Part number for a taper pin on RV-10 step?

[fehdxl]

While away on business I am looking ahead a couple sections to "Section: 30 Step Installation" and want to use a taper pin to secure the step to the mount rather than the AN3-20A bolt. This should alleviate any 'getting loose' issues in the future. Does anyone have the exact part number to use by chance? It looks a bit complex on Aircraft Spruce's site to determine the right size.

Thanks!

Jim

http://www.aircraftspruce.com/catalog/hapages/an386taperpin.php

Keywords
Taper pin
Wd-1008
Wd-1007
page 30-4

 

[fehdxl]

Also, about the part number convention on the AN386 taper pin...

Does an AN386-1-9 have a grip length of 1-1/8"? Normally hardware would go from a -7 (indicating 7/8") to a -10 (indicating 1") then to a -11 (indicating 1-1/8"). Maybe this is an exception and it is literally 'measured in 1/8's of an inch.

Thanks!

Jim

 

[Phil]

Jim,

I don't know of any taper pin installations, but that doesn't mean they won't work.

I do know of these and they work great.

http://www.tcwtech.com/RV-10-construction-project.htm

I used them with an3's and left myself an option to enlarge to an4 later if they do manage to work loose for some strange reason.

Some go straight to 4's, but I don't like that option because you don't have anything to grow out too if you need it.

Phil

 

[fehdxl]

Thanks for the link Phil. I'm sure I had seen those before, but had forgotten about them.

It seems to me that those blocks allow the bolt to be tightened in tension to create enough friction between the step and the mount in order to prevent rotational movement. I don't doubt it works, but it's my understanding that generally (there are exceptions for sure) bolts are meant to be used in shear not tension. I do realize these are not flight critical components, but a loose step would definitely be annoying and something I want to avoid if possible.

Am I missing anything? Just trying to make an informed decision on which way to proceed.

Thanks again,

-Jim

 

[Phil]

Hey Jim,

The issue with the step isn't a fastener issue at all. The AN-3 bolt can hold more then enough weight whether it's in shear or in tension. The bolt is fine, it doesn't flex, and the nut doesn't work loose. So from a fastener perspective it's more than adequate.

The issue is the thin walls on the 4130 steel. As people step on the steps over time, those thin walls are bend and you ultimately end up with an irregular shaped hole at the bolt. That's what causes the loose step.

The irregular shaped hole can also be caused by some sloppy drilling too. I'm guilty of one of those.

The bushing does two things.

1) It keeps you from collapsing the thin walls of the 4130 when you tighten down the nut.

2) It spreads the load of the step across the entire bolt on the interior of the 4130 tubing. In other words, the bushing keeps the load from being focusing where the thin 4130 meets the side of the bolt. With the bushing, that load is spread across the entire length of the bolt it reduces the forces at the point where the 4130 meets the bolt. By using the bushing/bolt combo to share the load, the 4130 will be less likely to deform around the bolt.

The bushing also gives you some options in case they do happen to work loose for some reason in the future.

1) Since you don't have to worry about collapsing the tubing, you have an option to crank the nut down tighter if desired.

2) If that doesn't work, you can enlarge the hole for an AN-4 bolt and get a fresh hole to start again.

3) If #2 happens to work loose, you can go back to #1 with the AN-4 this time. After that, you're probably pulling a step and welding the holes closed.

Some folks go straight to an AN-4 bolt, but that doesn't really solve any problem that the AN-3 won't. The AN-3 will handle everything you can throw at it. I like going with a -3 and having the option (when I really do need it) it enlarge to a -4 down the road.

The steps really aren't that difficult and I think they get a little too much thought based on reputation. It's actually a pretty easy problem to solve.

The real issue isn't the fastener, it's the thin walls on the 4130.

Phil