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Preparing the Bell Crank Bushing

April 13, 2012

I alluded to having made some mistakes in an earlier post.  One of them was reaming the bell crank bushing.  You have to bore out a brass bushing that is a tad undersized to its final diameter of .25″.

Brass Bushing for bell crank

There are two ways you can accomplish this.  You can use a 1/4″ drill bit or a 1/4″ reamer.  What is a reamer?  A reamer is a tool that is used to create a smooth, flush hole.  In precision machining you would use a drill bit to create a rough hole that is slightly smaller than the required finished hole, you would then use a reamer to complete the hole.  The drill bit is sort of a brute.  It grinds away at the material leaving behind striations that can later cause an abrasive action on a bolt in the hole.  The reamer has straight flutes that scrape the metal from the inner surface leaving behind a nice clean hole.

The proper way to do this is using a reamer.  Of course I didn’t have a 1/4″ one so I had to order it.  There are a lot of posts on Vans, though, that say a drill works fine, the reamer is over kill because the bolt doesn’t move.  Well…I have two bushings, lets try it out.  Uh…lets just say it didn’t work very well and leave it at that.  The hole it made was a mess, there was no way I was putting that in my plane.  So I just waited around until my reamer arrived.

Reamer

I assume you know what a drill bit looks like, well the picture above is a reamer.  I put the bushing into my vice and got to work.

Ready for reaming

Oh wait a minute.  You don’t even know what all this is about…ok.  You saw the picture of the bushing above.  Here is the bell crank you keep hearing about.

Bell Crank

Obviously Vans made this, not me.  Now here is how the bell crank and the bushing work together.

where the bushing goes

When this is put into the wing there is a bolt that will pass through the bushing.  The bolt, with its accompanying nut will hold the bushing still and the bell crank will rotate around the bushing.  Ok?  Back to reaming.

The reamer, while a very nice solution, is challenged by the fact that it cannot clean itself while in use.  You have to grind some metal then pull the bit out, add some Boelube and repeat until you are done.  It does take a bit longer than a drill bit, but the results are worth it.

Reaming complete

I tried to take a picture of the inside of the bushing, but just couldn’t make my simple camera do it.  The one I messed up with the drill bit, when I looked down it, was gnarled and gouged up.  The reamed one was smooth and shiny.  I am now a complete convert to reaming.  This is the only way to make a finished hole, in my opinion.

Next up I hope to have the bell crank assembled for good in the wing.

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