Simple math when creating a pattern?

[Ariel]

Hi guys, can anyone share their knowledge on the math used when creating a pattern, lets say for a wallet? 

What measurements you use? What do you account for, etc

 

Thanks in advance

[Northmount]

Allow for seam allowance whether lacing or sewing.  1/4" to 1/2" on all sides.  It can be trimmed after assembly if edges don't match up.  Allow for the fold difference between the wallet liner and the back.  About 1/2" to 3/4".

It's easier to use extra length and width up front until you gain more experience with your specific projects and style and have to trim excess off than it is to stretch a piece that is too short.

Tom

[Stetson912]

The basic 4 slot billfold I made followed northmounts suggestion more or less. The seam allowance was 3/16" and the back panel was 1/2" longer than the front. I think a 1/8" seam allowance would be better than 3/16" to be honest. 

I ended up with pockets being 2"x4" the outside pannel being 9"x 3 1/8" and the inside being 8 1/2" x 3 1/8". Two of the pockets we're t-slots. The outer pannel being larger so the wallet will fold. 

This works for wallets and things that are fairly "linear" in nature. If the leather is to wrap around something it gets a bit more complicated depending on how thick the leather is. Things like collars and cuffs and some holsters  and the like. Usually thinner leathers don't offer much of a difference where thicker leathers do. 

For instance a bracelet made out of 2 oz leather compared to 8 oz leather will need differing amounts of length added to them to fit correctly. 2 oz being thin will wrap around the wrist easier and use less length whereas 8oz won't, and will require more length. 

For example, the formula is (distance around object) + pi(material thickness) + slack for comfort. 

So 2 oz bracelet around a 5" wrist with 1/4" slack: 5 + 3.14159(.0313") + .25" is 5.25" + .1037" = 5.4"

Whereas an 8oz bracelet will be 5.25" + 3.14159(.125) is 5.25 + .3927" of 5.6"

That's nearly a 1/4" difference in length between the two. Doesn't seem like much but its enough to be short haha. 

But even this doesn't always work. I made a harness for a dog and used this formula. It got me close but I still had to add length to make it come out right.

Sometimes making a mock up out of cardboard or something makes a big difference and helps visualize how things will come together and point out where you need to make adjustments. It'll save some money too. Anywho, hope that sharing my way of figuring things out helped some.