Finishing a tray

[chrisinoz]

Hi. Started recently on teaching myself some woodworking and cutting my teeth (and some timber!) on a few trays and had some interest in them already. The sides are jarrah or vic.ash. Inside is a feature pine panel.

I am checking about the finishing process.

This is what I do.

1. Prepare the panel and finish with a matt poly (wipeon that I made myself 60 poly/40 mineral turps.)
2. Cut the sides.
3. Rout a rebate.
4. Stain/Satin the inside face of the sides.
5. Cut the mitres for the corners
6. Glue up the sides.
7. Add spline mitre joints for extra strength
8. Then sand , stain etc the rest of the side faces

I get a fairly good fit in the rebate however there are obviously minor gaps here and there where the panel and the rebate meet. Is that satisfactory or should I add some more coats of poly after all constructed to get a seal.

Or is there a better order of doing this?

Thanks
Chris

[Kuffy]

I use danish oil for my trays. That way I can sand the bottom panel and inside faces before I assemble. Then assemble the five components, cut miter keys and glue them in. sand the outside faces. then I can slap on a couple coats of danish oil and it will seep into the groove housing the bottom panel and coat everything. I don't want the sides to be sealed to the bottom panel. I want the bottom panel to be firmly free floating in the grooves so that if the bottom panel expands it won't blow the miter joins apart.

Sometimes I will aim for a shiny finish, which will be 4-5 coats of danish oil. But the next batch of trays I am making will be "sealed and water resistant, and maybe shiny, maybe not", this should only be 2 coats of danish oil.

I wouldn't worry about having a watertight seal between the sides and bottom panel. If you achieve such a seal, the tray will fail. If you don't achieve the seal, the tray shouldn't be soaked in water anyways. A light wipe with a damp rag. no different from a timber benchtop, coffee table top, dining table top etc etc

[Arron]

Much better, I think, to concentrate on eliminating the tiny gaps then bogging them up. Given you are making multiples of the same thing you should be able to get that joint neat all round, though it might take an upgrade in machinery.

Good luck
Arron

[chrisinoz]

Thanks Kuffy for your input. At least I have my processing order in a similar vein.

On checking again and I think my issue is in the variance of thickness in the recycled pine I am using. Varies (say) 7.9mm, 8.0mm, 8.1mm. There is a good reason why I am using this pine so I have to work around that. I realise I should now be using my thicknesser to try to even out those variances.

Cheers
Chris

[chrisinoz]

Thanks for the input Arron. If you read my other post the comments on using the thicknesser should help my issues.

Cheers
Chris

[Kuffy]

Chris, I put my bottom panels through the thicknesser which makes them a consistent thickness and also flat. But then I sand the panels with an orbital sander. I am not good enough to sand a panel from thicknesser->finish-ready without dubbing the edges a little bit. This is where the gap between the side groove and bottom panel comes from for me. I have no intention of matching each individual groove to an individual side of a particular bottom panel.

A better way to do it would be to make the bottom panel 1" longer and wider than needed, then sand it, and then cut it to final size. It removes the issue dubbed edges from sanding. But my bottom panel finishes at 300mm wide and my thicknesser is 300mm wide so I can't do that.

[Arron]

Thanks for the input Arron. If you read my other post the comments on using the thicknesser should help my issues.

Cheers
Chris

Yeah, I used to do this a lot and refined the technique. The main thing was a couple of jarrah spacers which were placed under the blade carriage of the thicknesser - poking out front and rear. The carriage was lowered onto the spacers in such a way that the spacers contacted the edges of the carriage just wide of the blade. With the carriage resting on the spacers and locked in place, you get consistent thickness down to a few microns - and repeatable each time you use them.

The jarrah spacers were tuned to the width of the dado blade combination which cut the dados, so both dado and panel are the required thickness each time, whether cut in the same session or not.

Cheers
Arron

[chrisinoz]

How much play (movement) should have one for a pine panel into grooved hardwood. Naturally it should not rattle and slide around in the tray frame nor should it be hammered into the grooves to fit.

Thanks

[Christos]

For me I have thought of it in this way as my general guide.

I have thought of a 10 percent wood movement when making large pieces of furniture, which I think covers most species of wood to the extreme. If we take that thinking for a tray with a width of 500mm wide with a 10 percent movement of 50mm, I don't think so.

There is one more thing that comes into consideration and that being the panel thickness where a thin piece is going to move less than a thick piece. One great example is when using veneers wood movement is so small that when glued onto the substrate(eg. MDF) it does not come into the equation.

The gap in the grove for me has generally being about 5mm for a panel of 500mm wide which is 1 percent movement. The panel thickness have being between 5 and 8mm thick.

I am sure there is some calculation that can be used which would give a much clearer understanding.

[chrisinoz]

Thanks for replying to my post Christos. I don't quite understand the 5mm.

As an example

A panel of 8mm thick.
A tray internal width of 500mm.
A groove 8mm deep which would give us a maximum width of 516mm.

Do you mean you would cut the panel length to 516 -5mm (511mm) to allow for the 5mm 1%?

Also, considering the panel is 8mm thick would the groove need to be 8.1mm (to allow for the 1%)?

There are calculators on the web that calculate rates of expansion but they seem complex and require one to know the moisture content of the wood.

Cheers
Chris

[Christos]

Yes I would have a gap of about 5mm which should be more then enough for the amount of expansion in the wood.

As for the thickness of the grove I would keep it relatively the same as the panel just ensure the panel can more freely within the grove.

I should also add that 10 percent wood movement for most species is extreme.

[chrisinoz]

Thanks Christos.

I understand that there would be less expansion on the short side so what would you suggest for that?

[Christos]

Should not be that much of a difference to be of a concern.

[Xanthorrhoeas]

Generally speaking, there is much more expansion and contraction across the grain in timber than there is in length with the grain (Exceptions do occur though). Different timbers have different expansion/contraction amounts and these are recorded in the texts and can be researched. However, floating panel joinery (which is what you are talking about here) is a pretty well known science. I do not make trays (or not yet anyway as we have too many antique/old trays to need any more) but I do make boxes. The bases are usually veneered ply - almost no change in dimensions with these so fully glued in all around - but the lids (often circa 300 mm x 250 mm in size) are solid timber floating panels. I allow about 1 mm each end and about 1.5 mm along both sides. The sides of the boxes are mitre joined, glued, no splines. No problems so far.

However, if I were using unknown timbers I would either check their expansion/contraction stats or else allow a generous 2 mm each side and 1.5 mm each end. There is no great need to have the dado/groove/slot much wider than the thickness of the timber. You do not want it to rattle around, but a firmish fit is OK (so about .5 mm wider than the edge thickness of your panel say).

[chrisinoz]

Thanks for your reply Xanthorrhoeas. Helpful for me when I progress to boxes!

I have also just read that expansion occurs across the grain more than with the grain so I shall work with that in my calculations.

Cheers