Drilling firewall for rotisserie mounting

So I'm getting ready to put my fuse on a rotisserie, and trying to work out mounting it to the firewall. I've read the threads here and the consensus seems to be that drilling the engine mount holes to 3/16" is OK, since they'll be enlarged later on for the mount itself.

My concern, though, is that drilling from the firewall side, there's a seam in the underlying spacers, and I'm concerned about the drill bit wandering:



On the cabin side, there's a preexisting hole in each weldment, which I think would be a better spot to drill from (note: I'm referring to the larger of the two holes here):



I'm assuming that this hole is in the same location as the prepunched firewall hole, but I'd like a sanity check before I go making holes in things. Thoughts?

Firewall

7 is similar.
I used a bushing to keep the bit (#41) centered and drilled from the forward side then sanity checked through the weldment to verify it was centered. Then progressively larger bushings were used up to final size.

Firewall

Drill the firewall side.

I used a cup with the preexisting holes after I measured the dimensions as per the plans...never had a problem with the rotesserie or my engine mount.

Cheers,


Don

Rotisserie

I used the engine mount as a guide to locate these holes. Drill bushings in the mount holes then undersize drill bits to start.

Don Broussard


RV 9 Rebuild in Progress

Rotisserie

I used 1.5" steel angle iron to make a H frame that bolts to the outer attach points. To space it off the firewall I cut some plugs from a 2x4 with a hole saw. This 1 &3/4" spacer clears the "lip" formed by the skins. A better way would be to use 2 spacers per bolt and get longer hardware store bolts. This would space the frame 3.5" off the firewall and allow some work to be done with the frame in place. I can send some photos of my rig.

Don Broussard

email: [email protected]

So the answer to me question was "yes." When I went out to work this evening, I did a more careful survey of the location of the weldment hole. Sure enough it was in the same location as the prepunched firewall hole. So I drilled all four holes to 3/16" from inside the cabin and all was well.

Now I can spin my fuselage around!