The Murphy Builders Site

Ken,
I found they are available with plain heads and shanks. I will try some, and
be more careful reaming in the future. I didn't want to run the reamer
through the bushing because I thought it would dull it quickly. I guess you
could find a way to space the bar/bushing away from the work enough that the
flutes would not be inside the bushing, and come at it from the front. I
don't have the proper size bushing to fit the reamer shaft anyway so it
doesn't matter. I think I'll use a drill press for sure next time, and get a
couple different size reamers.
You are probably right about worrying too much, but then some people make it
sound like your plane will fall apart if it's not precise in every way. I
fall somewhere in the middle. The strut attach bolts/fittings must take a
punishing though, and I don't want to worry about it later on. I did read in
the archives, and confirm in the Standard Aircraft Handbook that up to .006
clearance is acceptable for a 5/16 bolt, and other sizes "in proportion".
Seems like a pretty loose fit though.
I am confused about the meaning of "interference fit". When reading about
close tolerance bolts and reamers designed for them, I saw where a .5 to 1.5
thou interference fit was specified. Does that mean the hole is supposed to
be that much smaller than the bolt, or the other way round?
Jesse

From: Ken <klehman@albedo.net>
Reply-To: <rebel-builders@dcsol.com>
To: rebel-builders@dcsol.com
Subject: Re: Bolt fit
Date: Tue, 17 May 2005 22:48:04 -0400

Drilled shank or head should not make any difference especially since
these are loaded in shear.
These bolts should ideally be snug but I'm sure many aircraft were not
even reamed and most were drilled and/or reamed by hand with no guide so
perhaps one doesn't need to be overly critical??

I've never heard of pulling a reamer through backwards. The front has a
slight taper (maybe 5 thou or so) specifically to start into the hole.
If one wants to use a block why not use it on the front side? A drill
press definately works nicely if available.

Ken

Jesse Jenks wrote:

Thanks for the replies guys,
I think for the other wing I will find a way to use the drill press,
probably put it on the floor and block up the spar. I do have a drill bar
with bushings, but didn't think it would be good to run the reamer

through

it. I didn't think about pulling it through from the back. Will they cut
like that? Anyway, for now I need to figure out how to solve my existing
problem.
I am looking at AN-174 in a reference book from Genuine Aircraft Hardware
Co. They show the max diameter as .2492, & min Dia .2487. That's not
oversized, but slightly undersized. I put the micrometer on a few of my
bolts, they are all about .2475 ish, so I don't think the close tolerance
bolts would do the trick if they are only say 1.5 thou bigger. I guess

it's

worth a try though. Also it seems like they only come in the drilled

shank,

or drilled head and shank variety? I guess that's OK though? I will send

an

email to MAM about going to 5/16 bolts, but the last question took Robin

a

month to respond to.
Just my way of saying that you guys on this list are really a great

asset!

Thanks again.
Jesse

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Exactly. An interference fit means that the hole should be smaller than
the bolt and the bolt has to be pushed or lightly tapped in.
Ken

I am confused about the meaning of "interference fit". When reading about
close tolerance bolts and reamers designed for them, I saw where a .5 to 1.5
thou interference fit was specified. Does that mean the hole is supposed to
be that much smaller than the bolt, or the other way round?
Jesse

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Jesse Jenks wrote:

Ken,
I found they are available with plain heads and shanks. I will try some, and
be more careful reaming in the future. I didn't want to run the reamer
through the bushing because I thought it would dull it quickly. I guess you
could find a way to space the bar/bushing away from the work enough that the
flutes would not be inside the bushing, and come at it from the front. I
don't have the proper size bushing to fit the reamer shaft anyway so it
doesn't matter. SNIP!

I thought you might like to hear about how we work with reamers, it might give a
bit of perspective.

When we have a hole to be reamed we have a jig made from a piece of 1" x 1/8"
steel square tube that we have drilled & reamed to the size of the reamer, we
clamp this over the hole to be reamed, aligning it using the reamer and ream
with it as a guide. We aren't worried bout dulling the reamer as much as the
guide hole getting larger with time and since it is a piece of scrap tubing it
can be replaced when need be. We have used this method to do things like the
wing attach fittings that you can't get into a drill press and it gives nice
holes perpendicular to the surface. Our success with this method has been good
and if we have any concern with wearing the reamer then we can always replace
them too and that is not that costly in the big picture.

Our experience, hope it helps.

Dave


--
David A. Ricker
Fall River, Nova Scotia
Canada






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