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Medium-Duty Metal Track-Based Dolly

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This section describes how to build a medium-duty metal dolly that will run along a track. It is designed to handle heavy cameras and tripods, but the cameraman must walk behind the dolly when moving. This makes it useful for digital video cameras with a flip-out screen, but may be difficult to use with a film camera when the cameraman has to keep their eye glued to the eye piece.

After working on a 16mm film, I quickly discovered a need to redesign my original PVC dolly to accommodate the heavier film cameras and tripods. During this redesign, I kept more detailed snapshots. Construction of the track is explained in another section.

The main components in this dolly design are 4 metal Tees and 4 metal 90º bends (found in or near the lumber section of a hardware store), and two 3' slotted L-shaped metal bars (found in metal working section). I cut the metal bar that appears vertical in this picture to make the short section of metal bar you see at the bottom of the Tee. All of this costs around $20-$30.

I assembled the vertical part of the dolly (the portion that appears vertical in the picture above) as follows. First, this is the piece that is shorter. The L bar is 36" long (3'), and I cut off 6" of it with a hacksaw to make the wheel structure for this odd end of the dolly.

I also shortened two of the 90º angles so they could fit on the 6" L bar and yet not overlap. Be sure to still allow two places to bolt onto the L bar (in other words, only remove what you must from the angles to fit them on the 6" L bar). I removed about 2" from each of the two angles, on just one of their sides. I recommend using a Mitre box for all hacksaw work (and hand drilling for that matter).

  

For added rigidity and structure, I drilled a second hole in each of the Tee braces (so there would be two bolts to secure it versus one along this direction of the structure). I strongly recommend this step. I used two Tee braces sandwiched around the slotted metal L bar. I did this for both end of the L bar I had cut, and then attached the short cut-off piece of the L bar to one end. I then attached the two 90º angle bends I had cut down (again, so that they wouldn't overlap on the short 6" L bar end).

I bolted this and every component of the metal dolly structure with 1/4" 20-thread (Coarse Thread) 7/8" long bolts, a 1/4" hole 1-1/4" diameter fender washers on both sides of any given hole in the L bar or Tee brace, and 1/4" 20-thread (Coarse Thread) nylon-insert lock nuts. In other words, through any given hole, there is a bolt head, then a fender washer, then it travels through the hole, then another fender washer then a lock nut. Here's the completed "vertical" section of the dolly:

I then attached the two un-cut 90º angles onto the un-cut 3" L bar, again always using two bolts for any given structure to insure rigidity:

I then took the same wheel components from the original PVC design (after spray-painting the wood to be flat black).

Each block of wood has had a section removed to allow for the bolts that are sticking out of the angle iron. The angle iron has been screwed into the blocks using wood screws. The skateboard wheels, which have two ABEC-5 bearings each and a bearing spacer, are bolted through the bearings into the angle iron (the angle iron comes with a 90º bend in it) with a 5/16"-18 (Coarse Thread) bolt of 2" in length and nylon-insert lock nut. The bolt head is a hex head and, as is obvious from the picture, the head is on the outside of the wheel. Due to the width of the wheels and the angle at which both wheels are to each other, the wheels can actually accommodate a range of sizes of track. This designs accepts a track from 1/2" to 2".

  

A bolt is locked with a lock nut through a hole in the angle bend that I had to widen to accommodate the bolt (using a drill), and continues on to a square block of wood. I used a 5/16"-18 (Coarse Thread) bolt of 2-1/2" length to attach each wheel block to the 90º angle bend, with the bolt head on the outside and the nylon-insert lock nut and fender washer on the inside. However, no matter how tight I made this bolt, the whole wheel block could still rotate. Fortunately, I didn't cut the excess end of the 90º angle bend, so I used one of the other existing hole in the bend to put a wood screw through to prevent the wheel block from rotating.

Here is a close-up of the short 6" end's wheel assembly:

  

Follow the same steps for the longer end of the dolly. Then attach the shorter end to the longer end using two 1/4" bolts and wing nuts (allowing it to be disassembled). Note the wing nuts are on the part of the Tee brace sandwich (which sandwiches the L bar) that attaches to the longer un-cut L bar. This is because you have more ability to insure alignment this way due to the back wall of the un-cut L bar acting as a backstop when assembling your dolly on location.

I found some small end braces in the wood work section of the hardware store that I attached with wing nuts onto the dolly to hold the legs of my tripod. The wing nuts are nice because I can always move them on location to adjust for various tripods.

  

I found some springs to help hold the tripod legs into place. They aren't terribly secure, but the weight of the tripod and camera fixes that. You can also use a durable twine or cord to tie the tripod feet in tight (and I carry twine just for this purpose while on location).

And finally you can spray paint the metal with a flat black. Use primer first! (Otherwise your paint will flake off the metal easily.) Don't paint your nylon-insert nuts at all (mask them off or remove them), and don't paint your wheel assemblies (except the block of wood) to insure the paint doesn't eat at the non-metal components (which can happen).

  

The next section explains the construction of a heavy duty track system.

The total cost to build this dolly was approximately $100. Most of the expense is in the wheels and bearings. The wheels were $18 for four, or $36 for all eight. Be sure to get the poly-urethane wheels (they are softer and run smoother and quieter), and don't waste your money on designer wheels. For the ABEC-5 bearings (or you can get ABEC-7, but don't get ABEC-3), buy them where they sell bearings for inline skates and you'll get a pack of 16 bearings (the number you require). Mine were about $20.

Be sure your bearings are the same size as the wells for the bearings in the wheels. Also, be sure that when you put the bearings in, you have them ALL the way in (they go in deep). If you buy them at a sporting good or skateboard shop, they can put them in for you, otherwise you can use the largest socket of a wrench and socket set that will fit to force them in. Finally, bearing spacers are optional but a good idea to get considering they are only a few dollars (they go between the two bearings of the wheel and thus are sitting in the very center of the wheel).

Be sure to construct with as little glossy metal as possible, since shiny surfaces reflect lighting used in filmmaking, often producing negative results. Hence most photography and cinematography equipment is black.

Finally, use nylon-insert lock nuts whenever possible. These usually require a good socket wrench to put on, but the advantage is they need a socket wrench to get off as well. In other words, they won't work themselves loose over time.

Here's a picture of this dolly being used by my friend, Kevin Brunkhardt, for one of my previous films, A Matter of National Security:



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