Grrrrr...Gear Weldment Reaming

[YellowJacket RV9]

So I thought I was doing everything right, reaming my gear and gear weldments to .311, but I have still ended up with a sloppy fit. Part of the issue is that it appears that one hole in the gear weldment was not exactly aligned with the other, resulting in one perfect hole, and one elongated hole. So elongated in fact, that I'm concerned even a twice oversize bolt won't fit (max diameter of the hole is .345). I have ordered a new weldment from Vans to the tune of $300. Maybe not needed, but I'd really rather do this right the first time. I will return it if I get a good fit with a twice oversize bolt...

Also, I have found that even though I reamed the gear legs to .311, they are measuring .320, and the bolts are not a tight fit. I figure I can fix this issue with either close tolerance or oversize bolts. One thought is that maybe the gear leg was not perfectly aligned in the socket when drilling, causing everything to enlarge slightly. If so, any hints on how to get the holes lined up exactly? It is so tight once in place that small adjustments are about impossible. BTW, I have double checked and the reamer is .311.

Also, should I try reaming the two pieces separately, rather than in assembly?
Thanks for any advice!

Chris

[Greg Arehart]

Been there, done that. I would absolutely ream them together if you want the best fit. No particular advice other than what you're doing. Mine are definitely oversized with close tolerance (at $30 each!) fit.

Edit: just saw that you are doing a 9A, but the process is the same.

Greg

[TX7A]

Chris
Are you 'pulling' the reamer through the hole or pushing it through. I'm not sure it makes much difference, but I inserted the shank through the hole, chucked it to the drill, then pulled the reamer through using lots of lubricant. Came out fine.

[YellowJacket RV9]

Thanks for the encouragement. After calming myself for a bit, I went and did the right side, with zero issues. On that one, the fit of the gear in the tube was much looser, and I was able to position the hole exactly. Also, I noticed that the hole in the gear leg was almost exactly the right size already - I could put a bolt halfway through. So I reamed one side of the weldment, put the gear leg in place, and put a bolt through that side and into the leg as far as it would go to hold things in place. Then I reamed from the other side about halfway, and that was all it took. Now the standard AN5 just goes in with a few whacks of the rubber mallet. Perfect.

My left gear leg is already oversize now, but I think if I can get the gear leg a bit looser in the socket, I can follow the same procedure with my new adjustable reamer until I get a good fit on an oversize bolt. Live and learn...

Also, is there any way to repair the weldment with the elongated hole? Maybe either by having a machine shop drill out and install a bushing, or have the hole welded and re-drilled? Or should I just suck it up and buy the new one?

Chris

[jrs14855]

Find someone who is an artist with a TIG welder. They can run a weld bead part way around or all the way around the hole in the gear weldment.
No need to close up the hole, that just makes things more difficult. Open up the welded hole a little bit at a time with files or rotary files until you get reasonably close, then run the reamer thru again.
I think I start with a .309 or .310 reamer and then go in increments until the bolts are a tight fit.
I bought a 1/2" capacity electric drill for this. Slower speed and a lot more torque. Straight flute reamers work best for me, some kind of heavy bodied tapping lubricant. Take your time and don't get the metal hot.
Hardware store 5/16" bolt for alignment, cut the head off and file polish the bolt to a light drive fit into the unreamed end of the hole. When the reamer touches the alignment bolt, back the reamer out, remove the alignment bolt and finish ream.

[jrs14855]

One more suggestion, if you buy a variety of bolts from different suppliers you may find some that are a better fit than others. Up to .0025 variation in bolt diameter, sometimes substantial variation in diameter along the length of a long bolt.

[YellowJacket RV9]

Thanks - Will head to a few local welders tomorrow and see if any are up for the task.

Chris

[bruceh]

It's always a good idea to put a micrometer on your bolts before you pick out a reamer to use. I've found that there can be quite a bit of variation on the standard bolts.

[gtmule]

I'm not a builder, but I design lots of repairs on aircraft. Is there a reason not to just go up to 3/8" and try again? Use a way undersized ream and work up, as someone said above....

[Zuldarin]

Make sure you are supporting the drill when you are doing the reaming. I found that just the weight of the drill itself can cause the reamer to elongate the far hole.