cutting the firewall

[jacksel]

Does anyone have a good technique for cutting a clean 2" hole in the firewall for the cabin heat fitting? Cutting stainless is always a pain and I see this 2" hole as a real challenge.

[N941WR]

Yep, it is a real PITA!

I bought two hole saws and lots of cutting oil. Turn the thing slow and keep it lubed and all will be good.

Don't forget to deburr it. SS will cut you like a knife!

[rv4ross]

I used a new hole saw and had a helper back it up with a piece of wood. It did a real nice job. And watch your hands, that stuff is sharp!

Ross Scroggs
Locust Grove, GA
RV-4 #3911

[MarkW]

Since I learned the finer art of drilling I have had no problems with Stainless.
Like Bill sayes slow speed and like Ross sayes back it up so you can put pressure. What tears the bits up is heat. When you use a high speed and low pressure it just causes friction and no cutting. If you can keep the speed down and the pressure up it will cut and create burrs. These burrs take away heat. You just have to keep it cutting.

[BillL]

Knockout punches do a pretty good job with this stainless. Lube it good and it cuts better. HF has a manual set for $25 but the largest is only 1.25". Maybe an industrial rental would have a hydraulic version with 2" included. That makes it very quick and very clean edges.

Wear boning gloves or be ready to bleed. NEVER touch the edge to check the finish.

[agirard7a]

Use a Lenox hole saw blade. Slow speed,pressure and cutting oil.

[alpinelakespilot2000]

Ditto a hole saw, but get a "bimetal" hole saw (as opposed to a cheaper plain steel hole saw, but both should be available at Lowes/HD) and do back it up with wood as suggested. I'm assuming you are doing your cabin heat valve? If so (and assuming you have not yet riveted on your firewall recess), you can clamp a piece of wood to the firewall to serve as the back up. Good luck.

[grayforge]

A GreenLee punch worked perfectly. Klein Tools makes one too. Just a few minutes and done.

These are expensive, so look for a set on eBay or borrow/rent a set.

[Stoo]

I just used my Dremel.

Stewart Willoughby
6, finishing

[Rupester]

Hopefully, you can find a metalworking shop or friend with a set of Rotabroach hole cutters, or similar product. They cut thru the FW stainless like the proverbial hot knife thru butter. Totally amazing...takes maybe 5 to 10 seconds with a battery powered drill motor.
I also used a carbide rotary file (available at all the aviation tool houses) that was verry effective in enlarging holes in the stainless.