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 Living on the Road :: Wothahellizat Mk1 :: Construction Diary :: #12

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 following path.

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 stall constantly.

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.

Here we see one of the mounted tanks complete with new straps. Note the use of padding between the tank and the strap.

An overview of both mounted tanks.

All up this job took most of the day but that included buying a new drill. The tanks aren't connected yet, that's a job for another day, but I needed them in place because I'm about to start on the body and I wanted to know the exact location of the tanks.

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PO Box 450, Gin Gin, QLD, Australia.