Drilling the firewall

Dave Qualley · Post by **Dave Qualley** » Fri Feb 17, 2012 9:37 pm

Also, what's the secret to drilling large holes through the SS firewall??!!!
I've used very sharp bits, tried slow feed, fast feed, slow speed, fast
speed but the dang bit keeps grabbing and damaging the hole!

Whenever I need to cut a large hole I use spade bits, usually meant for wood..
They work beautifully on aluminum, however I did trash one bit drilling the 4
holes for the engine mounts in the SS firewall.. The 4 holes did turn out OK
though, just couldn't use the bit on aluminum again afterwards..

Dave
#057SR

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CBFLESHREN · Post by **CBFLESHREN** » Fri Feb 17, 2012 9:37 pm

In a message dated 1/5/2002 3:54:24 AM Eastern Standard Time, dqualley@shaw.ca writes:

Also, what's the secret to drilling large holes through the SS firewall??!!!
I've used very sharp bits, tried slow feed, fast feed, slow speed, fast
speed but the dang bit keeps grabbing and damaging the hole!
Whenever I need to cut a large hole I use spade bits, usually meant for wood..
They work beautifully on aluminum, however I did trash one bit drilling the 4
holes for the engine mounts in the SS firewall.. The 4 holes did turn out OK
though, just couldn't use the bit on aluminum again afterwards..

The only safe (non-destructive) way , short of water jet , laser or machine shop , to cut nice large holes in stainless is w/ knock-out punches . The most popular brand is Greenlee . Aircraft Spruce carries these . You might even find s ome on Ebay . They are relatively expensive so maybe your Local EAA Chapter might go in on a set if they don't already have them . I have a pretty good selection if you live near Washington , D.C. ( for loan , not for sale ) . Good luck , Chris.

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LisaFly99 · Post by **LisaFly99** » Fri Feb 17, 2012 9:37 pm

In a message dated 1/5/02 7:58:29 AM Central Standard Time, CBFLESHREN@aol.com writes:

Greenlee . Aircraft Spruce carries these . You might even find s ome on Ebay . They are relatively expensive so maybe your Local EAA Chapter m ight go in on a set if they don't already have them . I have a pretty good selection if you live near Washington , D.C. ( for loan , not for sale ) . Good luck , Chris.

If you have an electrician friend they usually have or can get a hold of a set of Greenlee punches. They use them all the time for panel knockouts of various sizes.
Phil&Lisa Smith

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Gordon Mohr · Post by **Gordon Mohr** » Fri Feb 17, 2012 9:37 pm

A duller bit will not grab as much because it won't try to pull itself
through as fast. For SS try a titanium coated bit and slow speed so it
doesn't just melt the tip. But if you are using a twist drill , try this.
If you can access both sides of the stainless sheet, sandwich it between
two pieces of of 1/4" aluminium or steel and drill through all three pieces.
You'll get a perfect cut. That also works for drilling almost any thin
material, even plastic.
I use a "unibit" , one of those step-tapered single edge drills, to cut
holes up to 3/4" in thin material and they work great. They leave a perfect
edge and even deburr the hole. They're indispensible for sheet metal work.
Regards, Gordon #222

----- Original Message -----
From: "Dave Qualley" <dqualley@shaw.ca>
To: <murphy-rebel@dcsol.com>
Sent: Saturday, January 05, 2002 12:52 AM
Subject: Re: Drilling the firewall

Also, what's the secret to drilling large holes through the SS

firewall??!!!

I've used very sharp bits, tried slow feed, fast feed, slow speed, fast
speed but the dang bit keeps grabbing and damaging the hole!
Whenever I need to cut a large hole I use spade bits, usually meant for

wood..

They work beautifully on aluminum, however I did trash one bit drilling

the 4

holes for the engine mounts in the SS firewall.. The 4 holes did turn out

OK

though, just couldn't use the bit on aluminum again afterwards..

Dave
#057SR

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Legeorgen · Post by **Legeorgen** » Fri Feb 17, 2012 9:37 pm

Dave,

Like Gordon said, use a Unibit and you'll have better results, for drilling
SS, or any sheet metal. Every builder should have one of these bits. They
drill a more perfectly round whole than a drill bit and won't grab and tear
your sheet. You can buy them at any good hardware store.

Bruce G 357R

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