Article by: Jim Picton - Aug.14,2015
Crawler Tracks
The making of Crawler Tracks always poses problems as to how to drive the tracks. We have all seen photos of how to make the tracks with several ideas on a driving wheel. We build them as described but with less than favourable results.
I recently saw a set of tracks made up but the drive wheel was not engaging properly. Wondering why, I spent an afternoon making up a test section of track to discover just why things didn't line up. The tread was made up with a 2-1/2" Flat Girder bolted to a 1/2" x 1" Flanged Bracket. To each end of this bracket were 2 Fishplates.
I tried running a Sprocket Wheel over the pins to see what the spacing looked like. The Sprocket ran rough and was not suitable at all. Then while staring at the section stretched out on the desk I realized that the Fishplates created uneven spacing between pins. The Bracket is spaced at 1/2" but due to the slot on the Fishplate the spacing between pins is 9/16" - There-in lies the problem. If 1" - 2 hole strips were to be used you would not be able to use the Flat Girders as they are over 1" in width.
I recently saw a set of tracks made up but the drive wheel was not engaging properly. Wondering why, I spent an afternoon making up a test section of track to discover just why things didn't line up. The tread was made up with a 2-1/2" Flat Girder bolted to a 1/2" x 1" Flanged Bracket. To each end of this bracket were 2 Fishplates.
I tried running a Sprocket Wheel over the pins to see what the spacing looked like. The Sprocket ran rough and was not suitable at all. Then while staring at the section stretched out on the desk I realized that the Fishplates created uneven spacing between pins. The Bracket is spaced at 1/2" but due to the slot on the Fishplate the spacing between pins is 9/16" - There-in lies the problem. If 1" - 2 hole strips were to be used you would not be able to use the Flat Girders as they are over 1" in width.
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Here we see a section of track showing the 1" x 1/2" Brackets and Fishplates being held together by Pivot Bolts and Jamb Nuts. We can also see that the spacing of the pins is different. This is why the drive wheel can not evenly grab the pins correctly.
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Here is a mock-up of an all Fishplate chain assembly. When stretched out the pins are all spaced evenly at 9/16 inch. Small Plastic Spacers are used to allow the drive wheel to run on with the Fishplates keeping the track centralized.
(Drive Wheel not as yet assembled.) This arrangement is a lot more challenging to build but once a routine is set up as to sequence of parts assembly, things move along quite nicely. |
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With this design the tread has to be mounted in a different manner. I used 3 x 1-1/2" x 1/2" Angle Brackets. 4 could be used for cosmetic reasons but this is just a demo sample.
The two Angle Brackets on the right edge are firmly bolted to the Flat Girder while the Bracket on the left is held in place with a loose Bolt and Jamb Nut to allow the tread to move with the Fishplates through the slot. The other reason for the Bracket is to keep the Flat Girder from flopping around. |
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Topside of tread.
Extra Bolts can be used to maintain a even pattern on the tread. |
This photo shows the different spacing of the pins using Brackets & Fishplates. 1/2" verses 9/16"
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C/L of Pins evenly spaced at 9/16"
More to follow regarding the Drive Wheel........
