The Louet Megado has been highly refined so that a loom with quite a 'short' distance between breast and back beam creates a rather large shed. The above photo is the warp at rest, under tension. The shuttle race is slightly 'off' level when it is at rest. (This is not a 'fault' - it's how the loom has been designed.) The warp is resting at about the bottom of the reed, and just grazes the front tip of the shuttle race.
When the shed is opened, the back beam rises to about the same height at the breast beam. The warp then rises as well so that the bottom of the shed is now slightly above the reed bottom and well above the shuttle race. THIS IS NOT A PROBLEM. The shuttle does not ride on the shuttle race but on the shed floor.
The shuttle race is ONLY necessary if you are using a fly shuttle. The shuttle race was developed to make a fly shuttle possible - a bridge to get the shuttle from the fly shuttle box over to the shed, then out the other side and into the box on the other side of the loom.
This is the schematic provided by Louet in their owner's manual. It clearly shows how the warp is being raised to create the best shed possible. However, it shows the shed opening from the maximum points in the loom - the outside edge of the breast beam to the outside edge of the back beam. The warp at rest slants downwards as the breast beam is about 37" or 94 cm in height while the back beam is about 32" or 81.5 cm.
When we weave, the shed does not form all the way out to the outside edge of the breast beam but to the FELL. This alters the shed geometry as it changes the angle of the threads as they travel from the back beam to the fell. The angle of the warp from the heddles to the fell becomes more acute as weaving builds. As the fell approaches the reed as weaving proceeds, that angle becomes even more acute. This increases the tension on the threads and is one of the reasons why new weavers are urged to keep the fell in the 'sweet spot'.
If the warp yarn is 'tender' weaving beyond the sweet spot can begin to stress the warp and is often when breakage will begin happening. Selvedges can begin to develop weft loops as tension on the selvedge ends increases.
Where is the sweet spot? Depends on the loom. The Megado has a gigantic shed and a very large sweet spot. I have been able to (carefully) push the weaving area to about 3". This is not something I recommend for every weaver, loom or warp. It works for me, but I know it's part laziness. I might be very close to finishing an item and rather than advance the warp for the matter of a few picks, I will continue weaving, even though I know I'm pushing the loom and the warp to its limit. But I also know the yarn I am using very well, and know it can handle the extra tension. BUT I have to be very careful with my shuttle handling and not add any additional stress.
In the above diagram I have added a red mark showing approximately where the fell needs to be for proper clearance of the beater and the breast beam. It may not seem like the change in angle is important, but it becomes important in terms of being consistent in beat and to make sure the shuttle race isn't scraping across the web below, especially if the web is loosely woven. The rubbing of the shuttle race can shift the picks so that the picks are no longer consistent, creating areas of much less and much higher density.
Bottom line? Understand what is happening. If your loom is a counter balanced or counter march loom and doesn't have a shuttle race - that's because it doesn't need one. No need to add one. If you want to add a fly shuttle, then you *will* need to add a shuttle race.
Get to know the sweet spot on your loom and stay within it unless you know the warp can tolerate the extra stress of weaving beyond the sweet spot.
Get familiar with the signs of weaving too close to the reed - the loops that suddenly appear at the selvedge, for example.
Get comfortable advancing the fell and re-setting the tension. I've written about this extensively (and have an essay on that in the Next Big Project for those that haven't come across the info - yet).
And for those who haven't seen it yet, here is the link to the You Tube video I posted to Facebook.
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1 comment:
Thank you for this information. Through practice, I have found that advancing the warp after about one inch of weaving gives me the results I want from my loom. I had never considered that in terms of changing shed geometry. Always something new to learn.
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