F-443

Soon I will have to drill the F-443 bracket to the spar. That is the important bracket that transmit loads from the engine mount, through the fore/aft bulkheads between your feet, into the wing spar. Its a fiddly little thing because it fits into a corner which is less than 90 deg.

My question is this. What is the 'correct' way to drill it to the spar. Clearly I can clamp it into the corner, but how to get a perfectly aligned hole? If I use the spar as a drill guide I will almost certainly take some of the spar away and no longer have the correct fit for the NAS bolts.

I could buy a .25 centre drill (Avery no longer seem to sell them) and use that, though I wonder how tight the fit would be?

What solutions have others come up with? Thanks,

Steve,
I just did this a month or two ago on my RV4 project. I purchased a short length (12 inches) of steel tube at the hardware store that fit inside the spar bulkhead hole. It cost less than $2.00. I had to use a little clear plastic tape to tighten it up a smidge. The tube was then my drill guide. I then used the tightest drill bit in my collection (I can't remember which one) and then drilled it. I then removed it from assembly and drilled to spec. on the drill press. I don't recall that I put a whole lot of time into this whole process. I apologize for not offering a Boeing Aerospace solution but it worked for me.

If you want to buy one

Steve, I did what Brian when I had to replace the tail bulkhead on my Tiger. I didn't want to "hurt" the existing hole, but needed accurate alignment.

If you prefer buying drill bushing, MSC has them pretty cheap. they will also sell you a reamer to get the hole to the final size you need...

If the OD is slightly too large - they are designed for a press fit - you can gently file one end while it's held in a drill press.

http://www1.mscdirect.com/CGI/NNSRIT?PMPXNO=1766975&PMT4NO=12373666

It takes longer to type this e-mail than to actually make the hole, once you have the bushings....

gil in Tucson