This project was created for my son who plays piano, trumpet, clarinet, & who knows what he will pickup next. He was using a shopping bag to carry his music books around in. It was time for an upgrade. So I planned it all out, cut it out and started putting it together and he says "I don't want a shoulder strap, I want a handle.", so plans changed. Messenger bag almost became a briefcase.
I am going to assume you know how to sew and work leather, or that you can research how, so I am just going to guide you through the steps I took.
Like many things I build, I build it around the purpose to fit the need, rather than following a set plan with set measurements.
Step 1: Design
I wanted a music design on it, so I sketched out something the size I wanted for on the front flap. I grabbed his music books and took "note" of the size and thickness needed to hold them.
First I cut out the pieces for the front, back/flap, inside pocket, sides/bottom strip, leaving room for stitching.
It would have been easier and more uniform, if I had stained the cow before I cut out the pieces, but I didn't and I do like the mottled look from using a wool dauber to apply the dye.
Step 2: Image Transfer
Draw design on paper.
Trace onto tracing film (paper does not work well in wet conditions).
Using a stylus trace again onto damp leather.
Cut lines with a swivel knife into leather.
Stain and colour leather.
Step 3: Sew Now We Just Have to Put It Together.
I used contact cement to glue the bottom and side edges of the inside pocket to the back/flap .
Punched holes for stitching on the back/flap and front, counted the holes and punched the same number in the bottom/sides strip.
Attached a D ring on each end of the strip that I was going to use to attach the shoulder strap that may now never happen.
Attached the clasp to secure the flap.
I knew I wanted the front and back to be straight so I dampened the strip, so it was more flexible and as it was stitched I worked it into the shape I wanted.
When it was all put together, I marked the location for the handle to attach, riveted and sewed it on.
Under the strip of leather that holds the handle, I put a strip of flexible plastic to stiffen it and reduce the sideways flex. Also the D rings for the handle are pulling on the plastic and not the leather so it won't stretch out of shape.