On Not Always Right someone working in a deli was grumbling about a customer ordering a third of a kilo of ham and then bitching. I was picturing the scenario,
“Okay, 300 grams… 320… 335, take some off and we got 332 – much better. 333… 333.31… point 32… point 34 – Dammit!”
“That’s close enough.”
“No, you ordered a third and that’s what you’re gonna get. Point 325… 328… 331, Shit.”
If this is about folding a letter to fit it into an envelope, It’s important to remember that a perfectly folded page is much harder to open than a half-assedly folded page. It’s just like fitted sheets.
Ypu get it right before you crease it, like @solost describes in post 5. I am not at all coordinated, but I can do that, after practice.
My way for folding the paper I think comes down to a similar way of solost. As I write it out it sounds difficult and complicated but it actually works very naturally. I roll the paper into an overlapping circle and then gradually flatten into an oblong oval while scrolling the inside edge so that is stays along the edge of the oval on the inside and rolling the paper so that the outside edge lines up against the edge of the oval on the outside. If you keep doing this as you flatten circle you will end up with a very good folded in thirds paper.
ETA: here’s a video showing the technique 5 Ways to Fold a Paper Into Thirds - wikiHow
Practice is key. I can look at a piece of fabric and find the center by eye. Once I have the center point, everything else falls into place. I might be a thread or two off but never more than three. I didn’t learn how to do this overnight, I have been playing with string and fabric for over 60 years
First thing that popped into my mind, and easily one of the neatest tricks to learn as a woodworker.
And will forever more. Yes, I do know why this is so. Of course, that is for angles. Trisection of lengths is trivial.
Nope, that’s still part of the classical geometry toolkit-- That’s what the compass is for (or at least, the compass combined with Euclid’s second proposition). The trisection construction (and it is a construction, not merely an arbitrary-precision approximation, as some are suggesting) requires sliding the ruler along the page while maintaining the set distance on the ruler.
And in fact, the ancient geometers knew how to divide a line into three (or any other integer) equal segments, and the method was very similar to this.
You could mimic that with a straightedge and a modern compass* though, and in the idealized world of geometric construction you would get the correct result.
*I.e. one that holds its shape when lifted from the page, which is a feature you’re not allowed to draw advantage from in strict construction. (Though an irrelevant feature in the idealized world where you can just use however many steps you want from where you are to where you want to go without loss of precision.)
With rope, string, bungee cords, etc., it’s even easier than with paper. Lay the rope (string, etc.) on a flat surface and form it into an S shaped curve. Then, holding one end and the looped portion on the same side together in each hand pull it tight to flatten out the curves. With very little practice you can hook a finger into the curved section and accomplish the task quickly and easily without laying it on the flat surface to begin with.
Years ago my mother worked at a military base in the personnel moves department. Every so often they would get new equipment and the employees got first dibs on the old stuff. One day she brought home a machine, she gave it to me figuring I could make something else out of it. It was the size of a small printer available today with a crank on the side. Insert up to 4 pieces of 8½ x 11 paper, turn the crank and out popped the paper folded perfectly into thirds. I kept that thing around for quite a few years till I found I wasn’t using it any more. It was one of the first things I ever sold on Ebay back in the late 90’s.
This works great! The bend in the rope slides over my finger to get the segments to the same size. I would imagine that with a very long rope, the same thing could be accomplished with 2 people where one person is on each end/loop.
This is somewhat related, but one trick I have to cut a circle into thirds is to visualize the circle as a clock. Cut a line from the center to 12, 4, 8 o’clock to get 3 even segments. I personally can “see” the clock on the circle easier than I can eyeball where 1/3rd is. Handy when you have to split a pizza for 3 kids and want to avoid any arguments over who got the bigger piece.
I saw a machine like that many years ago. You could adjust the location of the folds.
Do you remember how much you got for it?
That is similar to how I fold an 8½” x 11” piece of paper into thirds to put it into a standard business envelope.
Bend the top edge of the page over the front while simultaneously bending the bottom edge over the back, being careful not to crease either curve. When the 3 segments are as equal as possible, pinch a nick in the top corner with your dominant hand. Place the paper flat on a surface. Bend the top edge down, and slide a finger across from the nick. Unfold the top. Fold the bottom edge up almost to the crease, then slide your finger again.
I usually ask for 33% of a kilo.
If I’m folding a sheet for an envelope I just put it on top of the envelope and make the first fold close to the max that will fit.
This is what i was going to suggest. It’s very accurate for any practical purpose.
When i fold a sheet for an envelope i try to place the folds between lines of text, so I’m not creasing any words. There’s plenty of slop, and i never thought the goal was perfect thirds.
If you have to fold a lot of letters into three and the paper size is standard, then it should be simple enough to rig up a little jig for it - tape a ruler down to a large piece of card; draw a long pencil line on the card parallel to the edge of the ruler, at a distance equal to one third of the paper length.
Then just butt the top edge of the paper up to the ruler and fold the bottom edge up and over to meet the drawn line and press that fold flat; flip it over and fold the top edge down to meet the previously made fold (assuming you wanted a Z fold).
I think I got $17 for it. It was a bit heavy so shipping cost quite a bit too.