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