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Dean Pichon

Well Known Member
After 8 years of flying, I've decided it's time to put heat in my -4. During the building phase, I found it very difficult to put even moderately sized holes in the firewall. What have other builders found to work to make nominal 2" diameter holes for heater plumbing?

Thanks!
 
Dean Pichon said:
After 8 years of flying, I've decided it's time to put heat in my -4. During the building phase, I found it very difficult to put even moderately sized holes in the firewall. What have other builders found to work to make nominal 2" diameter holes for heater plumbing?

Thanks!
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I was going to say a double barrel 12 ga might work...I used a metal cutting 2" hole cutter from Home Depot. Don't recall the brand but they are white and cost more than the red ones hanging next to them. It is a good idea to have someone hold a piece of 2x4 on the other side so as not to flex the firewall too much.
 
Did the same

I did the same and it worked well. A word of caution if using something like a Greenlee slug buster. All the dies actually cut a bigger hole than what they are labelled for. A 2" cutter actually leaves a 23/8" hole. The home depot hole cutter did the job very nicely in about 5 seconds.
 
I just used the biggest unibit I had, then enlarged the hole from 7/8's to 2 in. with a carbide burr in a die grinder. Finding someone to back up the firewall with the 2x4 has never been convenient for me, but may be less messy.
 
if you can get a hold of a hole punch for the panel 2 1/4, makes a real nice hole, easy to do. That's how I did my hole for the heat.
 
The heat box on my 9 is attached with a couple AN3 bolts on either side of the large 2" hole. I drilled the holes for them before drilling the larger 2" hole and then used a couple large wood screws and washers to fasten a piece of 2 by 4 behind the FW for backing. I then drilled the 2" hole with a typical metal hole saw, go very slow to avoid heat build up and use some type of lube.
 
allbee said:
if you can get a hold of a hole punch for the panel 2 1/4, makes a real nice hole, easy to do. That's how I did my hole for the heat.
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Same here - looks good and the flange on the valve is more than big enough to cover the extra 1/8" all around.

Jim Sharkey
 
647jc said:
The heat box on my 9 is attached with a couple AN3 bolts on either side of the large 2" hole. I drilled the holes for them before drilling the larger 2" hole and then used a couple large wood screws and washers to fasten a piece of 2 by 4 behind the FW for backing. I then drilled the 2" hole with a typical metal hole saw, go very slow to avoid heat build up and use some type of lube.
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Save yourself lots of money and do it Joe's way. Will work great! I just clamped a block on the firewall, but using the heat box screw holes is slick (particularly if you've already riveted in the firewall recess)!
 
Dremel

Dremel with a cut-off wheel
Did mine last week took 30 minutes.
Cleaned up the edges with a dremel sanding drum.
Easy but noisy
 
As usual, the tools that work the best are higher priced. I borrowed a commercial grade carbide hole cutter from a friend and it cut the 2" hole in the firewall like the proverbial hot knife thru butter. So clean a cut it left almost no burr. The hole cutter was similar to:
http://www.hermanscentral.com/produ...e-tooth-hole-cutter-for-sheet-metal-14327.cfm
There are complete hole saw sets like these for around $160. A great buy if you can share it with other RV builders, like in an EAA chapter.
 
If you use a Greenlee, back up the firewall with some scrap .063 alclad so the Greenless has something substantial to bite into. Else you will have a flared hole.
 
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