Riveting Plywood to Metal

Today I'll give you a quick rundown of my experiment riveting aluminium to plywood.

2.8 mm Plywood Riveted to 1.4 mm Aluminium

If you've read my blog before you may know I like boxes and storage solutions.  I made some prototype storage boxes last year out of 19 mm pine and plywood, and since then they have been used quiet a lot.  The main problem I have with them is they are heavy, use more material than is really needed, and are complicated to make.  I wanted to simplify things and for inspiration I turned to an ammunition case that I have from 1958.  It's made from ply and is riveted together with metal edges.  All the components themselves are not specifically strong, but when assembled the case is rather sturdy.

Ammunition Box

I happened to find some brass rivets on AliExpress that are used for material, you may be wearing some now. Have a look at your jeans.  The type I purchased are called double capped, meaning they have flat rivets on both sides.  They consist of a cap and post that are pressed together.

Brass Rivet Cap

I ordered these because they were listed as 10 mm long.  I thought that this would mean I could join materials up to 10 mm (leaving room for compression of course).  Unfortunately I was mistaken. The length of the post is 10 mm but this only leaves 8.5 mm space for materials, and after compression of the rivets only about 5-6 mm are feasible.

Brass Rivet Post

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Rivet Test Compression

For my test I planned to join some 6 mm ply to a piece of aluminium angle, but because the rivets are smaller than I planned I used 3 mm plywood.  Two 3 mm holes were drilled into the aluminium and the posts were inserted. A hole slightly larger (about 3.75 mm) was drilled in the ply, the caps inserted and the the rivets clipped together. For the final compression step no fancy tools were used. They were placed in a vice and I squashed the hell out of them.

The results speak for themselves. I think they look awesome and they will not budge.

Aluminium Side

The dark wood and brass look nice together gives the strength I need. I think I'm on to something.

Plywood Side

I'm not actually building a box in this post. This is just a test, and besides I don't think the size of box I want to make will work with 3 mm ply. I need slightly bigger rivets. So now we wait the standard 2 or 3 weeks for a shipment from China. :-(

There are plenty of designs for storage boxes that may be better than mine, but what I'm aiming for is a good strength to weight ratio box that can be easily assembled by people at home without exotic materials and tools.  The idea is that if you want a box you go and buy some ply and metal and use rivets you've purchased.

Back up Git repositories to Google Drive

I'm trying to come up with a decent backup strategy and I'm almost there.  Figuring out a way to back up git repositories was a little confusing though.  I use GitHub to host repositories that I'm working on locally, and that's an OKish backup, but I don't check every file into Git.  For example, if I'm working on an electronics design I don't really want the manual for the micro-controller to be tracked by version control, but I do want a backup of the manual just in case they change it for some reason.  So for files like this I keep them with all the others and add them to the .gitignore file.  This is great, but they're not backed up anywhere.

Normally I use Google Drive for my backups.  There are other services that are probably better and have desktop syncing apps that are more polished, but I can easily access files from any device and I trust Google not to go broke in 6 months.  So a simple solution to my problem might be to store local repositories in the Google Drive directory.  That may work, but I just don't trust Git and the Google Drive app to get along together.  So what I ended up doing was just copying a backup of the repository to Google Drive.

This works, but if you copy files to the Google Drive directory and overwrite the old versions it wants to re-upload everything even if the files are unchanged.  You could do a copy where only newer files are overwritten but then another problem arises, files that are deleted from the repository remain in the backup taking up space.  That might be ideal in some situations but I want this basically to be a mirror of the current state of the local repository folder.  In reality what I want is a one way sync to the backup location.  Luckily the robocopy command can manage this.

cmd /k robocopy "Repositories To Backup" "Backup Location" /e /purge

By placing the above command in a batch file, anything new in the "Repositories To Backup" directory will be copied to the "Backup Location".  Don't worry about the cmd /k part, it just lets the command window stay open after it runs robocopy.  By default robocopy copies a file if it's changed in any way.  If unchanged, it will just skip the file.  This will prevent Drive from wanting to upload the file again.  The /e option means it will also copy empty subdirectories and the /purge option means that it will delete files from the backup location that don't appear in the source directory.  This keeps the backup location synced to the source location.

I keep all my git repositories in a Projects folder, so I just set the "repositories to backup" to the this folder, so that when I run the batch file it backs up all the repositories at once.  I run the batch script it manually, but you could schedule it to run automatically too.  I know it's not the best solution, but it works for me.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Usage Example

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Idea For A Mass Producible Wooden Storage Box

I like things to be organised.  Over time, I've found the best way to accomplish this is to store similar things in labelled boxes.  It looks neat and tidy and makes it easy to find exactly what you want when you want it.

The exact form factor of the boxes has so far been an iterative process where I learn the pros and cons of each design as I use it.  I currently use cardboard boxes, but the long term goal was always move to wooden boxes.  I have only a few requirements.  They need to be big enough to hold a sheet of A4 paper (297mm x 210mm), and they need to have a lid to prevent dust covering the items I want to store.

The title of this post mentions the term "Mass Producible".  I should clarify that I mean making about 100 boxes, not millions.  With that in mind, I also want to be able to use automated manufacturing methods like CNC routing and laser cutting to make the parts of the boxes.  It would be great if I could get some furniture grade plywood delivered to a workshop, have them cut the pieces, and all that was left was a bit of assembly.  I haven't been able to find that capability yet, but it'll happen one day.

So what have I come up with?  Nothing too ground breaking.  In the image below you can see that there are standard box joints in the corners.  For this job, box joints are pretty much the only way to go.  Although the image below has been rendered with a plain piece of timber, I actually want to use plywood and making the thickness of the ply as small as practical is important as it reduces the weight of and size of the box.  With thin pieces of ply, nailing or screwing into the ends can cause problems with splitting, the box joint eliminates this as an issue.  It also make assembly easy.  Glue and clamp.

Storage Box with Sliding Lid

With the lid removed you can see the rebate that allows it to slide in and out.

Rear View of Box with Lid Removed

With the back and side removed you can now see a couple of extra features.  There are grooves cut into the sides that allow removable dividers to be added and removed as needed.  The shape of the base is now visible as well.  Traditionally you would just cut a rebate all around the bottom for the base.  So why have I gone for the convoluted tabs?  Once again, plywood.  Depending on the depth of any rebate and the direction of the grain in that layer of the ply, there is a risk that when a heavy item is placed in the box, the ply could fail.  This stitches the base and sides together for greater strength.

Rear view of Box with Back and Side Removed

Of course this creates some problems.  If you're laser cutting the tab holes and they go all the way through, everything is fine, but if they only go half way, they need to be routed and need t-bone fillets added to allow the tabs to be inserted.  This is because you can't cut an internal square corner with a router bit.

Box with Base Removed

I don't have the capability to manufacture these at the moment.  Ideally I'd start off by routing all the features that don't go all the way through on a 1200mm x 2400mm sheet of plywood.  At this point it's still one sheet that's easy to move.  It would then be laser cut to produce the final pieces.  I don't even know if this is something that's done commonly.  The reason for this is that you need the nice square internal corners that a laser produces for nice box joints.  I might be able to play around with the joints to make it a one step process by routing though.

So what's next?  Like I said, I can't manufacture them they way I want yet.  That doesn't mean I can't play around with the form factor though.  Stay tuned.

Cheap and Easy DIY TV Stand

Recently my mother asked me to sort out a problem she was having.  On top of a cupboard in the kitchen she has a 26 inch LCD TV she likes to watch.  It's at a height of about 2.5 meters, and when sitting, she's looking up at an angle of about 30 degrees.  At such an extreme viewing angle the image becomes unwatchable.  What she wanted was a way to tilt the TV so that the screen was facing her when she sat down.

I thought this would be easy, the TV has 200mm x 100mm VESA mount points on the back, it's not too heavy (8kg), all that was needed was a stand that allowed it to be tilted down.  The cheapest bracket and stand that met our criteria was over $150 and that was more than we were willing to pay, so it wasn't going to be as easy as I thought.  I decided to just buy a tilting wall mount bracket for $35 and figure out what to do with it when it arrived.  Building my own tilt mechanism would've taken way too long and wouldn't have been as good.

B-Tech BT7522B LCD wall mount bracket

After receiving the tilting bracket I went to the local hardware and walked around to see if I could find something to mount it to and make a TV stand.  It wasn't long until I found the post stirrup section.  Just in case you don't know, post stirrups are metal brackets used to keep timber posts of buildings elevated above ground to prevent rotting. They're concreted into the ground or bolted to a concrete base and the post is then attached to the top part.  Perfect, for $7 I get a sturdy metal bracket that can be mounted to a ply base to complete the job.

Post stirrup TV display stand

I just happened to have an offcut of 19mm plywood under my bed that was perfect for the base.

Ply base

It always pays to keep large offcuts.  Originally the ply was left over from my removable drawer project.

Drawer slide holder

It then became a side of my standing desk experiment.

Standing desk add-on

As the stand sits on an L shaped cupboard in a corner, I had to cut out a section so there wouldn't be an overhanging bit.  To attach the post stirrup to the base board I used 4 bolts and a metal plate as a washer.  This meant that the bottom was no longer flat and needed to be elevated.  To do this I used a hole saw to cut some circular feet out of the scrap ply section that was removed.  These were glued and screwed in place.  The parts that were going to be visible when installed were then painted white.

Base with feet and washer plate attached

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Washer plate

The tilting bracket was then attached to the post stirrup with some metal screws and lock nuts.  It's not the most attractive piece of furniture, but it's not too hard to imagine how to make it look like more like a professional product.  A new piece of ply the right size and a bit more time planning, painting, and sanding, this wouldn't be out out place in a living room.  Depends how good you are at finishing wood though, I took some shortcuts because I wanted this to be a one day build.  The TV hides all of the ugly stuff anyway.  The only part you can see is the edge that I painted white

The best part however is that it only cost me $50 maybe $65 if you bought everything new.

Tilting bracket attached to post stirrup

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Tilting bracket attached to post stirrup

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Assembled TV stand

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Drawers for Rack-It Shelving

The Rack-It shelving that you can get at hardware stores is great, but I have one problem with it, it doesn't come with any decent drawer options.  So I built my own.  I have previously described the construction of the Custom Wooden Drawers.

The design is pretty simple.  Two panels with drawer runners are pressed against the posts on either side by spreader bars, these panels are attached to the shelf underneath, and this is all connected to the main frame so that when you open the drawers they don't overbalance.

It's designed to be disassembled so it can be transported easily by one person.  I think I have it sorted, I'd do certain parts differently if I did it again, but this does the job and was fun to make.

I still have to put the handles on the front and dress it up a bit, but that's a job that can be done later on,
but for now I have about 11 cubic feet of drawer space to play with.

The assembled drawers

The frame with the drawers removed

Left side supporting panel with drawer runners and spreader bars fitted

The routed channel the spreader bars fit into

M3 threaded rod with lock nuts on either end hold the spreader bars in place

The middle drawer clearing the spreader bars

Steel angle bolted to the underside of the shelf locks the frame in place

Custom Wooden Drawers

Now for something completely unrelated to anything electronic.  Lately I have been building some drawers to fit into a storage unit I bought from Bunnings.  Usually I would go out and buy this kind of thing, but I couldn't find anything the right size, so I had to custom build it.

Basically I wanted something cheap and big.  After looking around Bunnings I found some cheap pine in various widths that is 19mm thick.  It'll do the job but it's full of knots and you'd be hard pressed to find a straight piece of wood, but we can deal with this.

The design I'm going to use is pretty simple, front, back, two sides, and a base.  The sides slot into dados in the front and back and the base fits into a routed channel at the bottom.  Then it's all glued and screwed together.  Below are a few pictures of a drawer.

All the pieces ready for assembly

Dado for the side and routed groove for the base

Close up of the corner

Routed stopped dado in the front panel

A knot in the wood glued and filled to stabilise it

The side fitted to the front

The drawer assembled with a notch chiselled out for the drawer slides

Drawer slide attached

Drawer slide extended, clearing the cut-out

Most of the problems with warped wood are taken care off when it is assembled.  The sides are straightened when they slot into the tight dadoes, and the front is pulled straight when it's screwed to the sides.  It's not completely straight, but it's close.

The base is 7mm thick ply and seems to be sturdy enough.  I loaded it up with 50 kg of text books and it held all right.  Initially I planned to use cheap drawer runners but they were terrible and and too unstable.  They might be OK for smaller drawers, but for something 2 by 3 feet they are useless.  I settled on full extension drawer runners from Hafele. They are smooth and work beautifully.  www.elraco.com.au had them at a decent price, and I wish I could have bought more just to get the price break at 10 units.

It's all still  a work in process, but I'll post more when I'm done.