Board thickness vs. width guidance

[space.dandy]

Hi all,

Considering strength across the grain, are there any rules or guidelines to help determine how thick a board should be? As an example, I want to make a box around A4 size and about 4" in depth, probably in Oak. It is intended to hold a max of around 2kg. How thin can I make the sides, given that it's quite shallow? How thick would the base need to be?

 

[Cabinetman]

As you probably guessed – it depends - partly on how it’s jointed, I think personally you could go down to 6 mil. The base being wider probably eight or nine mil. Ian

 

[space.dandy]

As you probably guessed – it depends - partly on how it’s jointed, I think personally you could go down to 6 mil. The base being wider probably eight or nine mil. Ian

Thanks, I hadn't considered that joinery would make a difference. The box will be constructed essentially like a drawer, with dovetailed sides and the bottom panel sitting in a groove. I haven't decided how to do the top yet, but I think it will be a 'lift off' lid rather than hinged.

 

[Cabinetman]

Yes dovetails will be fine, you could glue the base in a rebate, I know it’s not the way it should be done with regard to expansion/contraction but the size is small and with well seasoned timber I think you’ll be ok. Ian

 

[Jacob]

2kg is two bags of sugar. They'd fit easily into a 4" x A4 size box and no great strength would be required.
However for maximum strength is better to glue and screw or pin the bottom board underneath the box direct to the sides. Slots/rebates introduce weak points.
I did a set of utility boxes/trays slightly bigger than A4 and 2" high with DT sides 8mm and 4mm ply bottom stuck on. Pretty sturdy really. Making them 4" no prob with same materials.
I made them because I hate plastic storage stuff and I've got loads of little offcuts , plus exercise in freehand dovetails.
Didn't pin the bottoms just glue and stacked with a weight on top instead of clamping.
PS Oak for the bottom - 4 or 5mm. I've got a very old tea tray here 20x15" been in use for years which is oak with a 5mm thick bottom glued and screwed to the moulded rim, not flush - 5mm bigger than the rim all round and rounded off.

 

[Hornbeam]

A veneered plywood base glued all round into a groove will give yo extra strength but it depends on the thickness of the sides. That is why for drawers with thin sides you fit drawer slips. 8mm thick sides with a 3mm groove wound be more than fine

 

[space.dandy]

Thanks, that’s given me what I need.