Stretching
lead came is so ingrained into the literature and general thought that it is
difficult to regain the purpose of the practice. But I will try.
The purpose is to straighten the came
Purpose
The
purpose of putting the lead into a clamp and pulling on the other end is to straighten the lead came. It is much easier to work with a straight
came than one that is curved or kinked.
It gives visually straight lines, it provides smooth and sinuous curves
without interruption in the line of the curve.
It is said
that some came is “pre-stretched”. This
is really the result of alloys contained in some lead to make it stiffer. It still needs to be straightened before
use. If the lead came is already
straight, you do not need to do anything else before using it. If you drop or otherwise accidentally bend
the came, you need to straighten it before continuing.
Stretching can weaken the came
Stretching
Pulling on
the lead came is not to stretch it, it is to straighten it. Stretching the lead can make it weaker. Lead drawn beyond its structural limits will break. But you can weaken it before the break. You
can test for this weakening of the came by observation. If you see
"alligator" marks on the surface, you have weakened the came by
putting too much effort into the pull. Straightening the lead must avoid
so much force as to weaken the structure of the material.
Straightening not Stretching
Straightening
The amount
of effort to be put into straightening
the lead came is just enough to make it straight. This will vary depending on
how straight the came is at the start. The reason for drawing the lead
toward yourself is that you can see as you look down the length when the lead came
is straight. If you are pulling vertically, it is more difficult to see when
the lead becomes straight.
If the
lead is badly kinked or twisted, it may be best to cut that section out. If you
continue to pull to straighten a difficult section, you can weaken the whole
length of came. First, ease the kinks
and twists out as much as you can by hand. Then do an initial straightening
pull. This initial straightening pull
will show where the problem(s) lie. You
can cut that section out and straighten the remaining pieces without stretching
the lead to the point of weakness.
Safety
Of course,
you must employ some basic safety rules.
Make sure the lead is securely clamped.
In the cleat style lead vices, you can give the lever a thump with the
pliers to ensure the teeth are set into the lead before pulling on the other
end. Other vices need to have other ways
to ensure that the end is held securely.
The other
basic safety rule is that you should brace yourself against any break of the
lead, or slip from the vice. One foot
should be placed behind you so that in case of breaks or slips you will not
overbalance and fall. This has the added
advantage of ensuring you cannot put your body weight into the straightening
effort.
There are
other common sense rules, such as gloves, removing obstructions behind you,
etc.
Conclusion
Remember that the
purpose is to straighten, not stretch the lead came.
If you are putting your foot on the bench to add force to
the puilling of the lead in a vice on the bench, you are putting too much
effort into the job and risk falling when the came breaks or slips out of the vice. If your whole body weight is being used to
draw the lead toward you, you are using too much force. If you can see signs of
a pattern developing on the surface of the lead, you are using too much force.
Straightening the came is not an exercise in a workout
programme. It is a steady firm drawing
force until the came is straight. If you
have to use more than usual force, stop and figure out why. Cut out the difficult section so you do not
weaken the came. Then straighten the remainder and continue leading.
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