Choosing
the Right
Underpinner Nail
t first glance, using V-shaped nails to join moulding seems fairly
A
By Patrick Sarver
simple. Known as V-fasteners, V-shaped nails, V-Nails®*,
wedges, staples, bull cleats, and just plain nails, these angled fas-
teners are inserted at strategic points on the back of a frame to hold the
corners together. In practice, however, there are a number of variations
Making the best joint in the design and use of these fasteners that makes choosing the right
one important if you want to make well-joined frames that offer the
possible in the least quality that clients are looking for. For production framers, it’s a matter
amount of time means of choosing the nails suited to the type of moulding so that strong
choosing the nail best joints are created in the least amount of time.
suited for your
Nail Types
production needs. First, some basics. There are two main types of V-shaped nail: a tradi-
tional nail with straight legs that form a 90 degree angle and a corrugat-
ed nail, which has creases in each leg. Corrugated nails are also often
made of somewhat thicker or harder steel than standard V-fasteners. “A
V-shaped nail has no real pulling power,” says Les Moriconi, president
of Tech Mark. “The angle of the crease in a corrugated nail gives it
strength and ‘pulling’ power so a corner is under mechanical tension
from the nail itself.” For this reason, manufacturers often recommend
corrugated nails for use with hard wood and MDF moulding.
There are also some specially designed nails that offer variations on
these types:
❚ The Power-Twist from ITW AMP is a tapered V-shaped nail, wider
on the top and narrower on the bottom. “As the nail is inserted into
the moulding, it draws the moulding tighter together,” says Justin
Convey, sales manager.
❚ The Talon, offered by Tech Mark for the Taurus underpinner, is a
cross between a corrugated and a V-fastener and has a horseshoe-like
shape. “It was developed because of all the moulding materials being
introduced, from plastic to MDF to exotic woods,” says Joe
Moriconi, vice president of sales. “While a V-fastener has a tendency
to push the material together as it goes in and push a joint apart,
“with the Talon’s horseshoe shape, it’s much easier for the displaced
material to find a place to go.”
❚ The Superflute for the MitreNailer from Active Sales is a corrugated
One nail was inserted close to the inside corner
and another just beyond the center of the miter, nail that uses a different angle. “It is designed to pull tighter on hard-
positions recommended by many manufacturers er woods,” says Clay Simpson, national sales manager.
to get the best joint.
32 PFMPRODUCTIONSpring2006 * V-Nail® and Vee Nail® are registered trademarks of Pistorius Machine Co.
Grinds and Materials
Underpinner nails come in different grinds—that is,
different angles on their cutting edges designed for either
soft or hard wood. They are normally ground primarily
on one side, with a small grind on the other to remove
burrs. MDF nails are ground equally on both sides so the
point is in the center of the nail. A softwood nail also has bigger the
a sharper angler than a hardwood nail. nail, the more
“A softwood nail is sharper and cuts through the material you press
fibers like a knife to create a stronger assembly in softer into, the more impor-
woods,” says Convey of ITW AMP. “Hardwood nails are tant it is to have the
blunter and crush through the fibers of the wood. The proper grind. MDF
also takes a thicker
nail. While our hardwood
nail will work in a lot of MDF,
what’s called MDF is often high
density fiberboard. That takes a
thicker nail because a normal hardwood nail will bend in
the material.”
“A softwood nail is good for wood with less grain,
like pine,” says Eric Pistorius, vice president of Pistorius
Machines. “It has a sharper angle (about 30 degrees) and
is designed to slice through material like a chisel. A hard-
The Tech Mark Taurus underpinner uses strips of fasteners that are
inserted into the machine with reloadable cartridges.
Five different-sized Power Twist tapered nails were inserted in this A cross-section of a mitered corner illustrates how nails are stacked
moulding cross-section by ITW AMP’s multi-channel underpinner. by a Pistorius underpinner for different thicknesses of moulding.
PFMPRODUCTIONSpring2006 33
wood nail has only a 20 degree angle, so it’s blunter and ferent variations.
smashes through the grain. A sharper angle would catch The Cassese uses disposable cartridges, one for each
between the grain on hard wood and curve and split it size of “wedge.” The Taurus uses cartridges that are
open. And if you use a hardwood nail on soft wood, it reloadable with strips of nails. The other brands of pro-
has a tendency to bunch up the wood instead of slicing duction nailers covered here use nails that come in strips
through it. This might open up a corner or create some only.
problems when you stack nails. An MDF nail is ground The only other type of feed is a coil feed, used by cer-
to about 35 degree angles on both sides. Resin com- tain Brevetti models, that contain up to 20,000 nails.
pounds form a tough skin on the bottom of MDF, and “The nail coil is fed into the side of the machine,
this sharper point cuts through that. It used to be that advanced with a foot pedal, and cut into individual nails,”
when V-Nails would hit that skin, they would crumple. says Haines.
The wedge shape on today’s MDF nails, along with Most nail strips are held together with silicone glue or
beefed-up steel, allows more force to be applied for a tape. “We use clear silicone glue on top to hold the strips
good clean cut.” together,” says Pistorius. “The silicone won’t dry out and
“The grind angles of destroy the driver. We found
hardwood and softwood nails that tape generally had a
differ a little bit but are still strong acrylic glue that even-
fairly consistent among all tually gets into the mecha-
the competitors,” says Curt nisms. It will also harden
Brey, vice president of mar- and dry on the shelf over
keting, the Fletcher-Terry time, which pulls the nails
Company. “From our per- closer together. That can
spective, the big difference cause a machine to misfire
between hardwood and soft- and jam.”
wood nails is the composi- Loading a new strip or
tion of the steel. Hardwood changing to nails with a dif-
Power Twist is a tapered nail MicroCorr, made for the
nails can be used on any used for all ITW AMP machines MitreNailer, shows the “creases” ferent grind is easy with all
wood material. If you use a to create more “pulling” power. used in a corrugated nail. the machines. And changing
softwood nail on sizes rarely takes
oak or maple, even a minute to
however, it will do at the most.
not perform as “Changing
well.” nail size is done
Corrugated from the top of
nails, which are the machine,”
used primarily says Pistorius.
for hard wood “Two roller
and MDF, often wheels click into
come in just one different nail
grind—a medi- sizes as they are
um sharpness rotated. After
designed for a nails are loaded
wide variety of Nails are fed into Cassese underpinners with disposable cartridges, color-coded by size. into the track, a
materials. “If switch on the
you’re doing pre- machine applies
dominantly MDF or hardwood, I would recommend pneumatic pressure to seat the strip properly.”
using a corrugated nail for everything,” says Gary Haines, Similarly, the Fletcher-Terry underpinner is just as
marketing and product development manager for PAM easy: “You flip a switch that opens the nail cavity, drop
Fastening Technology. “It has a superior holding power the nails in, hit the switch again, and it pushes them in
because of its ability to penetrate and provide a very tight and auto-loads them,” says Brey.
corner.” The Inmes IM-5 is similar but has an elevator where
you place a nail strip. “You rotate the indicator to the size
Nail Feeds nail you’re using, so you don’t need a spacer or a plate to
Depending on the company, nails are fed into joiners in change to a different size nail,” says Haines.
cartridges, magazine strips, or coils, with a number of dif- Changing nail sizes on ITW AMP models that are
34 PFMPRODUCTIONSpring2006
Company Traditional Corrugated Semi- Specialty Nail Nails in a Nail Coil Cartridges Color Coding Rust
V-shaped nail nail Corrugated Design Grinds Strip Inhibitor
Brevetti 6, 8, 10, 12 & 6, 8, 10, 12 & Medium to No No Coated
strip feed 14mm 16mm No No hardwood 250-300 —
4, 6, 8, 10, 4, 5, 6, 8, 4, 6, 8, No Softwood, — 7.5K-20K No No Coated
coil feed 12 & 16mm 10,12 & 10, 12 & hardwood,
16mm✝✝✝ 16mm✝✝✝✝ MDF
Cassese 3✝, 4✝, 5✝, 7, No No No Softwood, 275 No Disposable Cartridge color Prelubricated
10, 12 & 15mm hardwood by size;label
for hardwood
Fletcher 4✝✝✝✝✝, 7, 10 No No No Softwood, 325 No No No Coated
12 & 15mm hardwood
Inmes 5✝, 7, 10, 12 No No No Softwood, 250-300 No No No Coated
& 15mm hardwood
ITW AMP No No No Power Twist softwood, 200 nails; No No Black stripe Dessicant in
3✝5✝, 7, 10 hardwood; MDF 180 for MDF box; oil on
12 & 15mm MDF nails
(20% thicker)
Mitre-Nailer 7✝, 10, 12 & 6✝,10,12 & No SuperFlute Softwood, 156 nails No No Tapes show Coated,
15✝mm 15✝mm 10, 12mm hardwood. grind type Prelubricated
MDF: Corr.,
SuperFlute
Pistorius 3/16, 1/4, 3/8 No No No Softwood, 200 nails No No No No
1/2 & 5/8”✝✝ hardwood,
MDF
Taurus 3.5, 5, 7, 8, 10, 3.5, 5, 7, 8, No Talon V-Nail: soft 250 nails No Reloadable No Dessicant in
12 & 15mm 10, 12 3.5, 5, 7, 8, & hardwood; box
& 15mm 10, 12 & Corr. & Talon:
15mm medium wood
✝ available for softwood grind only ✝✝ available for softwood and MDF grind only ✝✝✝ available for hardwood and MDF grind only ✝✝✝✝ available for medium and hardwood
grind only ✝✝✝✝✝ available for hardwood grind only
not multi-channel requires changing the nail head, which takes about an hour to do, says Haines. He points out that
still takes less than a minute, says Convey. “On the multi- most people tend to buy equipment geared towards one
channel machine, that’s done automatically.” type of nail or another. “If someone buys a machine to pri-
marily do MDF or hard woods, we steer them to a corru-
Changing to Corrugated Nails gated nailer,” he says. “If your production needs change,
Changing from a V-fastener to a corrugated nail often then you can buy a kit for a standard nail. On the coil
takes a bit more time for those machines that accommo- machine, a universal head can accommodate corrugated,
date both types of nails. Usually it means changing driver semi-corrugated, and double sharp [MDF] nails. For V-
heads. shaped nails, however, you need a specific head. The
“If you want to change to a different type of nail on machine also comes with a head for corrugated nails only.”
the Taurus, you have to change the head in the machine,
which is about a 20 minute process,” says Les Moriconi. Price and Convenience
“The MitreNailer can be swapped in a couple of min- Given that there are no real differences between softwood
utes to change from a corrugated to a standard fastener,” and hardwood nails other than grind, it’s not surprising
says Simpson. “Corrugated nails use an air-fired mecha- that there’s little, if any, price differential. And the price for
nism. For V-shaped nails, there is a different firing mecha- corrugated or thicker HDF nails is typically about 10 per-
nism that mounts into the same spot.” cent more. The biggest difference is in the size of the nail
Changing from standard to corrugated nails in the because a bigger nail uses more steel. V-nails are such a
Brevetti requires changing the head on the machine, which small part of frame cost, however, that time and quality are
36 PFMPRODUCTIONSpring2006
far more important. how a machine is operated. The only thing we learned
The fact is, most people feel that changing nails or from our research is that knock-offs never work as well as
stocking different sizes or grinds are hassles that they want the original manufacturer’s nail. We looked at 10 different
to avoid unless production demands vary so much that knock-offs, many from other countries, and they never
these things are unavoidable. “In our experience, people work as well as the original.”
don’t like to change nail sizes,” says Pistorius. “Although The reason, Pistorius says, is that most machines are
we offer different sizes, about 75 percent of the nails we made for nails with specific dimensions. “If the nails are
sell are 3/8” [10mm]. And, for the most part, we have also too thick or thin, they’ll jam the machine. Over time, they
narrowed our nails down to one grind that is sufficient for can destroy the nailing fixture. Most manufacturers do sell
most materials.” nails for other companies’ machines. But you need to be
“Most customers go with either softwood or hard- careful and be certain a nail is compatible.”
wood nails based on their product mix,” adds Convey.
“Hardwood nails work well for about
80 percent of their material.”
“It’s important to pick the nail
that’s designed to work the kind of
material that you’re predominantly
working with,” says Haines. “If 90 per-
cent of your production is soft or medi-
um woods, having a machine and using
nails designed for hard woods is really
overkill. You can also run regular V-
shaped nails into MDF, but if you want
the best joint possible you should use a
corrugated nail. On the other hand, if
you only do a small percentage of MDF,
don’t buy a nailer or nails just for that 5
percent or so of your production.”
“The cheap nail doesn’t always have
the cheapest price,” says Moriconi. “It’s
amazing how people worry about saving
5 or 10 percent on nails when they’re
spending a lot more on the frames.
They compensate for having cheap nails
by using more of them. I just don’t
think putting six or eight nails in a 3”
wide moulding is a good practice. It’s
better to join with fewer nails that are
taller and can hold the moulding from
top to bottom.”
Matching Nails and Underpinners
Brey says that Fletcher-Terry was in the
underpinner business years ago but that
the machine failed because it shot
instead of pushed nails into the mould-
ing. “When we got back into the under-
pinner and nail business, we studied
everyone’s nails very closely,” he says.
“We put them under a microscope, and
what we saw was the same design over
and over. All V-shaped nails create a
wedge effect, but none of them really
pull a miter together all that well. That
really comes down to the material and
PFMPRODUCTIONSpring2006 37
Stacking vs. Multichannel Nailing four nails, which that can wear a machine out faster.”
The advantages of stacking nails—inserting more than one “The advantage of stacking is that it minimizes having
at the same spot—versus using a multi-channel machine to change nails,” says Haines. “You put one size in and use
that can insert nails of different sizes depends a lot on that for most of your application. The downside is that
which manufacturer you talk to. ITW AMP has a new stacking can sometimes cause weakness in a joint, especial-
machine that can insert up to five different sizes of nails in ly with special sizes or types of moulding—especially deco-
the same corner. The Taurus has a double-headed under- rative trim mouldings that might be 1/2” wide. For con-
pinner that can insert two different nail sizes. ventional framing, a multi-channel machine also has more
“The advantage of using a proper sized nail compared moving parts. And there is an advantage to keeping things
to stacking is that you get a superior assembly,” says as simple as possible, using one nail size and stacking.”
Convey. “If you use one 15mm instead of two 7mm nails,
you’re going to get a stronger joint. You’ll also save money How Deep Should You Nail?
because you’ll use 20 to 30 percent fewer nails. With a “You want to use the tallest nail that can be put in a par-
multi-channel machine, certain mouldings that have ticular profile without opening the joint,” says Moriconi.
required glue in the past will no longer need it because the “This varies from substrate to substrate. A professional
nail assembly will be stronger. Plus, when you stack nails, becomes familiar with the wood he’s working with. If
they have a tendency to either curl back or slide next to you’re going to put 1” oak frame together, probably the
each other. This displaces more fibers in the material, so tallest nail you can put in it would be 10mm. Some
the joint will be weaker. Using a larger nail will create a machines don’t have the power to put a 10mm nail in
stronger miter.” solid white oak. So a framer will use a 5mm or 7mm nail.
“With our double-headed joiner, you can put a 5mm Instead of two or three nails, they’ll end up using five or
in a low point and a 15mm in a high point in the same six.”
cycle,” says Moriconi. “If you’re stacking three 5mm with Both Convey and Pistorius say that a nail should
a single head machine, it’s cycling a total of four times. cover about 80 percent of the material—about the same as
And in production, where speed is an issue, that means Moroconi suggests—while Simpson feels that a nail needs
extra time. Rather than using two nails, you’re also using a minimum of 2mm headroom. “That varies depending
on the finish of the moulding and the
wood type,” he says. “Some mouldings
that have very fragile finishes might need
more room. If you’re clamping directly
over a nailing point, you can also drive a
little closer to the surface.”
Brey takes a more subjective
approach. “We don’t recommend a cer-
tain minimum clearance across the board
because different mouldings perform with
different clearances,” he says. “Knowing
what size of nail to use is mostly a matter
of having experience with different mate-
rials.”
To Glue or Not to Glue
“When people don’t have a good miter
cut, they use glue as a gap filler,” says
Moriconi. “A frame doesn’t close up if it’s
not cut accurately. There are a lot of
purists who feel that that a frame has to
be glued or else it will never work. But I
don’t like glue for several reasons. One is
that I was always taught in my years in
woodworking that end grain does not
glue very well with traditional wood
glues. Another is that using glue in pro-
duction usually means it will get into the
throat of the driver and clog it up. Glue is
38 PFMPRODUCTIONSpring2006
also more labor intensive because it gets on the corners,
and someone’s got to clean it off. People who make photo
frames all day never use glue. They get enough strength
from a good cut and nails. In my opinion, the optimum
is to cut it right, join it right, and eliminate the glue. The
right glue would have to be very viscous, but that takes up
space and makes it harder to put a corner together.
“The primary place where glue is necessary and works
well is with MDF,” he adds. “You need the extra strength.
Nails don’t work as well in MDF because there’s no cross
grain to hold the material together. And the kind of glue
you would need on plastic moulding—a mastic or a sort
of isocyanite—can really muck everything up. Most of the
people I know don’t consider using glue on plastic.”
Many underpinner manufacturers see more value in
glueing—except on small frames. “The concept of a V-
Nail is to act as a clamp until the glue sets up; that’s where
the real holding power is,” says Pistorius. “Put five V-Nails
in a corner, and you can still break it open with your
hands. Do the same thing after glue has set, and you can
barely break it over your knee. On a 5”x 7”, where not
much torque can be applied to the corners, you’re usually
fine with just V-Nails. When you get into bigger frames
and more weight, a corner might snap without glue.”
“Glue tends to be more of an enemy than a friend,
and most people tend to overglue joints,” says Haines. “It
is there as an assist for the mechanical fastener. You want
to use just enough glue to create a contact point between
two surfaces. The nail provides mechanical fastening and
holding power, and the glue keeps the integrity of the
joint sound. Using too much glue also means having to
clean the excess off the moulding. It also gets into the nail
head and gums up the work surface, which leads to inac-
curacy in positioning the miter.”
Making Better Joints
After you have the right nail type and grind for the mate-
rial being joined, you can also benefit by following some
of the following suggestions from manufacturers on how
to get better and more reliable joints:
❚ “The most important thing is to start with a good cut,”
says Moriconi. “I check this by assembling three cor-
ners. If the cuts are right, the fourth corner should have
about 1/8” gap. If the last corner is closed, then you’ll
open up the insides of the other corners when you join
it. If it’s open more than 1/8”, then you’ll open up the
outsides of the other corners. It’s also possible to have
two wrong miters and still end up with a 90 degree cor-
ner. If you have 44 and 46 degree cuts, a corner will still
form a right angle—but one mitered edge will be longer
than the other. You’d be surprised at the number of
places that do that. Also, the closer a nail is to the out-
side edge, the bigger the tendency is for it to open the
outside of a corner. I like to put a nail at least a third of
PFMPRODUCTIONSpring2006 39
the way in from the outside corner and another nail ❚ “The sequence in which you drive nails may yield a
within 1/8” of the rabbet, depending on the moulding.” better joint than inserting them in the same order all
the time,” says Haines. “Some experimentation, espe-
❚ “Some people put a drop of oil in the driver; others oil cially on ornate profiles, may reveal that a different
nails before putting them in the machine,” says Pistorius. starting and ending position will yield a better joint.
“That way, every time you fire a nail, it puts fresh oil Conventional wisdom may be to insert nails from front
into the track. Any glue that gets into the driver will to back, but getting the best joint may mean starting
constantly be wiped away.” from the back, the front, or even from the center.”
❚ “Place the nails closer to the inside corner of the miter— ❚ “Apply glue evenly and in the center of the miter,” says
from the middle to the inside,” says Convey. “You get Simpson. “Use it sparingly. Excess glue causes work in
better assembly that way. You can start with a nail within cleaning up the frame and the machine. When you’re
the first 1/4” of the inside corner of a miter.” using too much glue, you’ve got it everywhere.”
❚ “You need to know your mould-
ings,” says Brey. “If you don’t have a
really good understanding of the
materials, the nails that apply to
them, and how you set your machine
for each material, you won’t be able to
do a proper job. No one can do a
good job joining with an underpinner
they haven’t been trained on and 50
different moulding materials they
don’t know. Experience and training is
important.”
❚ “When joining plastic moulding,
some of our clients put a nail on the
outside of a corner and a corrugated
nail on the inside. They have found
that this creates a very strong joint,”
says Moriconi.
❚ “I get calls all the time from framers
who can’t get their underpinners to
work right,” says Haines. “It often
turns out that they have the nails in
upside down. You’d be surprised at the
number of people who do that.”
A Final Note
The idea of a V-shaped fastener is
straightforward enough, but the dif-
ferences in nails, materials, and
machines require careful considera-
tion. While nails are a small piece of
the framing picture, they still play an
important role in achieving a quality
joint in the least amount of time.
The real payoff is not in saving
money on nails but in reducing the
amount of waste and keeping your
customers satisfied with your
quality. ■
40 PFMPRODUCTIONSpring2006