Post 21. Making the front bellows v2

 Well, I tried and tried glues, and rib materials, and ways to lay out he bellows and cut the ribs, and I might just as well scrap the last post and start over, because the sheer size of the thing throws wrenches in at every turn:

     1. Drawing on the fabric doesn't work because it is hard to keep it stretched perfectly even, and if it gets loose or stretches a little, that throws the whole drawing off and distorts the lines.

    2. Solvent based fabric glues were recommended by Google AI, and would be good for a small bellows, but it would take too many tubes for one that size, and the nozzle on the tube is too small.  Water based Acrylic glues like Modge Podge can be brushed on, but make the regular paper based poster board ribs bend, and they don't dry flat. Talas lay Flat bookbinding glue(similatrto Yes Paste) works, but it dries brittle and causes problems in the folds. Tacky Glue is not strong enough.  Neither is rubber cement. Contact cement has unhealthy fumes and doesn't allow repositioning. 

    3.  It seems that such a large bellows would require heavy rib material, so I tried a thicker board I had. But then the ribs have to be spaced quite far apart for the bellows to fold, and add to the whole unit thickness. 

    4.  Most of the poster boards available these days are a lot thinner and flimsier than they used to be, more like thick paper.   I found at the Dollar Tree a cheap poster board that is reasonably stiff, and seems plastic coated or impregnated. One side is actually almost waxy.  The good thing though is that the water based acrylic glues don't make it buckle.   However, adhesion is just OK, not great and the fabric can be peeled off.  Roughing it up with a light sanding does helps it stick well enough, so pairing it with Modge Podge is a viable option.

   5.  The ribs have to be held in place and positioned for gluing with strips of tape to maintain the spacing:

  There are two ways to cut the ribs:

        a. Draw the whole side of the bellows on the poster bard, draw the spaces between ribs and cut them out leaving spacer tabs to be removed after the tape strips are in place.  To that effect, I made a double bladed cutter with a 2.5mm spacing:

    The problem I ran into is that the blade that is pressed against the straight edge bends in, and the width of the cut ends up uneven and less than desired. That could be avoided by extending the aluminum spacer all the way to a point between the two blade tips. But it is also almost impossible to keep the ribs even in width.

     b. Cut a bunch of plain strips on a jig that will provide consistant precise widths, cut he ends at the proper angle on another jig, and assemble them on top of a template of the full bellows side, taping them together as they are lined up.  It seems at this point this may be the easiest and more accurate way.

   I glued together the test corner shown above, brushing Modge Podge on the fabric for half of it, and on the ribs for the other half.  The ribs are pressed down with a steel roller. When the glued is applied to the fabric, it oozes out between the ribs, gets on the roller and makes a mess that has to be wiped off, so it is better to brush the glue on the ribs one at a time.  But the white glue doesn't show on the white poster board background, which makes it easy to miss spots, so either the glue or the poster board should be colored.  The inside fabric panel was glued using 3M #77 Spray Adhesive sprayed on the ribs.  The corner test was then folded and placed under pressure overnight. I am quite pleased with the result, the corner folds are clean, and the ribs are stiff enough:

   So here is how I will proceed:

      1. Draw a perfect zigzag pattern of 25 x 35.5mm folds on the computer.  That 35.5mm figure was chosen to get the width of each group of 2 successive ribs as close as possible to the 50mm I had settled on.

   Print it on poster board, and cut it out to use as a template. 

     2. Draw a bellows side tapered from 55cm to 20cm on two pieces of poster board taped together, and use the cut out template to draw the side zigzag lines as precisely as possible, flipping it over . Draw the fold lines as precisely as possible between the points of the zigzag. The total length of the bellows came out to be 1244mm, just 6mm shy of the original plan of  50mm x 25 = 1250mm. So the folds widths are going to be just a hair shy of the 21.5mm and 28.5mm I had originally calculated.  

    Then I realized that for the white ribs to show against the template, it needed to be colored, so I redrew it on green poster board:

     3.  Cut the ribs 1" and 3/4" wide, cut the ends to fit with a 3mm gap for folding the corners, and tape them to the template 3mm apart:

     4.  Use 3 strips of tape to hold the ribs together:

    5.  Glue the ribs down. That is where I had to change course, the colored Modge Podge I used for the first three ribs making a mess, bucking the card tock and oozing between ribs. The glue got all over the roller pressing the ribs down and I had to wipe the excess with paper towels. 

   So I used the 3M #77 spray adhesive instead, using as a mask the zigzag patterns and pieces of scrap poster board, and gluing the whole side in 3 sections to make sure the adhesive wouldn't dry and remain aggressively tacky:

    The second and third sides required some minor adjustments to keep the zigzag spacing sufficiently even. 

    The remaining 1/2 sides were done in on piece on the same green template with an added 1"strip in the middle, and then cut in half. 

     I first intended to overlap the poster board ribs, but decided to butt the ends instead, leaving a 1" strip of fabric on opposite sides front and back to attach them together.  

    In order to do that and form a cone, I built a makeshift stand out of three scraps of plywood to hold the bellow shape up.  That also made it easier to fold the bellows because the large cone was supported:

      Here is the finished bellows partly extended:

        After putting it under weights to flatten it out and set the folds, it compressed to less than 1":