Welcome to my Instructable detailing Leash Lock, a product that I've designed in my Senior Industrial Design studio course at Appalachian State University. Leash Lock is a product aimed a making dog walking easier for everyone, pets and owners alike. It uses a 3D printed handle to enclose a Figure 9 rope tensioner and a 1/2" tape leash, and provide the user a way to adjust and lock in the length of leash between themselves and their dog. Many problems, including tangling and tripping, can be solved simply by allowing having the appropriate amount of leash between you and your dog. Standard retractable leashes serve to keep the leash taught, but don't give the user any way to reel their dogs back in if they get into trouble. Leash Lock lets you do this manually, and provides a dog walker with superior control over their pet when walking, playing, and socializing.
I designed this product over the course of the Fall 2015 semester toward the goal of producing a limited number and testing them in a retail environment at a cost of $12. This event was successful, but as I don't have the capital to pursue patenting or further production, I've decided to release this Instructable detailing how to make one yourself using some easy-to-find hardware and a 3D printer. Alternatively, if anyone would like to purchase one, I still have a few left (shipping not included)!
Step 1: What You'll Need
In order to produce a Leash Lock dog leash, you'll need a couple things:
First, access to a 3D printer. I used my own Prusa i3 to produce the parts, but any decently-functioning machine should do. It's a fairly long print (8 hours on my setup), so be sure to have plenty of filament and calibration set for a long run. I recommend Hatchbox filament for a good quality/cost ratio.
Secondly, you'll need to order some hardware, which I'll provide links to below. You'll need (4) 6mm M3 screws (I prefer black oxide for aesthetic reasons), (4) PPB-M3-2 knurled press-in inserts, and one Figure 9 Rope tensioner.
Lastly, you'll need some half-inch webbing or similar material for the leash itself. I used some retired climbing rope in my limited run because it was inexpensive, easy to find, and strong. A standard tape leash of similar width should do nicely, though. If you choose to go the webbing route, you'll need to find a suitable clip, such as a carabiner, and a way to attach it to the leash. Tying or lashing should work just fine.
Step 2: 3D Printing
I've attached an .stl model of the handle and enclosure. As I mentioned in the previous step, it's a fairly long print, so make sure the machine you're using can handle it! I recommend ABS for strength, especially if you'll be walking a large or strong dog.
After printing you'll need to remove a significant amount of support material from the parts to make room for the leash and tensioner. I recommend 15% fill with 1.3mm spacing. Once removed, a bit of sanding or a sharp chisel will remove any material that might cause excess friction with the leash when pulling it through to shorten it.
Step 3: Assembly
Once you've got your finished printed pieces, it's time to start assembling the leash. Start by press fitting the threaded inserts into the 3D prints. You may need to add a slight chamfer to the holes first. This can easily be done by inserting a sharp pocket knife into the holes and twisting a couple times. Then press the inserts into the holes with channel locks or pliers. For best results, put something in between your pressing tool and the outside of the part so it doesn't scuff up the surface.
Second, install the Figure 9 rope tensioner into the handle. Insert it from the left side with the loop facing inward. With some force it should snap in. After that, slide your leash through the top of the left side, out the bottom, and then through the hole in the Figure 9 forming a loop below the handle. Tie a knot in the leash above the hole. Sandwich the Figure 9, the knot, and the leash in between the left and right halves of the handle checking to make sure that the leash can move freely when you pull down on the front of the loop. Finally, insert the 4 m3 screws into the handle to hold everything in place.
Step 4: Functional Notes
I've attached a brief infographic detailing the proper use of Leash Lock. Simply unwedge the leash from the rope tensioner and then pull down on the front of the loop that hangs below the handle to shorten the leash. Lock it back in place when the leash is at a satisfactory length, and unlock it to let it run out again. This simple but powerful feature allows a dog walker maximum control over their proximity to their pet and, therefore, a much more enjoyable experience all around.
I've also attached some spreads detailing how I came up with this idea and the process I went through to create it. Any feedback is much appreciated! I hope everyone enjoys.