I recently had a problem with my messenger bag. I purchased the M51 engineer's field bag a little while back to replace my former bag which suffered catastrophic strap failure. The field bag was actually an excellent bag, for awhile. Anyone who has read a review of this bag knows that Rothco, the company that reproduces the bag, is notorious for bad stitching and each bag is hit or miss as to whether or not it fails. Part of it is wear based, how hard you are on the bag. For me I carry about 10-12 pounds to school and back each day, which is about a 2 mile trip. Not that far but the bulges and size of stuff I was carrying caused the latch to pop off, and the cloth flaps which held the anchoring rings for the strap began to fray until one almost failed. The latch is a separate problem that I still have to deal with, but the strap needed to be fixed fast. In the reviews I read everyone said they broke out the sewing machine and restitched the flaps back together. I know nothing about sewing so I used the mechanical knowledge I do have.
My solution is a bar inserted into the bag and bolted on to the original thin bar that held the top rigid. The new bar supports the strap and takes the full weight of the bag. While it was designed with the express purpose of fixing my bag most messenger bags are similar enough that the solution can be adapted to another bag.
Lest I have discouraged you from the m51 bag let me say this: it is an excellent bag which has served me exceptionally. So far only the latch and strap have failed, everything else has been fine and has replaced my former bag fitting everything in despite being half the size, and I still haven't filled the map pouch or the all of the back pocket. It is comfortable, well sized, and filled with more pockets than I have ever seen. Add this to being cheep and it makes a bag that is absolutely worth having.
Step 1: Materials and Tools
Not much is needed for this, only one power tool and a few hand tools. Nothing to serious like a table saw or a CNC mill(which I really, really want).
Lexan sheet 12 x 24, .09 inch thickness. Weird thickness I know, but it was the thickest available at my local hardware store. The exact dimensions of the sheet are not super important. All you really need is a sheet wide enough to extend from one side of the bag to the other and have enough material to build up to a 1/4 inch thickness.
2 number 8, 1 1/2 inch eyebolts.
1 number 8, 1 1/2 inch bolt.
6 number 8 washers, I used finishing washers for looks.
Super glue which will work on lexan, if it works on fabric as well super bonus.
Total cost: about $25. The lexan sheet was the most expensive at $15, but I had a lot of leftover material, so it was worth it.
Power Drill, mine is old, I know. Its single speed with serious torque, but just about any drill will work. If you have drill press you have my envy and can certainly use it.
1/4 inch drill bit. The bolts I got were number 8, so they took a 1/4 bit. If you have different sized bolts you'll need the appropriate sized bit.
Screwdriver. This is really whatever type matches your bolts, mine was a number 2 philips.
Saw. This is flexible, any saw which can cut your lexan sheets. I used a miter saw, but almost any saw will work. Again if you have fancy shop tools like a band saw you can use them.
Measuring device. Whatever you got should work, I used a square with inch marks.
Clamps. Again whatever you got should work, I used the cheep clamps available at your local hardware store.