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pilot28906

Well Known Member
I am ready to rivet the bracing and have drilled the holes for the brake plate and fuel pump plate. When is the best time to drill the throttle, mixture, carb. heat, and the 2" hole; now or some time later?

Also, what is the best way to drill the 2 inch hole?

Thanks
 
On my -4 I did all of the holes after engine was hung. For the 2" cabin heat hole, I used an instrument punch, it worked great.
 
I did mine while I was building the firewall. I also drilled for the battery box, gascolator reinforcement as well as nutplates while I was at this stage. Made access easier while off the plane. You have to read ahead in the drawings to find the dimensions. Also as far as the gascolator you need to look at the firewall forward plans to get the part numbers. Don't know where your plans suggest these items go
 
holes

I cut the holes while building the firewall. Lenox 2" hole saw, and step drill for smaller holes. Go slow and use cutting oil.
 
Klein Tools Knockout punch

If you know an electrician they usually have a series of punches for making holes for conduit runs. There is one that will punch a perfect two inch hole.
You start your hole with a unibit so the pilot will line up. Insert the knockout tool and presto a perfect (no distortion) hole.
 
Grezdlitn said:
If you know an electrician they usually have a series of punches for making holes for conduit runs. There is one that will punch a perfect two inch hole.
You start your hole with a unibit so the pilot will line up. Insert the knockout tool and presto a perfect (no distortion) hole.
Click to expand...

I would add: use some .063 sheet aluminum behind it to give the Greenlee punch something to bite into. My experience was that the stainless steel firewall is malleable and left me with a flared (distorted) hole that had to be ground down. Backing it up with the aluminum sheet would have allowed the punch to cut the firewall before punching out the .063.
 
mikehoover said:
I would add: use some .063 sheet aluminum behind it to give the Greenlee punch something to bite into. My experience was that the stainless steel firewall is malleable and left me with a flared (distorted) hole that had to be ground down. Backing it up with the aluminum sheet would have allowed the punch to cut the firewall before punching out the .063.
Click to expand...

Same thing happened to me...in fact, a little bit of the edge "tore" more than punched, and got itself stuck in the punch and it was a *booger* to get it out, and then grind the hole to make it nice and round and smooth and flat. A very frustrating evening...wish I had thought of your idea of backing it up.
 
Backup !

Ditto what these guys said about backing up the punch. I left this part out ! Hadn't had my second cup of coffee yet.
 
One more tip ...

...if you know someone with a set of Rotabroach (or similar) rotary cutters, they go thru the SS firewall like butter and leave almost no flashing or edge burr to remove. It also takes less than 10sec per hole. If you have an EAA chapter with a tool crib, a set of rotary cutters is a great addition.
 
i used the 2.250 instrument punch. neat and no problem w/2.25 hole. i drilled my thr mix etc at the same time.
 
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