Thorp Air Command - T18.net

.128 minus .125 equals .003 less that the size of your hair, Yes you can A thirty punch will not go through a 1/8" but a 1/8" punch will go through a 30 hole. You use just the punch. Make a transfer strip using the spar holes as a template, then transfer them to the skin, "alla, matched hole tooling.
WHOLESALE TOOL carries the Roper Whitney number 5 JR. punch Do Not buy a cheap one from Harbor Freight
I have built several Thorps and a RV , three with hand held dimpler and two with a C frame . The frame does make it a little easier, but it comes with using it correctly. The sheet metal needs to be held perpendicular to the set.

Spare holes?

I'm not sure how to make a transfer strip from a spar cap. I can see how wrapping the skin and holding it tight and then using the existing holes in the spar cap as the guide to take a transfer punch and a hammer to mark the bottom of the skin with the transfer center punch mark.

is there an easier way to accurately do this?

I could in some cases use the existing skin. but I'm just not confident after pounding the dimples flat and marking the new skin that they would exactly match.

Again to make things easier, I think I have resigned myself to buying all new ribs. That way the new kit skins from Cubes come pre marked and I don't have to worry about it, EXCEPT for the holes for the spars which much match exactly.

I finally got the entire wing skins off the right wing. This is the wing with the spar cap "ding".

I have some more photo's with a metal straight edge. I have yet to download them from my phone. I took a bunch so I will have to go through them to get the better shots to show the extent (or lack of extent) of the "ding".

unstiking the pro-seal on the nose ribs and spar for the wet wing was not as bad as I thought. A putty knife from the back of the spar moving forward towards the leading edge worked well. I did have to drill out and remove the flap brackets in order to remove the skin which I didn't originally think I would have to do. But the fit of the skin around the baracket was just too tight to effectively remove the skin easily.

The left wing I have all except the rivets in the main and rear spars. Not sure with the heat this week whether I will be able to remove this skin before Oshkosh. Depends on how much I could get done tonight! Really heats up thursday and Friday. and Oshkosh is next week!

Finally getting the order with cubes for ALL new ribs for the outer wing panels. Including 0.032 nose ribs as I plan to do wet wings. Along with both rear spars and prebent wing skins.

So now I will only habe to identically match the holes in the skins for the top and bottom Of the main spars.

Which of the following would be the moat accurate way to perfectly match the holes in the skin to get the holes and dimples to fall exactly into the existing spar caps.

1) get the skins clecoed in place on each rib and then roll back the skin without kinking it, and rhen use a transfer center punch from underneath to mark the center of the holes. The thickness of the extrusion should help align the center punch and with the skin held in place with cleco’s should hold the skin stable in place.

2) flatten the existing wing skins I have from the original wing. Cuddle up the new skin inside of rhe old skin and just drill through the new skin.

3) Flatten out the holes along the spar cap (top and bottom), then cut transfer strip for each top and bottom. Then locate the left and right edge holes, drill and cleco the transfer strips on the putside of the skins. then drill through the new skins.

Is there another better or more accurate option I have not thought of?

Hi, Fool.
I don’t have any experience to share, or even much advice, but I share your frustration with trying to understand matched-hole transfer strips. I think it’s one of those things where you have to take a week or two and just dive in with a bunch of scrap and figure it out for yourself. People who have done it, understand it. I’ve read the articles several times and the words just don’t quite convey the details.

If you do figure it out, please share a photo series or a sketch. I think you’d be the first to do so.

The technique goes far beyond the T18. So many builders and repairmen could benefit from a clear explanation. Where’s Dick Penman when we need him? ;-)

If I go the transfer strip route. I will have the old wing skins to use for practice and see how well another practice strip from the wing will dimple and then fit onto the spar. I realize I cant practice too mich or risk elongating or opening up the holes in my original transfer strip being it is only thin aluminum.

Option #2-“cuddling up” may be preferred as I can cleco tightly the skins together. I just don't know if the offset of the thickness of the two skins will slightly throw off the exact alignment. Whereas transfer strip laying directly on top would not have this inside/outside radius issue.

Maybe I am just over thinking this. I have a bad habit of doing that. While this is an airplane, it is not a Swiss watch.

I'm rebuilding a left outer wing panel. Actually I'm making another one.
I couldn't get past all the questions you are asking.
Also, although I built my RV-8 slow build wings, I did not build my T-18 and I don't understand the transfer template system.
I intend to build my wing panel 'RV-4 style' and have built new spars and ribs. My next push is to bend then drill-on the skin. I have built a standing jig for it.
I'm not in any real hurry (IAC Aerobatics, RV-8 upgrades etc) but I keep noodling away at it. It's not hard. It just takes some time.
I have moments of indecision like you, but eventually the way becomes clear and I forge right thru it... or make that part a second time.

_________________
Scott Emery
EAA Chapter 326
T-18 N18TE

What ever you do, use a #40 drill first.

_________________
Bob Highley
N711SH
SN 835
KLAL

OK.

But how do you precisely get dead center of a template with a #30 hole with a 3/32 or #40 bit?

Even with the transfer strip method. I need to align the two ends. This has edge access so I could borrow or buy a Whitney punch to directly transfer the two end holes and cleco the strip in place.

use the #30 punch from a Whitney punch(I have a spring loaded center punch that has it on the punch)or a set of transfer punches to transfer the hole center then drill with a 40. This will give you about a half hole wiggle room for the 30 when final drilling

Not recommended
"Option #2-“cuddling up” may be preferred as I can cleco tightly the skins together. I just don't know if the offset of the thickness of the two skins will slightly throw off the exact alignment. Whereas transfer strip laying directly on top would not have this inside/outside radius issue."

Take your time and put some thought into it. What you're up to can be a small challenge. As you guessed above with Option #2, the thickness will definitely throw off the alignment when sheets are not flat. You can try it with scraps.

As you say, I'd suggest this:
"1) get the skins clecoed in place on each rib and then roll back the skin without kinking it, and rhen use a transfer center punch from underneath to mark the center of the holes. The thickness of the extrusion should help align the center punch and with the skin held in place with cleco’s should hold the skin stable in place."

This means you'd locate bottom spar locations with top of skin pulled back, then afterward flip it and locate top spar locations with bottom of skin pulled back.

Les Krumel
Albuquerque

Here is a picture of my progress rebuilding the left outer wing panel.
I'm using plywood tension boards repurposed from building my RV-8. Unfortunately, the skin does not lay on the ribs behind the leading edge, as you can see in the picture.
Perhaps I need to bend the leading edge some more, but the previous wing was bent too much (too sharp) so I'm trying to avoid that. I'm working to have 'Feisty' ready for Sedona, but there is much to do.

_________________
Scott Emery
EAA Chapter 326
T-18 N18TE

Nice work Scott. Maybe try putting a block of wood under the strap in the high spots. I did this strapped down to a table and used tonnage where I found I needed more pressure on the skin.
Also, I used straps around the wing itself. And I also used straps to hold it down to the table to keep things straight and aligned.
Cubes