20 May 1999
Quite a lot of the work on this project involves
drilling fairly large holes in steel. Anyone who has tried this
with a hand drill will, I'm sure, have found out what a pain it
is. You have to apply a lot of pressure to the drill while keeping
it square in both directions and hoping the drill doesn't grab.
After a couple of holes you're getting tired and
then the drill grabs and half tears your arm off. This tires you
even more but you persevere. Then the drill grabs again. And you've
got another ten holes to drill.
There must be a better way. Well there is, it's
called a magnetic drill. These drills clamp magnetically to the
job and allow you to slowly crank the drill into the steel until
it's through. They also cost about $2000.
I'd been thinking about this for a while and putting
off some jobs because I couldn't stand the thought of drilling holes
in the chassis rails. Then I got to thinking that it's easy to drill
steel in a drill press. It's pretty difficult to take the truck
to the drill press but what about taking the drill press to the
truck? Well my press is too large but the thought sent me down the
I bought a $50 "convert your drill to a drill
press" gadget, stuck my drill into it, G-clamped the whole
contraption to the chassis and, voila, my patented "drill-o-matic"
chassis drilling thingy.
In the following photo we see the drill in position
and ready to drill.
While in this photo we see the drill swung out of the way to give access to the job.
The system works great. It's a little bit of a
handful when the G-clamp is loosened but easy enough with practice.
It's very easy to apply pressure to the drill and to swing the drill
aside to change bits, for example after drilling a pilot hole and
inserting the bit for the finished hole.
While on the subject of pilot holes etc, I found
it very convenient to use two drills and swap the entire drill rather
than just the bit. If you don't have a second drill then maybe you
should buy one because, almost certainly, your current drill is
not really suitable for drilling largish holes in steel.
If I remember correctly the rule-of-thumb for
drill speed is 9000 divided by the drill size, so for a 14mm hole
you should use a speed of about 650rpm. Even two speed drills only
go down to about 900rpm but, more importantly, they don't have enough
torque. And you can't use the electronic speed control because this
reduces the power considerably to the point where the drill will
The answer is available in the form of some new
drills from Bosch and Metabo (probably others as well). These drills
have what is called "triple reduction gearing". This means
that the drill speed is reduced further than with normal drills
and that this reduction is achieved with an extra set of gears.
This gives us the slower speeds required but equally important is
the fact that the reduction is mechanical not electrical, this gives
a massive increase in torque at the sharp end.
I bought the Metabo because it has a clutch and
because I've used a Metabo drill for years and it's been very reliable.
Remember, when looking at these drills, not to be confused by the
apparently low "power" in watts, it's torque at the front
end that matters, not how much power the motor consumes.
Mounting the fuel tanks
Originally I planned to have someone else mount the fuel tanks
because I was unsure of my ability to properly drill the chassis.
However, with my new drill-o-matic I'm brimming with confidence.
Justifiably as it turned out.
Seen below is a shot of me hard at work drilling
one of the 16 holes required to hang the tanks. Note the strain
involved in this back-braking job.
Fortunately four hangers came with the tanks,
but I had no straps. I had four cut from 1mm steel at 50mm wide
so all that was left to do was attach a method of mounting to the
hangers. What is needed is a bolt that passes through existing holes
allowing a nut to be tightened and pull the strap down tightly on
the tank. This is pretty simple but remember not to weld the bolt
directly to the strap, it's too thin and I think would shear in
time because the strain would be placed on too small an area.
To spread this strain around I welded a small
piece of 3mm steel to the strap and then welded the bolt (minus
head) to this thicker plate, as shown below.
A diagram of the tank mounting appears below. The red arrow indicates a brace that I have not added yet but will have to. At roughly 400kgs for each full tank I think there will be too much stress placed on the hangers, especially when off-road. Also it seems that this is a good place to put the black and grey water tanks and this brace could perform the second function of supporting them.