Intro: Toy Mack AC Bulldog - Part I - Wheels
The photo shows a toy truck I made for my grandson. It is a facsimile of a 1920s Mack AC Bulldog dump truck.* It is not an exact replica to scale. It is made from steel scraps I have collected, including the outer skin from an old washing machine. The toy truck is about 14 inches in length.
This project will be described in several linked Instructables. Each will treat a different part of the project. I am providing an overview of the building process, but without exact dimensions and without all procedures described in detail. I had no exact plans to follow, only photos I found on the Internet of these trucks. I pinched my finger and thumb together to determine how many wheels would fit between two points in the photos I viewed. I knew the diameter of the pipe I was using for my wheels. That allowed me to arrive at a reasonably accurate set of dimensions for the toy truck. Part 1 will describe the process I am using for making wheels with five spokes and a large center hub.
* Here is a page with photos and some information about the Mack AC trucks.
- Google SketchUp
- Wood lathe
- Angle head grinder with grinding disc and cutting disc.
- Drill press and drill bits
- Hammer and center punch
- "V" block made on a table saw
- Vise-Grip pliers
- Cut off saw for steel
- "C" clamp
- Wire feed welder
- Wire wheel
- Measuring tools
- Marking pen (fine point)
- Steel pipe
- 3/4 inch steel form stake
- 3/16 inch steel rod
- Masking tape
Step 1: Cutting Wheel Rims From Pipe
I have some steel pipe with an outside diameter of 1 7/8 inches. The wall of the pipe is a little more than 1/8 inch thick. The ends are not square or smooth.
I am cutting rings from the pipe to make the wheel rims. I mounted the pipe on a 2 x 2 inch length of pine wood I am able to mount on a wood lathe. Then I used an angle head grinder with a cutting wheel to separate the rings from the rest of the pipe.
Step 2: Mark the Wheel Rims for Drilling
The points of a pentagon are 72 degrees apart from one another. I used Google SketchUp to make a precise pentagon. I could mark the exact center, add concentric circles for centering my wheel rims, and add radiating lines to mark the drilling points for the wheel spokes.
In the photo you can see how the various concentric circles are used to center the wheel rims as accurately as possible. I covered the outside surface of the wheel rims with masking tape and marked the position of the radiating lines. I used a square and measured to mark the centers of the holes. I used a center punch to make an indentation for accurately starting and drilling a small pilot hole.
In this photo, the pilot holes have already been drilled and then expanded for the 3/16 inch rods that will make the spokes. This photo does not represent an actual step, but illustrates what the final outcome will be.
Step 3: How Drilling Was Done
I made a "V" block for holding the wheel rims on my drill press. The vertical line was drawn by following a drill bit in the drill press with a marking pen. The flat piece across the back of the "V" block helps to keep the wheel rim vertical. The line helps to get the location of the spoke hole at the very top of the wheel rim. Still, there are several things in this process that require using one's eyeballs rather than a precise indexing tool. Little inaccuracies can creep into the process, especially when drilling spoke holes in the smaller hub.
In the photo the masking tape is still on the wheel rim. After all of the holes are drilled, the tape can be removed.
Step 4: The Hubs
I found a concrete form stake on the road while out riding my bicycle one day. I used a cut off saw arrangement (See this Instructable for how I made it.) to cut sections from the 3/4 inch diameter round stake. The aim was to make the hubs the same width as the wheel rims.
Just as with the wheel rims, I wrapped the outer surface of the hubs with masking tape and used the Google SketchUp pentagon pattern to center the hubs and mark where the five spoke holes are to be drilled. It was not easy to hold the hubs in the "V" block for enlarging the small pilot holes. Eventually, I used a Vise-Grip locking pliers to hold the hubs, but that also opened the door for slight inaccuracies. See the second photo.
Step 5: Alignment Jig
It would be very easy to assemble the wheel parts (rim, spokes, and hub) so that the hub is still badly off-center. I turned this jig on my lathe faceplate. Both the rim and the hub fit into recesses to center them. Still, the spokes will be welded to the rim.
In the photo burn marks can be seen from welding the spokes into the rim of the wheel. A rim and a hub are also shown in the photo, but they have not been drilled, yet.
Step 6: Prepare to Weld
The spokes fit snugly into holes in the hub. The spokes are sized so the end is a little below the surface of the rim. The parts are fitted in the jig from the previous step. I used a "C" clamp to hold the hub down. The welder's ground clamp attaches to the "C" clamp to complete the welding circuit, but the ground clamp does not show in the photo. I used a wire feed welder.
I welded one spoke. Then I fitted another opposite it and welded it. Eventually, I had all five spokes fitted and welded in place. After welding all five spoke ends at the rim, I ground excess weld bead the outer surface of the wheel rim smooth.
Step 7: Drill the Axle Hole
I decided I want the axle hole to be as precisely on center as possible, even if the hub might be a tiny amount off-center. I used a center finder I made to mark the center of the wheel on some masking tape. (See this Instructable for how I made this center finder.)
Step 8: A Nearly Finished Wheel
This is my first wheel of four. It appears the hub is not quite on-center, but the axle hole is. The wheel will roll smoothly, and that is the most important part. (I did eventually make five wheels and set aside the one wheel on which the hub was the least centered.)
I did use a small wire wheel to remove rust inside the pipe that became the wheel rim, but the photo makes it appear quite a bit remains. There is not quite as much rust as it appears, but I will use a wire brush on a Dremel tool to remove more, yet.
Step 9: True the Wheels on Their Centers
As careful as I was, the axle holes were not quite perfectly on center. I have a radial arm saw, but a drill press would have worked, too. I cut a piece of 3/16 inch rod and threaded one end. The nut on the threads was tight enough to make the wheel spin. I held an angle head grinder lightly to the rim to true it so the axle hole truly is the center of the wheel. This was useful for truing the side edges of the wheel rims, too.
See the next installment in this project here.