Dragline Crawler Build

[modelman]

Jim-welcome to the world of old shovel style tracks. This was a nightmare for me, but after many ruined parts I made it work. I don't think this formula will work for you because you have already determined your pitch by making the track pads first. All I can tell you is what I did. I think you need to wrap your pads around the sprocket and measure the pitch in the circle. Of course it will be different than with the pads lying flat but You will need to set the pitch that will work on the circle and in the transition from the flat to the circle. This is the tricky part. If the pitch is perfect for the circle the drive dogs may catch on the edge of the sprocket cut out. If you cannot make the math work on degrees you may have to change the dia. of the sprocket and this is where the never-ending circle begins. You may have to angle the sides of the drive dogs and put a greater angle on the sides of the sprocket grove to keep the drive dogs from catching on the edge. You may also have to round the top corners of the drive dog.Here is a diagram-

You may also have to have divider plates for your rotary table depending on how the math works. Good luck-hope this makes sense.

[RCP57]

This could be totally wrong but it worked on my Bruder dozer conversions. I took the chain pitch in my case- 0.375 and times it by the number of teeth I wanted. This number gives you circumference. Divide that by pi (3.14) which gives you diameter. Then divide this number in half which gives you(radius) the distance from center in which you need to cut the teeth. Divide 360 by the number of teeth and that's how many degrees apart they need to be. Use an end mill or drill bit to pop in the appropriate amount of teeth. For me making regular sprockets I then go back over them with a slightly larger cutter moved outward on the teeth. This gives the tips more angle to clear as the chain moves on and off of them. Clean them up a bit with a file and I'm good to go. It should be noted that your disc of metal needs to be slightly larger than your intended pitch circle for this to work. Hope this works if nothing else makes sense.

[modelman]

Originally Posted by RCP57

This could be totally wrong but it worked on my Bruder dozer conversions. I took the chain pitch in my case- 0.375 and times it by the number of teeth I wanted. This number gives you circumference. Divide that by pi (3.14) which gives you diameter. Then divide this number in half which gives you(radius) the distance from center in which you need to cut the teeth. Divide 360 by the number of teeth and that's how many degrees apart they need to be. Use an end mill or drill bit to pop in the appropriate amount of teeth. For me making regular sprockets I then go back over them with a slightly larger cutter moved outward on the teeth. This gives the tips more angle to clear as the chain moves on and off of them. Clean them up a bit with a file and I'm good to go. It should be noted that your disc of metal needs to be slightly larger than your intended pitch circle for this to work. Hope this works if nothing else makes sense.

Your math is good but chain drive pitch never changes. This type of track pads with the drive dogs coming up from the center causes the pitch to change when it goes around the sprocket. He can work it out with a few practice cuts (maybe).

[RCP57]

Originally Posted by modelman

Your math is good but chain drive pitch never changes. This type of track pads with the drive dogs coming up from the center causes the pitch to change when it goes around the sprocket. He can work it out with a few practice cuts (maybe).

Good point! I hadn't thought of that.

Looks like you have it figured now anyway Jim!

[Rvjimd]

Tom,

Thanks. I thought I would probably need to angle the drive dogs on the pads. I have dividing plates so I can try that if it comes to that. I think I might start by just making a few more samples and make them a bit smaller each to see if it get better.

Also, I figured it would be simple to just drill the holes like I did and use brass tube to see if it looked close. Then, if I get where it looks like it should work I will make an actual tumbler and mill it to look like it should.

Jim

[Rvjimd]

Reg, yea, that does make sense, thanks

Jim