I use a backpack when I commute to meetings on my bicycle. A few days ago I stooped down to pick up something and the extra stress on the backpack straps caused the plastic ladder lock buckle to snap. The rest of the backpack is in good condition. Backpacks are only one item that uses nylon straps with adjustable buckles.
This Instructable will provide two solutions to a broken ladder lock buckle. One is for those who can weld and one for those who cannot. The welded version will show how to make your own ladder lock buckles. The non-welded version will show you how to use "D" rings, either those you purchase or those you fashion yourself.
If you make the "D" ring version, you will need "D" rings you purchase and a hacksaw or a Dremel tool with a cutting wheel.
If you make the ladder lock buckle version, you will need a hacksaw, a grinder, a vise, a hammer, and a wire feed welder.
Step 1: Stitching
I wanted to fix my backpack without cutting the stitching on any of the nylon straps. My wife says it is not difficult to make new stitches. But, I am trying to avoid that and leave the original stitching undisturbed. That means I will make a ladder lock buckle that begins by feeding part of it through the nylon strap loop sewn to the backpack. Shown is the beginning of the welded version. The next steps will describe using "D" rings for the non-welded version. Then I will explain how to make the welded ladder lock buckle. The ladder lock buckle will be easy to release with one finger. The "D" ring, non-welded version will be easier for most people to manufacture at home, even if a little more difficult to release.
Step 2: Non-welded Version
It is possible to buy "D" rings about the same size as the width of the nylon strapping. Although there is an on-line link in the previous sentence, look for them in women's fabric stores and in generic hardware stores. Cut about 1/8 inch from the center of the straight side on each. See the photo. Slip the nylon loop through the opening you make in the straight side. Two "D" rings are needed for each nylon loop. While this works very well, the straps may not release as easily or as quickly as they do with a ladder lock buckle. But, this makes a quick and effective solution.
The photo shows two "D" rings I made. See the next steps for more details.
Step 3: Making "D" Rings
If you wish, you can make your own "D" rings from rod. Bend a half circle in the rod using a piece of pipe. (The diameter of the pipe should be about the width of the nylon strap.) Bend the ends sharply. Leave an opening where they meet. Slip the nylon strap through the opening you made in each ring. Thread the strap under the bottom ring and the upper ring. Loop the strap around the upper ring and under the bottom ring. Pull tight.
Step 4: Protect the Strap Loop
In the welded version some welding will need to be done on the ladder lock while it is on the backpack. The nylon from which the backpack is made will melt with too much heat. The nylon needs to be protected.
Cut strips of paper, fold them over, make a roll, and insert the rolled paper into the nylon strap loop. Use four or more thicknesses of paper. These strips of paper will insulate the nylon strapping from welding heat in the rod used to make the ladder lock. The paper can remain inside the nylon strap loop forever.
Step 5: Protect the Nylon From Weld Spatter
Weld spatter will burn holes in the nylon backpack. Surgeons cover bodies with sheets that leave a hole where the surgeon wants to operate. I made something like that to fit around the nylon strap loop, using scraps of sheet steel. (First and third photo) I also bent a "U"-shaped piece to cover the nylon strap where it comes through the hole in the protective cover. (Second photo) This "U"-shaped piece goes into place first. Then the cover for the field slips over it. (Third photo)
Step 6: Bend 1/8 Inch Rod
I used some 1/8 inch steel rod that had been part of the mesh used to reinforce concrete. A friend built a garage and gave me stubs of wire about five inches long after breaking them off from the finished concrete foundation. Bend a piece of the wire so the space between the two halves is the width of the strap. Insert it into the nylon loop so it is surrounded by the paper from the last step.
Step 7: Buckle Design and Strap Pathway
This shows a profile view of the strap (red line) in its pathway through the ladder lock buckle. The gray portions show cross sections of the parts. The black area is the 1/8 inch rod from the previous step. The green areas are welds. The relative positions of the different parts are important to causing the strap to bind and release well. As much as possible, the orientation of the parts follows those of the original ladder lock buckle.
Cut a piece of 1/2 inch strap iron so it is as long as the strap is wide. Grind one long edge to 45 degrees.
Step 9: Begin Welding
Position the strap iron and tack weld it in place. When welding on the ladder lock buckles, keep a wet sponge nearby to cool the steel before excess heat can soften the nylon strapping. This is mostly a precaution. The paper strips from step 4 should be adequate to protect from excess heat.
Step 10: The Rest of the Ladder Lock
Weld a 1/8 inch rod across the ladder lock frame. Cut excess from each side. Grind smooth. Be careful about the shower of sparks from a grinding wheel or a cutting wheel on a Dremel. A concentration of sparks can burn a hole in the nylon backpack. Make the spacing approximate that on the original plastic ladder lock buckle. See the finished ladder lock buckle in the second photo.
Step 11: Pull and Release
The first photo shows how to pull the nylon strap to tighten it. The second photo shows how to push upward on the ladder lock buckle to release the strap. This works well with the backpack. It is easier to put the backpack on and take it off if the straps are loose. But, the backpack fits better, especially while riding a bicycle, if the straps are snug. Fortunately, backpack buckles are located at the front and side of the rib cage on each side, making the strap ends and the buckles easy to reach and manipulate. There is an advantage to the ladder lock buckles in that they can be operated easily with one hand. "D" rings are more likely to require two hands, especially for releasing them.