Hi guys,

I'm following this mailing list for a while but still have a few 
questions about designing (ideal :-) CNC machine for use with woodwork 
mainly.

Here are the preliminary specs:

tool motion: 120 x 90 x 20 cm (X-Y-Z)
frame material: T-slotted aluminum
motors: 3 stepper
drivers: 3 geckorive (1 opt.)
controller: Mesa 5120 (?)
power supply: linear 35-55V 600-800W (?)
X-Y motion: moving arm (X-Y axis) (with ball bearings and steel rod)
Z axis:
optional: 4th axis for rotating parts
table: fixed
Software: EMC of course

Questions: what size of the stepper motors should I pickup for X-Y? I 
was thinking in a range of 500 - 800Nm for X-Y and 200 Nm for Z but am 
not sure about it. Brand names are also a question. Are  
http://www.anaheimautomation.com/hightorquesteppermotors.aspx good 
enough? Is brake mandatory for Z-axis?

What kind of a moving mechanism would be the most cost effective for 
each axis? Lead screw, pinion gear and rack, belt, or something else? I 
haven't seen anybody using steel cable to move the arms around in CNC 
machine for example.

What comes to mind here is an old HP plotter model 7221 which uses a 
rather complicated but efficient and precise mechanism with steel cable, 
pulleys, and two motors in fixed position to move the pen. While the 
cable will wear out faster than a lead screw for example, it's way less 
expensive and easier to setup with no backlash IMO. Steel cable doesn't 
collect much dust either making it suitable for the job IMO.

I tried to find a source for plastic cable track to protect and guide 
the cable but Google did not respond kindly. What kind of flexible 
cables are used for connecting power/data to stepper motors and encoders?

All suggestions are welcome but note that there is a budget limit :-) 
which should be significantly or reasonably lower than a commercial 
product of the same size and capabilities.

Thanks,

-- 
Rafael


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