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RV-7A main gear leg match drill to mount

R

RobinHou

Well Known Member
Vans instructions make it sounds so simple: Slide gear leg into the mount and align the hole. Match drill the leg to the mount.

I finally slide the right leg into its mount enough to align the hole. I brought a 5/16 cobalt drill bit, used a lot of cutting oil. 1 hour later, I have a slightly enlarged hole about 1/2 way in on one side, and an elongated hole about 1/4 way in on the other side. I then stopped, and admitted defeat.

I will take the left leg and mount to my friendly local machine shop to match drill. But, can I salvage my right leg and mount by drilling them for an AN6 bolt, or should I order a new right mount and right leg?

Thanks in advance,

A-Very-Frustrated-RV-Builder
 
You can probably use a 1/64 oversize bolt. GAHCO has them. I don't remember the part number, but it has been talked about many times.

The hole in the gear leg should already be to size. It should be a snug slip fit, so it will not just drop in, but it should fit.

The mount is the part that needs to be just slightly enlarged. One side should already be to size, it is the other that needs to be reamed to fit. You should be able to buy a 0.311 reamer that will do the job nicely. NOT a 0.3125. use a 0.311

Just my idea on the whole hole enlarging dilemma.... :D

Richard
 
Here is what Vans said ...

... It is acceptable to enlarge the holes for the main or nose gear attach
to accept AN6 bolts. AN6 is the largest acceptable fastener for this
application. scott at van's

Richard, thanks for the clarification. I only wish Vans instruction could have been more clear on this "match drill" business...
 
RobinHou said:
... It is acceptable to enlarge the holes for the main or nose gear attach
to accept AN6 bolts. AN6 is the largest acceptable fastener for this
application. scott at van's

Richard, thanks for the clarification. I only wish Vans instruction could have been more clear on this "match drill" business...
Click to expand...

I am pretty sure the construction manual tells you to use either a .311 reamer or a 7.9 mm drill bit (might be wrong, going from memory).

A 5/16 drill bit (.3125) would be difficult since the hole in the gear leg is drilled .311

When done correctly, the only material that should be removed is on the bottom side of the leg mount (none on the top side or the hear leg itself)
 
My Bad ...

... After re-read the plan, it is now clear to me that all necessary instructions are there. Although the instruction did say using a 5/16 drill bit for match drill is OK, which now I know from my experience is a bad idea.

I ordered an AN6-22A from Spruce, and will take my right leg and mount to a local machine shop to drill for a snug fit.

I will take Steve's suggestion and order a .3110 reamer. What other size reamer would I need for the rest of the build?
 
It was a 7.9mm (.3110") reamer on my RV-10 legs for the AN-5 bolt.

On the RV-10, really the only hole that's seriously undersized is the exit hole for the bolt in the bottom of the mount.

Here's how I did it.

1) With the gear leg removed, I reamed the top hole of the mount to the proper size. Mainly this was removing the powder coating.

2) With the gear leg on the bench, I ran the reamer through it to clean up any edges and rust inside the factory hole and ensure the bolt would drop through it. It took maybe a second or two on the reamer and everything was done.

2A) Do any deburring you need to do now.
2B) It's also a good idea to polish the inside of the mount and gear leg with scotchbrite to remove rust and other debris that can make it difficult to insert the gear leg.

3) I lubed the inside of the gear leg socket with AeroShell #6 (General Airframe Grease) and also lubed the gear leg itself.

4) I slid the gear leg into the socket and roughly aligned the holes.

5) Remove the reamer from the drill (so you can work with it a little better) and with a little luck you'll get it to line up pretty quickly. For me the tolerances were too tight and I never really could get it to drop into the mount and through the gear leg to the bottom hole. So I had to use a punch to get it close, then I used a really small punch and literally felt my way around hole and tweaked the gear leg up/down/side-to-side until both holes aligned perfectly. Once they were aligned the (unchucked) reamer dropped all the way down to the bottom hole of the mount. (The only one that is under sized at this point.)

6) Drop a little lube down the flutes of the reamer, attach the drill, and give it a quick bump on the trigger.

Done!

No need to remove things to deburr because you've already done that. The bottom hole is the only hole that might need it. But usually with a reamer you get a nice hole anyway. Drop your bolt in, torque, and torque seal. You're done.

It took maybe 10-15 minutes for each leg on my plane and that was wasting a lot of time. If I had it to do again I think I could get it done in less than 5 minutes.

Phil
 
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RobinHou said:
Vans instructions make it sounds so simple: Slide gear leg into the mount and align the hole. Match drill the leg to the mount.

I finally slide the right leg into its mount enough to align the hole. I brought a 5/16 cobalt drill bit, used a lot of cutting oil. 1 hour later, I have a slightly enlarged hole about 1/2 way in on one side, and an elongated hole about 1/4 way in on the other side. I then stopped, and admitted defeat.

I will take the left leg and mount to my friendly local machine shop to match drill. But, can I salvage my right leg and mount by drilling them for an AN6 bolt, or should I order a new right mount and right leg?

Thanks in advance,

A-Very-Frustrated-RV-Builder
Click to expand...

It probably makes sense to read some VansAirforce archival material before attempting any critical build operation such as this. A little bit of research can save a whole lot of pain. ;)

There has been a lot posted previously on this topic, all of which points to the fact that the gear leg/mount really needs to be reamed to final size to get a snug fit. I personally used an adjustable reamer and came up a couple of thou at a time to get a really snug (tap in) fit. It was very easy to do.

Builders who have oversized holes from drilling will have hole elongation and wheel shimmy problems down the track.

Vans instructions to "drill the hole to 5/16" is just terrible advice.
 
RobinHou said:
I will take Steve's suggestion and order a .3110 reamer. What other size reamer would I need for the rest of the build?
Click to expand...

Well, as long as you're buying them ... I find a 3/8" reamer great for the AN6 holes (RV-10 brake mount collar on the gear leg), 1/4" for the AN4, #12 for the innumerable AN3s, and #30 and #40. I know some folk advocate using reamers to enlarge the pre-punched holes in the kit but I'm happy enough using jobber bits most everywhere. But on the holes with some depth or through steel, I like the reamers.
 
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