Guest Post (part II)

 Note correction in the comments section

How to measure warp tension

 

As a student I have been given information on various practices for setting tension, such as gently releasing the brake, which ratchet and pawl to tune first, counting the brake clicks and feeling the warp itself. I wanted to find a way to measure warp tension, so that I could use numbers to guide me in resetting my tension after each warp advance.

 After searching on Amazon, I found a precision spring gauge, referred to as a dynamometer (also known as a tensiometer)  with a scale of 1 Newton or 100 grams. The price was right, starting around 8 dollars and I purchased the Eisco precision spring scale at a cost of twenty -four dollars. After experimenting with different ways to attach the tensiometer to my loom , I finally settled on this set-up. I first advanced the warp and did not reset the tension, next I hooked the scale ( yellow end) onto a few warp threads in the middle of the warp. The other end of the scale ( measuring hook part) was attached by a slack Texsolv cord to a central treadle on my Glimakra loom.

 

 Now that the tensiometer was  positioned  I started my measurements. I measured how far my warp threads sagged under the weight of the tensiometer alone and then I started tightening the warp, one click, two clicks and so on and at each point I measure the displacement and noted the force being measured on the tensiometer. The table below summarizes my observations. The direct measurements are the displacement and the force from the tensiometer and these two direct measurements are sufficient to provide guidance on resetting the warp tension after advancing the warp. The right side of the table shows the calculated warp tension in both newtons and lbs. The warp tension is calculated using the formula T=F*L/(4*d), which is a reasonable approximation for small displacement, d and large distance, L between the breast beam and the warp beam. 

 

 

Number of Brake Rachet Clicks        (increasing tension)	Warp Displacement (d,cm)	Force (F) Measurement from the scale ( Newtons)	Warp Tension Calculated ( Newtons)	Warp Tension Calculated      ( lbs)
0	5.5		-	-
1	5.0	0.01	-	-
2	4.0	0.16	1.45	0.32
3	3.5	0.22	2.28	0.50
4	3.0	0.28	3.40	0.75
5	2.5	0.34	4.90	1.10

 

So what did I learn from this little experiment? First of all, warp tension is measurable, just like they measure guitar string tension or the string tension on your restrung badminton racquet. The tension on the warp in this particular experiment increased by 30 times from an initial brake position to the tightest brake setting. For my cloth I learned that I was looking for a displacement of around 3 cm and a force of about 0.3 N on the tensiometer. This setup is unintrusive under my loom, so I can leave it on and practice resetting my warp tension as my weaving progresses.

 Changing materials,  looms and many other factors will change these numbers and therefore these exact numbers are not to be relied upon, but rather demonstrate the possibility of learning how to effectively reset warp tension through measurement. I hope  you will give this a try and develop your own guidance for the materials you like to use.