Constructing Bellows

Construction of Camera Bellows


Through necessity, I taught myself how to make camera bellows.   I hope to share much of the information in this page to allow others to make just as much mess with glue, paper and fabric as I have!  The pictures are a collage from a number of different bellows, so I apologise if the size and shape of the bellows hops around a bit between sections!

1.  The Maths

For straight bellows, the maths is easy as each of the stiffeners is the same width and the angles for cutting are all at 45 degrees.  For tapered bellows, life is a little more tricky as one of the stiffeners must be wider than the other in order to make the sides taper.   The stretched length of the bellows should be about 1.5 times the required maximum working length.  For example, if the stretched length is 600mm, the maximum working length will be 400mm.   

If the stiffeners are an average of 20mm deep, then for 600mm, there will be 30 stiffeners and 15 folds (2 stiffeners per fold).  If the stiffener was 100mm wide, the inside width when folded will be 100-20=80mm and the outside will be 100+20mm=120mm.   Thus the basic stiffener depth and number of stiffeners can be calculated.   It is possible to change the depth of the stiffener along the length of the bellows, but the mathematics is not easy (the stiffeners in my 8"x10" bellows are 20mm expanding to 25mm then reducing to 15mm).

If the bellows side is to taper, the stiffeners have the same average depth, but one side is deeper than the other.  If the bellows go from a width of 100mm at the wide end to 50mm at the narrow end, each side must lose 25mm over the length of the bellows.  If there are 15 folds, we need to lose 25/15=1.67mm per fold.  Thus if one stiffener is 20.8mm deep and the other is 19.2 mm, the overall change is just enough to make the bellows taper in the folding.

There are geometrical methods to allow tapered bellows to be drawn out and the stiffeners to be drawn without having to measure accurately; I have made a PDF file of instructions that can be found here.

Most importantly, make a set using paper first to check the bellows will be the right size.  Scoring in the fold lines by drawing along the folds with a ball-point pen works very well.

2. Marking out and cutting the stiffeners

Using a thin but stiff paper or card (the paper folders/ Manilla envelopes are ideal), mark out the stiffeners for one side of the bellows directly onto the stiffening material; often it is easier to actually do the top and one side of the bellows stiffeners at the same time as it means the line spacing and joins can be done more precisely (as in the diagram below).   The ridge of a fold on one side will be adjoining a trough on the adjacent side of the bellows.  The image below shows how I mark out the ends of the stiffeners.

Marking out locations of stiffeners 


There will be two identical sets of stiffeners for each side so they can be cut out in pairs.  I lay two pieces of the stiffening material on top of each other on a cutting mat and then using a scalpel, remove the sections of paper between the stiffeners. It is a good idea to cut 1mm of each side of each stiffener so that it leaves a little space for the material to fold into.  The process is very tedious....

The images below show how I have cut a top and side out, being very careful to leave them just about joined together down the centre, and leaving an uncut strip down each side to help to stabilise the structure and also to help in joining the strips to the other sections of stiffener 'ladders'.   I fold up the strips left along the side of the ladder and staple them together so that I have all the stiffeners joined together in a very fragile lattice.

Although not shown in these pictures, it is a good time to place long strips of masking tape diagonally across the latticework to help to brace it and make it more dimensionally stable; if it twists when gluing it, the bellows will warp and not fold properly.

Cutting gaps between stiffeners

Stiffener sections cut and joined together

3. Gluing stiffeners to first layer

Measure the area the stiffeners cover when they are laid out and cut a section of the liner material (black cotton dress fabric here) that has very generous margins to give yourself some leeway in positioning the stiffeners.   Lay out the stiffeners on the fabric and double check everything is the right size and is aligned properly.  Imagine the stiffeners being labelled '1 2 3 4' as panels, starting from the left.  Panel 4 should be arranged as being the very top panel of the bellows when they are mounted in the camera.

Stiffeners laid out ready


Place a sheet of newspaper along the 'fold line' of the panels 2 and 3 and then fold the sets 3 and 4 back over the paper; the rack of stiffeners is effectively folded in half now.

Cover set 4 of the stiffeners (you will be looking st the 'back' of the set now) with newspaper as a mask so that only the back of stiffener set 3 is visible.   Spray the stiffeners with an aerosol contact adhesive and also spray the section of cloth that they will be stuck too.   Wait until the adhesive is dry (and therefore ready to stick) and then place a sheet of newspaper on the cloth to cover up the glued area.   Unfold stiffener set 3 onto the just-placed newspaper and check the alignment; there is a sheet of newspaper between the two glue surfaces so now is the time to make any final adjustments!  Pull out the newspaper slowly, pressing the glued stiffeners onto the glued cloth as you go.

Spray contact adhesive is best as it does not soak through the cloth and degrade the inside surface of the bellows.  It also stops the stiffeners going soggy and warping too much.

Repeat the process for stiffener panel 2 and panel 1.

For panel 4, only glue along half of the stiffeners in a slight diagonal line from top to bottom.  The cloth must be joined on this side.


Gluing one section at a time
 Once the  strips are glued (half glued for panel 4), the bracing strips and any masking tape can be removed.
All stuck down and support strips cut away
This last picture is a different set of bellows, but shows section 4 being completed.   The bellows can be turned over and section 1 folded back on to the other sections and the remaining material to the side cut in a diagonal to match the diagonal on section 4; leave a 20mm ish overlap allowance for the material.  It is important to make the join across a face of the bellows as if it was on a corner, the extra layer of material would stop the bellows folding properly.

Use paper as a mask and then spray the cloth flap with glue and also the trailing edge of the stiffeners of panel 4 and the region of cloth overlap.  When the glue is ready, cover panel 1 with newspaper and fold panel 4 over.   check the stiffeners of panels 4 and 1 align properly (they will be next to each other at this point) and then slide out the paper and press the glued surfaces together.

The bellows will now form a tube but it is best to leave them folded flat at this point.   Alternatively they can be placed on a cardboard former that has been cut to taper in the same way as the  bellows.
Gluing joint in the cloth along the face of side 4.

The bellows forming a tube.

4.  Gluing Last layer

The outer covering is glued in a similar manner by spraying the two sides to be joined with contact adhesive. The process starts with panels 1 and 4 and ends with the material joint on panel 2  (which will be the bottom of the bellows when in the camera).  For each panel, the bellows can be re-folded flat so that the panel being glued is facing upwards.

Gluing outer layer
If a former is being used, simply glue each section at a time, wrapping the outer material around.  Start by gluing on panel 2 but only do a diagonal from top-to-bottom so that the seam will run along the face of panel 2.  The diagonal is important as it spreads the extra cloth thickness across the width of the bellows and makes them fold better.

Gluing with bellows on a former; liquid glue was used here.

5. Folding

Once the bellows are glued, they must be left to dry a fair bit before being folded as the glue will soften the stiffeners and make them liable to distort.

Start folding at the wide end of the bellows so that you have the maximum aperture available at the narrow end to get your hand in.  If the narrow end is very narrow, then fold that first as access will be restricted whatever.  Feel for each stiffener and then start the forward/back process on each band of stiffeners.  It takes a little practice, but pay attention to forming each corner properly as you go.   It helps to have old bellows (or the paper prototype) handy to remind yourself of what they should look like!

Bulldog clips are useful to keep the already folded sections in line as you go.

View inside bellows as they are being folded.
Once the bellows are all folded, squash them down and place between a stack of heavy books for a few days until the glue dries fully.  The bellows are now ready for trimming and gluing into the camera.
Folded bellows
Glueing into the camera.


No comments:

Post a comment