Latest... and Farewell

On 11 January 2016 Kayla was put to sleep. She passed very peacefully, at home, content, and in our arms. She suffered from a brain lesion, probably a tumor or clot. We'll miss her more than words can say. Goodbye, our beautiful girl. Here's one of my favorite photos of her, snoozing away, all wrapped up and content.

01 Intro

Kayla demonstrating her wheelchair

Do you have a dog who has suffered some kind of disabling event, whether disease, accident or abuse? Does your dog have limited mobility? You may have searched online for dog wheelchairs or carts. There are some excellent models out there, some custom made, some fully adjustable. Unfortunately, all are expensive.

If you're like me, you'll go to the ends of the earth to find a way to make life rewarding and as stimulating as possible for your canine family member. Our three-legged dog, Kayla, had a tough start to life, losing a rear leg in very traumatic circumstances. Since then, she has developed Spondylitis in her lower spine due to the constant hopping impact when walking. She also has some ligament issues in her remaining back leg.

I did a lot of research, and after reviewing all the different cart designs out there, I thought I could come up with something that would work, and so decided to attempt to build one myself. My goal was to make a functional rear-end support, using basic materials and at minimum cost. I have little formal training in this kind of fabrication, though I can turn my hand to most things. I did however once work for a software company that produces industry-leading CAD (Computer Aided Design) and 3D modeling software, so I was able to experiment with a couple of ideas along the way.

All the materials for this project were purchased at local hardware stores. I'd like to plug Ace Hardware and their excellent range of fixings and fasteners, but I also made good use of Home Depot.

I can accept no responsibility for the results if you choose to use the information presented here. It's offered simply in the hope that it encourages someone to build a cart that helps their own canine best friend. This site is presented for non-commercial purposes; please do not copy for personal gain. (c) Peter Heald 2009 - 2016.

02 Frame

I spent quite some time looking around at options for constructing the frame. Thin solid or hollow alloy tubing would have been strong enough for a small dog, but Kayla weighs in at 45lb. Solid steel bar was too heavy, but half inch diameter cold-rolled steel tubing is light enough and strong enough, a good compromise, plus many wheels are designed for half-inch axles. Cold rolled steel (marked CR) is typically a little stronger that hot rolled for the same sizing. Many local hardware stores have selections of rods, angle iron, sheets and tubes aimed at the hobbyist, usually to be found at the end of an aisle. My local Ace Hardware had 48-inch lengths of CR half-inch tubing for around $12.

The first thing I did when I got the tubes home was carefully and accurately mark them at key divisions, say every 6 or 12 inches, using a wax marker. It's a lot harder to measure these accurately once the tube has even a single bend in it!

Be sure to mark the pipe before bending

A four foot length of tubing turned out to be pretty much the perfect length. Width of the frame at the back needed to be around 12 inches, to give Kayla's back end plenty of clearance (and to make the cart wide enough to not topple too easily if she tried to turn while running). Since I planned to use large 14 inch diameter wheels, the axle height would already be 7 inches off the ground. So I decided to start by bending the tubing into a 12-inch wide U-shape.

I'm being a little vague on measurements, since every cart will be specific to the needs of the dog. Just be sure to provide clearance should your dog need to hop.

A word about pipe bending. I managed to find a decent pipe bender (a Ridgid 36132 model 408) on Ebay for relatively little, but then again I'm a tool freak. It's quite possible to bend the tubing without such a tool. Just be sure to take precautions against flattening the tube at the bend. An effective way to do this is to compact sand in the tube prior to bending. The sand will resist the temptation of the tube to collapse. Bend the tube a little at a time, around an appropriately curved object, such as a lamp post, power utility pole, or even one of those iron pipes they embed in your garage floor to stop you driving into your water heater or furnace. (That's how I put the gentle bend into the shoulder bar.) Once the bends are correct, empty out the sand. As an aside: my Dad's uncle Ern was a professional industrial pipe bender fifty years ago, bending huge pipes (many inches diameter) on a big jig by, you guessed it, first filling them with sand.

Fill the pipe with sand to stop it from flattening

Whether using a tube bender or not, be sure to work away from the center of the tube. In other words, once you've bent one side, say, by bending from a given wax mark, bend the other in a mirror-image of the first, so you're still bending from the equivalent wax mark on the other end. Why? This way, if the first bend isn't exactly as you expected - perhaps the bend radius stretched or shrank the tube very slightly - the second bend will make the whole thing symmetrical, so it's not the end of the world. This is also where your pre-measured wax marks will be a great help.

Keep all the bends on the same flat plane, aided by using a spirit-level. Minor corrective tweaks are possible afterwards so don't break into a sweat if the thing doesn't lay exactly flat first time.

Keep the bends in the same plane

Next, bend the tube to form the wheel axles. If you have enough tubing, be generous here, because some wheels have quite wide hubs - perhaps three or four inches. Also, if you intend to make your wheels splay outwards a little for reasons of stability (much like many modern human wheelchairs do), now is the time to tweak the bends slightly to achieve that. Bear in mind that some wheel hubs are not designed to take that kind of angular strain, but most will be fine. See the 'wheels' section for more information on hubs and bearings. Once you have finished bending your first frame tube, it should look something like this:

The main vertical pipe and wheel axles

Now to form the second part of the frame - the horizontal piece that should rest lightly on the dog's shoulders, with the shoulder bar vertically in line with the front legs to avoid any pressure on the back or neck. When you measure and bend this tube, hold it up against your dog as a sanity check that all is as it should be. My tube bender let me do some tight bends close to each other. If you are not using a bender, you can achieve similar but simpler geometry by putting a gentle bend into the long 'arms' of the frame rather than the 'up and over' close bends shown here. Also, the addition of a very gentle arc to the shoulder bar will help with comfort once the padding is on.

The horizontal pipe for the shoulder harness

Congratulations - the most nerve-wracking part is over!

Update: I revisited Ace Hardware to track down some info on the parts I used. I have no affiliation with Ace, I'm just supplying this info as a courtesy.

Steel tube (1/2" cold rolled)
SKU# 5014634 (in the hobby metal section)
UPC 0-53538-35410-7

03 Wheels

To be completely honest, the wheels were the first thing I bought. I had a very clear idea of what I wanted. They had to be large diameter, to cope with grass and dirt, and to roll with the least resistance. They had to be light weight, and they had to have steel bearings in the hub. There were some wheels in the local hardware store, but they were all steel and very heavy, even the small ones.

After a few searches on eBay, I found exactly what I wanted. A pair of wheels for a grass cutter, designed for a half-inch axle, and for just twenty-something dollars. I found others on eBay that almost fit the bill, but they had 'nylon bearings', which are not really bearings at all. If you don't find what you're looking for right away, on eBay or Craigslist etc. then don't give up - you'll find them. It took me a few days to find mine. You might even try lawnmower parts specialists.

A pair of grass cutter wheels found on eBay

You might want to hold off fixing the wheels to the axle until after the two parts of the frames are joined, depending on how easy it is to unmount and mount them. I couldn't wait - I wanted to try out the wheels. To secure them, I had planned to use large washers and a couple of split-pins through holes drilled in the tube, but in the end they were a good tight fit and didn't need anything apart from a couple of shiny press-on caps to hide the tube ends. With the tube secured in the vice, I used a heavy rubber mallet to avoid damaging the wheels.

Tap the wheels on to the axles with a soft-faced mallet

Ensure the wheels turn freely, and double check alignment and camber (rolling angle).

04 Joining Frames

Joining the frames was a problem I thought long and hard about. I came up with various schemes, and even considered brazing them together. I didn't want to use any kind of clamping plate, since that would interfere with the belly sling. In the end, a chance discovery in my local Ace Hardware store solved the problem for me. I found a threaded core that would screw into the inside of the tube. The core, designed I think for furniture assembly, is threaded on the inside to take a bolt, and has a coarse thread on the outside. It's cut across the top to take a large screwdriver, so I was able to screw two of them into each tube end.

Two threaded cores screwed in to each pipe end

Although the cores were a fairly tight fit, I wanted to be sure they wouldn't move, so I thoroughly cleaned the inside of the tube ends, then added some strong metal adhesive as I screwed them in. Let the adhesive cure completely before attempting to assemble the frame, even if it takes a couple of days, but do screw the bolts in occasionally to ensure the thread doesn't get gummed up. If you can't find cores that fit exactly, you could try crimping the tube very slightly to stop the cores from migrating out the end of the tube during assembly.

Please read this! Why use bolts in this manner? The tension in the bolt compresses the joint. It's this clamping action that provides most of the strength in the joint. Don't be tempted to cut a thread in the vertical tube, or to just glue it all together, since you'll actually be reducing the joint strength, and it will be difficult to correct any flexing. The key is to ensure the threaded inserts can't move (screw them in very tight and be sure to let the glue set completely). This way, you can even tighten the bolts later should you need to - and of course, you can take it all apart too, for storage or travel.

Use a rasp or curved file to shape the ends of the tube to fit the vertical tube nicely, so the join is flush.

Hex bolt and washer test fitted to the threaded cores

It's important to get the location of the join exactly right, unless you want to make the frame fully adjustable by drilling a sequence of holes. If your dog is over a certain weight, I wouldn't recommend that, because too many holes will weaken the tube at a point where it might be vulnerable to flexing. Get someone to help your dog to stand naturally, or as close as possible given his/her likely back-end trouble, and hold the frame so you can judge the right point for the join. Most important is that the horizontal frame be slightly higher that your dogs belly, so that resting his/her belly in the sling will result in your dog's back being naturally level. See the 'belly sling' section for important information about its role and design.

The two frame parts finally joined

With the correct points marked at the exact same distance from the ground, clamp the frame in a vice and use a punch (or a large nail) and a hammer to notch the tube. This will help the drill bit start without wandering all over the curved tube surface. Use a small bit first for a pilot hole, then a drill bit that is exactly the right size for the bolts you're using. You don't want the holes to be larger - it'll introduce unwanted movement in the joint. Clean up the holes and assemble your frame... then do a little dance!

Update: I revisited Ace Hardware to track down some info on the parts I used. I have no affiliation with Ace, I'm just supplying this info as a courtesy.

Metal thread inserts (8/16" male, 1/4" female)
#329-4 (found in one of the red-marked trays)
UPC 0-39008-17564-9

05 Harness

The harness was another part of the project that I thought about for a long time. Since this wheelchair is for back-end support, the front-end harness isn't really taking any weight - its main purpose is to keep the cart frame positioned correctly. Another important function - it stops the front of the frame from lifting and flipping over backwards if your dog decides to slip into reverse gear.

Some of the dog wheelchairs out there include custom harnesses, and some list harnesses you can buy separately. These are certainly an option, but they are expensive. I decided a conventional on-leash chest harness would do the trick. These harnesses have two adjustable flat nylon looped straps, for the neck and chest, joined top and bottom by thick nylon straps - one between the shoulder blades, the other along the chest. They typically have a metal ring on the top for attaching a leash.

Click here to see the harness I used, but there are others that are much the same. I found this one for half price at PetSense, a discount pet supplies store. Be sure you get the right size; it should adjust to be firmly around your dog's chest, but not constricting in any way. If you can easily insert a couple of fingers between a strap and your dog's chest, that's probably fine. Make sure your dog's neck strap is not uncomfortably tight. Remember - this harness isn't taking much weight. Depending on your dogs size, body length, and neck length, you might need to move the leash ring or insert another onto the harness at a better spot. You'll be able to figure this out once your dog tries the wheelchair for size.

Also - make sure the harness is fitted correctly! With some models, it's easy to mistakenly fit it upside down, which will be very uncomfortable for your dog.

06 Shoulder pads and hook

Thinking back to my childhood, I remember playing with the pipe insulation my Dad had lying around when he was remodeling the house. When wondering how to cushion the shoulder bar for Kayla, this stuff seemed perfect. I bought a length of it, designed for half-inch pipe, from Home Depot for 97 cents. I also bought a snap hook to attach between the shoulder bar and the chest harness ring. Make sure the snap hook has a large enough ring to slide along the shoulder bar tube.

The snap hook and pipe insulation (for padding)

Loosen the frame bolts and slide a couple of lengths of pipe insulation down to the shoulder bar, with the snap hook in the middle. Cut enough insulation so both butt up against the tube bends, thus holding the snap hook in the middle of the shoulder bar.

The snap hook and padding in position

Don't open the pre-cut slice in the insulation - that'll take some of its strength away.

07 Belly Sling

Now for the part of the project that is definitely outside my area of competency! To complete this step, it helps a great deal if you have a significant other who is a wizard on a sewing machine. My wife is a dressmaker, so I lucked out there! Actually, being something of a control freak, I'm not too proud to say I asked her to show me how to do some of it.

I had intended to get some material similar to that used for backpacks; some kind of strong thick nylon. While self-consciously perusing a local fabric store, I realized that the leg of an old pair of jeans would not only do, it was probably even better than nylon. Denim would have some 'give' in it, which would surely be more comfortable for Kayla.

An old pair of jeans sacrificed for the belly sling

A few important points about the belly sling. I'm very aware that having a dog place some of its weight on its soft underbelly for lengthy periods can't be a good thing. Personally, I don't even like laying on my belly. But, there are some mitigating factors here for Kayla:
  • She is still able to walk, so we'll only use the wheelchair for longer hikes, and probably only for the latter part of those when she tires.
  • I want her to still take some of her weight on her good leg while using the wheels, if we can possibly get her used to that, since I don't want her to stop exercising her good leg completely. I want the cart to take enough weight to stop her hopping heavily and aggravating her spinal complaint.
  • With one leg completely missing and the subsequent muscle wastage around her hip on that side, her back end is very light.
So what about your dog? Every dog should be evaluated according to its own situation. Is it a small, light dog or a big heavy dog? Does it have the use of one leg? Do you intend for the wheelchair to be used a lot, and for extended periods?

Don't despair if you decide the belly sling solution isn't for you. There are other options. For example, we have a body sling (click here to see a similar one) for Kayla, that I use for helping her climb stairs. It has a handle on the back so I can lift her like a suitcase, though in fact I just take enough of her weight so she can navigate the stairs herself. It would be a simple matter to have this attach to the frame instead of the belly sling, and in fact I may do that if Kayla becomes sufficiently accustomed to the cart to want to use it more. The point is - do what's best for your dog.

Anyway, back to the belly sling. Cut the leg off an old pair of jeans, and trim the length so it is approximately three times the span of the frame. Wide velcro strips will be used for securing the sling, so there needs to be plenty of overlap. Also, being generous with the length means the sling 'sag' can be adjusted to fine tune its height, and perhaps to be a little more comfy too.

Attaching velcro to form the sling loop

I stitched all around the edges of the denim, and in a line all the way up the middle, to add some strength and to make the two layers of material act as one. Next came the velcro. I bought the 3M version of velcro because they came in packs of two inch by three inch adhesive-backed patches. The adhesive was enough to hold the patches on the denim while I figured out exactly what placement was needed, then my wife securely stitched them on. She had worried that the adhesive would gum up the needle, but the 3M patches didn't have lots of gummy glue, so it worked out fine.

The sling and harness in place

As you can see from the photo, the idea is to provide plenty of surface area for the velcro so it forms a very strong link, and also so the sling can be loosened to let it sag a bit if necessary.

08 Summary

Put it all together, and you have your doggy wheelchair. I've seen a lot of advice online to the effect that your dog is much more likely to take to the cart if you get him/her used to it while the dog is still independently mobile. Kayla is a very tolerant soul and puts up with pretty much anything, but I still find I'm tweaking the position of the snap hook and the sag of the sling to try to get the best fit possible.

Kayla getting very bored with all the photographs!

Building carts for others?

I've been asked whether I would make doggy wheelchairs for others. I think it would be difficult and error prone to try to design and make a custom cart using only photos and measurements as a reference. However, I'd love to hear of anyone's efforts to make a cart!

What's next?

The next step is to paint the frame. My wife suggested a bright snazzy yellow to match the wheels...

Also, I'm considering adding a 'stirrup' for Kayla's foot. There are times when I don't want her to use her back leg. Other carts on the market have slings that hold the leg or legs either suspended behind or in front. I'm thinking of using one of the little dog booties we have, attached to a cord or chain, to suspend her foot under her belly. I'll post photos if I do this.

Thanks for taking the time to read the story of Kayla's wheelchair.

(c) Peter Heald
Oregon, USA, 2009.
California, USA, 2016.