Riveting - Part Two

Riveting 101 - continued (Part 2 of 3)

So... you've got some coupons and you got some rivets.

Down the middle of one of your 2x6" coupons, drill a series of five #31
holes. (No, not like that. You've gotta back-up the metal with something.
Here... put it on this piece of 2x4. Hold the drill-motor vertical. No,
DON'T push on the thing! The weight of the drill-motor and the sharpness of
the bit is all it takes to make a clean hole. Okay... now you got it. Go
ahead and do the other holes.) [If you're using a punch you're about to
discover it's principle limitation. Normally, you use a punch to create
holes in a part when doing flat-work on the bench. When it comes time to
fasten that part to some other part, the matching holes are usually drilled.
But for the purpose of this exercise, if you don't have a drill but do have a
punch, stack the coupons and punch both at the same time.]

Gottem drilled? Now feel the holes.

Feel that turned edge? That's the infamous 'burr'. Shot Hamilton in the
gizzard and completely upset the course of American history.... (Why are you
all looking at me like that? Oh! Sorry... I thought it was Thursday...
[Aviation Sheetmetal... Mon-Wed-Fri. American History, Pre-Civil War Era,
Tue-Thur])

To debur the holes take a 5/16" drill bit in your bare hand, hold the coupon
in your other hand and press the drill-bit LIGHTLY into the burred hole and
give it a twist. You want to remove the burr WITHOUT chamfering the hole.
(A little harder... Not that hard... ) Use your FINGERS as your gauge --
feel to see that the burr has been removed.

Deburring with a drill bit assumes you're using a bit with the standard 118
degree included angle. You may also use a fine tooth single-cut file, with the
understanding that you'll only do so when the hole is so positioned -- and
the file wielded in such a manner -- that you won't scratch the surrounding
metal. The popularity of 'patent' deburring tools is that with some of them,
you can debur both sides of the panel at the same time (!). This allows you
to debur holes which open into voids or other spaces where you can't get at
the other side.

Now take a second coupon and drill a MATCHING line of holes. Call when
you're done, I'll be outside copping a smoke.

Didn't work, did it :-)

Unless you've got a CNC computer screwed to your ass there's no way
in the world to produce two matching rows of holes using only a hand-drill.
Unless... Did you try using the first coupon as a template? Drilling thru
it? Ummm... slipped, eh? Okay, let's try clamping the two coupons together.
You can use a C-clamp, a G-clamp, a spring-clamp or a pair of visegrips. Of
course, it'll probably bugger up the metal. Buggering up the metal with
clamping marks is considered bad form, especially since it can make the plane
crash. (So you glue little cork pads to your clamps, or buy the real thing,
which comes equipped with little nylon pads.) So go ahead -- clamp the
coupons together and try again.

By the time you've drilled the third hole it's becoming obvious that
clamping the EDGE of your coupons only works for one or two holes. After
that, they start to wander. (Edge clamping WILL work... if you clamp the
entire edge. This works well for match-drilling small parts. Simply fit
your bench vise with soft jaws and clamp both parts in the vise.)

What you need is some form of clamp that centers on the hole itself!

This need became evident in Roman times, when rivets were used to join panels
of armor. By the late 1700's when boilers arrived on the scene, metalsmiths
already had a variety of tools for positioning and aligning rivet holes.
Most of the tools you'll be using for aircraft work are simply modified forms
of earlier tools which accomplished the same task. Most of those
aviation-related sheetmetal tools were developed in Germany in conjunction
with airship fabrication, the frames of which were Duraluminum (yes, it's a
proper noun although not in common usage). Both Duraluminum and all-metal
airplanes originated in Germany.

Try using a sheet-metal screw. Go on; try it. Number six sheet metal
screw, half an inch long... goes into that #31 hole a treat and takes a fair
grip on the two coupons as well. Of course, the head of the sheetmetal screw
is going to leave a mark... (Another trick is to use the sheetmetal screw to
fasten the parts to the bench-top(!) or backing-block (ie, the thing you're
drilling against). This is perhaps the most common method when drilling and
works equally well using clecos.)

Feller named Parker came up with the solution for the scratches. Special
sheetmetal screws having a little rubber or nylon washer made right onto the
screw. Manufactured by the Kenton company (Kelon? Something like that). We
called them P-K's. Handy.

Well... sorta handy. You gotta screw the thing in... then you gotta screw
it out again before setting the rivet. And sometimes the screwdriver slips and
you scratch the panel... which ruins the whole thing. So they made
hex-head P-K's. Run them in with a nifty little socket-tool, takem out the
same way. Of course, that's an extra tool to keep on your belt. And those
threads DO bugger up the hole a bit. But they really do keep the parts
aligned and don't scratch the work. (Hint: A piece of masking tape makes an
adequate temporary washer.)

Nobody uses P-K's any more... unless they need to. But the use of threaded
temporary fasteners is a valid procedure and was the industry standard for
more than thirty years, before being displaced by the more useful (but far
more expensive) spring-type sheetmetal fasteners introduced by Cleveland
Equipment Company. The use of P-K's... or sheetmetal screws and masking...
remains a valid method for the homebuilder... and for doing emergency repairs
when you don't have a lot of clecos handy.

(Pop Quiz #2: Why do we call 'cleco's' clecos? Hint, hint... read the
last paragraph :-)

P-K's will allow you to match-drill the second coupon. Then you remove the
P-K's, take the coupons apart and deburr the second set of holes. At this
time you'll notice that the P-K's have left a burr on the original holes(!)
Some days it don't do to get outta bed, eh?

Okay, put the two coupons back together using your sheetmetal screws which
we are calling P-K's. Chuck a #30 bit into your drill-motor and lets rivet
that thing up.

Of course, you gotta figure out which rivet you're going to set first. I
mean, you got five holes, right? Where you gonna start?

Ever stitched up a wound? (Don't look like that. It's a handy skill to
have in your warbag. Ditto for knowing how to give shots and starting an I.V.)
To close a wound with stitches you generally start in the MIDDLE. The idea is
to keep
things nice & even. You do the same thing when you're setting a row of
rivets. So remove that middle sheetmetal screw and drill the hole to
rivet-size with your #30 drill. Any burr? If so, remove it. Now insert the
rivet, position the assembly on your anvil and use a hammer to form the
shop-head.

Hey! Nice job.

So keep doing it. Remove the screw to one side of your rivet, drill, deburr
and set another rivet. (Hey! This is going pretty good!)

Now go to the other side of center and do it again. Then back, then back
again.

Five nice neat rivets in row.

Okay, so they aren't all perfectly symmetrical. That will come with
practice. And that's what I'd like you to do -- practice. Do AT LEAST four
or five pairs of coupons. You don't need someone looking over your shoulder,
you can tell a good set from a bad one; just do the best you can. And the
more often you do it, the better they'll become. (Don't sweat the mistakes.
We all make them at first. Now's your chance to make all the mistakes you
want, the coupons ain't gonna fly.)

Working with coupons and P-K's, you will have seen how the sheetmetal screws
touch the anvil when you try to head the rivet. The usual solution is to use
a narrower anvil. But in the real world there are riveting tools called
'hand-sets'. These are round or retangular steel bars having a polished face
that is machined to match the head of the rivet you're setting. In use, you
can clamp the hand-set in a vise and use it to support the head of the rivet
while you form the shop-head with a hammer. Or, you might turn the work
over, pressing the shank of the rivet against the anvil and hammer on the end
of the hand-set. Hand-sets are fundamental to riveting. I'll have a bit
more to say about them later.

Working with two flat coupons, the riveting is very easy. But most aircraft
components aren't flat. Take a coupon and bend it length-wise -- turn it
into a six-inch long piece of angle stock. (Just clamp it between something
and fold the edge over with your hand.) Now you may call it a stringer, if
you wish :-) Drill five holes down the center of one of the flanges then go
ahead and rivet it to another coupon.

The flange limits your access and will make the riveting more difficult. You
may find you need a hammer with a smaller head. Indeed, the head of the
classic riveting hammer is made from hex or square steel and is typically
about 3" long from the handle-hole to the face. As with rivet-sets and
bucking bars, riveting hammers came in an almost infinite variety, each
shaped to allow the riveting of a particular shape of panel or stringer. The
same is true for their matching hand-sets.

But eventually you simply run out of room -- you can't get at the rivet with
a regular hammer. For example, take a coupon and bend it into a 'U' about an
inch across the bottom. Now figure out how to set a rivet with the shop-head
in the bottom of the 'U'

If you're like most folks, you will have reached for a drift or flat-faced
hand-set that is long enough to reach the rivet in the bottom of the 'U'.
But unless you have a third arm and prehensile tongue, you also discovered
that the parts were more difficult to hold and position than in previous
examples.

You've already seen the need for positioning and locating the components
prior to riveting. Working with angles and deep 'U' channels should bring
home the need for some means of positioning and holding the work. 'Relative
to what?' ...someone always asks, which is a good question, given the
three-dimensional nature of aircraft structures. Do you position the work
relative to the anvil or relative to the hammer?

The most correct answer is that you should try to position the work relative
to YOU --- to the person doing the riveting. You will do your best work with
both feet on the deck and the panel at work-bench height. And yes, this is a
bit of a trick question because up to now the anvil has been fixed in
position and we've been positioning the work atop it. But the anvil -- the
mass against which the rivet is 'bucked' or deformed -- does not have to be
fixed in position. So long as it has sufficient mass, we may even hold it in
our hand and do a good job of forming a shop-head, thanks to the laws of
inertia. But before freeing you from the bench, let me tell you a bit more
about hand-sets.

Hand-sets used to be like mother's milk to an aviation metalsmith. But with
squeezers and pneumatic guns having become ubiquitous in the trade, the
traditional
hand-set has largely vanished, replaced by a simple block or bar of steel,
drilled to accept the die from a squeeze-set or rivet gun.

The sets for squeezers look rather like a rivet, being a button of steel with
a shank extending from the bottom. The top of the button is shaped to match
the head of a rivet and is normally hardened and polished. The shank, which
comes in various standardized sizes to match the wide variety of squeezers
and tools, is three-sixteenths (actually, .187 ) in diameter for small tools
(and smaller rivets) and goes up to three-eights (.375) for the larger.
Among that range, as a homebuilder, you will probably find the three-sixteenths

sets (ie, .187" shank diameter) to be the most useful.

To make yourself a hand-set you simply chuck a suitable bar of steel into the
lathe and drill a #13 hole about five-eighths deep in one end. If
you were an apprentice, you would be expected to knurl the thing and polish
the hammering face but in the real world you will find yourself creating
hand-sets as needed, from whatever stock is on hand and in whatever shape is
needed to insure the rivet is properly headed.

Which brings me to perhaps the most important bit of information you're liable
to get from this exercise: Most rivets are NOT set in what
Conventional Wisdom insists is the 'traditional' fashion using a rivet 'gun'
and bucking bar. The overwhelming majority of rivets are set using various
forms of squeezers, or in the case of homebuilders, are headed by hand. The
pneumatically powered riveting hammer and bucking bar is largely reserved for
what is called 'panel work', where it's impossible to use a squeezer...
(although aircraft manufacturers have built squeezers so large the entire
panel can be pushed through them).

The popularity of squeezers and presses over guns & bucking bars is well
justified. A squeezer takes no special skills yet produces a shop-head of
perfect proportions and uniform quality. Since the object of riveting is to
create the best possible fastener, anything that promotes that goal should be
used.

If you haven't already realized the obvious, let me say now that I can't
teach you to rivet via email. Indeed, I can't teach you to rivet even if we
were in a classroom together. Riveting is a senso-kinetic skill, akin to
riding a bicycle. Riveting, like riding a bike, is something you can only
learn for yourself. What I'm hoping to do with these articles is to show you
the natural progression which lead to riveting as we know it today. That
progression begins with forming the shop-head by hammering directly on the
shank of the rivet. The next step is to form the shop-head using a pneumatic
rivet hammer and bucking bar. According to Conventional Wisdom that would
appear to be the logical goal of any treatise on riveting but the reality of
riveting is that most of it does NOT involve the use of rivet guns and
bucking bars. Explaining why this is so and introducing you to some of these
extremely valuable tools and techniques, is the ultimate goal of these
articles. The fact that you might just happen to learn to rivet along the
way is just frosting on the cake :-)

---- to be continued ---