Stretch-fibers

Pic 1

This tool consists of two wooden clamps (Pic 1).  Each clamp consists of two wooden planks (Pic 2), which on two of their surfaces are covered with elastic window sealing strip for a better grip on the UND cloth (Fig 1). 

Pic 2

Fig 1

The first clamp is slightly different from the second one; the first clamp has a lock which grips the UND cloth strongly (Pic 3 and 4), the second clamp has an adjustable lock so one can adjust the pressure on the cloth (Pic 3 and 5).  Now I'll try to explain how the tool works:

Fig 2

Fig. 3

Having placed the cloth in the clamps, the first clamp locks and holds the cloth strongly in place (Fig 1), then I adjust the second clamp (Fig 2) so that when I and a helper pull the clamps in opposite directions, the
adjustable clamp (with its rubber sealing strip) holds only the slack
 

Pic 3

Pic 4

Pic 5

(traslation by Lambros Papadopulos)

thankyou Lambros

Pic 6 Drill a hole for adjustable clamp