Rack and Pinion Calculations

[krazycnc]

Trying to set up Mach2 for my plasma table. Section 5.6.1.1 describes "Calculating Steps Per Unit". To find the tooth pitch for rack you count 100 gaps and take this measurment, I get about 15.6 inches. To get a number for the calculation I would divide 15.6/100 = 0.156? The inital calculation goes "motor revs per unit" or "shaft revs per unit = 1 / (tooth pitch x Ns)" Ns = number of pinion teeth = 30. After calculation I get "Motor Revs = .21367". Upon further reading in the Mach2 manual, to arrive at final revs per unit I would multiply my stepper motors geared ratio 7.2:1. So 7.2 X .21367 = 1.538 motor revs per inch? Does this sound right to plug into Mach2 setup? Is 1.58 revs per inch a good ratio? Does anyone have any other calculations like IPM-Rapids, Drive force, from this info?

Thanks Much

[Al_The_Man]

There is a simpler more accurate way than see this previous link.
http://www.cnczone.com/forums/showth...3679#post83679
You just need to know the circular pitch and the number of teeth on the gear, this information should be known when you buy the rack.
Al

[krazycnc]

Thanks AL,
That link led to a PDF that gave me a circular pitch of .1571 as opposed to my measured .156 which gives (shaft,motor) revs per unit at .21231 instead of .21367 and a final motor rev per unit of 1.528 instead of 1.538, so I guess I am on to something here. I'm just trying to confirm these calculations and expand them to include other info that myself and other people may find important in considering what parts to buy. Just trying to get a grip. Besides looking thru the archives here my googling on this subject ranged from Lego design to pages of engineering calculus, none of which helps with my questions. Any help is appreciated!