Dimpling and riveting pressures

Can anybody tell me what are the typical pressures required to dimple
a skin and also to compress a flush rivet? I know that squeezer tools
are rated at typically two to four tons, but what are the actual
pressures required? I'm trying to work out the dimensions on a hand
operated gantry for dimpling and back-riveting the skins on an RV, and
I don't want to over-engineer the thing too much...

Thanks,
--Max

Max, go to the Matronics RV-List and you can ask guys that do this everyday.
If you don't know how to get there email me and I well point you in the right
direction.

Jerry

Max Krippler wrote:
Can anybody tell me what are the typical pressures required to dimple
a skin and also to compress a flush rivet? I know that squeezer tools
are rated at typically two to four tons, but what are the actual
pressures required? I'm trying to work out the dimensions on a hand
operated gantry for dimpling and back-riveting the skins on an RV, and
I don't want to over-engineer the thing too much...

Thanks,
--Max

Earlier, Max Krippler wrote:

Can anybody tell me what are the typical pressures required to dimple
a skin and also to compress a flush rivet?

Forming the shop head will require the same pressure regardless of
whether the other end is universal or flush.

My experience with using a small hydraulic ram to squeeze MS20470AD4-6
for HP-18 wing box spars is that it took about 3500 psi behind a 1"
diameter piston. Given that the area of the piston is (.5")^2*pi =
..785 in^2, the force would have been .785 * 3500 or around 2750 lbs.
It might have been a bit less, but I'm pretty sure that's what the
neighborhood was.

For AD3 rivets, I imagine that the force would be proportionally
smaller according to the area of the finished shop head.

As for dimpling, I never measured the pressure, but I believe that
it's substantially less than required for riveting.

I hope that helps some.

Thanks, and best regards to all

Bob K.
http://www.hpaircraft.com

On Sun, 09 Nov 2003 19:23:45 GMT, Max Krippler
wrote:

Can anybody tell me what are the typical pressures required to dimple
a skin and also to compress a flush rivet? I know that squeezer tools
are rated at typically two to four tons, but what are the actual
pressures required? I'm trying to work out the dimensions on a hand
operated gantry for dimpling and back-riveting the skins on an RV, and
I don't want to over-engineer the thing too much...

Thanks,
--Max

until you get a sensible answer...
take a piece of dressed soft pine
place the rivet hammer on it and pull the trigger.
adjust the pressure down until the hammer action fails to mark the
pine.
that should be just about right.
Stealth Pilot

Earlier, Stealth Pilot wrote:

...place the rivet hammer on it and pull the trigger...

The way I read Max's question, he wants to build a machine for
squeezing rivets, not hammering them. That's why I responded as I did
in this post:

http://groups.google.com/groups?dq=&...g.googl e.com

(use cut-and-paste if the newsreader breaks the link into multiple
lines)

Of course, I could have just misread or misunderstood Max's post. My
apologies to all if so.

Personally, I prefer to squeeze rivets whenever possible, and only
hammer them when squeezing is impractical. What I found while riveting
the HP box spars is that it is possible to squeeze the rivets using an
elaborate set of jigs, rams, and cradles. But the job just went faster
when I went ahead and hammered them with my horseshoe-handled 5x. Less
pleasant, yes, but faster.

And, while I'm on the topic, I just noticed my basic conceptual error
in my earlier post cited above: squeezing rivets to a given shop head
diameter requires a specific force, not a pressure (which is force
exerted over an area). However, that force induces a pressure in the
rivet material, since the force required is related to the
cross-sectional area of the shop head. Let's have a bit of a look at
that.

But first, a bit of a warning:

*** Warning: I'm not an engineer, and what follows is not engineering
advice. It is rather more of a tentative application of high school
physics to data found in the Aircraft Spruce catalog. ***

Going back to my earlier assertion that it takes about 2750 lbs to set
an AD4 rivet, we can compare that with the .025 in^2 area of a .18"
dia shop head, and see that the pressure on the shop head is 2750/.025
= ~110000 psi, or about 3 times the 38000 psi tensile strength of the
rivet material. That does sound a bit high, so I begin to doubt my
memory about how much pressure I had to put behind the 1" dia. ram
piston I was using. However, I am confident in my memory that the
pressure _was_ on the high side of a 3000 psi pressure gauge; and I'm
pretty sure that the guage was accurate to within about 5%.

As a for-example, if I was pumping the ram to only 2000 psi to set
rivets, the force exerted by the 1" dia piston would have been
pi*(.5"^2)*2000 = 1571 lbs. If that's the case, the pressure on the
..18" dia shop head would have been 1571/.025" = ~63000 psi, or about
1.65 times the tensile strength of the rivet material. Somehow that
sounds like a more reasonable number. Probably the truth lies between
the two values.

Anyhow, based on my experience using hydraulics cobbed together from
broken bottle jacks, it's an easy enough thing to test.

Sorry for rambling so, and best regards to all

Bob K.
http://www.hpaircraft.com/hp-24

Despite all the science, the composition and temper of rivets varies slightly
from batch to batch. With smaller rivets the deviations from the norm are
usually not significant but for larger sizes you must fine-tune your equipment
to ensure an acceptable shop-head.

The numbers give us a handy place to start, as does experience, but if all you
have to go on is numbers then it would be wise to lay the books aside and use
data from that particular batch of rivets. Which can get a bit tiresome.

I think most will agree that one-off fabrication of small airframes remains as
much a manual art as a science.

-R.S.Hoover