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Old 02-28-2021, 01:22 PM
wirejock's Avatar
wirejock wirejock is offline
Join Date: Oct 2005
Location: Estes Park, CO
Posts: 4,379
Default Drilling the Stainless Firewall

I'm sure this isn't the proper way but maybe it will help someone a little.

Don't assume you're perfect measurements and punch marks will result in aligned holes when drilling stainless. Stainless is hard. You can measure, mark and punch all you want. Holes still wander a tiny bit as you enlarge them to final dimension bcause the bit tends to cut away material in an irregular pattern. The error is nore pronounced, the bigger the bit and hole.

Use the part to check every hole before drilling the next. Drill the first hole. Enlarge in small steps. Stick a bolt in. Mark and drill the next, repeat. It takes forever, but insures the bolts will fit where they belong.

Use Vans preexisting rivet holes whenever possible. It's one less hole to drill.

Buy small bits for pilot holes. Best you can find. Buy several. 1/16"-5/64" seem to work best. Strong enough to apply pressure without snapping and small enough to cut a tiny hole without wandering. Drill super slow and apply firm pressure as the bit and drill will allow. Go slow enough to count the turns. Use a really good cutting oil. I use Kroil in a spray can. The bit will cut and break through much quicker with tiny bits, before the stainless work hardens and drilling becomes almost impossible. Once you have a tiny hole, enlarging is easy in tiny steps. Don't be tempted to go for the final size. The bit will grab, cut off center and distort the metal. Go up no more than 10 at a step.
Example. A #12 hole starts at 5/64", ~#40, ~#30, ~#20, ~#14 then #12 reamer. Yes, takes a long time.
Good luck deburring. Lots of turns to remove the burrs. A Carbide burr in the Dremel works well for big holes.

Big holes are not so bad. Follow the same steps and ream the hole to 1/4". A sharp Unibit works pretty well up to 1". Same technique. Super slow with lots of cutting oil. If you see smoke, stop and add more oil. Hole saws work fine for 1" or larger with a polished steel pilot rod. Oil the pilot and the hole saw. Super slow. It actually cuts pretty quick. Spray with cutting oil often.

Don't go so fast you let the smoke out!
Larry Larson
Estes Park, CO
wirejock at yahoo dot com
Donated 01/01/2021, plus a little extra.
RV-7A #73391, N511RV reserved (2,000+ hours)
Empennage, wings, fuse, finishing kit, now FWF
I cannot be, nor will I be, held responsible if you try to do the same things I do and it does not work and/or causes you loss, injury, or even death in the process.
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Old 02-28-2021, 01:51 PM
scsmith scsmith is offline
Join Date: Jan 2008
Location: Ashland, OR
Posts: 2,815

Good advise. Thanks for documenting what many of us learn the hard way.

I think most of the time I went 1/16", 1/8", then used the Unibit.
Steve Smith
Aeronautical Engineer
RV-8 N825RV
IO-360 A1A
WW 200RV
"The Magic Carpet" Flying since Sept. 2009
Hobbs 635
LS6-15/18W sailplane SOLD
bought my old LS6-A back!!
VAF donation Dec 2020
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Old 02-28-2021, 02:28 PM
PhatRV PhatRV is offline
Join Date: Mar 2018
Location: Buena Park, California
Posts: 436

I use the floating nutplates on the firewall in case the drill bit wanders just a bit to the side. The floating nutplates will selfcentered for the not-perfect holes.
RV8 standard build: Empennage 99% completed
Wing -- Closed
Fuselage -- Canopy Done. Fiberglass 80%
Avionics Installation -- 90%
Firewall Forward -- Prep for cowl install
Electrical -- 90%

Donation paid through 2021
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Old 02-28-2021, 02:58 PM
wcalvert's Avatar
wcalvert wcalvert is offline
Join Date: Jan 2019
Location: Anacortes Wa
Posts: 184
Thumbs up

Chassis punch ... Greenlee
RV-7 Tipper
Bill (Wild) VA-165 '90-'93
Anacortes, Wa

Start 2/19 Emp complete 4/19 Wings complete 11/19 Fuse complete 6/20 Finish kit Complete 8/20 Electric/Avionics complete 9/20 Engine hung 2/21 Moving soon for assembly 4/21 - truckin' on...
- Been there, Donated 2021
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Old 02-28-2021, 03:21 PM
bjdecker's Avatar
bjdecker bjdecker is offline
Join Date: Jun 2005
Location: Georgetown, TX
Posts: 632

...and everything Larry said; lube and go slow...
Brian Decker
Retired Firmware Guy and Airplane Builder

2020 RV-14 QB -- Under construction - Tailcone & Empennage Complete.
2018 RV-7 QB -- Built, Flying
2007 RV-7 QB -- Built, Drowned, Resurrected and flying
1998 RV-8 QB -- Started, Sold
1986 Mooney 205SE
1980 Mooney 231

Aided and abetted building a number of other RV's.
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Old 02-28-2021, 03:57 PM
KiloFoxtrot's Avatar
KiloFoxtrot KiloFoxtrot is offline
Join Date: Oct 2007
Location: IL
Posts: 58

Good advice Larry. Thanks
I'm working on firewall now.
RV7A tip up
Superior IO-360-M1S Aerosport build school=Excellent. See post: Engine build school pictures IO-360
Tail / Fuse / Wings are complete + painted. I used Sherwin Williams JetGlo solids and AcryGlo metalics.
Leather seats by Flightline Interiors.
Still to do: Firewall forward, cowling fit and paint, G3X avionics.
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Old 02-28-2021, 04:48 PM
wilddog wilddog is offline
Join Date: Feb 2008
Location: va.
Posts: 619

When drilling the pilot hole, back it up with a piece of steel or aluminum to conduct the heat away.
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Old 02-28-2021, 05:36 PM
blaplante blaplante is offline
Join Date: Jan 2010
Location: Southern California
Posts: 186
Default My trick

Roper Whitney #5 Junior punch. If it can reach, this is the way to go. If nothing else it gives you a starter hole, and then it is *so* much easier to drill up to the needed size. I think I used this to make the holes where the top of the firewall joins to the top fuselage skin and asked myself why hadn't I bought one of these sooner!
RV6A in phase 2 as of April 2016
Donation made Oct 2020
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