Tiedown spacer gap?

I'm making the tiedowns. When I lay the spacer (W-725) on the spar web, and place the tiedown (W-731) resting on the reinforcement bars, there is a gap between spacer and tiedown. The reinforcement bars on the spar are 0.196" thick and the spacers are 0.186" thick, so the gap is 0.01". That seems excessive. What to do? Do I need to make shims?

If I were to assemble this and torque the bolts that go through the spar web into the tiedown nutplates, the spar web might be distorted or preloaded excessively.

Also, one of the tiedown extrusions I received is a bit tweaked. The two flanges of the extrusion don't lay flat, one side is bent up a bit. Will it just flatten out when I torque the bolts, or should I attempt to bend it flat?

spaceflightmeow said:

I'm making the tiedowns. When I lay the spacer (W-725) on the spar web, and place the tiedown (W-731) resting on the reinforcement bars, there is a gap between spacer and tiedown. The reinforcement bars on the spar are 0.196" thick and the spacers are 0.186" thick, so the gap is 0.01". That seems excessive. What to do? Do I need to make shims?

If I were to assemble this and torque the bolts that go through the spar web into the tiedown nutplates, the spar web might be distorted or preloaded excessively.

Also, one of the tiedown extrusions I received is a bit tweaked. The two flanges of the extrusion don't lay flat, one side is bent up a bit. Will it just flatten out when I torque the bolts, or should I attempt to bend it flat?

Click to expand...

I don't recall having any gap when I installed my tiedowns. Maybe you could polish off 0.01 worth on each end of the tiedown?? You could email Vans and ask them for a replacement tiedown, because the one you got seems to have some twist in it. They may replace it for free. If it were mine, and I was going to use it, I would try and flatten it. While I was emailing, you could mention the 0.01 gap and see what they have to say about that too.

Tiedowns

Buy a set of these. Already drilled and tapped with a nice tiedown bolt. Three per set.
http://www.cleavelandtool.com/mobile/Tie-Downs/products/111/

Maybe you've noticed already but when I put my first set on using the Vans instructions, there was a gap between the skin and the end of the tiedown bracket. I didn't like it so I built a new set using the Cleveland brackets and made sure it would be flush to the skin. Much cleaner.
Also, when you finish, take a piece of scrap a few inches long. Lay it on the skin where the hole will be. Back drill it for the rivet holes. Now move it to the spar and back drill it from the opposite side to locate the tie down bolt hole. Take it off and and drill it the size of the bolt. Now you have a jig to locate the bolt hole in the skin. The Vans method didn't work well for me.

Straighten the bent part. Properly shim as required and carry on building. Don't let the small stuff hold up progress. As I tell potential builders, "it's an exercise in patience and problem solving".

Aircraft Spruce's sheet metal runs as thin as 0.016". I need a 0.010" shim. It seems like I'm almost better off not shimming, and instead shaving the AEX down a bit.