Measure Twice Cut Once, But What Is The Measure?

[RKCrowe]

Good day to all, I am new to leatherworker.net and have really enjoyed it. So much info and talent here it's kind of overwhelming.

Anyway, I am making a koozie for a 12 oz. can, it's going to have a 2mm foam sheet lining. The leather I am going to use is 3-3.5mm. So after hurting my brain relearning some math, I cut some test pieces of foam and leather and test fitted...I sat back and scratched my head and went huh!

The fit was almost perfect, the leather ends butted up nicely, However, I meant to have a 10mm overlap to glue and rivet. I gave consideration to the thicknesses of foam and leather, My question is; Is there a formula, rule of thumb, etc. to determining dimensions for cylinder projects like my koozie?

[Wild Bill46]

Sorry; RK I'm not going to be the Talent your looking for on this project !

I'm in the exact place as you, (so to speak) !

Last year I wanted to make some stylized-and personalized Coozies myself.

As Christmas gifts to pass out among family at the lake.

I began , but never completed my projects,

I just had too many other projects ahead of this !

But I'm sure !

the Talent is here somewhere among this diverse group ! --- Wild Bill46

[Halitech]

usually I will cut a bit longer then I want then dry fit and cut again if needed. Personally, I like the butt fit with sewing over a rivet edge.

Edited June 22, 2015 by Halitech

[DavidL]

illustrator Adobe or photoshop can figure that out for you. Plot out the pattern on offset the pattern by the thickness of leather (ex. add 2mm around the perimeter of the pattern), use some setting in the program to measure that line.

The other way is to do it by paper and measure using thread. I never tested this but it should work more or less, the stretchiness and stiffness may affect this?

[Jim]

The solution is actually right in front of you as it was with me. With the varied thickness of leathers used and the folds, the bends, the twists . . . no wonder I don't have any hair left!

Oh, sorry . . didn't mean to get off track. The answer is to use a 1" wide strap of the intended leather to wrap around the foam to determine the length or width of the leather for the project. Once wrapped around, mark the spot on the strap that gives the needed over lap and then measure this mark from the end of the strap.

I used this method for measuring everything from wrists for Cowboy Cuffs to coke cans for Cowboy Coozies. It works.

Jim

[Jim]

To give you an idea of just how useful the Strap is, everything shown here was first measured out with a strap of the intended leather. Then the pattern making began.

[RKCrowe]

I would like to thank all for their suggestions and support. I stumbled onto this site and I'm not letting go. I thought I had worked out a solution, but no, it must be a math formula above my pay grade so… I will use what I learned from you.

Jim, awesome work there. On use of the strap; on the not so round projects, you just brought the strap around until it met back with itself and added some for the stitching?

Thank you all again and good day!

[Jim]

Actually the strap is cut longer than the actual length (width) of the project would require. This way you can figure the needed length including the stitch or rivet line. When you start trying to figure distance and then adding or adjusting for stitching things will more often than not go horribly wrong.

[RKCrowe]

Thanks again, I will try your suggestion.

[Jim]

I'm thinking real hard about writing a tutorial on this. Might help some folks keep their hair on their head longer.

Jim

[camano ridge]

Actually Jim has a western holster making tutorial pinned on these forums. The first page shows how he uses the strip. I have used the method and it does work. http://leatherworker.net/forum/index.php?showtopic=19338&page=1

Edited June 24, 2015 by camano ridge

[RKCrowe]

Jim when I think real hard, I usually lube the brain with some Makers Mark. I think I will think hard tonight.

[byggyns]

If you want the math, take the diameter of your object, add the thickness of the foam x2, add the thickness of the leather x2, add 1mm for interference- nothing fits together exactly with no gaps. Multiply that sum by Pi ~ 3.14. That would get you a close to perfect butt joint. Since you want a 10mm overlap, add that 10 mm to the total, then add the leather thickness x2. That should get you pretty close to the measurement you want.

An example is a 70mm cylinder, 2mm foam, 3mm leather. Add them together with the allowance for inexact fit, you get 81. Multiply that times Pi, and you get approx 254 mm. This should be very close for a butt joint.

Add your 10 mm overlap and your leather thickness twice, and you end up with approx 270 mm.

The biggest issues most people have with the math are

1. forgetting to add the thicknesses of the wrap layers twice before multiplying: my normal mistake- I only add the thicknesses of each layer once
2. forgetting that the leather measurement should be for the outside of the leather, since the outside grain does not stretch much, but the flesh side will compress more easily- so they don't add the leather thickness at all before multiplying
3. not giving any allowance for the inexact fit between the layers
4. not taking into account the leather thickness for the overlap: not adding it at all, or not adding an additional allowance for the bend outwards

ETA: If you are overlapping the foam, you will have to add even more length onto the leather for that added thickness.

Edited June 25, 2015 by byggyns

[billybopp]

Doing the math is often the way to go, but sometimes the practical - simple approach is best!

It reminds me of a story that I've heard, but cannot say if it is fact or fiction. Thomas Edison came across one of his engineers hard at work with pencil and paper looking at the glass globe part of the prototype light bulb that was sitting in front of him. When asked what the engineer was doing he replied that he was trying to calculate the volume of the bulb. Edison grabbed the glass globe, filled it with water and drained it into a graduated cylinder and told the engineer "There's your answer".

Bill

[Jim]

And is why I use the KISS method;

Keep

It

Simple

Slim

Leather work has it's own rules of math that is not found in any books.

[byggyns]

Honestly, Jim, I use your method more often than doing the math. The practical, rather than theoretical approach tends to be faster.

Mostly, I use the math when making an initial pattern for a prototype. That way, I can layout any other pieces of the project and / or the tooling pattern to see how the composition will come together. Then, I revise the final dimensions with the test strap. The math also helps if you don't have the object on hand to test at first.

Mainly, I provided the math because he asked for a formula due to being frustrated with his own calculations. If he used the same calculations I provided and still came up short, then I can't explain that. It gets me pretty close each time, but as you said leather has its own rules and all hides are a little bit different in how they behave.

[RKCrowe]

Yep, byggyns, I left out the step of multiplying the sum by pi. I will use it for initial project planning and verified by Jims strap method.

[RKCrowe]

Well, I finished the koozie! I used the math formula and the strap method to come up with my measurements. I decided to use butted joint instead of the overlapped joint.

The project came out great, the can goes in/out with just a hint of resistance from air pressure/vacuum.

Thank you all for your advice, suggestions and experiences.

Richard

[ENC]

The formula is C= 2 x pi x R. where C is circumference R is the radius of a circle and pi is a constant, 3.14. So any change in radius is going to change the circumference by 6.28 times the change in radius, regardless of what the radius change is.

Ray

[silverwingit]

One thing to be aware of any time you intend to use a lining with a curve in the primary leather. You need to glue the lining to the primary in close to the same curvature. If you cement the liner to the primary when they're flat, the lining will wrinkle badly when you bend the primary leather to shape.

Michelle

[RKCrowe]

Good day,

To update all, again thank you for your help.

I have made several koozies of different sizes, using the help I got here on the forum. I made templates and ready to make koozies at will.

I attached a pic, I think, of the latest made. I made it for long neck bottles. Using what I learned here, it finished spot on.

Take care,

Richard