Tricky Pattern Making Question.

[DavidL]

Perimeter of the piece below is 61cm not including the top piece because its not connected to the single piece rectangle that will wrap all the way around the bag.

How long should the rectangle piece be to match up with the 61 cm side piece.

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If I wrap a piece of 9 ounce leather around a perfect cylinder that is 40 cm in length a 9 ounce leather of the exact circumference of the cylinder won't wrap around and meet together. On the other hand light weight fabric will probably meet up nicely. In the example above the only part that the rectangle has to be adjusted longer is the semi circle curve on the bottom section of the side, it may be exactly the same length as the actual perimeter of the piece because its stitched flesh to flesh not wrapped around.

Would I add the thickness of 2 pieces of leather to the diameter so that it will calculate the extra bulk that the leather adds to the circumference. I know there are variables because the leather may be really stiff and thicker and thinner in some areas by an ounce or two.

40 + 7.2mm and then find the perimeter of the total piece? 40cm + 7.2mm = 40.72cm = 127.8cm compared to the 125.6cm of the cylinder circumference.

For the first question:

For the rectangle to just add the extra distance for the semi circle = 66.26cm compared to 61.13 cm.

(3.6mm (9 ounce leather) X 2 divided by 10) = .72cm

(9cm = diameter)

9cm + .72cm X 3.14 = 30.5 divided by 2 because it is a semi circle = 15.26 +23.5 + 23.5 = 66.26

any one have any ideas, I'm stumped.

Untitled-1.pdf

Edited October 16, 2014 by DavidL

[DavidL]

Just figured out the answer. It may not be exact. From the few samples I made I came to these conclusions:

when stitched grain to grain side the you do not have to add extra length.

Stitching around a round object you have to add the double the thickness of leather to the diameter and then multiply by pi to find circumference to get the correct length of leather.

[silverwingit]

While I'm not sure I fully understand your question, your answer seems totally wrong. If you wrap two layers of leather around anything, the outer layer ~must~ be longer because of the thickness of the leather. Period. In fact, the thicker the leather, the longer that outer piece must be. You surely would have seen that in your experiments.

Better re-think it.

Michelle

[electrathon]

I do not understand what you are doing either, but the simplest and most accurate way is to take the first piece and wrap it around something, then wrap it with the second piece and mark it.

[DavidL]

Silverwingit, I found when the leather is stitched flesh side to flesh side, exactly like how a shirt is sewn along the sides, that along curves there doesnt need to be any adjustments.

Your right about the a piece of leather wrapped around a cylinder it needs to be thicker, my first post had incorrect answers.

What I was trying to do was try to find the correct length to for a specific piece of leather to wrap around a round object. I also wanted to be able to do this straight from Adobe illustrator without physically testing, until prototypes are made.

For people that are interested. It is complicated at first.

the length around the circle = pi times diameter. To find the extra distance of the leather add double the thickness.

pi times diameter + ( 9 ounce X 2) = total length for 9 ounce leather to wrap around object

A 90 mm diameter cylinder

pi= 3.14

9 ounce X 2 = 7.2mm

PI X (Diameter of cylinder) + double thickness of leather = Total length of leather to wrap around cylinder

Plug in Pi, diameter of cylinder in mm + double thickness of leather into the equation

Add the numbers in the brackets first then multiply by 3.14

3.14 X (90mm + 7.2mm)= 305mm

=30.5cm

I think to get a completely flush butt stitch around a cylinder that you could just wrap it around the object with the piece of leather and mark it on the overlap.

Or you could use the formula above and it will either be exactly right or a bit smaller and from there you could sand equally on the flesh side slowly to get it

fit flush.

Edited October 18, 2014 by DavidL

[camano ridge]

I don't know if someone is trying to impress us or just way over thinking things. Silverwingit is right, if you are using two individual pieces of leather. However if you are gluing/ laminating them together you treat the end result as one piece of leather. If you have two pieces of 5oz leather glue it together and you end up with a piece of ten ounce leahter. Treat it as one piece of leather. I do it in holster making all the time.. Like electrothon said take either an over long piece of your laminated leather or a piece of the same thickness wrap it around the object and mark. You now have your length. When wrapping around a cylinder to get a good tight butt (all right you guys) cut each end on a slight opposing bias. Then mate the ends together. No algebradic headaches required.

Edited October 19, 2014 by camano ridge

[DavidL]

Thats what I have originally been doing, taking the leather and scratching a mark. Works good. When it comes down to designing the pattern and adding the tolerances its so much easier IMO to just do the equation

I just figured out taking the total of double thickness X 3.14 will give you the same answer just a little shorter.

9 ounce leather extra length = (double thickness of leather) X 3.14

9 ounce leather extra length = 7.2mm X 3.14

= 22.6mm extra

When it comes to doing something a bit more advanced like wrapping leather around a curved vase object the ability to be able to accurately create a pattern with a not too difficult equation comes in handy. Saves a lot of trial and error.

Instead of wrapping leather which is difficult to do especially if its thick and if the object has a lot of curves like a vase. You can just tape up the entire vase, cut straight down the middle, transfer the tape design to paper and use a scratch compass and add 22.6mm to the design.

Edited October 19, 2014 by DavidL

[camano ridge]

I agree wrapping odd shapes or complex curves with paper and tape is easiest way to develop a pattern. We have customers do it all the time with rifle stocks that can't be sent to us. http://www.veoh.com/watch/v18183118m2eEtc53?h1=How+to+make+a+template+for+my+custom+butt+cover

[DavidL]

edit: The formula is 3.14 X thickness of leather to find the extra length for the pattern.

Edited October 21, 2014 by DavidL