SmittysRV

SmittysRV

Well Known Member
I used this bit for the battery box. Will it work for the firewall 2 inch vent hole?

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Deleted. I had the other end in mind. The firewall does need the 2".
 
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I think you're right Scott. So far my drilling experiences with stainless steel are a real pain. I read on some of the builder websites that they drilled several small holes and dremeled their way out to the edges.
 
The punch method has problems, too. I used conduit punches and at the end the stainless sucks up between the dies. I was left with 1/4" that I had to cut as best as I could and an edge that was hard to deburr. I ended up smoothing the cut and then planishing the edge with a flat rivet set on a back-riveting plate.
 
I don't know the right way to do it, but one of the more miserable afternoons during my build was trying to drill that 2" hole with a hole saw. There was a Home Depot 10 minutes away from the house so I went back and forth to the store about 3 different times, eventually going through one of every brand of hole saw they had.
 
Greenlee punches for firewall

I've used Greenlee punches for all the big holes in the firewall (2x cabin heat, 2x wire penetrations, and just today the nosegear bolt hole). They work great with almost no deformation. I put a piece of scrap aluminum in to back up the thin stainless. Sometimes the edge gets a bit rolled by the punch. That is easy to fix with your rivet gun and a bucking bar.
 
unibit and a nibbler, then a bunch of grinding

. . . .That's how I did it. Took about 30 minutes. It was miserable, on the order of fitting the leading edge wing ribs the first time. :)

Unless it's a really sharp / good punch, I would expect it to jam up. The FW material is pretty ductile for stainless. I tried a 1" and gave up, and I know it was a good tool.

A friend, long gone (he was 70 when I was 15) had a can-opener looking thing - essentially a rotary hand shear. Never seen anything like it since, I think I would find a million uses. It would have been perfect for this. Back then, to my teenage mind, it was another pc of junk in an old tool box . . . who knew.

Rick 90432
 
Ditto

I did what Rick did...unibit followed by nibbler and die grinder. Came out fine, but I did mine way back before the firewall was even on the fuselage.
 
Used a fly cutter

I used a fly cutter in a handheld drill. I went slow (about 1 revolution per second) and used some Boelube, but it still only took about 10 minutes and produced a nice clean hole.

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hole saw worked for me...

i have had great success with lenox hole saws (made in usa) stocked at lowes. for the firewall i just used a some boelube and chucked it in a hand drill and it cut it no problem.
 
Thanks guys! I appreciate all the ideas.

Well, here it is. I remembered what a pain it was using the 2 inch drill bit I bought for the battery box. It worked OK for that application, but only because I had board behind the metal to support the drilling on the drill press. Not so here. I couldn't figure a way to put a board behind the firewall, much less trying to hand drill the hole with a monster bit in an electric drill. So I decided to go with my unibit, making connecting holes all around the edges of the hole. Then I used my Dremmel with a sanding drum to clean up the excess. I went through about 4 sanding drums in the process.

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Here's my unibit and the Dremmel with the sanding bit. The drill is ancient but still works.

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I second the fly cutter. Works real well and does a clean job. Just make sure you have your drill set so it does not devolope so much torque or will ratchet easily if the cutter getsstuck as it cuts through the stainless. Work slowly.
 
I used that same hole cutter (from Home Depot) on several holes in my firewall. Cuts through like butter. No worries.
 
Look for someone who'll loan you a Rotabroach ...

..or equal. (Hougen makes the patented Rotabroach cutters)
I struggled cutting the 1" and smaller holes in the SS firewall and vowed I would NOT use a hole saw on the 2" opening. There are a couple of companies who make fancy hole cutters similar to the Rotabroach, and luckily I was able to borrow one. It cut the 2" hole so cleanly it didn't need any dressing up ...took maybe 30 sec. Yes, the fancy hole cutters are pricey, but they work like - well - magic. Once you've used one ..especially on the $%^& SS firewall ...you'll use nothing else.
 
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