Hi Transtar,
Yes I have a home-made cnc router; some of the electronics I scratch built and some I bought in kit form. The actual travels achieved are 500 x 400 x 50 mm. Control is by Mach2 in Demo mode - I will buy it when I have finished ironing-out the snags in my 'mechanicals'. So far my outlay has been about 20,000 baht or 300 pounds or 500 dollars US, including hardware, electronics, and motors, but not the router. Most of that went on electronics and motors.
My frame, to give it a more glorious term than it deserves, comprises two ends of 15mm plywood (about 4" x 30") separated by conduit as X-axis rails about 850mm long.
These end pieces are woodscrewed to the base (1 inch ply - 'cos it was there!) via small steel brackets. It all rests on top of a once-upon-a-time twin tub washing machine casing, which now houses my electronics and power supply.
The gantry, as some of you call it, is one round tube and one square tube spacing two substantial blocks of wood. These 'bogies' run along the X-axis on skateboard bearings, presently relying on dead-weight to keep them down.
My X- and Y-axis screws are supported in bearings outside of one rail. They are 5/8 UNC threaded rod and the nuts (sorry, followers) have a bit of iron welded-on for atachment to the carriage. I had a local machine shop turn the ends of the rod to 8mm dia to suit skateboard bearings and threaded M8 about an inch for a clamping nut. Said nut clamps the inner bearing-race, a spacer and a timing-belt pulley.
A bloody-awful mess comprises the Y-carriage carrying the Z-axis. Some more about that another time.
Motors! My Z-axis carries the full weight of both itself and the 1.5 Kg of the Bosch POF500 router. As the travelling part is a lump of 3mm plate plus guides, we are probably talking about near up to 3 Kg. A 100 oz-inch motor from IM Automation in Bangkok drives this soooo easily. The motor is rated for 2.5 A but I drive it at less for the sake of my driver electronics.
On the other hand, for X- and Y-axes I bought 200 oz-inch motors from Ocean Controls in Australia. They are hopeless! At stationary but with power applied, I cannot budge them by hand - good. But when stepping, and at their rated 600mA a light touch of finger-and-thumb simply stops them - Not Good!
Their coil current is low because their resistance and inductance are high (12 ohm and 43mH respectively) == not suited to high speed, so I cannot gear-down to gain torque at decent speed. Take a look at
http://www.active-robots.com/product...r-motors.shtml where you will find (about halfway down the page) Sanyo Denki 103H7123-0151 rated at 7.35 lb-inch (~117 oz-inch) and Ohm/Phase: 6.7, Inductance/Phase: 15.0 mH, Current/Phase: 1 Amp or their next item Sanyo Denki 103H7123-0440 (also 117 oz-inch) but Ohm/Phase: 1.6, Inductance/Phase: 3.8 mH, Current/Phase: 2 Amp. Of these, the former will be better suited to low speed while the second one will maintain torque at higher speed due to its lower inductance. (I am not suggesting these 117 oz-inch motors for your purposes.)
When I save enough I will certainly replace these two with high-current, high torque motors of a reputable make (like IM, mentioned above)
Sorry to go on so much. I didn't mean to get you lost. IMHO use a 100 oz-inch motor for the Z-axis and 200 oz-inch for the X- and Y-axes. You are probably not looking for speeds in the hundreds-of-inches-per-minute range (like some commercial machines) but as I said before, the cutter needs to cut not rub the work.
For drivers, I use KT5191 (L297/L298 combos) bought from Ocean Controls and they are excellent. Having hammered the motors, I reckon I should also publically praise Peter Simmonds of Ocean Controls for his patience with me and great service. Thanks Peter.
Yonks ago I started to make some sketches of my machine but I got carried away with 'just fix this/improve that...' I will do more, and soon.
Geoff