S

szicree

Well Known Member
I recently drilled my rear spar attach and all went well in terms of fit, alignment, incidence, sweep, blah, blah, blah. So here I was reading through another builder's account of a similar accomplishment when I came across "I used a hardwood block to make sure the drill remained perpendicular to the material". AAARGH!!!! I knew I was forgetting something. I had even made several sizes of maple blocks specifically for this task! Dangit! So I went out to check and found that the worst of mine goes through at a 4 degree nose down angle. This is not good and I'm looking for ideas. I'm gonna contact Van's as well. My first idea would be to carefully reface the spar carry-through to match the angle of the hole, my thought being that the goal is to have the bolt or nut sit squarely on the underlying surface. The problem here is that to reface the whole surface would require taking about .070 of material off of each face. That seems like too much. Ideally I could find some type of tool that I could insert in the hole and rotate against the face until it created a surface for the bolt/nut. Any ideas would be greatly appreciated.

Steve Zicree
RV4
 
Possible solution

I read about somebody who a booboo similar to yours and the solution was to go redrill to a larger bolt. As long as you have the edge clearance all the way around this should work.

No cause to panic, YET!!

Darwin N. Barrie
Chandler AZ
 
What about a shim like washer?

Would a shim like washer on both sides of the bolt work? This would keep the standard washer and bold head from gouging the spar when tightened down. I would think you would want to make it slightly larger than the standard washer. You would also need a longer bolt to accommodate the extra layers.

I like RV7GUYS solution, but if you don't get the edge clearance this may be an option. Good luck.

PS: Bob, the maple block (or steel or aluminum) acts as a jig when drilling the hole.
 
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The jig is nessesary but don't buy one.

We are airplane builders Man, we don't buy jigs. ;)

All you need is a drill press that is accurate for drilling a hole perpendicular to the jig material. The upper and lowers surfaces of the jig material MUST be parallel to one another.

You may want to make several jigs with progressively larger holes (you want to start small and work your way up to final size). Use a reamer for final size if possible.
 
spot facing tool

The tool you need is called a spot facing tool, uses a pilot in the hole to guide a cutter that will make a flat normal to the bore.

Check machine tool suppliers, or a local machine shop.

Mike
 
szicree said:
I recently drilled my rear spar attach Any ideas would be greatly appreciated.Steve ZicreeRV4
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Steve,

If I understand you correctly, the hole is drilled at an angle so the bolt will not seat properly? If so, the fix is fairly easy. You will have to fabricate a square tapered shim using .125 stock approximately 1" square. Taper the stock as required. This "may" mean a taper ranging from .125 on one end of the shim down to .005 on the other. Drill a hole in the center of the shim to .312 to accept the bolt shank, maintaining e.d. Just like any washer, the tapered shim MUST contact the entire head of the bolt. The threaded end is to be dealt with the same way UNLESS you can find a combination nut/washer that is designed to float on a slanted surface such as the one shown. Of course, the bolt will have to be of a longer length as required.

150th.jpg
180jj.jpg


This was a common fix on the production line. You are not the first person to drill a less than perpendicular hole. Just a little rework and you are good to go.

Rick Galati RV-6A "Darla"
 
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Awesome ideas

Wow, too many good ideas. Here's my options in order of appeal:

1. I've got gobs of edge distance so I really like the idea of just re-drilling (straight this time) to a slightly larger size. I figured out that with a 4 degree correction and a half-inch hole depth, the hole will be .035 over by the time I'm done. Lucky for me the existing hole is actually .010 under right now because I didn't ream it to final size yet. So if all goes well I'll be .025 over spec by the time I'm done poking a new hole. This would mean I could use an 11/32 bolt, which is so close to the 5/16 nobody will ever notice the difference.

2. The spot facing idea seems mighty appealing since I wouldn't risk screwing things up worse. However, I'd end up having to remove about .035 of material to get things perpendicular, which seems like quite bit.

3. The shim idea was actually the first thing I thought of when I realized my screw-up, but I hate the idea of a big ol' shim under there. I've never used anything like that and I'm curious about how I go about getting it into just the right orientation. Eyeball I guess?

I sure appreciate everybody's input on this one, so if anybody would like to comment further that would be great. Thanks again.

Steve Zicree
RV4 (with a honked up spar stub)
 
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szicree said:
Wow, too many good ideas. Here's my options in order of appeal:

1. I've got gobs of edge distance so I really like the idea of just re-drilling (straight this time) to a slightly larger size. I figured out that with a 4 degree correction and a half-inch hole depth, the hole will be .035 over by the time I'm done. Lucky for me the existing hole is actually .010 under right now because I didn't ream it to final size yet. So if all goes well I'll be .025 over spec by the time I'm done poking a new hole. This would mean I could use an 11/32 bolt, which is so close to the 5/16 nobody will ever notice the difference.
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Steve,

The best way to get them straight is to take a block of steel and have a machine shop drill a "straight" hole in it. (Let them know what the block is for and they might heat treat it for you.) Use your drill bit to center the guide over the existing hole prior to drilling and clamp it in place. You could use wood but it might allow the drill to wonder a little and you might not get a straight hole.

FYI- A reamer will not work because they are designed to follow the existing hole.

This will not help you but it will help others following this thread who still need to drill these holes.

I marked the hole location, dimpled it, then drilled a starter hole in it with a #30 bit. The starter hole did not penatrate the bracket, it was just enough to enlarge the dimple. A small block of oak was then clamped to the aft spar, using a #30 bit to center the block over the starter hole. The #30 hole was then drilled through the spar using the block to make sure the bit went in straight. Progressively larger drill bits were used to enlarge the hole and a reamer was used to attain the final size.

There are three pictures, dated 10/7/05, on the fuselage page of my web site that should give you and idea of how I did it.

If I remember right, after the step in the instructions telling you to drill the hole, they talk about using a block to keep the drill bit straight.
 
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Stop Removing Metal

Steve,

I read your post and immediately thought of a tapered washer, but Rick Galati beat me to it. That's the way to go. Easy. Quick. If the first washer isn't quite right, make more until you get a pair that's right.

Leave the drills alone. Using a drill bushing after the fact is fraught with peril. The larger drill will want to follow the hole. There's very little clamping area to assure the bushing won't walk where the drill tells it to go. The hole won't be round in an instance where a tight reamed hole would be most appropriate. Your prospects of success will diminish as metal is removed with each attempt, then what's your alternative?

This bolt primarily resist shear. It will do that just fine even if passing through the interface at a 4 degree angle.

Here's how I'd make the washer. Get some 5/16 ID tubing. Clamp it in a vise at the desire angle with the end just proud of the jaw face. File flat to the face. Cut of the filed end, chuck in a drill press, and use a saw to make a square cut off (poor man's lathe). You'll get a thick washer tapered on one end. It will find its own position under the bolt/nut, with a little prepositioning by you.

John Siebold
 
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RV7ator said:
If the first washer isn't quite right, make more until you get a pair that's right.... Using a drill bushing after the fact is fraught with peril..... Your prospects of success will diminish as metal is removed with each attempt, then what's your alternative?

John Siebold
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John,
These were exactly the thoughts running through my head last night as I tried to fall asleep. I've learned through experience that things often get screwed up even worse while trying to fix them. For example, replacing a bad rivet. I know my wings are perfectly aligned with the existing holes so I really hate to tempt fate. It's certainly not an easy part to replace if it gets ruined. I'm gonna mull it over for a while, but am probably going to go the shim route. Thanks for the nudge in the right direction.

Steve "bags under eyes" Zicree
 
If Vans says all you have to do is get a flat bearing surface for the bolt, the thing you want is called a spherical washer. It's more trouble to explain than it's worth....just do a web search...one picture's worth a thousand words. Once you see it, you'll be like "Duhh....of course that's what I want".
 
Rear spar bolt at an angle - fix from Van's - don't sweat it

Steve,

Did the same thing on my -7A on the RS rear spar. I actually used a block to drill my holes but the drill press table was off from 90 degrees! How's that for being born under a bad sign!! Should have checked it before but i didn't.

Anyway, Gus and Ken at Van's told me that enlarging the hole WAS NOT the way to go as the edge distance was far more critical than the perfect perpendicular orientation of the bolt. They warned that if I started messing around with it that I would probably get a loose fit and not enough edge distance.

My fix and their suggestion was to just use a slightly longer -5 bolt and then use an additional AN washer on each side of the hole with one side sanded at angle to distribute the bolt head pressure accross the rear spar bracket. It took me about 30 minutes to make 2 good spacers from the AN washers and fix the issue using vise grips to hold the washers and my belt sander.

I double checked the fix and suggestions from Van's with 3 A&P's at my home field and my DAR and all agreed with the suggestion and my fix from Van's.

This bolt is entirely in shear under load and as long as you keep the bolt head points and washer edges from digging into the spar bracket you'll be fine. The more I thought about it and that this bolt really serves to not allow the rear spar to move up and down as the load changes from flap and aileron position changes, I would venture to say that it could be at a 45 degree angle and still be ok given the safety factor in the designing of the wing structure.

Jeff - N247DE - flying 11 hrs and climbing
 
I've decided that any more removal of metal is just too risky, and am going with either shims milled from .125 stock, sanded washers, or these guys:

http://www.mortonmachine.com/washer/swash.shtml

I'm sort of leaning towards the spherical washers as being the most simple and reproduceable solution. Any comments would be appreciated.

Steve Zicree
 
Assuming Vans says it's okay, I'd personally use the spherical washer because:

a) I know myself and I know that it'd take me 20 years to sand a washer down with a 4 degree taper. This is because I'm persnikety when it comes to things holding my wings on so I'd fiddle with it until it was perfect, which it will never be because I'm not all that handy at things like precisely sanding down washers with a 4 degree taper :)

b) I'm lazy

That being said, if I knew a way to do it that would give me good results in, say, an hour (as opposed to my estimated 20 years), I'd probably just try it on a washer and see if I like the results before bothering with fancy shmancy stuff. :)

One warning on the spherical washers.....different washers span different angles. It's not uncommon to find washers that only go to 3 degrees, for example. If you go that route, just make sure it can handle your 4 degrees.
 
jcoloccia said:
a) I know myself and I know that it'd take me 20 years to sand a washer down with a 4 degree taper. This is because I'm persnikety when it comes to things holding my wings on so I'd fiddle with it until it was perfect, which it will never be because I'm not all that handy at things like precisely sanding down washers with a 4 degree taper :)........................., if I knew a way to do it that would give me good results in, say, an hour (as opposed to my estimated 20 years), I'd probably just try it on a washer and see if I like the results before bothering with fancy shmancy stuff. :).................
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You guys are way over-analyzing this stuff. I produced the tapered shim required and drilled it......produced from .125 stock in little more than 5 minutes. Fine tuning it to the specific angle for the specific application would take another 5 minutes.
i77le.jpg

The photo illustrates the shim with excess material used to hold it with vise grips and would be trimmed off before use.

Rick Galati RV-6A "Darla"
 
I don't mean to over analyze things, I just wasn't looking forward to fussing to make all four of them perfect and then having to clock them properly to do their job, not to mention having to prime them. The washers just seemed like a nice easy fix.

Steve Zicree
 
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