What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Drilling the Stainless Firewall

wirejock

Well Known Member
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!
 
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.
 
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.
 
When drilling the pilot hole, back it up with a piece of steel or aluminum to conduct the heat away.
 
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!
 
Will be starting the firewall soon. Was debating using the cheapest drill bits available, since it sounds as if they will be ruined anyways, or going high quality due to the nature of the job. Or using the best HF as to offer!

So, are there any 'best drill bits' to use on stainless?
 
Cheap bits

The firewall is not the place to chintz out. Follow the advice offered above & go slow.

Agree. I buy replacement bits from ACE. They are probably not super duper but not cheapo either. The tiny bit worked best for a starter hole. What really helped was going super slow with oil. Like count the turns slow. You can hear the bit working and see the chips. It actually sounds kinda painful for the bit. Any faster and the stainless got hard really fast and bit got dull. So bad getting any hole was pretty frustrating. Like trying to drill glass with a wooden dowel.
Once a pilot hole is drilled, going up is easy but resist the temptation to go up too fast. The bit will grab and distort the stainless.
 
Stainless is not a hard metal. It is a dense metal that will work harden easily. You can use standard bits like sold at ACE to drill with. Go SLOW and keep it from heating as others have said. On thin material, switch to a stepped bit as soon as possible to keep the heat down and have more control.

Sharp bits, cutting oil, and go SLOW..... Start the bit rotating before applying pressure will keep you from breaking bits of any size.
 
Back
Top