-tool...rn-guitar.html
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Old 13th Oct 2020, 11:22 pm   #15
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Default Re: Presses / Clamps etc

I have those beech-block worktops in the kitchen, and one small section is over a cupboard and a built-in freezer. This one warps. As fully paid-up vintage radio people, I'm sure you'll approve of my weight-based method of flattening it.... Two AR88s on their sides!

Of course that worked. Plan B was the anvil from the garage... equivalent to about 4 AR88s in real money. Not sure what that is in double decker buses or olympic swimming pools.

David
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Old 14th Oct 2020, 12:57 am   #16
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Default Re: Presses / Clamps etc

Learn to hammer veneer? In many ways it's the best method for small and medium sized panels. Requires little in terms of tools.
I have a go bar deck and for veneering it's only probably good for pretty small panels. They don't exert much force compared to a G-clamp.
If you want to use a caul then a number of curved batons on top of the plywood will distribute the pressure. You might be surprised just how difficult it is to get even pressure on something as small as 1 ft x 2 ft. Unfortunately clamping either end without having a helper isn't easy. It can be done though. The larger the area that you need to veneer the more problematic caul veneering becomes. Vacuum veneering works of course but relies on equipment. The PVA/iron on method can work but it isn't reliable, certainly not long term. Same with contact adhesive. At the end of the day you can't beat hammer veneering for the small home workshop. It's also stood the test of time.
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Old 14th Oct 2020, 9:47 pm   #17
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Default Re: Presses / Clamps etc

Ply, I'd forget. I have some fairly thick (12mm stuff) that is fairly curved after storage. Any timber based material can do this, and I've even seen kitchen worktop and other chipboard based materials get curved. In fact any of the materials mentioned, including steel and even concrete (the slabs) can and do flex. Have you ever sat in a staionary car on a concrete bridge as heavy vehilces have come past? But then it comes down to how flexible they are compared to what you are trying to do.

For veneering, I used a spray on contact adhesive and a veneer roller for a job I did. No need for force over any long term.

If long term pressure is required, I'd be using a smooth but thin layer (MDF) sandwiched between something as stiff as possible (like the paving slabs already suggested).
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Old 14th Oct 2020, 10:02 pm   #18
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Default Re: Presses / Clamps etc

Concrete is indeed flexible.

I remember a piece on Tomorrow's World about something like the research labs of the concrete marketing board who had made coil springs out of concrete! (Raymond Baxter era)

As often the case, the curse of the Tomorrow's World programme struck and they were never heard of since.

David
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Old 15th Oct 2020, 1:27 pm   #19
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Default Re: Presses / Clamps etc

An American carpenter tested three common shelf materials - MDF, Plywood and real wood, to see which type sagged the least.

Shelf dimensions and loading were the same.

To my surprise, the real wood sagged the least.
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Old 15th Oct 2020, 2:05 pm   #20
Michael.N.
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Default Re: Presses / Clamps etc

For that type of use MDF is pretty bad, unless it has supports every foot or so. It's also very hard on cutting edges (ply too). You find that out quickly if you hand plane a MDF edge. At first you'll almost see real shavings but not for long, the dust quickly follows. I try and avoid the stuff. If I have to use sheet material it's birch ply. Expensive compared to other types but I'm not going to skimp when I'm spending many hours making something.
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