SonexBuilders.net

I'm beginning the process of dealing with the bronze bushings for the Aileron bellcranks. The steel bushings have an OD of .315 and won't fit in the bronze bushings as I expected. I have looked over all the posts of different methods to deal with this and it looks as if reaming is probably the best solution. I'm not sure I trust a regular twist drill bit to do an accurate job. I would have to buy a reamer(or two) to try to tackle this. The question is should a chucking reamer be used in a drill press or should the reamer be turned slowly by hand? I've been looking over a drill size chart and a letter size("O") is .316. Would that be a good size to look for or do I need more clearance than that for a good fit and smooth operation of the bellcrank? Also, could scotchbrite on a dowel spun inside the bushing be used instead of reaming? I don't know if scotchbrite material would bother the bushing pores or not.

Regards
Gregg Kaat
Sonex B #0014

Hi Gregg,

I think I used an adjustable reamer. I bought plenty of extra bushings for experimentation, and turned the reamer by hand. When I tried to drive the reamer with a hand drill, it would chatter, and ruin the part. I've used a hand drill with non-adjustable reamers, and didn't have the chatter problem, but I didn't want to buy multiple reamers to find the correct size.

Take a wooden dowel and cut a slot in the end of it with your bandsaw. Take some sandpaper and cut a strip about 1" long and as wide as the slot you cut. Put the sandpaper into the dowel slot so that it acts as a two arm flap wheel. Use that chucked into your drill press to slowly open up the bushing ID. You won't harm the bushing doing it this way. Just go slow and when the bushing starts to get warm to the touch stop and let it cool off a bit. The worst that will happen if the bushing gets warm is that some of the impregnated oil will seep out and ruin your sandpaper. A reamer will work too but is far more expensive than the dowel method and you have to be more precise to ensure that the reamer is held perpendicular when using it so you end up with a hole that is square to the part surface.

Keith
#554

Like almost everything in my build, this is something I spent way too much time on.

I used a regular (sharp) drill bit, which was fine. I used a drill press. Because it is only very slightly enlarging the hole, there wasn't much issue - the fit was great.. I had more issues with getting the bellcrank to turn smoothly when the bolt was in place - this has been well described in other posts. One of the helpful people on this board pointed out that if the bushings turn well without the bolt in place, the head of the bolt might be causing the steel bearing to get canted in the bushing, which was exactly the case.

Reamer in a drill press. Trying to polish/grind to size with sand paper is going to give you an imperfect hole that is not round and will be tapered somewhat. Drill bit cut oversize as a general rule. Reamers are relatively inexpensive and don't buy the China junk. I did a lot of steel dowling when I was a machinist. We would always break new reamers in first by running them in a drill press in reverse and hitting them LIGHTLY with an abrasive stone so they would not cut too aggressively. Size for size will give you a nice press fit if you dressed the reamer first.

Thanks to all who responded. I look here often for advice since I'm new to building a more complex aircraft than I fly now. I know the subject has been discussed before and I apologize if it was old news but I wanted to see if there was more of a consensus on methods for a close fit before I tried anything. It seems there are many ways to accomplish this all with their own merits and pitfalls. I was reluctant to use abrasives because there was more than a couple against that idea due to possible contamination of the bushing. I would very much like to sneak up on the fit a little at a time to get a close tolerance if possible. I think my solution is to make the drive to my EAA chapter(45 minutes away). They have built several RV's there and may have a variety of lettered drill bits and/or reamers as well as somebody to look over my shoulder. Fortunately if I hog this up, the bushings are cheap enough to start over. It's the lost time that would disappoint. Right now a 5/16 drill bit slides through perfectly. Wish the bushings were that size to begin with.

Gregg Kaat
Sonex B #0014
Kolb Firefly

I used abrasives on some bushings and scotch brite on others. I'll try and report back in 20 years how it worked out.

T41pilot wrote:Fortunately if I hog this up, the bushings are cheap enough to start over. It's the lost time that would disappoint.

That's the key. Just give it a go. I spent way too much time thinking about this, and still had to order new bushings. They are really cheap. If you aren't happy with the fit or have slop, it's really easy to start over!

And more discussion is always welcome, no apologies needed!

Manufacturers recommend not sanding these to change ID - this clogs pores and diminishes performance.
Either a sharp cutter or preferably a hardened ball bearing pressed through:

http://www.oilite.com/bmp.asp

Like nearly everything else in the world, it doesn't look complex until you raise the hood and see the details that make things work - some better than others.

In our Sonex plans grease (or greese) is specified for our bushings rather than oil. What does this do to the pores of the bushings? Also, I'm curious how many of you are using vacuum to re-impregnate the bushings with oil.