strap duplicator and transfer screw for 8-32

[Saville]

Ok so I bought some 8-32 Transfer pins.

Tried them today - total failure as the pins were way too short - by the time you got them down to where the threads gripped in the nutplate the point was well below the flange - they left no mark

Second thing I tried was a home made strap duplicator using 2 hack saw blades. Total failure - 4 out of 5 holes were anywhere from 1/16" to 3/32" off

I ordered a #30 and #40 strap duplicator. Let's see if that works any better.

In the meantime I did try to run some screws up the nutplate from the bottom and that seemed to work ok. I might try chucking a screw into the drill press and filing the end to a point.

My concern here is that the screw metal is not hard enough to make a mark.

[Saville]

Ok I think my next two attempts will be:

1) Cut a piece of thick cardboard the exact same size as the new plate. Tape it to the underside of the plate. Grind some screw ends to a point and run the screw up the nutplates backwards to make an impression on the cardboard.

Then drill through that mark through the aluminum plate.

2) Something someone suggested earlier and which I did many years ago for my battery tray:

Make the holes in the test plate I used today much larger. Cut some small pieces of aluminum and drill a screw hole. Screw the plate down with the small metal pieces on top as "washers". Duct tape the "washers" to the old plate. Use that as a transfer template.

I will mark positions in #1 but before I drill the holes out I will overlay the template from #2 to see if they match well.

Any other ideas are welcome.

[Scott Hersha]

Another possibility is the use of vellum paper to make a template. Vellum doesn?t stretch and is transparent, so you can see through it to make marks to be used as a drill template. Use this template, taped on to your finished opening accurately, and drill through the vellum into the new finished piece. I did this on my first airplane - an RV6, not prepunched. That last piece of skin on the bottom of the wing was a challenge, until I came up with this idea while visiting my daughter at Ohio State, and shopping with her at an art supply store. I bought a large roll on vellum paper, and it made my life easier. I taped the vellum on the wing with the wing rib center lines marked, transferred these marked lines and drill points to the vellum, then taped the vellum to the wing skin exactly as if it were the skin itself, clamped the skin piece with vellum taped to it to the wing, and started drilling/clecoing to the wing rib structure. Every hole hit its mark on the centerline of each rib. You can use this same idea to make your new 8 X 12 plate. This won?t damage the existing structure because you do it on your work bench (on a piece of plywood, clecoe as you goe), and if you make a mistake, you can just do it over. If it?s close, but not quite right (unlikely), just enlarge the existing #19 holes to #12, and they should all line up. This isn?t structural and just needs to be tight.
Good luck. Sounds like a fun challenge!

[BlndRvtr]

A number 21 strap duplicator should work just fine, at least for a pilot hole. Then just open it up a wee bit (#16 drill bit) for a perfect fit.

George

[Saville]

The Vellum idea is nice but won't work in this case because a flange with nutplates is up against the fuselage skin and underneath the throttle quadrant and so you cannot get your eye over the hole to mark it accurately.

Other people said that the #30 strap duplicator is the way to go. I'll try that one first, since I ordered it. If that doesn't work maybe I'll try the #21.

I think the inaccuracy was due to an inaccurate homemade strap duplicator. Also the commercial ones have a bushing on the top strap which help keep the drill bit perpendicular to the surface.

I'm also going to try the duct taped "washer" idea.

[Saville]

Originally Posted by Richard Connell

I?d try a #30 strap duplicator.
That will fit in to the threads of the 8-32 nutplate (if the pin is deep enough)
just like the #30 countersink fits perfectly into the spar #8 nutplates.

Got my #30 today and tried it in an 8-32 nutplate - no go. The pin in the duplicator is not nearly long enough - the duplicator wobbles around way too much.

I'm going to try what I call the "screw plate" method tomorrow:

I cut out some 0.064 strips and put an 8-32 hole in one end. The strips are 2-3 inches long. I'm going to put the screws in the screw plate hole, through the enlarged plate holes, and into the nutplates far enough to grip.

Then I'm going to duct tape the "screw plates" down (after tracing around them).

Then use that for a template. We'll see how that goes. I'll take pictures.

[Saville]

Ok so I figured out a way to do it.

First I made a replica of the cover plate in this plywood.

Then I selected one of the seven holes and ran a screw upside down so that it was coming up out of the flange.

I then put a strip of duct tape on the underside edge of the wood cover plate, placed it in position and screwed the screw up.

It left a very nice impression in the duct tape. Crisp.

I then drilled that hole out, placed another screw at a different location upside down, screwed the wood cover plate down with the first hole I made to lock it into position and made an impression in the duct tape for the second hole.

Repeated the process until it was all done.

Thanks to everyone for their suggestions