Pantographing: the same pattern on differently sized glasses, how does that work?

The two functions of the pantograph are:
1.   copying a pattern from a template to max (on our machine) 24 glasses, and
2.   re-scaling it from a template which can be 20-30-40 cm to a size that will fit a glass. ("Glass" here means a drinking vessel, or at least something round)

Below is a video describing the mechanics.
The scaling occurs in two directions, in the vertical direction of the glass and also laterally, i.e. along the perimeter of the glass.
These two scales can be set independently of each other, which is necessary for the pattern to be adapted to various glass sizes.
The more the pattern is reduced, the easier it will be to follow the grooves in the template with the pattern stylus. If the scales are radically different, for example if the pattern is reduced only twice in height but ten times sideways, the sideways movments (when following the template) will be very light, but heavier for the vertical movements.

As also shown by the film, the scales are set by changing the angles of the two guides.
On our pantograph there are no "help scales" to set these angles. The most reasonable assumption is that the scaling was done by placing a glass of the current series in the machine, and then adjusting the two guides until "done" before production was started.

The picture of the five glasses above illustrate the need to be able to scale the pattern. The pattern is repeated five times around the circumference of the glasses. The patterns connect exactly, so as to form a continuous border around the glass.

Is there a need to re-scale sideways for different glasses?
It is easy to believe that the pattern needs to be scaled to reach around the entire perimeter of the coupe glass left compared to the Maderia glass to the far right. But it's not. The number of copies pattern around the circumference is determined by the number of needles used.
For this set there were five needles used to copy the pattern five times. The sideways scale was set so that the pattern exactly fills a fifth of a full turn corresponding to an angle of 72 degrees. This, each pattern copy fills exactly a fifth of a turn, will apply regardless of how large or how small the glasses are.

To re-scale the pattern sideways would thus, in this case, lead either to overlapping pattern repeats or to gaps between them, depending on whether the scale is increased or decreased. But as long as the scale is unchanged, the relationship around the glass, connecting patterns or gaps, etc., is completely independent of the diameter of the glass.

In height, however, the scale was adjusted between, for example, the coupe glass and the white wine glass which is second from left. This also means that the pattern proportions will be different. In the current example, perhaps it does not matter much because the pattern itself is complex and difficult to grasp.

But let us look at the set Elon instead.

The pattern Elon basically consists of a circle with inscribed and circumscribed pattern elements. When this pattern is placed on glasses with different bowl heights you can clearly see how it changes shape and becomes oval when it is etched on the shorter glass (see detail picture to the right).
To avoid this, you must either increase the distance between the pattern repeats or increase the number of needles and thus the number of repeats around the perimeter.

However, the ratio between the side and the height is also affected by the shape of the glass. The pantograph will raise and lower the glass vertically in a predetermined and constant scale relative to the pattern. But if the bowl - as in the lower part of a coupe glass - is very shallow, a small shift in the vertical will lead to a major shift in the horizontal direction.
Generally speaking, a large change in the diameter of the glass along the vertical will mean that the proportions of the pattern along the vertical will change. If the pattern is irregular or otherwise difficult to understand maybe this is not a problem, but if the pattern is more pictorial one must beware of these effects.

Gävle (a town in Sweden) celebrated its 500-year anniversary in 1946, by (among other festivities) creating a series of glasses with a panorama around the entire perimeter. This panorama was divided into three separate pattern templates. The patterns on these three plates must therefore connect exactly to each other around the perimeter of the glass. At the same time, the proportions of the pattern, ie the ratio between the height and side, should not become too different from original pattern on the plate. To make this to work get the glasses can not have a too bulbous shape.

Unfortunately we have not been able to find any picture of these Gävle glasses - should you have one to share, feel free to contact us!

We do not know exactly how this was done, but our guess is that the pantograph was equipped with three needles and that the sideways scale was such that each template filled a third of a turn. Two of the needles were then disconnected and the first template was scribed with that single needle. Subsequently, the first needle was disengaged and the second was connected. The second template was placed on the pattern table (fitted carefully), then the pattern of the second plate was scribed. Similarly, after the third plate was placed on the pattern table, the third needle was activated and the last pattern image was scribed. This demanded high standards for fit and scaling but because the templates are actually separate and the overall picture is too big to have had all the plates simultaneously on the pattern table, the above explanation is the only reasonable.

This is how the pantograph works mechanically (in English):