Building a rotocast machine, expert opinion welcomed -gears, sprockets, collar shafts

ThrowingChicken

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I am not quite sure where to stick this thread so moderators feel free to move it if you need to.

I am working on hiring a welder to make me a steel frame for a rotocast machine, but before I give him the go order I really need to make sure I am am not blowing it somewhere. I based my build off of this DIY and the Stelter Creative machine.

Here is what I have come up with so far.


The main frame is to be welded out of 1" square steel tube, and will rotate on 1/2" shafts. After settling on my shaft size I was able to purchase all my bearings, so I am not planing to change shaft sizes, but where I am left a little unease is with things like the roller chain and sprockets, and the method of securing the shafts to the frames.

For the chain and sprockets, I was looking at these 1/4" pitch sprockets with corresponding chain from McMaster-Carr. They appealed to me because of the narrow width, but after finding out the chain size is smaller than that of your normal bicycle chain I've become a little concerned about their strength for this application. They have a working load of 114lb, but I am not sure how that translates to something like this. My concern was compounded when I found a dealer for them was in the RC car business.

With the shaft and frame connection, I found mountable flange shaft collars, but they were a bit expensive so I started looking at these weldable kind (which are also a bit expensive when you need to buy 8 of them). The thing I don't fully understand about the weldable shaft collars is how you can loose or tighten them once they have been welded in place. I could just leave it to my welder to figure out but I would like to make sure I understand it just in case he is also at a loss. If there were something besides these shaft collars that would be a better solution to the problem then I'd be happy to hear some suggestions.

Additionally though to a lesser degree, I have to admit I have a little worry about the miter gears I have selected. I don't mind if I try these out and they only last me for so long and I have to replace them ever few weeks or months, but if they are a complete failure from the get go I worry I may have built myself into a bind if I can't find corresponding sizes made out of more lasting materials like steel. But, I have been told by someone who did tech work in the medical field that the miter gears on their massive cat scan machine were made out of nylon, so there is some easement of the mind there.

Before anyone mentions it, yes, the motor is missing from my diagram. Once I figure out suitable sprocket sizes I will know how to handle its implication, BUT as far as what motor I should use I am still not totally sure. I found this beast of an AC motor my grandpa used on his band saw before he passed, but it looks like I would have to use a pulley system to reduce the speed, but that still crosses out on-the-fly fine turning, so I will probably have to turn to a DC motor. I am thinking about picking up an old treadmill motor since you can find them for relatively cheep. Any thoughts on that?

Anyway, those are were my concerns lie. If anyone has any expertise and suggestions please share. If this works out I will be happy to add construction photos and all that jazz to show it works, and maybe others will end up building their own. It will not be as epic as Stelter's machine, but for the shavings of DIY (at least, partial DIY in my case, even better if you can cut metal and weld yourself) I don't think there will be much room for complaints.
 
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Re: Building a rotocast machine, expert opinion welcomed -gears, sprockets, collar sh

Thanks for the link. If you don't mind, what were the costs and size of the one you got from them?
 
Re: Building a rotocast machine, expert opinion welcomed -gears, sprockets, collar sh

I actually had them do a custom build for me- I'll have to look up the pricing when I get home tonight. They were the best cost around that I found- extremely easy to deal with, as well.
 
Re: Building a rotocast machine, expert opinion welcomed -gears, sprockets, collar sh

Thanks, let me know what you come up with. Even if it's just a rough figure, should give me an idea.
 
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