Since this seems to be turning into the "reference thread" for this type of fold, here is my variation on the "Two Ruler Technique", in case anyone finds it useful.
Except for very small parts, I do all of my folds with two thin steel rulers. I work mainly in heavy card (110lb/200gsm), which can be very stiff to fold. The two-ruler technique is fast and accurate. I use a pair of 6" rules for smaller parts, and a pair of 12" rules for much longer tabs.
This technique is a little difficult to describe clearly in words, so please see the attached photos.
First, I score the paper where I want the fold to take place (essential!). I always place the score on the inside of the fold. This usually means that the scores are "reverse scores", on the unprinted side of the paper. To make these, I use the puncturing method Golden Bear described to mark the location of the score.
Then I position the two rulers. The part is placed on the work surface with the scored side facing up. The first ruler is positioned just below the score, resting on top of
the main section of the part. It's used to anchor the paper. The second ruler is positioned just above the score, and lies under
the tab to be folded.
The ruler under the tab is then rotated along its edge to flip the tab up and over as far as needed - as much as 180 degrees, flat on top of the other straight edge.
Since heavy card is so stiff, I usually then use a rolling tool to crease the fold. A glass jar works great for this.
The positioning of the rulers doesn't need to be super-accurate, the fold will naturally happen right along the score.
PHOTOS 1 & 2 - The first attached photo shows the positioning of the rulers. I added a red dashed line to show the location of the score. The second (set of) photos shows the motion of rotating one of the rulers to fold the tab over (this shows a 180 degree fold - of course, stop earlier for a shallower angle).
This technique works great on tabs down to about 1/4" wide. For narrower tabs, I use the method Darwin described: first score, then "rough cut" the part, leaving a margin of extra paper along the narrow tab
. Next, fold with two rulers. Finally, cut away the excess margin.
Originally Posted by rixtoys
I need advice on the best way to fold long slender pieces multiple times. (...) The frame rails are long and require 4 folds .
I build architectural models, and frequently encounter this situation of close, parallel folds. This two-ruler technique works great for these.
First, do all of the scores. Then cut out the part, leaving a margin if needed. Position the rulers. Start the folding with the score nearest to you. After folding it, slide the rulers up to the next score, so the ruler on top of the paper is covering the first fold. Do the second fold. Repeat, working your way up the paper. Takes only a few seconds per fold. After all scores are folded, remove the rulers and crease the folds if needed.
PHOTOS 3 & 4 - Photo 3 shows a part with a series of close, parallel folds at the top, scored, with rulers in position to start folding. The last photo shows the finished part.