[daveyator]

This is where we must enlarge the hole in the firewall, and at the same time make "half a hole" in the flange of the underlying tunnel rib. Vans say to use a unibit and draw cross hair lines to keep the hole centred. Anyone care to comment on how this method works? The cautious side of my mind is telling me to drill the firewall, then mark the tunnel rib, and use a Dremel to carve out the flange. Any thoughts or opinions from those who have tackled this welcomed
Thanks

Dave Hastwell
120485

 

[rgmwa]

Dave, I followed the plans and it worked OK, but I like your idea better.

 

[DonFromTX]

I recall fighting this, my unibit wanted to wander off to one side.

 

[yankee-flyer]

Too long ago

for my aging memory to be sure, but not knowing anything at all about what I was doing, I pretty much followed the plans as well as I could and called Van's whenever I couldn't. Best piece of advice I heard somewhere was "you're not building a work of art-- it's a machine". I.e, the radius of that half-hole doesn't have to be perfect, the gascolator just has to go through it.

And somewhere in the plans we were told to use and adjustable metric crescent wrench. Being an engineer, I had to think about that a bit before I realized that was another attempt to lighten things up.

Wayne 120241/143WM

 

[AeroDog]

The unibit wandered, resulting in an off-center hole. I used a sanding drum in a Dremel tool to enlarge the hole as necessary. I'll seal it with ProSeal.

 

[Gagarin737]

If I could do it again I would drill the firewall first. The unibit will wander with the flange behind.

 

[bhassel]

I once remember Mel posting or saying something like...

'We measure with a micrometer, mark with a grease pen and cut with a hack-saw...press on!'



Bob

 

[RFSchaller]

If the hole gets ugly you can always use a washer on each side of the firewall and insert the bulkhead fitting. Don't ask how I know!

 

[rvbuilder2002]

If I could do it again I would drill the firewall first. The unibit will wander with the flange behind.

It will tend to wander with the flange only behind a portion of the hole, but you don't have to allow it to. That is the reason for the step to mark the cross hairs. If the hole begins to wander off center, apply a side load while cutting each successive step to make it go where you want. I have purposely used the technique while enlarging holes when I wanted to move the hole center slightly.