Originally Posted by
Neale
Don't worry about the steel quality - I didn't! I just bought something from my local steel supplier, probably generic "construction" steel. Doubt if it's stress-relieved or anything else. It is described as "Grade 43a", whatever that means. Welds and cuts OK, and I knew from the outset that I would need to build in adjustment/levelling, etc. Being fussy about steel quality is OK if you can actually buy the quality you are after in small enough quantities (a lot of suppliers will charge more in carriage than the cost of a small quantity of steel - that's not criticism, just a reflection of commercial reality) and if your design is actually sensitive to the steel quality. My design, such as it is, could be beefed up significantly by using, say, 4mm wall thickness rather than 3mm, and for the static bed and frame components, that might not have been a bad idea. However, 3mm works fine for the gantry and does keep mass down.
Don't think you've said how big this is going to be, or what you want to cut on it. This drives some aspects of the design. For example, my machine has about 1.5x0.75m cutting area. For that, I have used 2005 ballscrews. If I were only cutting wood, then 2010 would have been better - faster rapids and cutting speeds. However, I end up doing quite a lot of small fiddly bits and the speed isn't too critical so 2005 works well for me. Similarly, I use NEMA23 3Nm motors; for faster speeds I could have gone to 4Nm for a bit more torque but I'm OK at the moment. However, stepper motors need volts to get performance out of them; don't be confused by spec sheets that say things like "4.2V". That's a red herring. Most of these size motors will work best from about a power supply giving about 68V via a suitable stepper driver. There are plenty of threads that look at different drivers and how to build power supplies.
I'm using a "standard" 2.2KW spindle and matching VFD. Don't know much about ATC spindles apart from the fact that a decent one will cost big bucks.
