MOD1 Spur Gear query

[marbles]

I’m putting together my first R&P drive machine and i’ve got a couple of questions about the spur gear size and type I’m using. As the little 15T spur gears I have on at the moment have to do so much work and i’m unfamiliar with R&P seems logical to ask you guys if this is correct.

Q1. I am wondering if 15 tooth is a bit small and whether to optimise the set up with something larger. Should I be use a larger size, say 24t - 30t?

Q2: I’ve just noticed that spur gears can be stated as things like ‘Straight Teeth Positive’ or ‘right teeth positive’. Obviously my machine runs back and forth, which should I be using?

Q3: Perhaps I am supposed to use a particular type of pinion with the rack I have, which is not the chinese ones I currently have on?

Q4: Does anybody know what spring tension I should be applying to hold the pinion in the rack?

Any advice would be most useful. Thanks

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CNC working area 1800 x 1500 x 500mm
4nm steppers with 4:1 gearing, 48v psu
1/10th microstepping
10mm drive shafts
Rack: SR10/15/1 1 mod, C45 Soft Long Steel EN8 Gear Racking, Quality 9
Pinion: MOD1 15T
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build log
http://www.mycncuk.com/threads/12186...655#post104655
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stepper gearing pics