Post 20. Making the front bellows

   After looking at a lot of posts, tutorials and videos about making bellows, and making the set of straight bellows by myself, I feel I understand the principles well enough now to make them my own way. The best tutorial I found is here, and I will more or less follow it:

https://www.picto.info/RS_texts/bellows_RS.pdf

  I went ahead and ordered 3 yards of a blackout liner fabric for curtains that is fairly heavy, black on one side and light silver grey on the other, and 56" wide. I will make the front bellows the traditional way in  three layers with cardstock stiffeners sandwiched between the curtain liner and a black coton fabric I already have. The front bellows is tapered from 22"to 9", and must extend about 24". So the ribs have to be unequal in width to produce that 13" taper. In order to calculate the dimensions precisely, I will use millimeters instead of inches, and make a bellows that tapers from 550 mm to 200mm, with a total extension of about 750mm. The fabric panel for each side of the bellows need to be somewhere around 750 x 1.7 = 1275mm. The ribs on the straight bellow I mad were 1", so we want our ribs to be on average around 25mm, except that we need unequal ribs. So we will need around 50 fold for 25 ribs. Each side panel must taper a total of 175mm over 25 ribs, so the difference between the wider and the narrower fold needs to be 175/25 = 7mm, making the narrower one 25mm -3.5mm = 21.5mm and the wider one 25mm + 3.3mm = 28.5mm. Since there needs to be a space between the cardstock stiffeners so the bellows can fold , we could cut those stiffener ribs 21mm and 28 mm, leaving exactly 1mm of space between them for the folds. The total length will be 50mm x 25 = 1250mm. The entire set of top, sides and 1/2 bottoms will be drawn right on the grey side of the black out fabric stretched flat on a board(disregard the dimension on the sketch bellow):

  Here is a preliminary scale layout of one panel in inches:

 

    Actually, there are two ways to go: 

        1. Make all the ribs pointed following the zigzag folding pattern and glue them all. In that case, the two bottom halves need to be glue together overlapping about an inch, making a cone shaped unit that will need to be carefully folded making the bellows. Either the ribs will be made of two halves side by side(weak point), or overlapped (then there is a double thickness in the middle of the bottom).

        2. Cut the ribs for the side panels without the points, which allows using a plywood shape to glue the fabric panels together before gluing the ribs, and making a square tube instead of a round conical unit, which will have a stronger bottom panel and will be easier to fold, but will possibly have weaker soft corners, since the ribs on the sides don't have points.

    Different makers have used different glues: brushed on contact cement, acrylic, 3M Spray adhesive, etc... I would rather stay away from spray adhesive as my experience has been that the stuff will come loose 5-10 years down the road. I don't want to use contact cement either, as it will in places bleed through the fabric and make a mess. And then it may eventually come loose. Plus the ribs have to be spaced perfectly lined up with the drawing 1mm apart, and repositioning is not possible with it. My choice would be Yes paste, but it remains water soluble. There are several fabric glues on the market that I will try, as well as tacky glue, Modge Podge, Acrylic Gel Medium, and my old acid free PVA bookbinding glue. I will just have to do test patches with a few ribs.