> tool motion: 120 x 90 x 20 cm (X-Y-Z) > Posibly a little small. Remember it doesn't cost much more to go bigger. It does depend raher on what you want to make.
> frame material: T-slotted aluminum > Easy to work with though quite expensive if you can't get it second hand. Remember rigidity is the key so you want good cross bracing. A welded structure would be cheaper though it can be difficult to maintain accuracy when welding. > motors: 3 stepper > drivers: 3 geckorive (1 opt.) > I personally dislike steppers. Have you considered servos? IMHO, much faster and easier to get a reliable setup. They are a little more expensive and a little more work in the beginning but I think the results are worth it. > controller: Mesa 5120 (?) > Probably a bit OTT for steppers. You can use the parallel port and a breakout board. Mind you it does allow for a lot of future expansion. > power supply: linear 35-55V 600-800W (?) > If using steppers I would go for around 65 - 75V. 500 - 800W sounds about right. Linear power supplies have the advantage that they can take short heavy overloads, such as when accelerating hard. > X-Y motion: moving arm (X-Y axis) (with ball bearings and steel rod) > As long as the steel rod is supported over it's whole length this should work fine. I have seen too many machines using steel rod/pipe supported only at each end. They move in the breeze, let alone with cutting forces. If you are using ball bearings, fit wipers on the rail so the the beatings don't end up pounding dust into the rail. > Z axis: > optional: 4th axis for rotating parts > Get the XYZ working first. 4th axis usually falls into the 'occasionally useful but spends most of the time gathering dust' category. > What kind of a moving mechanism would be the most cost effective for > each axis? Lead screw, Trapezoidal screws don't have many advantages and have lots of disadvantages. Ball screws work very well as long as you keep them clean. They are also quite expensive. Unless you use a very coarse screw (industrial routers often use 25mm/turn or more) you have to spin the screw very fast to get sensible feed rates. > pinion gear and rack, Very common on industrial routers. Tough and reliable. Fairly expensive. If you use a reasonably small pinion you can direct drive it straight off the motor. > belt You can get special motion belting or you can use ordinary HTD or traditional timing belts. Best used as a sort of flexible rack. Fix a length of belting at each end and use two guide rollers to wrap it round the pulley. Obvuously the motor and pulley are mounted on the moving axis. Use reasonably wide belt, say 30mm or so. The main disadvantage is that the pulleys are quite big so you need quite a high reduction ratio. > , or something else? I > haven't seen anybody using steel cable to move the arms around in CNC > machine for example. > It has been suggested and tried before. I haven't heard of anyone actually getting it to work reliably. The biggest problem is that you need relatively large diameter cable so it doesn't stretch under cutting loads. It has to run on a drum with a spiral groove in it. This drum ends up very large, causing alignment problems as the cable moves along the drum. If you want to build an experimental machine, give it a go. If you want to build a machine to use, go for one of the more traditional methods. > 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, > Plotters have much lower loads than routers so they can get away with relatively thin cable. The real problems appear when you step the loads and cable sizes up. > 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? > Look for energy chain. It sometimes turns up on places like eBay reasonably cheap. Other alternatives are: Springy steel strip (think overgrown tape measure) with the wires clipped on. Shopbot uses this. You need a fair amount of room as the strip needs a very gentle arc. Ordinary flexible conduit. It needs to be well supported sideways but it can work well, especially on shorter runs Aim for a feed rate of around 2m/min at the very least and preferably around 4 - 6 m/min. Wood likes to be cut fast. If you cut slowly you get burning, a poor finish and wear cutters out quickly. Think about dist extraction. You will be producing a LOT of dust and it will go everywhere if you aren't careful. If you are using MDF you really don't want to be breathing it in. Dust extraction is hard to do right and you need to think about it while you are designing your Z axis. Les ------------------------------------------------------------------------- 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
