Flatten bowed table top - Parquet veneer

[gizmo1990]

I'd like to repurpose an old kitchen top as a table top. It was made by my girlfriend’s carpenter grandfather so has sentimental value.


Unfortunately, it's bowed (convex) a little, which I'd like to have made flat. It seems to be constructed from a pine plank base and bonded with (I suspect) a thickish oak veneer of about 5mm thickness, in a parquet fashion. See photo.


Could anyone give me some advice/options on how this could be achieved? I would presume that machines that thin/level wood would be non starters here because of the mixed grain directions? So hand planning would be the only way to go? Or perhaps not?


I’m not sure my current work area nor my experience/tool availability will be up for the task either. So if anyone could give me a ballpark figure a carpenter would expect for this task, I’d appreciate it. The table top itself is about 250mm x 700mm.


Any advice much appreciated.

 

[Burnerman]

Its probably bowed because the veneer is only on one side.....would it be possible to fix some timber on the underside to maybe correct it a little?
Work with a VERY sharp smoothing plane would have benefit, followed by a session with a random orbit sander.
John

 

[gizmo1990]

Thanks for the reply, @Burnerman Of course, stupid of me to not realise that! Yes that will definitely be why the bow is there. How much effect would bonding some other timber have to it though now at this stage? Would it have a fairly immediate effect of cancelling out the bow or only after a prolonged amount of time?

 

[Burnerman]

I guess it really depends on how thick the top is and how much the warp is, but you can certainly pull things flatter by screwing battens on the underside - if they are sturdy enough!
Obviously this may not be acceptable to you and could interfere with the way the top is to be held to the table itself.
Happily though, your parquet veneer is nice and thick and therefore quite a bit of material can be removed without disaster!
John

 

[Tigercubrider]

Not an expert.....
Would it be possible to approach this from the other side?

I.e. Use a thicknessor or router to remove material from the BACK. Hopefully making the base thin enough to bend the top face back to flat? It could be glued back down to a stable sheet material.
You might even get away with applying tape to the top surface, then removing (almost?) all of the backing before fixing to a new board?

 

[Tigercubrider]

 

[Deleted member 174758]

How thick is the parquet and how high is the crowning? True parquet is normally fairly thick (15 to 30mm) and can be machined flat successfully. If on the other had the timber is marquetry thickness (5mm or less) then that option is out.

If it is of machinable thickness then I'd possibly follow TigerCubRider's suggestion of building a router sled and using that (note that the larger the diameter of cutter the better - a 1/2in router with a 50mm diameter cutter is the way I'd go), following up with a random orbit sander - attempting this freehand with a power planer is not going to work (not to mention risking damage) and attacking it with a 4in belt sander will almost certainly result in badly dubbed over edges.

Even for an experienced woodworker this is probably not a task for hand planing due to the changing directions of grain.

There is one alternative, though, if the top layer is thick enough - take the item to a larger joinery shop where they have a wide belt sander and get them to face off the top for you. This a fairly straight forward task with the right gear, which can remove as little as 0.1mm per pass, although it may cost you £30 or so to get the job done as they will need to set the piece up on a base.

 

[gizmo1990]

Thanks again for all the advice everyone. Going by what @JobAndKnock says, the parquet is only marquetry thickness as it is 5mm. The planking it's attached to seems an unusual choice to me, but there you go.

Given this I would presume that attempting to bend the board back into shape is the best way to go. It's been suggested that routing out some thin grooves length ways underneath might make this easier. Would anyone here confirm if that's the case? Due to the planking I'm considering if this useful as the rough rounded edge planking is effectively doing this already? See the attached photos.


After that, sticking (or screwing?) some supporting material to the underside would then bend things back to a flatter shape, which would then allow the top to be sanded down true. What type of material would people suggest for bonding to the underneath?

Any advice greatly appreciated.

 

[Chunkytfg]

Something sturdy to attach to the underside. Think Angle iron! If you're making it into a table top you could possibly incorporate the design of the legs to to include the steel box section/ angle iron that would easily pull it straight

 

[mrrusty]

+1 for angle iron, provided you can get a good enough screw bite in the pine.

 

[conny]

When you lay the top flat how high is the convex in comparison to the edges?
I'm thinking, if the top of the convex is 5mm higher and the parquet is only 4 -5mm thick you are going to be sailing close to the wind with planing/sanding the bump out.
What about dampening the whole top then laying on a flat surface weighted down with heavy books/blocks? After it has dried out, (hopefully flat enough for you), you can then flip it over and fit cross bearers to the underside to help try to stabilise it.

 

[gizmo1990]

That’s again for the replies everyone. I’d prefer to not use metal due to its weight and aesthetic. Would another material not work? Like mdf or some marquetry thinkness planks?

 

[Deleted member 174758]

MDF has absolutely no strength in it at all.

 

[lostinthelight]

The table top itself is about 250mm x 700mm.

???

 

[gizmo1990]

As people have been pointing out, I think angle iron is the only way forward. Does anyone know where unequal sized angle iron can be purchased? Equal sized angle iron will substantially increase the table top thickness, so any saving I could make would be helpful. I've only seen unequal braces being sold in big sizes. Ideally I'd like a l-shaped brace around 10mmx20mm.