Friday, January 2, 2009

The wheels on the cart go round and round, part one

Let’s get some nomenclature straight first. The hub is the center piece which mounts over the axle. The spokes (if it’s not a solid wheel) radiate from the hub to the felloes (or sometimes fellies). The felloes are the parts of the circular structure which holds the spokes in place and to which the tire (or tyre for our friends across the pond) is mounted. “Wheel” can refer to either the circle of assembled felloes or the whole assembly of hub, spokes, and felloes. The tire on traditional wooden wagon wheels is usually a welded hoop of iron which is heated to expand its diameter, then forced tightly over the wheel and cooled in place for a snug fit.

Tires

Metal tires offer advantages for large wagons on dirt surfaces, but for SCA use they are disastrous. They're unacceptably noisy on asphalt, concrete, or gravel (we're talking fingernails on chalkboard annoying), will tear up wooden flooring, and snag on carpet. And they’ll get rust on everything in the trunk with them. Sometimes you can find nice spoked small wagon wheels with metal tires for sale on the internet at a not too exorbitant price. If you want to use a set of these make sure you check the quality of construction and strength. Many are suitable only for stationary lawn decorations. However, some are very nice, and if you’d rather buy than make, by all means do, but you’ll still want to cover the metal as below.

What about commercially produced wheels? There are ready made plastic wheels with hard rubber tires made for lawn mowers, small metal and hard rubber tires, like on a radio flyer, and even heavy duty pneumatic tires for use on wagons for warehouse use. I’ve used all of them successfully on small wagons, but they are hopelessly mundane. One of the goals of building a small wagon for SCA use is to make something that doesn’t scream 21st century. Commercially produced wheels will cost you as much or more than wooden ones and without doubt will spoil the ambiance we’re trying to achieve.

The wooden wheel needs a tire of some sort. If you skip this part the wood will pick up bits of gravel to the subsequent detriment of any flooring you roll over. It’ll chip, splinter, and crack along the edge at an unbelievable rate. I’ve tried many different wheels over the years and can say unequivocally that the best tire for our purposes is automobile heater hose. It wears exceptionally well, doesn’t pick up gravel, and is readily available at a reasonable price.

Applying duct tape over the wood of the wheel or a metal tire DOES NOT WORK. I’ve tried duct tape over the wood, over metal, and over heater hose. The tape abrades quickly; turning into a sticky mess that both spreads sticky crap to the floor and picks up all sorts of disgusting or abrasive junk. Then it dries out and spreads silver dandruff all over the house. Don’t do it. Leave the duct tape for your armor; where it belongs.

Bicycle tires can work, but they are designed to be used with an inflated inner tube, and have several drawbacks when used over a wooden wheel. They must fit tightly over the wheel and getting this tight fit is a pain. There is a wire at the side wall of a bicycle tire that prevents it being slipped over the wheel. If you do use a bike tire, you’ll need to cut the wire on at least one side. If the tire does not fit tightly to the wheel it flops around just like, well, a flat tire on a bike. If you’ve ever ridden a bike with a flat you can imagine just how much harder it is with four floppy tires.

A non-steel-belted automobile tire can be cut up and used, but it is very difficult to attach to a wheel less than 1.5” wide. The only way I’ve found to attach it is to screw it directly into the rim every few inches in the tread depressions. It’s a lot of work, but if you have an old tire, are really cheap, and don’t care if it looks like crap you can try it.

There are rubber tires made for modern roadable wagons such as the Amish still use, or those cute carriages around Jackson Square in New Orleans. These are not useful for a small wagon like we’re building. They have two heavy steel rods built into them, and require a special welding jig to compress the tire onto the wheel and expose them and weld them together, and they need to be set into a dado in the felloes. If you’re building a full size wagon for use with draft animals I’d strongly suggest buying the wheels from one of the Amish carriage shops. If you want to learn all you could ever want to know about how wagon wheels are designed and made read George Sturt’s, The Wheelwright’s Shop (ISBN: 0521447720). Yep, Sturt, not Stuart. If you want to see wheel making done in a really neat wheelwright shop, the one at Colonial Williamsburg is waaaay cool.

The best choice I’ve found for the small wagon is to use a length of automobile heater hose, slit it lengthwise, butt the ends, and SCREW, not tack, it onto the wheel sides.

Axles

Strictly speaking the axle is the part that fits into the hub on which the hub rotates. The cross piece that supports the axle is the axletree, and the piece that rides on the axletree and supports the bed is the bolster. An axlerod is a one piece metal axle or a twit in a BBC sitcom. On the small wagons I build I refer to the metal rod that passes through the axletree as the axle rod. In a full size wagon for heavy hauling the axle profile is not cylindrical, but conical. There are lots of really good reasons for this having to do with the physics of using a wagon on a sloped road where one side is higher than the other. We don’t have to worry about that, or dished wheels, either.

For my wagons I prefer to make the axlerod from 7/16 " round bar stock, but i've used 3/8” to ½”. 7/16ths will exactly fit a bearing from 1/2" pvc pipe and slide perfectly into a 9/16ths hole in the hub. I wish I could say I determined this through esoteric and complicated calculations, but I just happened to have some barstock in that size that I picked up on sale for about 2 bucks. There is no reason why you couldn’t use steel pipe as long as you beefed up the axletree, but it would be heavier, and not appreciably different in cost or availability.

Do not use threaded rod for the axle. It will quickly chew up the hub and lead to the wheels wobbling or binding. And you know those nifty bolts with the metal sleeves that lawnmower wheels are attached with? Fugeddaboudid. They’ll work loose. Even if you seal the threads with locktite or epoxy. The only way to attach them where they won’t work loose is to drill a hole through them and pin them, not easy with hardened steel, and it mounts them permanently, so you can’t pull the wheels off for transport.

Wheels

At this point it's probably appropriate to discuss wooden wheels. There are several ways to make them; for this project I’ve chosen the simplest, cutting plywood disks. All four wheels will be the same size, as was done on the inspiration piece, the Dejbjerg Wagon.


There are some drawbacks to using wheels of the same diameter. The turning radius suffers if the front wheels cannot travel under the bed. If we allow the wheels to travel under the bed we must raise the bed on bolsters for clearance. These taller bolsters suffer greater strain the more the wagon is elevated and therefore need to be beefed up, adding to weight and materials cost. Also raising the bed raises the center of gravity making the wagon less stable. This can be an issue when hauling active children around. In this one we’ll compromise by setting the bed height to where it almost clears the wheels, this will make the wagon look less top-heavy and will allow part of the wheel to go under the bed, decreasing the turning radius.

You may have seen other carts or wagons with plywood wheels which wobble unpleasantly. The problem with most plywood wheels is that they are not made with hubs. I feel a hub with a minimum of 3" depth is required for adequate strength and stability. The hub should fit snugly on the axle. I also don't like having the wood of the hub directly in contact with the axle rod. Wood is not a dimensionally stable material. It also suffers easily from abrasion from the dust of the road. The hubs on this cart have the holes fitted with a bearing made from PVC pipe, and the measurements correspond to that. You could use copper pipe but you will need to adjust accordingly. I’d advise against bearings made from steel pipe. It is inevitable that moisture will seep in around the axlerod and will rust and squeak annoyingly, if not stop turning altogether, and making it nearly impossible to pull the wheel off when breaking it down for transport.

The wheels of the wagon are of 3/4" thick plywood, with a diameter of 17 ¼". They are from another wagon, but will serve our purposes here. This diameter was chosen for two main reasons: first, it was about the largest diameter I could obtain and still get 4 wheels from a piece of scrap plywood I had, and second, I already had two 17" disks of 1/2" plywood which I’d used in several prototype mock-ups, so I knew the diameter would fit.

Once you have cut out the discs they are screwed together temporarily with a 3" drywall screw through the center and sanded so the they round and true. The easiest way to do this is with a 10 or 12 inch stationary disc sander with a circle jig, but hand sanding with an orbital sander will work. Use a heavy grit and wear a dust mask.

The four discs cut and screwed together through the center

The hubs are cut from 2x4 stock. Cut eight round pieces 3.5” inches in diameter. Make sure you mark the center well. Divide the eight rounds into four for the inner hub and 4 for the outer hub. Ease one edge of the inner hub pieces. Taper the outer hub rounds to a truncated cone with a slope of from 5° to 10°. I used the disk sander with the table set to 5° and 50 grit paper, I could also have angled the band saw table when cutting them but that requires more precision than I felt like aiming for. Do not ease either edge of the outer hubs. If you don’t have a band saw and are using a sabre saw for this, I’d suggest either using a wide piece of stock, or just cutting it to octagonal shape. Cutting a 3.5” circle from a piece of 3.5” wide stock while holding it is a recipe for disaster. Remember, we’d like to finish this project with the same number of fingers we started with.

Wheel discs, bearings, and hub parts

Once the hubs are sanded you’ll need to drill a hole through the center on your drill press. If you have a drill press capable of handling an 8 5/8" radius disk drill out the centers of the wheels, too. If not drill with a hand drill. Note these pieces should not be fastened together before drilling--you are more likely to end up with an off-center hole if you do. The diameter of the hole is going to depend on the diameter of the axlerod with the bearing over it. Make the bearings, slide one on the axle, and drill hole that will be tight.

Next prepare the hub bearings. Using a table saw with a blade with a 1/8" kerf (or a dremel, or very carefully with a boxknife) rip an 18" piece of 1/2" OD PVC pipe down one side. You should use a throat plate on the table saw with a narrow opening. Also clamp a piece of wood to the rip fence to hold down the PVC pipe. It is so flexible it will otherwise ride up on the blade. This produces a "C" shaped cross section with an opening of 1/8". When a length of this is compressed it will have an outside diameter of 9/16" and an inside diameter of 7/16". Which is perfect with a 7/16 th dia. axlerod, which the Tractor Supply near my house used to carry, but as long as it is snug to the axle it’s fine.

A pair of hub bearings--the holes were intended to serve as grease cups, but this proved unnecessary in use

Cut four 3 3/4" lengths of ripped PVC. Compress one end and start it into the inner (eased) end of the inner hub, drive it into the hub piece with light blows of a hammer. When it protrudes about 1/8" through the other end start it into the wheel. Set the hub piece against the wheel and drive two 1" drywall screws from the inside of the wheel into the outer hub piece, securing it in place.
Slide the inner hub piece over the bearing. The hub pieces should now be firmly sandwich the wheel between them. Screw in two 3" drywall screws at 90 degress from the previous two. These screws will secure the inner hub and further secure the outer hub. If the PVC is proud sand it flush. The bearing in the picture below is covered with black tape to act as a shim since my 9/16ths drill bit had broken and I was forced to use a slightly wider one.

Here the outer hub (the conical one) has been screwed in place and the bearing is ready for the inner hub piece

The inner hub screwed in place

The tires are made from 3/4" diameter automobile heater hose. To make the tires first measure the circumference of the wheel and allow a little extra as a 'fudge factor'. Cut a length of hose to length. Note that the hose probably will have a curl set into it from storage on a reel. Lay the hose on your workbench curl up and slice lengthwise down the hose through one wall only. Spread the cut and work the hose onto the circumference of the wheel. About every one quarter of the way around stop and use a mallet to set the hose on more firmly. Continue putting on the hose until you reach the end. It should overlap about an inch or so. Stand the wheel on end and pushing down hard on the wheel roll the tire back and forth a few times to set the tire well in place. Now take a sharp utility knife and cut down evenly through both hoses to the wood of the wheel. Peel back one end and smear the ends liberally with sealant/glue. I used locktite ™ "stick and seal" others brands will probably work as well or better--test on some scrap first. Put the wheels aside while the sealant sets up. It should not be necessary to nail or otherwise fasten the tire to the wood--the 'sidewalls' keep it in place quite well.

The "stick and seal" is not really necessary. I do it because I obsess, but I have used tires with the ends simply butted with no ill effect.

It is a good idea to seal the edges of the wheel with polyurethane or a good primer paint before mounting the tires.





A pair of wheels mounted on an axlerod.

The took a lot longer to edit than I'd hoped, but it's also the most complex part. Part two, coming tomorrow morning will deal with how to make fancier wheels than a plain disc, and some more pics, including setting the tire.


Parts of a wheel with false spokes

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