Hector, I've just gone through this w/ my system. From your size's I'm assuming your using it for Plazma? Have you got your Gantry designed? Do you have any idea's how much it weigh's? If I was to design a plasma table, I'd go w/ as big a Nema 23 servo as I could. Then I'd go onto the website of the plasma unit I'm wanting to use, and find out how fast it will cut the plate thickness I want to cut. Then I'd go on ebay, and find the gear heads I need [ search for Bayside Stealth or Bayside motion] the Nema 23 gear heads are usually dirt cheap. I've seem them recently for $30. Once I've found the gearheads I can buy or have bought. Then I'd do the math to figure out what size pinon I need [ DIA of pinion is all you need to know at this point] to get a rapid speed of about 25% more than the rated cutting speed [rated cutting speed X 1.25].
Next I'd calculate out what type for force this motor/gearhead/pinion DIA is going to generate, from this I'd then spec out the gear Diametrical Pitch [DP]
Once this is all done, check your resolution per step from your motor [ should be really small if your using a decent quad. encoder] and you know your spec's. I'd recommend the 20deg gearing over the 14.5 as it has better gear interface, it will be a bit noiser but be better in the backlash dept.
A great place for spec's is Boston Gear go to their open gearing section sign up so you can get to the cataloges [ signing up is easy and they've never bugged me since] . Pay special attention to the torque loads allowed for your spec'd gears as you can usually easily exceed the spur gear ratings pretty easily [ I'd shoot for 50% or less of the max rating].
I just purchased 60' of 12DP rack in 6' lengths from my local Bearing & Transmision store, and it wasn't to expensive.. I'm doing a milling maching that is 20' x 10' x 4'.
Jerry.. [ forget the vision's of sugar plumb's dancing in my head.. I've got gears and cutters and tools.. ]
JerryFlyGuy
The more I know... the more I realize I don't
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)