Earl CNC

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Brief: We need to build a functioning mini CNC machine on a budget using available components that just works. Preferable if some of the expensive components can be reused for the Mark 2 version.




The leading component appears to be http://www.taigtools.com/mmill.html which is also available as part of the http://microproto.com/ package. There is an importer in Birmingham http://www.peatolmac.talktalk.net/index.html


Stepper motors have a lot of drawbacks, but would be suitable for the Mark 1 version just to get something working. Supplies include:


There are three types:


The pulses need to be delivered real-time from the computer's parallel port -- in which case it needs to run DOS or realtime linuxcnc.

Delayed realtime

The pulses are all generated by the computer, but their precise timing is delivered by the controller. For example, rather than sending the signal, "pulse now", it sends the signal "pulse when your clock reaches time XXX ms"

G-code controller

The controller takes G-code and generates all the pulses itself, thus removing the possibility of improving this crappy interface.


The potential components I know are:

Also, there's this guy who's built one in his New York apartment

  • http://web.mac.com/tikka308/Herbie/Video_List.html


I've had a look around, and the simplest option seems to be the 3-axis kit from Xylotex (or 4axis if you want room for expansion)


The motors aren't the most powerful around, but there's a trade-off: larger motors have more low-speed torque, but also more inertia, which can reduce acceleration.

Similarly the drive isn't the highest performance, but it seems competent. A great drive is under development by a guy called Kreutz on CNCzone, but it isn't a packaged unit with a power supply.

What's the catch? Xylotex can't export to the EU because of the RoSH regulations (they're not lead free yet, maybe the US will catch up eventually...).

Gecko drives are well respected, but they're very expensive (you'd need one of these per axis http://www.geckodrive.com) and again they don't come with a power supply and are probably overkill unless you're going for really high torque motors.

This in the UK is fine for low speed work, but really won't match any of the others for high speed stuff (the drive voltage isn't high enough to overcome the motor's inductance quickly). http://cgi.ebay.co.uk/CNC-CAD-Milling-3-Axis-Stepper-Motor-Driver-Controller_W0QQitemZ310045397444QQihZ021QQcategoryZ26209QQssPageNameZWDVWQQrdZ1QQcmdZViewItem Plus you still need motors and supply.

Some motor companies (also make drives) http://www.danahermotion.com/website/eng/eng/products/motors/stepper_motors.php http://en.nanotec.com/steppermotors.html http://www.mclennan.co.uk/product/hybridmotors.html There's plenty to consider in trying to choose optimum motors - torque and inertia, inductance and rated voltage & current along with desired speed, acceleration and driver budget.

These motors are interesting: allegedly high spec, but no proper data sheet: http://www.homeshopcnc.com/page5.html

I take it you don't want one of the Microproto CNC Taigs? http://microproto.com/ Is this because the controller takes G code and doesn't give you step and direction access? In which case, what about this widget: http://microproto.com/adapter.htm Maybe they'd put a system with this together for you.

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