NOTE - This Instructable is a 'work in progress'. I accidentally published it when I was trying to share the draft with a friend. I logged in today to try and 'unpublish' it, but found that it had been commented on. Instead of taking it down, I'll update it to clarify which pieces are 'concept' and then replace them as we go along with photos and descriptions of what we actually end up doing.
The pooch with three feet...
This is Abbey. She is an absolute sweetheart (and a bit of a goof). I recently adopted her from an Australian Cattle Dog rescue group in Arizona. Unfortunately, we don't have a lot of information on her background. What I do know is that she came to the rescue from a shelter in New Mexico. Sadly, the adoption statistics from this shelter were frighteningly low. As luck would have it, someone there knew of the rescue group in AZ and made arrangements for the transfer. She arrived at the rescue skinny, fearful, pregnant and missing a foot. Only two of the puppies lived, this was likely due to poor nutrition during the pregnancy. The good news there is that both puppies were adopted shortly after being weaned. Abbey stayed with them a while longer while they worked with her on her fear and 'shyness'. As to her missing foot, she doesn't really let it slow her down. She can actually move really quickly when she wants to. Her stump was already healed when she arrived at the rescue, their vet said that because of where it ends, it probably wasn't a surgical amputation. Their best guess was that she had lost it in a claw trap. Luckily, she lost enough so that it doesn't scrape or drag the ground.
While she does get around the house without any problems, I'd like to fit her with a boot that we can use for longer walks, hiking, etc. so that she doesn't have to carry all of her back weight on the one foot. That's the purpose of this article...
Step 1: Abbey's Boot
This is a shot of Abbey's foot, or rather, her stub. It's not easy to tell in a photo, but she actually has a very small piece of the foot left. It wasn't removed clean at the joint so when her leg moves you can feel that part moving around. This is the one factor that I see possibly complicating this project. We'll see how it goes...
Step 2: Alginate Casting
This is the concept I'm working with right now (of course, this is subject to change as things progress):
- Get a 'true to life' positive cast of her leg
- Create a 'boot' that will close the gap between where her leg ends and the ground to allow her to rest her weight naturally on both legs (imagine something that would work like a pirate's peg leg)
- Use the positive casting and the boot together, cast soft silicone pads to line the inside of the boot. Provided that the positive casting is accurate enough, this should make it very close to a perfect fit once all of the pieces are assembled.
The Positive Casting:
Because her stub get bigger at the end, I don't think a plaster casting is a viable solution without doing a two-part mold. After doing some research, it looks like a fast setting alginate may be the way to go -
- Spread a thick alginate mix over the leg
- Allow it to set, some formulas cure within a few minutes
- Once dry, it will hopefully slide it off like a boot. The flexibility of the alginate should allow it to slide over the wider part of the stub without destroying the mold.
(in the image, picture the black sock as the dried/cured alginate)
Step 3: Negative Mold
Now I have an accurate negative that I can use to get an exact model of her stub (including the wider joint at the bottom).
Step 4: Pour Plaster
Imagine this blue roll is the plaster that gets pored in...
Step 5: Stub Replica
After the plaster has set, peel the alginate off and what's left is the '3D model'...
Step 6: Silicone Casting
In this pic, the brace would be the leather boot (although I would probably use something just like this to secure it). Mix the silicone from the kit and pour it between the plaster stub and the boot. Let it cure and then remove the stub. Fitting aside, her foot would plug right in...