Thursday, September 1, 2016

Custom Storage Box Prototypes

In my last post I played around with an idea for mass producible boxes that can be manufactured with laser cutting and routing.  Before going too far down this path I wanted to test the form factor of the box, discovering what works and what doesn't.  Besides, I actually need some storage.

I started with a cheap 1.2 meter long piece of pine from Bunnings.  The external dimensions of the box (350mm x 275mm) were selected to minimise waste from a single board.  The timber is 184 mm wide and is close enough to the desired final height of the boxes, it therefore didn't make sense to change it.  Ideally I think 10 mm plywood is optimum for the box sides, but 19 mm pine will be fine for this test.  As the sides are thicker it also allows them to be joined with a dowels instead of cutting time consuming box joints.

Wooden Box
Box With Sliding Lid
The construction is very simple, with two side panels placed between a front and rear panel.  All contain a rebate at the bottom to retain a piece of 7mm ply for the base.  The front and sides are also rebated at the top to hold a 7mm ply sliding lid.  The back panel is cut lower to allow the insertion and removal of the lid.  In the final design the groove for the sliding lid would also continue into the back panel, but it's quicker and easier to just cut it straight across.  Remember, the point of these boxes isn't for demonstrating my jointing prowess (still a beginner, but getting better) it's to quickly produce a box to use and test.  You'll also notice I wasn't too concerned about router tearout either.

Wooden Box
Rear of Box with Smaller Back Panel
When inserted, the lid prevents dust entering the box and items falling out.  However, in this rudimentary test the main problem is that if the box is picked up from the front the lid slides out the back.  It definitely needs some sort of retention mechanism and it also needs a handle.  Both of these flaws were obvious from the start, but I haven't really settled on how I want that to work.

Wooden Box
Top of Box
This is my favourite part of the design.  They're brass drawer pulls I bought on Aliexpress for about one Australian dollar each.  They allow small labels to be inserted and removed as needed.  The viewable area of the labels they hold are about 40mm by 20mm and you can fit a decent amount of text in there, but it's not that readable at a distance.  Unfortunately the proportions of the front panel look weird too.  As these boxes are designed to fit a specific location I had to make the long side the front, ideally the short side would be the front and these drawer pulls would be more suitable.  Luckily there are larger ones available, so next time I'll buy those.

Wooden Box
Brass Pull with Label Insert
I also decided to experiment with interlocking removable dividers.  There theory was to split the box up into 9 equal compartments to allow better separation of small items.  Due to tool and jig issues, I had to make the centre compartment on the long side larger than the others.

Wooden Box
Front to Back Dividers
With all the dividers in place you may notice a lot of space around some of the joints.  I was allowing a lot of clearance in this part of the job as I wanted everything to go together easily the first time.

Wooden Box
Side to Side Dividers
The big problem I discovered is that there's a minimum usable compartment size.  I can get my hand in the smaller ones but I can't see what I'm trying to grab.  If the box was only 25 mm tall that wouldn't be a problem, but as each compartment is about 150 mm deep it isn't going to work.  I think if the box was divided into 6 (3 x 2) roughly equal square compartments the result would be more usable.

Wooden Box
Compartments are too small
I cut the divider guides all the way across the board but they only need to extend to the top edge.

Wooden Box
Guide at Top of Box For Lid
I think this next detail is the most important thing I learnt that'll help make a more enjoyable design.  When the lid is inserted it's in contact with all four side panels and any misalignment during assembly or even expansion and contraction of the wood will cause the lid to catch on edges when inserted.  You can see in the image below that when inserting the panel in the back slot there's a small lip due to assembly misalignment.

Wooden Box
Misalignment of Back and Side Panels
This can also occur at the front.  To fix this, ideally the rebated guides in the sides should be tapered.  Let's say you have a 7 mm board for the lid and you're happy leaving 0.5 mm of clearance.  Instead of just routing a 7.5 mm slot, make it 8.5 mm at the back to allow for misalignment and then reduce it to 7.5 mm after an inch or two.  Then make the rebate in the front 8.5 mm wide.  By doing this the lid should slide in and out without hitting anything.

Wooden Box
Misalignment of Front and Side Panels
The top lid won't be perfectly flat either, it could bow up or down.  So you may want to make the front slot a little larger in the centre where it will bow the most.  You could also taper the sides of the front rebate to allow the lid to locate into the front slot smoothly.

Wooden Box
Curved Lid Not fitting into Front Slot
Dimensionwise, I was flying by the seat of my pants on this project and just making it up as I went.  Most of my rebates were 6 mm but that introduces a tiny problem.  You want the rebate for the dividers to be a small as possible.  If they're too deep, you leave a small hole that dust or insects can get into.  Just a minor thing.

Wooden Box
Divider Guide as Seen From the Top
While I was at it I made 8 of them. :-)  It took about three days of work and the the total price for each box comes to around $20.  The funny thing is that making 8 boxes takes about as long as making 6 boxes.  Most of the time was spent setting up tools, measuring and marking things.  That's partly why I'd like to use CNC equipment to cut out the parts for the boxes.  In the time it took me to make 8 boxes I could assemble 50 pre-cut boxes.

Wooden Box
Usage Example

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