Reamer question

Hey all

Quick question

I was planning on drilling my wing skins with a #40 reamer because i like the nice hole it leaves.

I found the following.

My #40 reamer is leaving a hole that is about .005 bigger then a #40 drill bit?

Has anyone seen this?
Is it typical that a reamer is actually slightly oversized?

It says #40 printed right on the reamer. I put a mic on it and it says about .102 or so but with some error depending on how you hold it.
A #40 drill bit mice out to about .094

What am i doing wrong here?

Is there anything wrong with going to a #41 reamer?

Reamer

Dumb question but is your caliper ok? My #40 bit and reamer both measure.098"
Nothing wrong with using #41. Just make sure the male die fits so you don't crack holes when you dimple. Some guys file the male die a bit so they can dimple #41 holes. You'll get a tighter rivet fit. Try some samples.

Yea i thought of that also

Tried with 2 different mics

The fit of a rivet between a #40 bit and a #40 reamer is very noticeable over here for some reason

Its noticeably looser with the reamer. not exactly sure whats going on. Its chucked properly obviously and I'm drilling just as perpendicular as i ever do.

The one thing i was wondering about

a #3 is 3/32 = .0937

Why is a #41 not the standard at .096?

A #40 is .098

This is rather odd.

Expert

ijustwannafly said:

Yea i thought of that also

Tried with 2 different mics

The fit of a rivet between a #40 bit and a #40 reamer is very noticeable over here for some reason

Its noticeably looser with the reamer. not exactly sure whats going on. Its chucked properly obviously and I'm drilling just as perpendicular as i ever do.

The one thing i was wondering about

a #3 is 3/32 = .0937

Why is a #41 not the standard at .096?

A #40 is .098

This is rather odd.

Click to expand...

Maybe the reamer is incorrect like a mismarked part? .102" is cloelser to #37.

I'm no expert but my guess is the #40 is used to allow some tolerance for the die to stretch the hole when it's dimpled. Too tight and the hole can crack. Seems like there's a thread on this somewhere. Again, just a guess.

Hopefully one of the experts will comment.

The #40 is not drilling a round hole. Look at them with magnification.

Try another reamer. Reamers should be close tolerance. Having said that, I would bet that 99% of rvs have been built with #40 drill bits.

BillL said:

The #40 is not drilling a round hole. Look at them with magnification.

Click to expand...

thought of that also

However under a magnifying glass it looks perfectly round to me

Much more round then a drill bit.

Being an engineer myself, I appreciate looking at details of the construction process. But, hundreds of thousands of airplanes (think WWII) have been built without reaming holes (unless you are talking about riveting a really thick stack-up like more than .5"). When the rivets being driven, it expands to fill the hole, including irregularities to create a fit that has no play. If you have noticed that when selecting a rivet to shoot properly for a deep hole in something like extrusions, you need a bit more tail before you start shooting, than for a shorter hole in something like 2 .032 sheets. That is because the rivet expands to fill the hole and the longer the hole the more material you need. If the hole is excessively oversize, the rivet will have a hard time expanding enough before it work hardens.

Ref: Mil-STD 403 for min and max hole sizes to achieve the proper rivet strength and avoid cracking the rivet. Anything inside these limits develops full strength and last a long time.

The problem with .041 holes is that you will find that getting rivets in the holes with any misalignment between the sheets will be tough, and if you force the rivet you shave some material off.

Lots of better things to spend time on.

Same thing here. When building my -12 I noticed the #30 reamer I was using was also slightly large than a brand new #30 bit. I felt it was close enough for government work.

jlfernan said:

Same thing here. When building my -12 I noticed the #30 reamer I was using was also slightly large than a brand new #30 bit. I felt it was close enough for government work.

Click to expand...

So did you stick with the reamer? I like the reamer mainly for the quality of the hole. Obviously less deburring and a truly round hole.

You might try some double margin bits. I bought a few and find they drill nice, round holes. Wish I had discovered them a few thousand holes ago.

ijustwannafly said:

So did you stick with the reamer? I like the reamer mainly for the quality of the hole. Obviously less deburring and a truly round hole.

Click to expand...

Yes, for those exact reasons.