Caterpillar tracks… let’s make some.
Hi YouTube, my name’s Geoff and I’m the VegOilGuy.
Caterpillar tracks – continuous tracks – dozer tracks – tank tracks – whatever you call
them, I’ve always had a fascination with them; that incredible ability to go places other
vehicles can’t. When I decided to have a go at making a fairly
large model I looked around for design ideas but was disappointed at the complexity of
some of those I found, way beyond the limitations of my basic tools. If I was going to build
one in my garden shed, I had to come up with an easier method.
One design I did like was by Matthias Wandel. I loved Matthias’ simple approach and even
toyed with the idea of using wood myself, but I wanted something a little more robust
so metal was my preference. Even so, the idea of making all those complex joints from metal
terrified me. Steel would be incredibly resilient but hard
to work, expensive and heavy, so I opted for aluminium. Whilst this might seem a soft metal,
it’s surprisingly hard-wearing. Plus the old engineering trick of using hard and soft
metals in unison comes to mind. The moment I started thinking about aluminium
it occurred to me that there were all manner of profiles (shapes). Looking online at one
particular website, I noted the dimensions of various profiles and had one of those Eureka
moments. I headed off to the local DIY store and purchased some smaller sections to produce
this prototype. If you look closely you can see there’s a
series of rectangular pieces connected together with nuts and bolts. Crucially there’s two
sizes of U channel involved, one of which fits neatly inside the other. This meant it
was possible to make a flexible metal chain using off-the-shelf supplies and ordinary
tools. Not with this stuff… but with something like…
This… This is what you’re looking for. If you build out of another material or use
other dimensions, this is what you need to source. Good thick material with one sliding
neatly inside the other. With these profiles I was able to make this mock-up which became
my continuous track. It’s still the same simple engineering.
It’s just two size U sections, the bigger ones being connected by the smaller one. Nothing
complex… Just simple cuts. And to make it look more like track, I added some L channel
stock to the sides. But before we can build any track, we need
a sprocket. If you look at this image of a bulldozer track,
you can see there’s a sprocket. You’ll be surprised how common the sprocket and chain
combination is. How about an ordinary bicycle? The sprocket is the bit you pedal and the
chain drives the back wheel. The teeth of the sprocket connect with the chain to create
the drive – as you can easily see here. I’m not going to cover the making of a sprocket
in this video because I’ve already covered that before. But don’t worry – if you
want to build this exact same sprocket and track, you can download a free set of plans
from my website here. This will enable you to:
• Make a wooden sprocket (template) • Produce several foam sprockets using the
template • Use Lost Foam Casting to cast your own
sprockets from scrap metal. I took ordinary soda cans and melted them
down in my home made foundry to make four of these.
I decided on the dimensions of my sprocket using Matthias excellent gear software. If
you want to build a sprocket or track system with different dimensions, you’ll probably
need to buy a copy. It’s cheap enough and well worth the money if you’ve any interest
at all in making metal or wooden gears or sprockets.
An important aspect of sprockets is that they need rollers to exist in the chain. The dimensions
of the rollers in part determine the size of the sprocket. Other factors are the number
of teeth, the diameter of the sprocket and the gap between the teeth. Matthias’ program
really makes figuring all this out nice and simple.
Sprocket chains generally incorporate free-turning rollers. I opted to use ordinary washers as
they make great, cheap but effective rollers. I had two things in mind, the gap (which I
wanted to be 25mm / 1 inch for simplicity) and the diameter that I wanted to be roughly
between 150 & 200mm (6 and 8 inches). The roller size was the diameter of the washers
which was 12mm (half and inch). The size of the gap is something you decide
for yourself. I’ve shown this measurement as X here but as I said for me this was 25mm
(1 inch). The gap between the teeth of the sprocket has to be reproduced exactly on each
link of the chain. Ready for some boring maths? Well if you want
to do your own thing you’ll need to determine the size of the links and for this you’ll
need: X – the gap between the teeth of the sprocket,
which is your personal preference Y – the diameter of the holes to be drilled.
Bolts act as pivot points in the links so holes are required
Z – the amount of material to the edge. The larger the better as strength is needed to
prevent the material ripping. But we’re limited by the overall size of the links in the chain
So this little formula will give you your link length: Link Length=X + Y + 2Z
Now this is garden-shed engineering so getting every single cut to be identical is difficult
so using a jig is critical. I opted to use a standard electric mitre saw for the cutting
work, fitted with an appropriate blade. I added a wooden fence to this and a bolt ‘stop’
to gauge length. I also attached a few homemade clamps to secure the channel whilst cutting.
The stopping, clamping, cutting, repeating process bored me senseless – but it’s necessary
to keep all the pieces the same size – so don’t skimp or rush. There’s a few jigs needed
to complete this project and the ones I’m showing here are really the minimum level
you should use. Take your time in constructing jigs. Make them accurate and secure. The more
precise your jigs, the better your results will be.
Once cut, it’s a good idea to run a file along all the cut edges to remove any burs.
It’s necessary to drill two holes in every single piece and the location of the holes
is critical to ensure the chain and sprocket effect works properly. So again jigs are required.
You’ll need to calculate exactly where the holes need to be drilled and more boring maths
is needed for this. In this diagram you can see on the left the
small and large U channel links. On the right you can see how the smaller piece fits inside
the larger and the positions of the holes. In my design the smaller piece rests on the
larger piece so we need to know the thickness of material, shown in the diagram as W. We
already know Y (the size of the hole we’re drilling) and Z which is the distance to the
edge, so distance A that represents the distance from either edge to the drilling point is
Z + Y/2. Calculating B is much easier… it’s pretty
much up to you. As long as you take into account W (the thickness of the material) and leave
plenty of space around the hole Y then you’re okay. I knew I wanted to add 12mm (half inch)
washers to my bolts to act as rollers (more about that later) and so I decided that B
would be 15mm (5/8 inch). I think without a drill press this would be
very difficult so if you haven’t got one, you might want to hire or borrow one for this
project. This jig appears pretty rustic thanks to the
very-scrap piece of MDF which acts as a back rest. The small metal tab which acts as a
‘stop.’ As crude as this is it’s still quite tricky to set up and don’t be surprised if
you waste a few. Once drilled, the piece can be rotated and
so the drilling point appears on the other side – allowing for two holes to be drilled.
As long as the lengths of pieces are consistent, this will work fine.
This jig is too crude if I’m honest. You’ll be drilling a lot of holes and mistakes can
slip in so the more supportive you can make your jig the better.
Here’s the same jig again being used for the smaller U channel. To compensate for the
depth of the material a scrap piece of the L channel is secured against the back rest.
Other than that, it’s just more of the same – drilling, flipping, drilling again.
When it comes to drilling the L channel, the same jig works fine for the left hand hole.
However, if we flip the piece over it cannot lie flat. This means we can’t drill the right
hand side without structural changes. I kept the existing back rest but positioned
a ‘stop’ on the left hand side. Furthermore I added a supporting piece to the front. This
meant that each piece was supported on 3 sides making it fairly stable, though ideally the
work should be securely clamped. The better the jig, the better your results will be.
With all the pieces cut, I chose to use a strong epoxy adhesive to bond the large U
and L’s. Gluing helps in handling for the further machine work that’s coming up, but
this is still an optional stage. Bolts are used to ensure alignment and the pieces rest
on a flat block whilst drying to make certain the bottom of each track section is nice and
flat. Hopefully if you’ve been careful with cutting
and drilling everything should align perfectly. If, however, some minor imperfection have
crept in, now is a good time to remove these. I found an ordinary belt sander made easy
work of this. Make sure the belt is spinning away from you. If you lose your grip and something
comes flying off, it’s best this goes in the opposite direction.
To enable the links to wrap around the sprockets, it’s necessary to trim off the corners. Again
the mitre saw is the ideal tool for the job. I found that an angle of 25 degrees worked
nicely. This allowed for the level of movement I required whilst not taking away too much
material. Of course trimming a small piece of metal
from a piece of already quite small metal is more than a little dangerous when using
a mitre saw, so jigs are once again essential. When it came to the smaller U bottom edge,
I inserted a bolt into the fence to secure the work firmly. Two bolts would have been
better. I decided to assist the glue with some permanent
fixings. I managed to find some small bolts which were actually advertised as Mecanno
compatible, so that should give you a clue how small they were. I bored four 3.5mm holes
into each main section and tapped each hole with a M4 thread. This enabled the bolt to
screw into the work itself. The addition of a little Thread Lock helped secure things
nicely. I then decided to round over the corners on
the belt sander. It’s not strictly necessary but I liked the look.
Assembly is easy though it can be a little fiddly. It’s simply a matter of beginning
with one fitting, say the larger link and inserting into it the smaller fitting. A bolt
and washers secure the intersection and a nylon (locking) nut. Then another piece is
added (the larger), then the next (smaller) and so on, forming an interlocked chain.
Inserting the washers that form the rollers can be very fiddly. My fat fingers struggled
this this. But here’s a handy tip that will save your sanity. Count out the number of
washers you need and place them on a spare bolt. These should fit comfortably between
the gap of the smaller U channel. Using tape, enclose all the washers and leave a scraggy
end to make removal easier. This roll of washers is much easier to insert.
Slide the bolt through, add a washer and a nut, then repeat the process.
The washers have a major advantage over rollers. Because they have a little play in them, they
allow for the slight inaccuracies of garden-shed engineering.
The nut should not be fully tightened A small gap is required to allow the bolt to rotate
freely whilst still hold everything securely. This is critical to ensure smooth and free
movement of each link. If you begin with a large section, you should
end with a small section, so these two can be connected to form the loop of the track.
Counting only the larger sections (for convenience), each track in my case was made up of 40 connected
links. And that pretty much covers the making of
a very simple continuous track. I made a frame from 1 inch (25mm) square box
steel, added a couple of wheelchair motors and two car batteries to power them.
One thing I realised as I put mine together was that the track really did need supporting
in the centre. As I was keen to test, I quickly produced a couple of wheels from MDF, not
the best choice of material but it was an ideal thickness that matched the sprocket.
I will be casting a couple of wheels, maybe four… I haven’t made my mind up. These
don’t need to be sprockets. Round will suffice. Will these tracks last forever? Of course
not. If I wanted heavy duty usage, I’d have gone with steel. But with that said I’ve
probably got 20 hours of play on this already and other than dirt and light scratching on
the underside of the tracks, there’s no sign of wear.
I hope you enjoyed this one guys and if you did please give Like it. Remember plans are
available for free from my website if you want to but one exactly the same. If not,
reading through the web page will help you calculate your own measurements.
If you haven’t subscribed yet guys, please do. Look out for my other videos and above
all, thanks for watching.