Tips on pattern design

[EfrainBG]

Hi, everyone.

Once again, bothering you in search of some wisdom.

I'm about to start designing a camera bag using the basic design of an old USPS mail bag, adding some modifications to adapt that design to my needs and to change the look a little bit. Mainly the changes will involve a change in size (not as tall and a bit deeper from front to end) to acomodate a padded insert, add a couple of pockets under the flap and a couple of straps on the sides to attach/dettach another set of pockets at will, depending on my carrying needs for the day... it's a bit of a Frankenstein monster from several different ideas I've seen around. I plan on using chrome/veg tanned leather, 4-5 or 5-6 oz, the likes of a Dublin or Chromexcel, but with what I have at hand to buy here in Mexico... (BTW, do you have something to sher about Chahin leather? I might get a good deal from them but I'm still working that out).

The design I liked the most to begin with is this one from Satchel & Page. Like I said, I'll be changing a lot of things, but the basic form and idea of this one filled my eye. For starters, I'll change the closing from a single buckle to a double strap, double D-ring fastening, since I found it easier and quicker. Also, I'll add a couple of sets of D-rings at the bottom to carry a blanket, or tripod or whatever that doesn't fit inside the bag. I'll keep the magazine pocket in the back because... well, you never know!!

Second of all, I'll change the front face of the base bag to acomodate two pockets more or less to the style of the ONA Brixton, since I find those very handy for keeping my cameras accesories, film, lightmeters, pens, notebooks and other stuff.

I love the gusset on this one, so I won't change a thing here (rivets and double seam). I'll just add a couple of straps sewn or riveted onto the gusset (towards the sides and top of the bag) as anchor points for a couple of dettachable pockets for storing lenses, cellphone, whatever...

Now, on to the questions about designing this thing. I don't care too much if I miss my target size by 1/4 or 1/2 inch because of the joints. But, since there's going to be two layers of leather at the front and at the back, I was wondering if anyone in here would be kind enough to share some light as to how much I should compensate on the size of the outer layer to fit the one on the inside. Say, if the inner front piece is going to be 14 inches wide from one stitch line to the other, how much should the outer piece be? 1/8" - 1/"4 extra to each side? Like I said, I'll be using leather of about 4-5 or 5-6 oz for this project.

Another doubt I have is how far should the stitch be from the edge of the leather. I will use waxed poly thread, 0.040 and I normally mark my stitch line at about 1/8" from the edge. But, since the stitches will be on the side, I have my doubts whether the fact that it's a turned bag with several layers would be too much of a load for such a small edge.

One other topic I can't decide yet is whether to use piping or not. If I do it it would be by means of a single narrow strap of the same leather I use for the rest of the bag, showing the cross section of the leather (burnished and all) instead of folding it over itself. I understand piping is used to release some tension out of the bent joints of the project. Is this at least somewhat true?

Anyway, I hope I made some sense with all this and to get some ideas as to how to skin this particular cat.

Cheers, everybody!

 

[RockyAussie]

If I were trying to work this all out I would start with a strip about an inch wide and duplicate the measurements you think and stitch it up. The piping will release some tension and could look better but not if you do not have experience on how to do. Practice on something smaller first.If the front is 14" wide then my guess would be 14 and 1/4" at the top and closer to 1/8" bigger at bottom. By that I mean the top will need more room than the bottom in width. Not sure though as the leather stretch if stiff will be more and less if soft. Stitch is a bit of same problem but I'd go 5mm or 3/16"+. Too close to the edge will make the stitching show a lot and be weak.

[EfrainBG]

5 hours ago, RockyAussie said:

If I were trying to work this all out I would start with a strip about an inch wide and duplicate the measurements you think and stitch it up. The piping will release some tension and could look better but not if you do not have experience on how to do. Practice on something smaller first.If the front is 14" wide then my guess would be 14 and 1/4" at the top and closer to 1/8" bigger at bottom. By that I mean the top will need more room than the bottom in width. Not sure though as the leather stretch if stiff will be more and less if soft. Stitch is a bit of same problem but I'd go 5mm or 3/16"+. Too close to the edge will make the stitching show a lot and be weak.

that's definitely the best I could do. I was just trying to see whether there was a rule or aid in figuring this stuff out... I'll try to find some crap pieces I can work with, but my main concern with this, as you mention is the scale. It won't bend the same way if the target piece is 14 inches and the scrap is only 7.

Thanks a lot for replying