Ivan's RV-7

Making spacers for F-704Timer icon3h

December 30, 2022

Today was a machining day.

The next task was to make spacers for the center section. Both the tube ones and the flat ones.

The tube ones are actually provided already, however, I wanted to measure the wing spars first to know what am I dealing with.

Here is the data I got (I used my electronic calipers as I don't have a micrometer for the 2"-3" range).

Scribbles with dimensions.

I measured the spars in two places: closer to the tip and closer to the outermost attachment bolt. There is some variation between the two measurements, but both spars seem to be in the range of 1.440" to 1.443". So I decided to make spacers on the upper side of that, 1.443" (assuming that bolts will pull parts together to close the remaining 0.003" if I get it).

However, the provided spacers were 1.438", plus they had rough edges (so they would be even shorter after sanding). Since I did not have any aluminum tubing, I tried to make the spacers from the round aluminum stock.

The front side is okay.

Tube spacers.

However, the holes are seriously misaligned on the back side. This is either because my tailstock is not aligned well or maybe because my drill bits are not good.

Holes are not centered!

I think it will do for now, but I ordered some aluminum tubing to remake them.

Then I switched to machining the "flat" spacers to fit at the wing spar locations. I happened to have two chunks of aluminum of a perfect size. They were 1.5" thick, slightly longer than needed, and the width allowed for two large bolts to be captured in the spacer.

Stock for the bar spacers.

Machined them in my mill using a 3/4" endmill.

Machining the bars.

The gibs in the mill seem to be loose in the center and tight at the edges (no surprise as I mainly use it in the center), plus maybe it is not aligned well, so there was some slight difference in the thickness. Maybe, 0.001" at most?

Machined bars.

I scuffed them to get a nice brushed finish (but of course, they got scratched immediately after that).

Scuffed the bars for the appearance!

And drilled the holes for the drift pins/bolts.

Drilled the holes in the spacers.

Also, I emailed Vans Support about some holes in the wing spars being too tight due to a slight misalignment between the spar caps and the spar webs. They said that relieving the holes in the web is approved (but only in the web).

To do that, I have built a simple tool that goes through the hole from the spar caps side and cuts just a tiny bit from the web to align the hole with the hole in the spar caps. I will be posting a separate article to explain the tool and the process.