Reamer size for rear spar attach bolt?

[szicree]

The bolt is 5/16 nominal (.3125), but appears to measure closer to .310. I'd like a nice fit here, since it holds one of the more important pieces on the plane (the wings!). So how do I decide what the appropriate reamer size is?

[RV_7A]

Steve if you use a .3125 for final sizing, you will have a snug fit. Thats what I used and you had to push the bolt in with a bit of force.

-Jeff

[Pmerems]

If you want a good fit get a few Close tolerance bolts NAS1105-XX to go along with nicely reamed hole.

NAS1105-XX have been superseded by ?????? but you can still buy them.

[tin man]

Also measure a few other bolts, they are all not exactly the same diameter.
Tom

[cytoxin]

if i had it to do again i would ream to .311 i used a 5/16(.3125) reamer and the bolts are not interference at all. i did use a 1 inch thick guide / pilot block.

[szicree]

Originally Posted by RV_7A

Steve if you use a .3125 for final sizing, you will have a snug fit. Thats what I used and you had to push the bolt in with a bit of force.

-Jeff

I just reamed a piece of stock to .3125 and the bolt is wobbly. I'm guessing these bolts vary a bit in diam.

[Captain Avgas]

Originally Posted by szicree

I just reamed a piece of stock to .3125 and the bolt is wobbly. I'm guessing these bolts vary a bit in diam.

You can get an adjustable hand reamer. This enables you to come up in very fine increments to ensure that the 5/16 bolt (ANY 5/16 bolt) is as super snug as you want it to be.

I used one on the bolts for my gear legs......now they're really tap in tight. There are places where a tap-in-tight snug fit are important and I'd say the rear spar is one of those.

[flybill7]

Where did you get your adjustable hand reamer?

[Captain Avgas]

Originally Posted by flybill7

Where did you get your adjustable hand reamer?

Any good engineering suppies shop will have them. I bought mine for about $50 from a second hand engineering supplies dealer. New they're about $100.

When I was installing my gear legs to the mounts I noticed that Vans instructions said it was OK to use a 5/16 drill. I was suspicious of that so I asked the Forum what it thought. Everyone who answered said: "Yeh, no problems". So I went ahead and drilled them and the supplied bolts were sloppy in the holes.

It seemed logical to me that this was an area where you really require a snug fit so I purchased 1/64" oversize NAS bolts and reamed up the holes with the adjustable reamer to a really snug fit. Tight as a fish's a..e.

The rear spar connection is also 5/16 so I'll use the same reamer for that as well. Mine is 5/16 to 11/32". They go slightly under and over that range.

If bolts under dynamic loads are not a really good fit they will deform the softer steel around them and become progressively looser with time. I don't think this would be good for the rear spar connection which is not steel but aluminium. It's certainly bad for the gear legs because it allows the leg to rotate in its socket leading to wheel wobble.

[jim]

One other consideration is variation in the reamer. I measure the reamer to make sure it is the size it is supposed to be. I have noted variation in reamers from the stated sizes.