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Last night I had a heck of a time drilling my lower firewall to the fuselage. I pilot drilled all the other holes in the firewall stainless with relative ease. But for some reason I am having problems now. All the bits do is scratch the SS. I have tried cobalt and titanium bits with lubricant and slow speed as well as fast speeds. Dors anyone have any suggestions?

I found using a slow speed with lots of pressure worked the best for me. I also noticed that the areas where I couldn't drill against a solid surface were much harder to do (I think this may be where you are at now). So if you aren't already doing it, you may want to see if you can get some wood pressed firmly behind the holes you are drilling.

There are lots of holes in the middle of the firewall where you will put things such as relays, regulators, etc and I wasn't able to back the drilling of these holes with wood...I just pushed really hard and the bit finally began cutting and went through.

Fyi...I just used the Cobalt bits from Home Depot (for some reason, I never had luck with the ones from Lowes).

I just found a good way to drill pilot holes in the SS of the filler box/upper firewall (after having broken several 1/16" bits trying to drill smaller holes per some suggestions.) Lots of pressure and low speed is definitely the key. Here is a video of the method I'm using.

http://youtu.be/OW64A-7KYlM

Gripdana wrote:Last night I had a heck of a time drilling my lower firewall to the fuselage. I pilot drilled all the other holes in the firewall stainless with relative ease. But for some reason I am having problems now. All the bits do is scratch the SS. I have tried cobalt and titanium bits with lubricant and slow speed as well as fast speeds. Dors anyone have any suggestions?

Sounds like you need to push harder. More feed less speed is the trick with stainless and always use cutting fluid. If you don't have swarf you're doing something wrong. Never use a blunt drill bit, throw blunt ones away. All a blunt bit will do is generate heat and make the stainless even harder!
With the correct technique should be possible to drill all holes in the firewall with one bit.

Steve
Sonex 892

sonex892 wrote:Sounds like you need to push harder. More feed less speed is the trick with stainless and always use cutting fluid. If you don't have swarf you're doing something wrong. Never use a blunt drill bit, throw blunt ones away. All a blunt bit will do is generate heat and make the stainless even harder!
With the correct technique should be possible to drill all holes in the firewall with one bit.

Steve is right on the money. The key to drilling stainless (whether it's the firewall or drilling out SS rivets) is a SHARP drill bit, low speed and high pressure. If you spin the drill too fast without enough pressure you just heat up the SS and harden it, making your life even more difficult. Take your time, press hard, and keep the drill sharp!!