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Tool for relieving the webs in the wing attachment holes

idubrov

Well Known Member
I was inspecting my shiny new wing spars and the fuselage carry-through (RV-7, parts F-704 and W-706), and I found (as many other builders did) that close tolerance bolts would not go through most of the holes. They would go through the thick bars but would catch on the web parts.

This seems to be a known issue that happens due to a slight misalignment between the bars and the web. One possible solution I saw on this forum is to "plug" the holes in the bars with wooden dowels and grind the webs using a Dremel or some other tool. I am sure it works fine and is not too difficult to do.

However, I wasn't confident in my dremeling abilities (it probably doesn't matter much if these "web" holes end up being slightly oversized?..), so I made a specialized tool instead! Or maybe I was too excited to use my machines that day?

Technically, the tool is a reamer (D-bit reamer), but the major difference from a regular chucking reamer is that it only has one small cutting edge so there is no risk of it cutting where it should not (the holes in the bars).

The tool is made from an O1 drill rod, which has a good surface finish and tolerance (for a 7/16" drill rod it will be 0.4375" +- 0.0005"). It is actually slightly larger than the corresponding bolt (bolt seems to have tolerance 0.4365" +- 0.0005", so a drill rod is one thou larger, on average), but it still fits through the "bars" of the spars and the carry-through. It might depend on specific parts, though, I don't know what is the tolerance of the holes.

First, I tapered the end of the rod. Actually, this idea came from the alignment pins I made from the same drill rod (just a short round bar, tapered on both sides). Then I simply milled almost half of the taper (I think, generally you leave 0.003" or so above the centerline for D-bits) plus a very short section of the untapered section of the bar. On the opposite side, I milled two flats so I can use the tool with the wrench.

This is what it looks like:

IMG_6721.jpeg

Technically, I should have hardened it (O1 steel is oil-hardening, heat until a magnet does not stick, quench in oil, then temper, I think, to a straw color). However, since aluminum is a very soft metal, I thought I could get away with an un-hardened tool.

Also, some relief at the root of the cut-out would have helped with sharpening. Plus, maybe, relief under the cutting edge, but for cutting small amounts, it works okay without any relief angle.



The usage is as follows. Carefully insert the tool through the bar section. The hole and the tool must be very clean and well-lubricated. No turning motions! It should go straight in (I did not have any issues with that -- after it aligns with the hole, it goes in with a finger push). Eventually, the tool will catch on the web, with the taper sticking out of the part slightly (based on the taper sticking you can tell if it actually reached the "web"). Then, you turn the tool with the wrench couple of times, it should shear a small amount of aluminum from the "web".

This is what it looks like. This is one of the worst holes I had, most holes would only yield a tiny speck. However, even that tiny speck would stop the bolt from going in easily (well, I am sure you can hammer the bolt in, but that just terrifies me!).

IMG_6723.jpeg

And here is the hole. The shiny silver ring is where the tool did the cutting.

IMG_6729.jpeg

Was it worth it? Probably, not. I did it mostly because I wanted to, rather than actually needing it, I guess. It worked well, though. It still wouldn't cut to a full diameter (possibly, a hardened tool would have done better here), so my pins still won't fit without some rubber mallet. The bolts, however, fit nicely now. I have no idea how much of an effect this will have on an actual wing fitting, however. Still few years away from it :)
 
So...

So you enlarged the hole diameter that receives a close tolerance bolt?

Kind of defeats the purpose of the close tolerance bolt...
 
Hmmm. What was your purpose for enlarging these holes? These holes and supplied bolts are close tolerance for a reason. They are supposed to be a tight fit in the hole. There are tried and true methods for inserting the close tolerance bolts in the tight close tolerance holes of the spar.

It sounds to me you have now reamed out these holes beyond the required diameter of the close tolerance design. Who knows what this will do to the wing attachment. I can only imagine what the engineers at Vans would say about this.
 
First, a disclaimer: obviously, don't trust random dude from the internet. Ask Vans, etc.

Second, as for the hole, I removed the material from the web sheet metal (but not from the bars / caps!), which was interfering with the bolt fit.

This is what I've got from Vans' support:
This is a common mismatch. Removal of material or “relief” of the web sheet metal material only, is approved!
 
Can’t say

Can’t say anything about a -7 but the holes in the -10 spar and webs were match drilled and there was no mismatch. Obviously, the mothership has the final say, so build on.

That said, you do realize that the shear web plays a significant part in the spar structure, and that is why people comment on it, right?
 
That said, you do realize that the shear web plays a significant part in the spar structure, and that is why people comment on it, right?

Of course. However, here is some data point to think about.

It seems like they have suggested to use Dremel at least in one occasion, which I would not call a "precision" method.

I would claim that my tool removes the minimum amount of material to make the web holes to be aligned with the holes in the bars.

Going back to square 1, the bolts I have would drop just fine from the thick bar side. And they would even wobble a bit (there is about ~0.001" of clearance between the bolts and the holes in the bars, based on my measurements). However, they would catch on the "web" side. In some of the holes, but not all.

If you hammer the bolt from the bar side it is probably not a big deal -- the bolt will tear / stretch the hole in the web, as web is quite thin. However, if you hammer it from the web side, the danger is bolt that will be misaligned enough that it will tear the hole that is critical -- the hole in the bar itself.

This is purely my speculation based on reading the internet and my (not very extensive) machining experience.
 
Of course. However, here is some data point to think about.

It seems like they have suggested to use Dremel at least in one occasion, which I would not call a "precision" method.

I would claim that my tool removes the minimum amount of material to make the web holes to be aligned with the holes in the bars.

Going back to square 1, the bolts I have would drop just fine from the thick bar side. And they would even wobble a bit (there is about ~0.001" of clearance between the bolts and the holes in the bars, based on my measurements). However, they would catch on the "web" side. In some of the holes, but not all.

If you hammer the bolt from the bar side it is probably not a big deal -- the bolt will tear / stretch the hole in the web, as web is quite thin. However, if you hammer it from the web side, the danger is bolt that will be misaligned enough that it will tear the hole that is critical -- the hole in the bar itself.

This is purely my speculation based on reading the internet and my (not very extensive) machining experience.

Again, I built a -10 so it may be different but I found that clamping the web/spar pieces together allowed the bolts to pass. The issue was the bolt would flex the web and create a "mismatch" that wasn't there if the web was not allowed to flex.

Anyway, Vans said it was fine, so build on...
 
Man’s brain allowed him to make tools and separate himself from other animals. Theory is still in play. Good job.
 
going south

I can see this can go south so fast. One misstep and a 6 year build can go down the toilet. Seems to me this is not something to do casually.
 
I can see this can go south so fast. One misstep and a 6 year build can go down the toilet. Seems to me this is not something to do casually.

Absolutely.

I would also say it explicitly that this is not to resolve any kind of misalignment between the assemblies (which are the front center section, the aft center section and the wing spars).

This tool is for a very specific issue where the web of an individual assembly is not perfectly aligned with the "long" holes in the bars, causing fastener to wedge when going through an individual assembly.
 
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