On Sun, 2008-07-20 at 14:35 -0700, Rafael Skodlar wrote: > 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.
I assume that you are planning a gantry/router type of machine? I hope to build one someday, so I haven't had any experience with this. I can only offer my opinion. > Here are the preliminary specs: > > tool motion: 120 x 90 x 20 cm (X-Y-Z) > frame material: T-slotted aluminum 1.2 + meters of aluminum channel may not be the stiffest material. My plan was to use steel and weld the joints. It may be that surplus steel would be cheaper (though less convenient) than extruded aluminum channel. Personally, I really enjoy welding. You may want to consider taking a welding class, so you can complete your project and pick up an enjoyable skill. > motors: 3 stepper > drivers: 3 geckorive (1 opt.) I have a bias against steppers, especially for traversing over a meter quickly. > controller: Mesa 5120 (?) > power supply: linear 35-55V 600-800W (?) > X-Y motion: moving arm (X-Y axis) (with ball bearings and steel rod) The ball and rod slides I have seen are usually mounted on stand-offs which doesn't seem rigid to me. I like the rectangular rails with ball carriages using a horizontal and vertical set. > Z axis: > optional: 4th axis for rotating parts > table: fixed > Software: EMC of course I think EMC is a good choice ;) > 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? I hate to admit it, but I tend to look at similar machines and then guess at motor size. I figure if I get it wrong, there is eBay. > What kind of a moving mechanism would be the most cost effective for > each axis? Lead screw, Too much friction for my taste. > pinion gear and rack, I have seen industrial routers with rack and pinions. I would consider this. > belt, I would think belts would flap at any length close to being considered long. > or something else? How about hydraulic cylinders? (Half joking here, but ... ) > I haven't seen anybody using steel cable to move the arms around in CNC > machine for example. I have wondered about steel cable. Because of the weave, I would think cables would be stretchy. Maybe you could preload the stretch out. A steel tape might be better, but you might still have a flapping problem. > 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. Give it a try, and let us know. > 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? The higher the number of small strands in a wire, will be more durable under flexing. I suspect that if you have a large arc or loop between the ends, most any common cable will work fine. Just keep an eye on it, and at worst, you might have to replace it in a few years. Oh, and maybe stiffen or support any areas of localized flexing. > 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, Keep and eye on eBay and Craig's List for surplus items or something that can be "repurposed", or even better find a machine in your area you can convert. Sometimes it's fun to try to make other people's trash into something useful in unintended ways. Watch for machines that are similar to what you want, that are known to work well. Remember, plagiarism is the sincerest form of flattery. -- Kirk Wallace (California, USA http://www.wallacecompany.com/machine_shop/ Hardinge HNC/EMC CNC lathe, Bridgeport mill conversion, doing XY now, Zubal lathe conversion pending Craftsman AA 109 restoration Shizuoka ST-N/EMC CNC) ------------------------------------------------------------------------- This SF.Net email is sponsored by the Moblin Your Move Developer's challenge Build the coolest Linux based applications with Moblin SDK & win great prizes Grand prize is a trip for two to an Open Source event anywhere in the world http://moblin-contest.org/redirect.php?banner_id=100&url=/ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
