Rivet types

[Ted Waltman]

Question: Should I use Avex rivets supplied by MAM or Cherrymax or
Cherry Q rivets? See below.

I'm getting ready to rivet new parts that MAM sent me to fix cracks
within my stinger attach bulkheads (previously posted on this list). I
got into a debate at the airport with several A&P's, including a United
mechanic, about using the MAM "standard" Avex rivet. One well respected
A&P said I absolutely had to use "Cherry Q" rivets; that he'd never use
an Avex rivet. Now, I know that the vast majority of pull rivets that
MAM uses on tons of planes that are reliabily operating are Avex rivets.
Nonetheless, I respect these folks opinions. I did a bit of research on
the web. Here's a couple of interesting comments about the Cherry brand
of rivets:

CHERRY Q-RIVET Cherry Q Rivet Diameter
<http://www.bonaero.com/images/CherryQrivet.GIF>
Cherry Q Rivet <http://www.bonaero.com/images/CQ42ASP.GIF> The poor
man's Cherrymax rivets. A commercial grade pop rivet that retains the
grip length of the stem within the rivet to augment shear strength.
Because of the mandrel, length selection must be accurate. Can be used
for structural applications (but not FAA approved).

...at http://www.bonaero.com/Rivets.htm

And here's what that same site says about Cherrymax rivets:

CHERRYMAX RIVETSThis rivet supercedes and improves upon all previous
Cherry blind rivet designs. By far the best stem retention system and
strength to weight ratio of all blind rivet systems. 3200 series are
aluminum rivet and steel stem, 3500 series are CRES.

--------------
I really, really want to always do things the best possible way that
makes sense. Seems to me that if I start popping rivets, breaking
rivets loose or such on these parts, e.g. FUS-358 where it rivets to the
fuselage, I have a major problem before the entire structure fails. I
would catch loose/problem rivets in a pre-flight (eventually), well
before the problem got critical.
-----------------------

Thoughts on rivet type?

Thank you,

Ted Waltman
Moose N142SR




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[Al Paxhia]

Hi Ted,
I am comfortable with Avex rivets because I think I understand their
properties. Avex rivets are just fine if the rivet spacing is designed for
that rivet. What I believe, your A&P is saying is that Avex rivets don't
have the shear strength of a same diameter Cherry. That's true but remember
the rivet count is the multiplier for total shear. The down side to Cherry's
is they are a pain to drill out. Some of the questions are, do you trust the
design, will you use fewer rivets, are the parts predrilled, were there
instructions for the install? The shear strength of an 1/8" Avex is about
165 lbs, remember the avex rivet is not a pop rivet.
Al
----- Original Message -----
From: "Ted Waltman" <tedwaltman@i1ci.com>
To: "'Murphy List'" <rebel-builders@dcsol.com>
Sent: Sunday, October 02, 2005 8:15 PM
Subject: Rivet types

Question: Should I use Avex rivets supplied by MAM or Cherrymax or
Cherry Q rivets? See below.

I'm getting ready to rivet new parts that MAM sent me to fix cracks
within my stinger attach bulkheads (previously posted on this list). I
got into a debate at the airport with several A&P's, including a United
mechanic, about using the MAM "standard" Avex rivet. One well respected
A&P said I absolutely had to use "Cherry Q" rivets; that he'd never use
an Avex rivet. Now, I know that the vast majority of pull rivets that
MAM uses on tons of planes that are reliabily operating are Avex rivets.
Nonetheless, I respect these folks opinions. I did a bit of research on
the web. Here's a couple of interesting comments about the Cherry brand
of rivets:

CHERRY Q-RIVET Cherry Q Rivet Diameter
<http://www.bonaero.com/images/CherryQrivet.GIF>
Cherry Q Rivet <http://www.bonaero.com/images/CQ42ASP.GIF> The poor
man's Cherrymax rivets. A commercial grade pop rivet that retains the
grip length of the stem within the rivet to augment shear strength.
Because of the mandrel, length selection must be accurate. Can be used
for structural applications (but not FAA approved).

...at http://www.bonaero.com/Rivets.htm

And here's what that same site says about Cherrymax rivets:

CHERRYMAX RIVETSThis rivet supercedes and improves upon all previous
Cherry blind rivet designs. By far the best stem retention system and
strength to weight ratio of all blind rivet systems. 3200 series are
aluminum rivet and steel stem, 3500 series are CRES.

--------------
I really, really want to always do things the best possible way that
makes sense. Seems to me that if I start popping rivets, breaking
rivets loose or such on these parts, e.g. FUS-358 where it rivets to the
fuselage, I have a major problem before the entire structure fails. I
would catch loose/problem rivets in a pre-flight (eventually), well
before the problem got critical.
-----------------------

Thoughts on rivet type?

Thank you,

Ted Waltman
Moose N142SR




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[Ken]

From what I can see, Avex are also the best choice for expanding
radially and filling the hole tightly. Yes I've used Q rivets in a
couple of specific places with thick metal for specific reasons but the
airframe is designed for avex and I'd stay with them especially for
repairs where the holes may be a touch oval. If you are riveting thick
(.062?) pieces that are known to shear rivets and you think it will save
more serious damage elsewhere for those rivets not to shear, then it
might make sense to use stronger rivets IF you can't increase the number
of rivets. Stronger is not necessarilly better.

Structural (retained mandrel) rivets are almost never the exact grip you
need and there is no strength advantage if the mandrel is a little short
with thin sheet metal. The quoted higher strength only applies in the
section of the rivet that has the mandrel retained within it. So you
almost have to use rivets that leave the mandrel protruding and then
grind the mandrel flush on every (&^#$ rivet to get a strength advantage
with think sheet metal! And there is no strength advantage if they
become loose in the hole - (see above ;)

I've been paying cdn$48. per thousand for British made Avex from Textron
in Toronto. Q rivets are about twice that. I've paid $1. each for
specific certified rivets! The A&P rarely has a choice.

Ken


Al Paxhia wrote:

Hi Ted,
I am comfortable with Avex rivets because I think I understand their
properties. Avex rivets are just fine if the rivet spacing is designed for
that rivet. What I believe, your A&P is saying is that Avex rivets don't
have the shear strength of a same diameter Cherry. That's true but remember
the rivet count is the multiplier for total shear. The down side to Cherry's
is they are a pain to drill out. Some of the questions are, do you trust the
design, will you use fewer rivets, are the parts predrilled, were there
instructions for the install? The shear strength of an 1/8" Avex is about
165 lbs, remember the avex rivet is not a pop rivet.
Al
----- Original Message -----
From: "Ted Waltman" <tedwaltman@i1ci.com>
To: "'Murphy List'" <rebel-builders@dcsol.com>
Sent: Sunday, October 02, 2005 8:15 PM
Subject: Rivet types

Question: Should I use Avex rivets supplied by MAM or Cherrymax or
Cherry Q rivets? See below.

I'm getting ready to rivet new parts that MAM sent me to fix cracks
within my stinger attach bulkheads (previously posted on this list). I
got into a debate at the airport with several A&P's, including a United
mechanic, about using the MAM "standard" Avex rivet. One well respected
A&P said I absolutely had to use "Cherry Q" rivets; that he'd never use
an Avex rivet. Now, I know that the vast majority of pull rivets that
MAM uses on tons of planes that are reliabily operating are Avex rivets.
Nonetheless, I respect these folks opinions. I did a bit of research on
the web. Here's a couple of interesting comments about the Cherry brand
of rivets:

CHERRY Q-RIVET Cherry Q Rivet Diameter
<http://www.bonaero.com/images/CherryQrivet.GIF>
Cherry Q Rivet <http://www.bonaero.com/images/CQ42ASP.GIF> The poor
man's Cherrymax rivets. A commercial grade pop rivet that retains the
grip length of the stem within the rivet to augment shear strength.
Because of the mandrel, length selection must be accurate. Can be used
for structural applications (but not FAA approved).

...at http://www.bonaero.com/Rivets.htm

And here's what that same site says about Cherrymax rivets:

CHERRYMAX RIVETSThis rivet supercedes and improves upon all previous
Cherry blind rivet designs. By far the best stem retention system and
strength to weight ratio of all blind rivet systems. 3200 series are
aluminum rivet and steel stem, 3500 series are CRES.

--------------
I really, really want to always do things the best possible way that
makes sense. Seems to me that if I start popping rivets, breaking
rivets loose or such on these parts, e.g. FUS-358 where it rivets to the
fuselage, I have a major problem before the entire structure fails. I
would catch loose/problem rivets in a pre-flight (eventually), well
before the problem got critical.
-----------------------

Thoughts on rivet type?

Thank you,

Ted Waltman
Moose N142SR

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[Alan Hepburn]

I think the Avex are OK if you have enough of them. When you look at the
rivet spacing on the Rebel vs. a production airplane with solid rivets, the
Avex rivets are a lot closer. I've heard it said that the design
calculations for the Avex riveted airframe are not allowed to take any
credit for the retained mandrel, whereas it looks like the Cherry rivets do
take credit. The mandrels have got to be worth something. Then, on my
fuselage, I sealed the joints with 3M 5200 to keep the rain out. Having
removed a few panels, I can assure you that that stuff also contributes to
shear strength. Probably a similar story with the epoxy material that MAM
supply in the kit.

There's enough of these planes flying, and they have been flying long
enough, that the weak points (e.g. forward door posts) have been identified
and addressed. Just don't put 1,000 hours on your airframe in the first
year, or you'll be a member of the small group leading the fatigue research
effort!

Al





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[Dale Fultz]

Ted, IMHO different manufactures use different rivets for different
purposes. MAM designed and used the avex rivets. So I am sure they are
suitable for your job you are doing, yes I am sure there is a stronger rivet
out there. However when you make one area stronger something has to give at
some point and it may not be where you want it to be. I personally would
use the avex and check it periodiacally when you do some other work in the
area. There are some A&P that really don't understand an avex rivet and
don't approve of them yet I know there are some in my area think they are
just an overrated pop rivet which in appearance are all that they are really
alike. Developed in WW II for quick easy repairs and haven't really come up
with anything better yet. Dale SR-033




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