Reaming horizonal tail bushing locations

[colospace]

So, I'm still on step one.
I have been assessing the six horizontal tail bushing locations for alignment. Just sticking the reamer into each as far as it will go without cutting, I find one lug to be larger than the reamer (reamer freely/easily passes thru) and one seems to be slightly off parallel. I have held off reaming these 6 locations thinking I should attach a rod to the reamer to help insure the finished holes are parallel to the stab and in-line. I want to avoid either slop or binding of this attachment.
What are others experiences on this step? Am I over working this?

[jtpitkin06]

I had one of my elevator bushings that was drilled a bit askew and oversize. I don't know if that is common. I just stepped over to the lathe and made a new one from bronze in a few minutes. If you or a friend do not have access to a lathe, order a new bushing. The bushing should not be forced in place. I used a "C" clamp to press the bushing into the stab using moderate pressure.

I found it easiest to keep things in line by using a 3/16 x 24 inch long electricians drill bit passing through 2 bushings at the same time.

John

[colospace]

John,
I am on line 3 (Section B, Horizontal Tail Assembly) reaming the six "bushings" (that I would have called lugs) that are a part of the welded stabilizer structure. I'm three pages away from pressing the bearings themselves into the structure or subsequently the bushings that press into the bearings. Your comments are leading me to believe I am overworking the line 3 task however. Probably have my mind stuck in spacecraft rather than homebuilt aircraft mode.

[jtpitkin06]

I looked it up in the manual to see what they call the parts on that particular page. The terminology bounces around quite a bit from chapter to chapter.

The "bushings" that you ream to 0.4375 I call welded sleeves. The "bearings" 93021.000 that you install on step 15 page 12 I call bronze bushings. I suppose if it mates with a rotating part, rotating bolt or shaft it is a "bearing" if it reduces the size of a hole, its a bushing. If it does both, anything goes.

If it's a short tube welded on a Kitfox assembly it's whatever the manual says it is.

Anyway if the"bushing" you are reaming to .4375 is crooked, ream or drill it slightly oversize. Make an oversize bronze bearing or knurl one of the supplied bearings. Then insert your 93021.000 "bearings" with a 3/16 alignment rod through the other bearings. That should fix the alignment problem.

Yeah, it isn't aerospace, but short of cutting off the "bushing" and welding a new one on it is a workable fix.

You can get a 3/16 rod at a hobby shop. You'll use it again when you install the rudder to line up the rod ends.

Hope that helps.

John Pitkin
Greenville, TX

[szicree]

I'm actually on this stuff right now and have a couple of bits of advice.

On mine the i.d. of the bronze part was a bit small and/or the steel inner bearing was too big. The manual said to take the steel part down a bit which I did, but have found that sending a .3125 reamer through the bronze part first gets things to fit a lot faster. To bring the steel part down to size I put em on a bolt, chucked it into the drill press and put a file to it while it spun.

Regarding alignment, the easiest way to assess it is to send a piece of string (I used dental floss) through the holes. Stick any sort of little cork in each end, poke a small hole in the center and stretch the string through the remaining open bushings. It'll immediately be apparent what's out of whack. I'm finding that the holes on both the h. stab and elevator aren't particularly lined up. On the elevator, I was able to put the ends on two sawhorses and apply a slight downward push to bring it straight. I haven't messed with the stab yet, but I suspect it's a lot stiffer.

If I had it to do over again I would have preferred to get all the bearing issues sorted before messing with installation of the wood tail parts, as they only get in the way.

[colospace]

John, I agree and think you are “spot on” regarding the terminology. For what it is worth, my wife has more experience with the ground side of aerospace and says that using “bearing” in this application is pretty common for them. I do not, however, understand how knurling the bronze “bearing” works to solve the problem. Could you please further explain that?
Steve, I have been using some 3/8ths rod to assess overall alignment, but it is only 36” long. I like your string/floss idea and will try that too just to improve the insight into the condition across all six lugs (sorry, “bushings”). I have also considered trying to shoot the laser on my level thru if I came up with a suitable target to place in the holes.

[szicree]

The string deal works very well and is standard practice on the RV builds. You can check the H. stab, V. stab, elevator and rudder all separately. On the RV's all of the tail surfaces hang on rod end bearings so alignment is very easy to achieve by simply threading them in or out. Our situation is a bit more difficult in my opinion.

As for knurling, the process does not remove material, but actually displaces it ever so slightly to create the familiar knurl pattern. They do the same think on the i.d. of valve guides to take up a bit of space.

[jtpitkin06]

Knurling is a process done on a lathe to increase the diameter of an object. The part is chucked in jaws or on an mandrel. Then a knurling tool is pressured against the part as it is spun. The knurling tool has either one or two carbide wheels with teeth or ridges.

As the tool presses on the part, metal is displaced by the wheel teeth. No metal is removed. The displaced metal pushes outward increasing the diameter.

The resultant surface has a slightly rough pattern that will grip the mating parts. Knurling can be straight, diagonal, or cross hatched.

The technique is also used to make nifty looking knobs on things like friction locks for airplane throttles.

JP