Recently, a couple of subscribers to the Digest asked me to tell them
what I can about the dimensions of Welte-Mignon T-100 rolls, sometimes
called "Red Rolls". I assume that this issue is of interest to other
subscribers too, so I have responded here rather than privately.
It is convenient to think of a T-100 roll as being divided into 103
strips of equal width along its length, where the width of each such
imaginary strip is equal to the center-to-center spacing of the tracker
bar ports. This is not a new idea; some early rolls produced by the
German firm actually have inked lines along the entire length of the
roll, indicating the boundaries of these strips. There are 102 (not
100) punch positions across the width of the roll; each punch position
is centered upon the boundary between the imaginary strips. As a
result, the overall width of the roll is an integral multiple (namely
103) of the port spacing.
The mating tracker bars have 100 ports, and therefore cannot detect
the presence of holes in the two outermost punch positions. However,
some rolls have holes in these outermost positions; their purpose is
unknown. In the interest of completeness such holes should be scanned
and perforated when making replica rolls.
I measured two T-100 tracker bars, one manufactured in Germany prior
to the Great War, and the other in the United States (i.e. in
Poughkeepsie). I found the distance across 96 ports to be 12.025
inches for both bars. Thus, the center-to-center port spacing is just
slightly larger than 1/8 inch (by about 0.2 percent).
It appears that T-100 roll dimensions are based on the "foot of Lahr,"
a traditional unit of measure in use in the town of Lahr (in Baden) and
many of the surrounding towns prior to 1840. The foot of Lahr is
12.025 modern inches in length, corresponding exactly with the values
I measured on my two tracker bars. At the time, the foot was divided
into 12 inches throughout Baden, and the inch was in turn divided
into 12 lines. (We think of the port spacing as being 1/8 inch of
Lahr, but it is actually 1-1/2 lines of Lahr.)
(For a discussion of units in use in Germany during this period, see
"Dictionnaire Universel des Poids et Mesures anciens et modernes," by
Horace Doursther (Paris, 1840); the foot of Lahr appears on page 411.)
[ Shortly before this reference book was published the "standard
[ meter" was established in France, and a team of researchers went
[ about the world recording the local units of measure. Of course,
[ they hoped that the locals would adopt the new Metric System
[ of measurements; it hasn't happened yet in the U.S. of A. !!!
[ -- Robbie
I went to Lahr two years ago for the purpose of researching this
matter. I wanted to know if the foot of Lahr was in use in
Unter-Kirnach, the town in which Michael Welte became an apprentice to
Johann Blessing, a noted maker of musical clocks, in 1827. (I assumed
that Michael Welte would have taken his tools, including measuring
implements, with him to Voehrenbach in 1832 when he opened his own
shop, the forerunner of the Welte firm).
Unfortunately, the destruction of records during the Second World War
was such that it appears to be impossible to determine exactly what
units of measure were in use in which towns in the 1820s and 1830s.
The other types of "foot" in use throughout Germany during the period
in question are all either too large or too small to have been the
basis of the T-100 roll.
The overall width of the T-100 roll is therefore 103/8 = 12-7/8 inches
of Lahr (exactly), and the port spacing is 1/8 inch of Lahr (exactly).
In modern units, the overall width is 12.902 inches (327.71 mm), and
the port spacing is 0.12526 inches (3.1816 mm).
Thus, although we cannot know for certain that T-100 rolls are based on
the foot of Lahr, the correspondence of the historical unit and our
measured values suggests strongly that it must have been so.