substitute for rack and pinion for a 4'x4' cnc

[luther]

hello, i was wondering if i could use a roller chaine and sprocket for a substitute for rack and pinion? and how to mount it thanks.

[joecnc2006]

The problem with a chain is you will not have enought teeth contact and will get alot of slop and backlash in the system.

Joe

[massajamesb]

Originally Posted by luther hello, i was wondering if i could use a roller chaine and sprocket for a substitute for rack and pinion? and how to mount it thanks.

These are plasma cutting machines, but it gives you an idea of how it works.
Plasma Table Build Log Including Free Plans Link, & Pictures by Weldtutor

and the last page of Smilewizards' thread,
4 x 8 Plasma Table Plans

I wouldn't say that chain is not an option, if installed correctly I believe you could get most of the slop out.

Perhaps it is not accurate enough for routing, but I know that it does work well on other machines, especially plasma

[joecnc2006]

Originally Posted by massajamesb These are plasma cutting machines, but it gives you an idea of how it works. Plasma Table Build Log Including Free Plans Link, & Pictures by Weldtutor and the last page of Smilewizards' thread, 4 x 8 Plasma Table Plans I wouldn't say that chain is not an option, if installed correctly I believe you could get most of the slop out. Perhaps it is not accurate enough for routing, but I know that it does work well on other machines, especially plasma

Yes your thinking is what i was also thinking, but after rereading his post i believe he is talking about using the chain as an actual rack and the sprocket as a pinion.

Joe

[massajamesb]

Oh, gotcha.
You are right about that, Joe. I would not try it (chain) as a rack and gear setup.
Now, if you were to make the chain taught from one end to the other, and have the driven sprocket on the gantry, with the chain going under an idler, over the drive sprocket, and under another idler, then that might work, but....

In reality, the cost of chain and sprockets is only a little less (perhaps 50 bucks or so) than using gear rack and spur gear.
Trust me, I found out the hard way

[luther]

hello and yes i was going to use the chain for the rack but now i think i will go with a rack and gear setup. can i used it for a router to? and wnere can i buy a cheap set of rack and gear? thanks

[joecnc2006]

http://www.stdsteel.com/gr_stock.htm

Joe

[joecnc2006]

Look at the Mechmate, Gerald still uses direct drive to it and his resolution is acceptable for his needs, others have geared the motor down, to improve their resolution.

Joe