[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]

Good fit

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NAS1105-XX have been superseded by ??????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]

do again

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]

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]

Adjustable reamer

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]

Reamer

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]

measure the reamer too

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.

 

[Rick6a]

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

Very true. I routinely measure the diameter a given AN Bolt with a micrometer and for an application as critical as the rear spar attachment, will ream the hole to .310, .311, .312 as required. Reamers are available in every conceivable dimension. I've never used an adjustable type reamer but it seems to be a reasonable and economical alternative for the average kit builder. Digital micrometers are widely available for less than you might think, many under $100. It is up to a given builder to decide for himself how much of a premium to put on producing the highest quality holes possible.

 

[az_gila]

Adjustable Reamers

Anyone know anything about these guys?

http://dewitt-tool.com/store/reamers_adjustable.html

Their prices seem way lower than quoted previously. They may not be tempered hard enough for steel gear legs, but I presume would be OK for aluminum...

The page also shows a picture of what an adjustable reamer looks like.

The last time I needed on for aircraft building (admittedly in the 1973 era... ...and it was for wing bolts...) I borrowed one from a local electric motor rebuilding shop... they have ones with long pilots that are used to ream bearings in each end of a motor case, keeping them in line.

gil in Tucson

 

[Captain Avgas]

Anyone know anything about these guys?

Their prices seem way lower than quoted previously. They may not be tempered hard enough for steel gear legs, but I presume would be OK for aluminum...

They look the same as the one I have. I'd say at the price they have to be (very) cheap imports but I'd say they'd probably be OK considering the limited use they'd receive building an RV. Probably the way to go.

 

[Kevin Horton]

While I appreciate good craftsmanship, and a desire for perfection, I don't think we need to go overboard on this hole. This is a pin joint, meaning it does not handle any of the bending loads. All the bending loads go through the front spar. The rear spar joint only handles torsion loads, such as are created by the airfoil's pitching moment, and/or flap deflection. The NACA 23000 series airfoils were specifically designed to have very low pitching moments. The result is that the loads on this joint are relatively low. I read a story about an RV-4 that flew for some time with no bolt in the rear spar attachment at all, due to a builder screwup.

So, pay attention to edge distance. Properly torque the bolt. But there is no need to go to the lengths of using close tolerance bolts, reamers, etc, in my opinion (worth what you paid for it). If there was, Van would have specified it on the plans or in the instructions.

If you do use a reamer to get a close tolerance, how much clearance should you leave for anti-corrosion primer? Corrosion is probably a bigger long term risk than a too loose bolt.

 

[tin man]

IMHO anyone who says you do not need to build your airplane as close to specified tolerances as possible is giving you bad advice. I seriously doubt the story about the RV4 flying without a rear spar bolt.
Tom
RV3 2000+ hours

 

[Kevin Horton]

IMHO anyone who says you do not need to build your airplane as close to specified tolerances as possible is giving you bad advice.

Of course you should comply with Van's instructions and specified tolerances. But, my RV-8 instructions specify using a drill for this hole, and no tolerances are given.

 

[cytoxin]

kevin is correct IMHO

i did want an interfrence fit, and i used a reamer. most people have used a drill bit and never had a problem. a while back someone bought an rv with a overlapping holes(kinda like an 8 silhouette) and was talking of fixing it. yet IIRC the plane was flying when purchased.i talked with vans about getting a nas bolt for mine and they said leave it as it was.. its not an issue. however i will address it again when i go to permanenty install the wings . if doing it again (and i never will) i would simply use the .311 reamer.