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How to cut 1/2" dia. Hole in firewall

walkman

Well Known Member
In order to pass my ignition harness from the cabin mounted ECU to the engine mounted sensor and ignition coil I need to cut a 1/2 or so hole in my firewall.

What is an appropriate tool and technique for this?

Thanks
 
Pilot hole followed by Uni-bit.

Greenlee punch will work, but not very well in my opinion. Stainless tends to "tear" rather than cut with punches.
 
Easy way

  1. Remove hole from 1/2 inch tubing (either end will work), if you find a perfect 1/2 inch swiss cheese hole it will work too.
  2. Deburr the hole (both side, let's be careful)
  3. Alodine, prime or use any anti-corrosion method (search this forum there is a lot of information on this, be careful there is supposed to be galvanic corrosion involved, especially with the swiss cheese hole)
  4. If access is very difficult, fabricate a stainless steel doubler twice the diameter of the hole
  5. Skip to step 6 if you didn't perform step 4, if not : prepare some pro-seal, and pro seal the hole to the doubler : any method will work, but I suggest fay sealing (search this forum)
  6. Rivet hole or doubler to the firewall, use coutersunk rivets on engine side of the firewall. Pop rivets are acceptable if bucking proves to difficult, search this forum for acceptable replacements for solid rivets.
  7. If you have to remove a rivet and enlarge the hole, you could even use screws or bolts and nuts, be careful you may get to much weight in the front and not be able to get a correct CG. This is very easily corrected by replacing the 1/2 inch hole with a 3/4 inch hole and repeating the whole procedure. If having again problems enlarge the hole in 1/4 inch increments.
  8. If you repeat step 7 too often, you might have to call Vans to get their input, maybe the firewall is structural !!
  9. Some say that when all is done you have to seal the hole again. A good idea is to use the rest of the swiss cheese, but I might be wrong. Search the forums (or is it fora !!!!!).
I'm already running, but in the end, I did as Brian suggests.
 
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What ever you use

Drilling stainless will ruin your expensive unibit unless
You go slow and use cutting oil
 
Been drilling stainless with my Uni-bits for years.

Of course you have to use standard drilling practices.
Hard materials (steel), use low speed, high force.
Soft materials (aluminum), use high speeds. low force.

I've only messed up one uni-bit. I let it get too hot while drilling my hangar purlins for electrical conduit. Too little lubricant.
 
Thanks

I'll try the cheese method first. If that doesn't work I'll save it for some Chateau Neuf and use a Unibit instead.
 
49clipper

I use some regular old Lard for lubrication when drilling SS. Best thing I ever found. Better than cutting oil. Turn the bit slow, start with a dab of cooking Lard on the tip. pilot hole then unibit like some said. I keep some in my hangar fridge so it remains solid.
Jim
 
I use some regular old Lard for lubrication when drilling SS. Best thing I ever found. Better than cutting oil. Turn the bit slow, start with a dab of cooking Lard on the tip. pilot hole then unibit like some said. I keep some in my hangar fridge so it remains solid.
Jim

Lard eh? I'm sure my dad has some, used for cooking. I'll try it. Besides, in retrospect I realize that the Swiss cheese holes will be metric. I need SAE. I'd better cut my own after all
 
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