Precise location of blind holes in panels

[Mark Worthington]

I need to make a new bulkhead panel for my RF. The original one didn't have the "ears" that bend and attach to the inner side panels, and it also had a bow in the aluminum sheet beneath the window opening to the engine compartment. The panel had been drilled and clecoed in place, but it is apparent that the part of the panel that is bowed wasn't clamped firmly to the frame member when the whole panel was drilled.

So the problem I'm faced with is how to precisely locate the holes that are in the steel frame onto the new panel. I obviously don't want to re-drill everything because it would weaken the frame...I want to re-use the existing holes in the steel frame. I figure I can use the old piece as a template and transfer the holes on one side onto the new panel. Then I thought I would cleco the new panel in place, along one side, clamp it into position so the metal doesn't bow this time, then somehow locate the holes on the other side. The only way I've been able to think of to do this is to tape some carbon paper to the steel frame where I need to locate the holes, then use a mallet to tap the panel all along the length of the carbon-paper-wrapped steel frame and hope that the existing hole show up as blank circles on the back of the new panel. I'm unsure whether this method would work and I'm looking for a better solution.

[Ron Earp]

I took a strip of aluminum, 0.049, and folded it in half back on itself. For example, take a piece the size of a book mark and fold it evenly in half width-wise.

Then, take a drill and drill a hole through both sides so the holes matches perfectly on both pieces. On one piece take a rivet and cut the stem off and push it through the hole.

Now you have a locator. When you put the side with the rivet into the hole on the frame, the other side with the corresponding hole and no rivet will show you where the hole should be on the panel.

I can photograph it if you need,

Ron

[Mark Worthington]

Excellent, Ron, that's exactly the kind of trick I was looking for but wasn't clever enough to think of mysel. Thanks!

[Scott]

Ron describes a homemade "strap duplicator" as used in the homebuilt aircraft industry. Available from places like www.averytools.com or www.cleavelandtool.com.

Another option, and one which I like for hard to reach places, is a blind-hole spotter or transfer button. www.mcmaster.com, p/n 3414A211 for 1/8". You just stick the shaft of the button in the hole you are interested in, maybe a piece of scotch tape to keep it from falling out, position the panel over it, give it a bump with a mallet, and you get a dimple where the hole needs to go.

Scott

[Peter D]

Scott, damn good idea. Something very similar is used in carpentry for marking matching holes for dowel joints. A set of 4 runs at about $2, but I suspect that they only make them for 1/4" holes ?

[Ron Earp]

Couldn't you make the same thing for 0.01 cents by taking a rivet and:

1) Cut the stem off about a 1/16" of an inch above the head.

2) Crimping the rivet body so the stem won't fly through when you pound on the sheet metal.

Ron