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strap duplicator and transfer screw for 8-32

Saville

Saville

Well Known Member
Need a strap duplicator and/or transfer screw for 8-32 nutplate holes

I need to locate seven, 8/32 screw holes on the periphery of a 12" x 8" plate.

The nutplates are installed on the underside of 0.064 angle. I have to drill the holes in the plate to match the location of the nutplates.

I see strap duplicators for 10-32 (and #21, #30 and #40) and I see transfer screws for 10-32. But I don't see strap duplicators for 8-32.

Why is that?

I did see transfer screws for 8-32 at McMaster-Carr:

https://www.mcmaster.com/3385A32

but I'm wondering if they are long enough such that the threads will fetch up solidly in the nutplate (and therefore center the point) , and sill have the point proud enough to make a solid mark.

I can't find dimensions of those transfer screws.

I also saw these:

https://www.mcmaster.com/3400a12

and there are none for 8-32.

If anyone knows a source - or has a better idea for locating the holes - I'd appreciate the pointer.

Thanks!
 
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you may struggle to get a screw started from the backside of a nutplate unless you run a tap through it first. I must admit that I have never tried that though.

Larry
 
FWIW I have used these hole finders to get a perfect matching hole. Then I tap them to the correct size.

Not sure if it will work in your situation.

:cool:
 
Template

You could make a template from thin clear acrylic or polycarbonate sheet 1/16 thick. First mark the holes in the template by placing it over the angle nutplates. Then transfer the holes from the template to the aluminium cover sheet by drilling through.

The clear sheeting should be available in the roofing/window department of a home hardware store like Home Depot.
 
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PaulvS said:
You could make a template from thin clear acrylic or polycarbonate sheet 1/16 thick. First mark the holes in the template by placing it over the angle nutplates. Then transfer the holes from the template to the aluminium cover sheet by drilling through.

The clear sheeting should be available in the roofing/window section of a home hardware store like Home Depot.
Click to expand...

Several of the screws are up against the fuselage skin and against the gear tower so I would not be able to get my eye over the hole to accurately mark it.
 
option

Saville said:
Several of the screws are up against the fuselage skin and against the gear tower so I would not be able to get my eye over the hole to accurately mark it.
Click to expand...

If a mirror won't help then another option for those holes is to make them oversize in the template, fit the template, put a right sized "washer" over and and a screw into the hole, tape the washer to the template and then remove it intact for transfer to the part. Where there's a will there's a way! :)
 
You could use 8-32 Allen socket set screws . Thread them through the nut plate backwards to the appropriate hight to use their point as the transfer punch
 
Easy to do

Just take some 8-32 screws, Chuck them in your drill, cut. The heads off, and sharpen them on a bench grinder to a point. The. You can thread them into the nutplates with the tips just proud of the surface. Put on your plate, and tap with a 2x4 or rubber mallet.. the points will transfer..
 
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.
 
I?ve done the same thing as Richard on the previous post. A #30 strap duplicator fit in the 8/32 nut plate hole just fine.

I also made a ?home brew? version of a strap duplicator out of two hack saw blades - the cheaper, the better. Take the two blades and pop-rivet them together so that the mount holes in the end line up perfectly with each other. Put in two rivets at the other end about 3 inches apart to hold that perfect alignment. Then install a short solid 1/8? rivet in the underlying blade, and squeeze it just enough to hold it in place. This will fatten the rivet, making it just right for a #19 hole. You don?t want to flatten it because it will need to fit in you 8-32 platenut hole. In fact this step of installing the solid rivet should probably be done before joining the two hacksaw blades. That way, if you mess it up, you can drill it out and try again. If you use a button head rivet (flush rivet is better) you can flatten the top of the button with a file to make your duplicator more stable during drilling. Using a drill bit stop will make it last longer because that solid rivet is soft and won?t last for very many hits by a drill bit. Worked for me. A real strap duplicator is better, but this works for a few holes if you need it right now. It only takes a few minutes to make this tool.
 
Scott Hersha said:
I also made a ?home brew? version of a strap duplicator out of two hack saw blades - the cheaper, the better. Take the two blades and pop-rivet them together so that the mount holes in the end line up perfectly with each other. Put in two rivets at the other end about 3 inches apart to hold that perfect alignment. Then install a short solid 1/8? rivet in the underlying blade, and squeeze it just enough to hold it in place. This will fatten the rivet, making it just right for a #19 hole. You don?t want to flatten it because it will need to fit in you 8-32 platenut hole. In fact this step of installing the solid rivet should probably be done before joining the two hacksaw blades. That way, if you mess it up, you can drill it out and try again. If you use a button head rivet (flush rivet is better) you can flatten the top of the button with a file to make your duplicator more stable during drilling. Using a drill bit stop will make it last longer because that solid rivet is soft and won?t last for very many hits by a drill bit. Worked for me. A real strap duplicator is better, but this works for a few holes if you need it right now. It only takes a few minutes to make this tool.
Click to expand...

This sounds like a workable idea. What did you place on the hack saw blade that goes on top the the plate to be drilled? Did you mount some sort of bushing?

Though I suppose that all I really need do is start the hole making a dimple and then I can finish drilling the hole at the drill press.

I'll try this idea.

Thanks!
 
A couple other methods are to draw a straight line from the hole, and make a reference mark at some specific distance, whatever is easy to measure and remember----then put the part in place, extend the line back onto the new part, and mark the hole center from your reference mark.

You can also cleco or screw a thin strip of metal to the hole you want to transfer, tape the metal strip securely to the structure, then remove the cleco and slide the new part into place under the metal strip, and mark through the hole in your strip of metal.

I have used both methods successfully over the years.
 
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With two hacksaw blades, one blade is on top of the plate to be drilled through the hole in it, and the other blade has a rivet in its hole that goes into the platenut target hole. It is essentially exactly like a strap duplicator, but not as durable, but doable for several holes, and pretty inexpensive if you only need one for a few holes.
 
Plus 1 for Scott's home made strap duplicator. I have made a few. I've even made various sizes by just riveting a couple of strips of aluminum together, drilling through both, then fitting a proper sized rivet into the hole of the lower strip.
 
Wow - I like that metal shipping strap idea. I should have thought of that myself. Keep that stuff out of the landfill for something useful...
 
Non-Progress report.....

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.
 
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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.
 
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!
 
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
 
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.
 
Richard Connell said:
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.
Click to expand...

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.
 
Success

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
 
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