There is a large variety in commercial pro-styles. This design was made from some steel and wood that was laying around. This dolly holds a tripod. It has 12 wheels (from inline skates) and runs on 3/4" schedule 20 PVC pipe.
This photo shows the dolly in use - without the top. We pulled some slats from a bed to create a more even surface for the PVC to lay on. Also, grass getting into the wheels is a mess and causes vibration. Also seen in the picture are additional weights - in the form of rail road ties. Two 2.5 gallon water bottles should work just as well (at 7 pounds a gallon that's 35 pounds).
Although there are a number of areas that could be improved on the result is more than adequate for high-school use.
Step 1: Materials
qty 2 ) 24" x 2" angle 1/8" angle iron (cold rolled)
qty 3) 30" x 1.5" steel straps (1/8" thick)
qty 1) 4x4 piece of 1/2" ply
qty 12) inline roller wheel
qty 12) 3/8" NC bolt, spacers, nuts
qty 4) 3/8" NC bolts to hold deck (i tried standard, over-sized, nylox, and jam nuts).
*) wood sealant - rattle can
*) blue lock tight
*) black spray paint (with rust inhibitor) for frame
Step 2: Using PVC for Rails
Again - this is all made from used stuffs - the wheels, the plywood, the metal for the frame just happened to be laying around. Getting the top to fit was almost as difficult as welding the frame and the whole project took two weekends.
Check out the gap between the top of the wheels and the angle iron. It's about 3/16" of an inch. Getting the holes drilled a the right offset in the angle iron is critical.
In this finished results view - please note the 3/8" NC bolt, the outer spacer, the wheel, the angle iron, the inner shim, and the nuts. You can only view one of the nuts - but i have stacked two locknuts on top of one another. Notice the grass on the wheels (this is after the shoot).
Step 3: Wheel Selection
We chose to use twelve white wheels (2" dia) to run on .75" PVC because they fit the 2" angle iron. The larger wheels are softer (and newer) and had better bearings. At the last minute we popped out the 3/8" ID bearings from the larger wheels to put in the whiter wheels.
Bearings are either 5/16" ID or 3/8" and have the same OD and are interchangeable.
Step 4: Drilling Bolt Holes in the Angle Iron.
Don't just guess at where the wheels will go - do the math . Our 2" wheels have an axle at exactly 1" centered. We measured the desired wheel distance at 3/16 of an inch from the angle iron edge.
After the pilot hole was drilled I went back with a 3/8" and drilled to clearance.
Step 5: Frame
In jigging it up I cut the cross bars the horizontal band saw at 45 degrees. I tacked the whole thing and then checked for alignment - and did the final welds. I then welded on tabs (1.5" x 3" or so) to allow me to hook the deck on. It was great that tech shop has the tools to make this happen. I decided to drill the holes in the tabs from the deck side.
Step 6: Making Hoops
advise: if you want two nice hoops, make three or four and take the best of the lot!
second picture shows hoops welded to frame. i cut the remainder of the hoop off with a sawz-all.
third picture shows the painted frame with hoops and the pads to hold the deck screws.
Step 7: Deck
After constructing the frame I started looking around for a top. I wound up cutting some plywood from a bunk bed down to 33"x30". But as I started to work the piece I realized it was warped by 1/4". It really doesn't have to be flat for this application, and it turns out that the deck screws pulled it down.
In the next rev of this i would use HDPE (seaboard) http://www.usplastic.com/catalog/item.aspx?itemid=24607&catid=705 But that is going to cost about $90 for this size. (tap plastics). It works just like wood but you can't glue it. But it is clean in appearance and strong.
I used an aluminum guide to cut the plywood. Set it back 1.5" using the small side of a framer's square. Followed up with a skill saw.
Step 8: Making Clean Edges on the Deck With Skill Saw
Step 9: Cutting the Holes in the Deck
The third picture shows keeping the blade of the hold saw clean using a stick of wood workers wax.
Step 10: Aligning the Deck to the Frame
To do this i started by clamping the frame to the table, and then clamping the deck to the frame. I used an 1/8" drill as a pilot. each time i drilled a hole i left the pilot drill in the hole to maintain the board alignment. This is a nice trick if you have extra drill bits lying around.
The other approach would be to swap bits out, drill to 3/8" clearance and drop a bolt in.
Step 11: Finishing the Plywood
When using Deft - or other spray products be careful with the fumes. I sprayed out doors, wore a mask, and took breathing breaks.
Shown here is a dirty mask - all that dirt wound up on the mask and not in my lungs. Deft is clear and won't leave signs like this.
Plenty of ventilation is important. Don't spray around open flames, heaters or in a closed area.
Step 12: Bolting on Wheels
First off - bolt sizing. We found skateboard axles (bolts) to be either 7/16" NC or 3/8" NC. Garden variety bolts are generally National Course - written 3/8" NC. These have 16 threads per inch. Also available are 3/8" National Fine written 3/8" NF. In addition there are different grade strengths for bolts in both course and fine. Here is a chart http://dodgeram.org/tech/specs/bolts/SAE_bolts.html
But there are quite a few types of nuts that can be used. To the left are nylox nuts. Next is an over-sized nut which is handy because you can use two different wrench sizes. Third from right is a standard 3/8" nut. All the way to the right is a half-height jam nut.
The issue here is keeping the nut tight. As this is not an adjustment nut, a spring washer would have worked fine. I would have used these if the bolts were long enough. I wound up with two jam nuts and blue loctite thread locker. There is also a red loctite - which you don't want to use here as it is seriously difficult to take apart. Like some no foolin around bolt glue!
Step 13: The Finished Frame
Step 14: Bolts, Bearings and Fabbing Spacers
In the end I did not use the (standard) shaft washers.
I went to a skateboard shop to find the short spacers - nothing in 3/8. So instead I cut them out of a 1/2" OD aluminum pipe (which has 3/8" OD).
Aluminum can be cut using wood tools. - it's that soft. So I jigged up the bandsaw to mark the cut at the correct length. I put a pencil in the end of the tube to catch the spacer as I finished the cut - so it didn't disappear in the room. I then finished them on sand paper to take the edge off.
The fourth picture shows the parts on their sides.
Step 15: Bolt the Wheels On
Step 16: Deck - Top View With Hoops Visible - Complete
Step 17: Finished Dolly With Tripod Strapped On
I've still got some touch up to do. One of the wheels is rubbing on the deck so I will pop the four wing nuts off and route along the path of the nuts. The wheels tend to pick up debris - and that can make them stick. But over all - the twelve wheel design seems fine.
Really - there are always things that we could add, but this is so much better than what we started with - nothing! And that's about what it cost us to build. Maybe $40 including the PVC.