The stainless steel bolt holding the wooden rudder blade to the aluminium rudder stock had corroded in place. I tried heating it up, but the thick aluminium conducts heat away really well, and the wooden blade will catch fire if too much heat is applied. So I decided to drill it out.
Stainless steel isn’t the easiest material to work with. It tends to work harden, after which you’ll end up with blunt tools very quickly.
I clamped the rudder stock into my mini-mill and lined it up as best I could.
The bolt appears to be 1/4″ UNC; i.e. around 6.35mm.
I started the hole with a centre drill, then followed up with a 4mm drill, then 5.5mm. The 5.5mm drill produced lots of ‘wire’ as the bolt thread disintegrated.
Once all was done this is what I ended up with on the other side:
Not perfect. Once tapped out the bolt looked like this:
That’s pretty accurate; however the drill appears to have bent slightly towards the centre of the bolt. The threaded end of the bolt has completely disappeared without any damage to the hole in the rudder stock.Unfortunately there is a bit of damage to the rudder stock at the head-end of the bolt. That doesn’t matter too much as I’m going to bush the holes with acetal, but I’d prefer accuracy!
Lesson learned: stop when the drill is deep enough to go through the rudder stock:
- A through-hole makes it harder to drive the bolt out;
- The first part of the hole is much less likely to go astray and damage the rudder stock;
- The threaded part is probably the bit that is corroded into the stock.
However, it wasn’t possible to try driving out the bolt with the stock bolted to the mill table. So any attempt to drive out the bolt would destroy the alignment.
Next step is make some acetal bushes for the rudder stock and centre of the rudder blade.