What I am really excited about is how well the engine mount drilling went. I was nervous because drilling through the stainless firewall is always a risk. The drill bit sticks, pulls chips in under the stainless, tries to lodge them where you can get them out, and deforms it etc.. In general it is just tough to drill through the firewall, and with these holes, they go through a lot of metal layers, first stainless firewall, then some aluminum doublers, then finally into a doubled over metal web that connects to the rest of the forward fuse structure.. Lots of metal for sure, but for good reason since it holds the entire engine on the front of the plane...
The mount was secured to the fuse by bungees and clamps.. Then I used two bits, first 1/4 inch bit inside some scrap tubing. This worked great as the tubing fit snug in the engine mount hole, and the 1/4 inch bit didn't wander at all. I drilled the top two holes, then used a AN4 bolt to hold the mount in place. Then I pulled the tubing and used my 3/8 inch bit, and with some BOE Lube, went to town. Pressing firmly on the mount to try to keep the stainless from pealing up underneath.. Turned out Great.. I am really excited how clean my holes are, and how accurate they are.. here are some pics, you can see the one with the bolts in place sticking through the firewall, the holes are clean !
After I did the 4 holes around the outside, I made some small spacers, and drilled the two lower central holes the same way. These were a bit easier, because once through stainless all you had to drill through was aluminum.
All in all, great progress !
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