Machinists: I’m Sorry

I have a confession to make. I’ve been making the machinists I work with drill some large hole diameters through some pretty thick steel. I didn’t think it was a big deal at the time, but I now know better. It’s kind of painful. Literally.

For mounting the power electronics box to the wheel chair chassis, I had to drill two 0.25in diameter holes through a piece of 1.5in X 1.5in steel tube. No big deal, I’ll just start out with a 0.125in drill bit and go from there.

Generally that wouldn’t be too bad of an idea, if it was actually a steel tube. The ends were plugged with some kind of threaded stud to mount the foot rest for the wheel chair. As I started drilling through the tube I quickly realized that this was actually a solid piece of bar stock.

The first 0.125in diameter pilot hole. It only took 30 minutes!

To make matters worse, I really didn’t have any sharp drill bits, just some old ones I bought at a garage sale years ago. It helps to have sharp bits if you’re going to drill through 1.5in thick steel.

I clamped the mounting plate to the chassis and started my first pilot hole using the plate as a template. Once I had a nice dimple in the frame I removed the plate and kept drilling.

About 5 minutes in my arms were killing me. The wheelchair is pretty heavy, but I still had to brace it with my left arm to keep it from rolling off the blocks that raised it to where I could get the drill on it. And my right arm started aching from pushing the drill into the wheel chair.

I knew I should drill slowly: too many RPMs and you will heat up the drill bit and dull the cutting edge. But even going slowly I wasn’t making much progress. I tried not to apply too much pressure to the drill either, but without it, it wouldn’t make any chips at all.

I did some reading and discovered that using some cutting fluid can allow you to drill at higher RPMs, so I borrowed some non-stick vegetable oil spray from the pantry and sprayed the bit and the hole with it. That seemed to help, but not much.

In the end it took about an hour for each of the two holes, starting with a 0.125in bit, moving to a 0.1875in bit and finishing with a 0.25in bit. I can’t tell you how satisfying it felt when the drill lurched forward as it broke through the back side of the bar stock.

So machinists everywhere: I’m sorry for all the holes I’ve made you drill in steel plate. I will at least have a very good reason the next time I ask you to do it. I understand (in a small way) your pain.

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