Drilling out a bolt – the hard way

After breaking my makerbot extruder head I decided I wanted to try my hand at making one from scratch. It’s a brass m6 tube with a nozzle screwed onto one end. How hard can it be!

It turns out it’s really hard, but I ended up having luck with a technique called the “afghan lathe”

Before I get too far into it I need to explain that most bolts are made of hardened steel. To de-hardened them all you need to do is to get them red hot with a blowtorch and let them cool slowly. Here is a pic of me doing just that to two m6 bolts.

After your bolt has cooled, it should look something like this.

Start out with a drill press, a vice, some c clamps and a drill bit. Put the drill bit lightly into the drill chuck backwards. Lower the drill press until you can grip the drill bit in the vice (which should be sitting on the drill press table) Clamp the bit in the vice, and the vice to the table VERY securely. Release the chuck on the drill press. Now you are going to take the bolt that you de-tempered and put it in the chuck. I left the head poking out. That will make it easier to get a good straight grip on it. Tighten everything down and grab some machining oil.

Set up your drill so that it is going absolutely as slow as possible. If it goes too fast then this will not work. Mine had 3 pulleys that can be arranged to increase or decrease speed. Turn the drill on and gently bring down the bolt to the bit. The start can have a tiny bit of wobble to it. Go very slowly and add oil whenever you even think the parts might be getting hot. Lift the bolt and clean out the threads of the bit very frequently as well. It took me around 15 minutes to drill each one out. If in doubt, then go slow. Speed (and heat) will ruin this for you.

The straighter of the two bolts was still a tiny bit off by the end. Believe it or not, this was because the heat from the drilling had cause the bolt to bend in the chuck! I think that to do this again I would move the bolt down in the chuck after an inch or so, so that I was always drilling something that was actively clamped.

This is what I ended up with. It ain’t pretty, but I’m happy!