Laminating with Formica

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I am making a new drill press table and matching worktop for the cabinet beneath. I have some Formica that I plan to use for the tops and I have made up two bases, each a lamination of 25mm mdf and ¼” birch ply (just some old stuff I had hanging around). The edges will be lipped.

The mdf and birch ply were clamped up flat when glued and I was thinking that when completed the top layer of Formica would balance out the unequal laminations beneath. I made these up ages ago and it seemed that the bases had not warped; however, now I want to get round to fixing the Formica, the whole thing has curled up somewhat, so I am just thinking what to do.

Options seem to be:
- clamp the base flat by bolting to a flat framework/cauls from underneath, before gluing the Formica
- relieve the birch ply with a criss-cross of saw kerfs and hope the base comes back to flat before gluing the Formica
- junk it and start again, possibly 2 x 18mm birch ply (my last little piece that I was keeping as my pension) - but then would I need to add a bottom layer of something to balance the Formica?

I suppose an underlying question is do you need to balance a Formica top layer on anything?

Here is a picture
60668B79-762C-4584-A62D-3183E79CA57A.jpeg


Cheers
 
I guess you should have balanced the 1/4" ply by putting it on both sides of the mdf.
But I reckon it's a waste of lovely formica to try to stick it on rubbish mdf.
I've used Formica on worktops and table tops on 18mm and 12mm ply where they are doubled up at the edges to show as 36mm and 24mm. Saves weight and saves ply!
Seems to work fine with no backing of any sort.
 
I guess you should have balanced the 1/4" ply by putting it on both sides of the mdf.
But I reckon it's a waste of lovely formica to try to stick it on rubbish mdf.
I've used Formica on worktops and table tops on 18mm and 12mm ply where they are doubled up at the edges to show as 36mm and 24mm. Saves weight and saves ply!
Seems to work fine with no backing of any sort.
Thanks Jacob - It is rubbish mdf, which is why I wanted to bury it in this composition (thinking it’s only a workshop item)!
I should have added the option of adding another layer of ¼” birch ply before the Formica - I don’t really want to make it that thick, but I probably need 30mm minimum as I am going to set in some T-tracks.

I will see if I have some 12mm birch ply which would make up nicely with the 18mm - just seems an extravagant use for my last bit of birch ply.
Cheers
 
You broke the makers' rules...what you do to one side of a substrate you must do to the other every time...you have to laminate both sides of the board to maintain balance and prevent bowing.
 
Formica one side has never caused me any problems. I think the mdf / ply laminate is where your problem is.
 
You broke the makers' rules...what you do to one side of a substrate you must do to the other every time...you have to laminate both sides of the board to maintain balance and prevent bowing.
Not necessary for all situations. I can squint along my ply/formica worktop from where I am sitting and it is dead flat, just as it was when built by Doug B of this parish, some 15 (?) years ago.
They are just covering their backs (literally!). Might not always get away with it.
 
You broke the makers' rules...what you do to one side of a substrate you must do to the other every time...you have to laminate both sides of the board to maintain balance and prevent bowing.
I was wary of this from the outset - my original thinking was (as well as the ply and mdf conveniently making up the thickness I wanted) that the ply would balance the Formica layer.

But…if the consensus is that you don’t need to balance the Formica, by the same token, it won’t balance the ply layer!

I think I will try a relieving criss-cross kerf cut through the ply layer which won’t be seen and hope it will then come back to flat. Nothing to lose.

Cheers
 
I was wary of this from the outset - my original thinking was (as well as the ply and mdf conveniently making up the thickness I wanted) that the ply would balance the Formica layer.
Only if you apply it at the same time
But…if the consensus is that you don’t need to balance the Formica, by the same token, it won’t balance the ply layer!
The consensus is probably that you can get away without a balancing sheet in some circumstances, ideally where a small deflection would not be noticed. A lot of table tops are more bent then you'd think.

I think I will try a relieving criss-cross kerf cut through the ply layer which won’t be seen and hope it will then come back to flat. Nothing to lose.
Except if you cut through it it won't work as a balancing sheet.
 
Only if you apply it at the same time

The consensus is probably that you can get away without a balancing sheet in some circumstances, ideally where a small deflection would not be noticed. A lot of table tops are more bent then you'd think.


Except if you cut through it it won't work as a balancing sheet.
I must watch Catch 22 again!
 
Thanks Jacob - It is rubbish mdf, which is why I wanted to bury it in this composition (thinking it’s only a workshop item)!
I should have added the option of adding another layer of ¼” birch ply before the Formica - I don’t really want to make it that thick, but I probably need 30mm minimum as I am going to set in some T-tracks.

I will see if I have some 12mm birch ply which would make up nicely with the 18mm - just seems an extravagant use for my last bit of birch ply.
Cheers
Is there not the potential that routing through the top layer of any sandwich, to let in the ‘T’ tracks, will result in weakening that layer and losing the balance?
 
Is there not the potential that routing through the top layer of any sandwich, to let in the ‘T’ tracks, will result in weakening that layer and losing the balance?
yet more Catch 22!

Well, if so it may be partly counteracted by the table being bolted to the cast iron table of the drill press, although that has a smaller footprint.

I think I am going to do some relieving cuts in the ply and leave it for a couple of weeks.

I will report back.

Cheers
 
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