Clarke Joe, Lynch Colleen C. M&R Professional Screen Printing Series
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PPrrooggrreessssiivvee CCoorrnneerr SSoofftteenniinngg
With the onslaught of retensionable frames and a meter in virtually every shop,
came the need to soften the corners of the mesh. Public opinion has it so the
mesh wont rip and of course this is the case. And if you simply poke the corners
to the table top, this is all you are getting but know that the corner can do more
for your tension level and stability than you might think.
The issue is how much to soften to allow the tension to get as close to the center
of the mesh as possible while maintaining a square opening throughout the sur-
face of the mesh. (Note with stretch and glue frames, this step is not realistic and
often not necessary).
The illusion of energy transfer is just that, an illusion but do not think that
because you pull the mesh evenly, that the result is equal over the entire frame
area. The reality is that the mesh openings can be greater at the edges nearer the
tension. If you have ever stretched a screen, you may have recognized the
extreme case as stall or no change in ten-
sion with an increase in elongation. There
are several causes of these phenomena
where stress is no longer proportional to
strain:
1. Imbalanced SS curves on the
mesh.
2. Necking of the filament.
3. Stress beyond the elastic limit of
the fabric.
The next graph shows the results of image
travel based upon retensionable frame travel.
It might seem that if you rolled the frame
¼-inch that that travel would translate to the center of the image and move ¼-
inch of fabric, not so. If you look at the graph you will see that 100 percent of
the travel equated to 35 percent movement at 15-inches (nearly the center of a
Challenger frame). And 3/8-inch travel took the mesh tension to dangerous lev-
els. (Note that the total edge travel was 0.375-inch or 3/8-inch and the frame was
at 25 N/cm² at the outset).
As you can see from the graph, after half or 3/16-inch travel, there was little
change in the meshs central areas. However, the mesh openings had been distort
Screens
Figure 1.27 This illustrates a filament that is
defective due to polymer necking. If this occurs dur-
ing the tensioning process, a ripped screen is guaran-
teed. The neck is the weakest part of the mesh and
is caused by too much tension too fast. It can be evi-
denced as isolated stress also (see page 1.38 for
details). Drawing courtesy of Printwear Magazine.
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edlarger nearer the point of tension and smaller in the interior of the frame. For
those of you doing halftone printing this condition leads to progressive moiré.
So one of the keys to proper tensioning is to relax as much of the corner as is
practical. On roller frames sized for Gauntlet and Challenger presses you will be
able to soften 6-inches along the long side and 5 inches on the short side. (see
figure 1.38).
Chapter 1
Frame Travel VS Center Elongation
at Half Challenger Distance
0%
5%
10%
15%
20%
25%
30%
35%
40%
100% 86% 73% 59% 45% 31% 18% 5%
Percent Elongation at the Frame Edge
Pct. Elongation at 15-inches
100% travel =3/8-inch
or (0.375") =35% transfer efficiency.
Figure 1.28 This is a
graph of the variance in the
mesh geometry from the side
of the frame to the center of
the frame if the screen is
retensioned. This factor can
lead to all sorts of problems
if the image happens to be
process color. The result will
be progressive moiré because
the mesh is no longer consis-
tent and if the line count is
high, moiré is quite likely.
Figure 1.29 This is a top view of a Stretch
Devices Roller Frame and the lines for progressive
softening are indicated. On a standard Challenger
frame, run the warp threads parallel to the long side
of the frame. Soften six-inches down the long side
and five-inches along the short side. At the ends of
the locking strip the slack should be 0.75-inches and
0.50-inches respectively. This will accomplish several
things; First, there will be no isolated stress areas to
lead to premature mesh failure. Second, the corner
will be taut enough to coat with emulsion without
leaving a puddle in the corner. Third, this technique
permits more balanced mesh geometry and more con-
sistent tension from corners to the center. Note the
actual dimensions are based on the SS-curve and the
actual elongation in the warp and weft firections.
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The amount parallel to the
direction of stretch is based
on the percentage of elonga-
tion of the fabric that you are
using. This distance will be in
the half inch to inch and a
half areas for most fabrics
and tension levels (refer to
figure 1.29 for details). Once
you have completed a frame,
use the tension meter to
check for isolated stress. Then
use the Mesh Counter to
check for distortion. If there
is no isolated stress and no
mesh distortion, the screen is
ready to be coated for expo-
sure, development and
production.
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EElloonnggaattiioonn
The best method of assuring
a square opening is to tension
by percentage of elongation
of the mesh. Begin with a SS
curve, available from the
mesh manufacturer, or at least
find out what elongation should result in what tension. Get this information for
both warp and weft directions.
After loading the mesh into the frame, use a Sharpie marker to make fine lines
on the screen at the following noted distances. Mark the Challenger screens at
22-inches apart, centered and going with the short length and 30-inches apart,
centered and going with the long length, similarly the Gauntlet screens at 20-
inches and 28-inches (see figure 1.30).
Use the next table (figure 1.31) to match a percentage of elongation to a dis-
tance stretched above and beyond the original marks. This table is not exclusive
to a particular screen mesh it gives the relationship between elongation and
tension for all fabrics. For example at 5 percent elongation the 22-inch marks on
Screens
1. Insert the mesh as prescribed by the
manufacturer.
2. Use a black marker to scribe a line on the
mesh against the channel for the locking
strip. Do this on all four sides
3. Relax the mesh beginning at the end of the
locking strip.
4. The depth of the softening should match
the distance that you will turn the roller.
5. Proceed with softening toward the center of
the roller.
6. Soften a distance of 6-inches for the long
side of a *Challenger frame.
7. Soften a distance of 5-inches for the short
side of a *Challenger frame.
8. Be sure that the black marker line is
straight, without waves.
9. Repeat on all eight points.
*Gauntlet frames are softened 5-inches on the long side
and 4-inches on the short side.
Tensioning With Progressive
Corner Softening
How To
Instructions
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the Challenger mesh would have elongated to 23.1-inches and the 30-inch marks
to 31.5-inches.
We took one of our test fabrics and with the use of its SS curve and modeled the
tensioning profile on the Challenger screens. The graphs below are an example of
the weft (top graph) and warp (bottom graph) and their resultant tension when
elongated to a specific percentage.
Note the fabric was marked at 22-inches and 30-inches and the percentages came
from the mesh manufacturers SS curves. The actual change in the distance
between the marks is noted on the left vertical axis. The horizontal axis lists the
percentages of elongation from 2 percent to 8 percent and immediately below
the percentage is the tension that would result for our test case screen mesh.
Caution: all mesh counts have an elastic limit and it is specific to the use and
abuse that the fabric is subjected to. The table is not to suggest that any or all
fabrics should be taken to a given percentage of elongation or resulting tension.
That information should come from the fabric manufacturer. The table is to be
Chapter 1
30
22
31.5
23.1
Figure 1.30 This shows two frames with mesh prepared to tension by percentage of elongation. The mesh is inserted into
the frame and opposing marks are placed on the top of the mesh near the edges of the frame. The fabric is then tensioned
based on the Stress Strain curve and the warp and weft count. The resulting frame will have a balanced geometry to elimi-
nate frequency moiré and balanced tension for stability on press.
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used to show the relationship between mesh elongation and resulting tension for
a specific 230 with a 40m thread with a near zero variance in the SS relationship
of the warp and weft directions.
The graphs below continue to describe the relationship between tension and per-
centage of elongation. They divide the process into two discrete steps of warp
tension and weft tension
.
Screens
Press
Frame
Marks
2%
3%
4%
5%
6%
7%
8%
26
22
22.4
22.6
22.8
23.1
23.3
23.5
23.7
Challenger
35
30
30.6
30.9
31.2
31.5
31.8
32.1
32.4
23
20
20.4
20.6
20.8
21.0
21.2
21.4
21.6
Gauntlet
31
28
28.5
28.8
29.1
29.4
29.6
29.9
30.2
Figure 1.31 This table lists the standard frame sizes for the Gauntlet and Challenger presses and
their marks for tensioning by percentage of elongation. Lets say that you have a 26-inch by 35-inch
Challenger frame and you have inserted and marked the mesh at 22-inches and 30-inches as
described. Check the stress strain curve on the fabric; we will use the Murakami 150 Figure 1.10 on
page 1.16 as an example. We see that a 5% elongation will take us to 30 N/cm² tension. If that tension
is sufficient to support the off-contact distance (refer to page 1.49 for details) then pull the 22-inch
marks to 23.1-inches and the pull the 30-inch marks to 31.5-inches. (Note that the same elongation
gives the same tension only when the mesh is balanced. It maintains the same count only when the ini-
tial count is equal or similar.)
230 / 40 Challenger Warp Elongation / Tension
29.0
29.5
30.0
30.5
31.0
31.5
32.0
32.5
33.0
2% 3% 4% 5% 6% 7% 8%
7.8 13.7 19.6 23.5 29.4 35.3 39.2
Percentage Elongation Over Tension
Elongation Beyond 30" Marks
Example: as the marks were stretched from
30" to 31.5", the elongation was 5% of the
30" and the tension in the warp direction
was 23.5N/cm^2.
Figure 1.32 This shows a fabric that has been stretched with the warp on the long dimension
of the Challenger frame. The mesh was marked as described and then tensioned to a percentage of
elongation to maintain a square opening and to achieve screen stability on press.
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Chapter 1
230 / 40 Challenger Weft Elongation / Tension
21.0
21.5
22.0
22.5
23.0
23.5
24.0
24.5
2% 3% 4% 5% 6% 7% 8%
7.8 13.7 19.6 23.5 29.4 35.3 39.2
Percentage Elongation Over Tension
Elongation Beyond 22" Marks
As the marks were stretched from 22" to 23.1",
the elongation was 5% of the 22" and the
tension in the weft direction was 23.5 N/cm^2.
Figure 1.33 This
shows a fabric that has
been stretched with the
weft on the short dimen-
sion of the Challenger
frame. The mesh was
marked as described and
then tensioned to a per-
centage of elongation to
maintain a square open-
ing and to achieve screen
stability on press.
a.
b. c. d.
a. Balanced TensionBalanced Opening
b. Balanced TensionImbalanced Opening
c. Imbalanced TensionBalanced Opening
c. Compromised TensionCompromised Opening
Four Possibilities of Tensioned Screen Mesh
Figure 1.34 This illustrates the four possibilities of tensioned screen mesh and there is only one outcome that is accept-
able. Viewing from left to right: 1. The tension is balanced and the mesh opening (mesh count) is balanced. This is the one
that you want to create it requires mesh with a balanced stress strain curve as well as closely related warp and weft counts.
2. The tension is balanced but the opening is imbalanced. This screen will be relatively stable on press but will cause prob-
lems with ink transfer and frequency moiré. 3. The tension is imbalanced but the opening is square. The screen will not be
stable on press but ink transfer and image artifacts will be under control. 4. The tension and the opening are compromised is
the nature of most screens made with a tension meter as the control.
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The measured elongation
procedure allows you to check
the balance of your screen
fabric as well as the specifics
of the tensioning methods.
You will find the lack of
information from the meter
(which may accurately meas-
ure tension) and the need to
maintain fabric orientation
and bolt specifications.
Should you have a bolt that
has an imbalanced warp and
weft (variance greater than
+/- 1.5%) then you have one
of three choices with that
fabric: First compromise the
shape of the opening but, be
on the look out for
inescapable radial moiré if
you are running halftones.
Second maintain the shape of
the opening but compromise
the stress between warp and
weft, which results in registra-
tion shift during the press
run. Or third, compromise
both of these parameters but
this is very risky since you are
subjected to both moiré and
misregister.
SSttrreettcchh AAnndd GGlluuee
With the popularity of the
retensionable frame in the US
garment printing industry,
stretch and glue will be cov-
ered but only briefly. Again
with the arrival of low elon-
Screens
1. Attach the mesh with the warp threads run-
ning with the short side of the frame. Warp
threads run lengthwise on the frame.
2. Insert the mesh in the frame so that it is
flat and the threads run parallel to the
frame sides.
3. Measure and mark opposing lines measure-
ments on the warp direction (figure 1.31).
4. Measure and mark opposing lines on the
weft direction.
5. Stretch the warp to half of the recom-
mended percentage.
6. Use the notches scribed on roller frames as
guides to 1/8 rotation.
7. Note the tension level and record the
results.
8. Stretch the weft to half of the recommend-
ed percentage.
9. Note the tension level and record the
results.
10. Finish up by stretching the warp to the
final percent of elongation.
11. Note the tension level and record the
results.
12.. Stretch the weft to the final percent of
elongation.
13. Note the tension level and record the
results.
Tensioning With
Percent Of Elongation
How To
Instructions
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gation fabrics, stretch and glue became more viable. The tee shirt printer howev-
er, will have to do some homework to accommodate static frames. First since
retentioning is not an option, the press must be calibrated. Second the use of tar-
like plastisols will not be accommodated: you will be better off with retension-
able frames. Third you will need to keep a true and sharp edge on your squeegee
blades. And the list continues with the tensioning procedures just as is the case
with the retensionable frames.
If you are using stretch and glue on a pneumatic system you will want to read
how to soften corners for retensionable frames (refer to page 1.35). Although the
execution differs, the principle is the same; you want the clamp or clamps to stop
short of the end of the frame. The distances short are: 4 inches and 5 inches on
a Gauntlet frame and 5 inches and 6 inches respectively on a Challenger frame.
Of course you will want independent air control for the warp and weft directions
(for details on percentage of elongation refer to page 1.37). Since the air systems
are very sensitive to resistance, it is easy to calibrate your system for repeatable
results. In practice take the air up to approximately two-thirds of its maximum
Chapter 1
Figure 1.35 This is a photo of the Max Newton pneumatic screen stretcher. The system adjusts to virtually any frame
thickness and size (up to its capacity). It consists of four channels that securely grip the mesh when the coated locking bar is
set into position. Warp and weft can be treated independently to compensate for frame shape and mesh geometry. The locking
bars can be shortened in length to accommodate higher tension levels without the risk of isolated stress. The Max Newton
can be manually pulsed to expedite the tensioning process and to help accommodate imbalanced meshes. If you choose to
pulse tension the fabric, do not pulse at maximum PSI. This will cause filament necking and weaken the drum tight fab-
ric that you have created. For details refer to figure 1.27 on page 1.35.
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for that mesh and then turn it off. Wait a few seconds and then turn the air back
on and go to complete tension. The relaxing of the knuckles and quick return
allows you to accelerate the tensioning process. Note three facets of pneumatic
tensioning on your log sheet: air pressure, percentage elongation and resulting
tension. With these three in place, it will be simple to troubleshoot should your
raw materials or your system take an unexpected turn.
MM
eeaassuurriinngg TTeennssiioonn
All of the tension meter manufacturers tout the accuracy of their meters and
present it as the ultimate tool for gauging screen performance and this is just not
the case. The problem is not
exclusive to the design of the
meters rather it is our reliance
on tension as an accurate
reporting of what has hap-
pened to a screen when the
mesh is stretched. Tension is a
form of pressure and cannot
be relegated to a North-South,
East-West domain. If you
want quick and easy then a
tension meter is fine but if
you want to know the reality
of what is occurring when
you stretch the fabric, read on.
The meter isolates the mesh
to be tested so that the ten-
sion reading is not affected by
the proximity to the frame.
The feet on the bottom of
the meter near the ends of the
base perform the isolating
function. The spring-loaded
probe centered in the meter
forces a section of fabric
downward until the resistance
of the mesh is greater than
the force of the spring. The
meter has been calibrated or
Screens
Figure 1.36 This is a photo of the ISPS Mesh Counter. The cross
check for tension is the Mesh Counter. It is a film positive set to be laid
on the mesh in both static form as well as tensioned form. The counter is
accurate to one thread and can be used to insure a square opening and
equal tension levels at all points on the mesh.
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preset to units of pressure, Newtons per square centimeter. If you want to know
tension the best way to gauge it is perpendicular to the tensile (stretched) force
and this is the way that the meters read.
The meter can and should be used and there are some equally valuable but lesser
practiced readings that will help your cause: If you are wise enough to identify
Chapter 1
a. Maximum
Image Size
b. Check Weft
Tension
c. Check Warp
Tension
Figure 1.37 This illustrates the use of the meter to check tension levels at the five marked points on the screen. It is criti-
cal that the tension be the same at the four corners and at least that high in the center. If the meter finds a perimeter reading
higher than the center reading, check your procedures and try again
.
a. Softened
Corner
b. Corner To
Center
c. Meter From
Corner To
Center
Figure 1.38 This illustrates the use of the tension meter to check for isolated stress. Begin at the corner and take read-
ings from the point of little or no tension. As you move the meter toward the center of the frame be wary of any peaks in
the tension level. If so you have isolated stress. First it will keep you from balancing the tension on the mesh. Second it will
be the most likely place for the screen to rip.