Like so many others, I've spent countless hours here on CNCzone, Mechmate forum, Joe's forum, MachSupport, etc reading everything I can about CNC and dreaming of someday owning my own machine. Well with the new year I've realized that at some point I have to bite the bullet and start a build, so here it is!
I'll preface this with the understanding that many people dream of 5-axis builds, plan them, start them, and sometimes even complete them. Unfortunately it seems like not many are completed or converted to 3-axis. I hope I don't fall into this category.
One of the first questions asked with any 5-axis build log is what CAM software the builder plans on using. I'm fortunate enough to have access to CAMWorks through my work, so I'm set there.
The work envelope I am aiming for is 4'x4'x2' though my design now is slightly above that in the X and Y, and just below in Z. The side trusses are made up of 4"x4"x.25" welded square tube topped by 80/20 2040 extrusion. The cross members are 2"x4"x.25" tube and they are bolted so I can disassemble the machine. As it is, the gantry is a mixture of 4"x4"x.25" tube and two pieces of 80/20 3060 extrusion. I have done this since I have heard it is unwise to try and mount linear rail directly to steel tube? The moments of inertia or much higher for these extrusions anyway, I believe they would do a better job withstanding torsion in the X-direction.
25mm linear rails lines are used on the three linear axes. I purchased these as a set of 62" rails w/ blocks and 120" rails w/ blocks. I plan to cut down the 10' rails to make up the long axis and Z axis (6' and 4' respectively).
I have rack and pinion set up on X and Y using CNCrouterparts NEMA 34 setups. I was planning on using a linearmotionbearing ballscrew for the Z, but now I'm thinking I'd prefer R&P if I can do it. Opinons? ~75lbs is weight that will be moved up, down, and held during power off. I don't know much about ballscrews - would 20mm diameter be sufficient or would I need to step up to 25mm? With either R&P or ballscrew, I plan to use a brake on my stepper motor to keep it from falling when I power down.
The B/C head is designed around a pair of Harmonic Drive SHG-25-80 gearheads I purchased off eBay. The 80:1 drive ratio is much higher than I would prefer, so I have a belt reduction designed in (the details of this are not set, but it will be at least 1:2). So we are looking at most 40:1 ration on the B and C axes. I plan to use smaller NEMA 23 motors to drive these, as I don't need the extra torque and help reduce the volume of the head unit.
The B/C head model won't be complete until I know belt reduction in place, center-to-center distance between the gearhead and stepper, and what stepper I will be using.
That brings me to electronics, where I admittedly have little solid plans. My original idea was to use dual G540's to cut down cost, but now that I'm looking at a little over 300lbs for the gantry+z-axis, I realize this is just a pipe dream.
My backup plan right now is to use one of the dual BOBs from CNC4PC (C23 or C32). I have not looked into the difference between them. Along with that, I will need some Gecko drives, power supply, and compatible NEMA 23 and 34 motors. I'm hoping for some suggestions in this area.
Depending on the final cost of the stepper setup, I *might* consider a DMM servo package. If I am going to see a great improvement for a few hundred dollars more, that would be hard to pass up.
The spindle I have modeled up is the 2.2kW fan-cooled spindle sold by love-happyshopping on ebay. I have asked him for dimensions of his new square bodied 3kW but I have yet to receive them. I have to draw the line somewhere and I think I may just go with the 2.2kW, though I'm sure I would prefer the water-cooled (noise concern).
I think that covers most of the basics. Another thing I need to figure out are home switches for the B/C head.
If anybody can spot any pitfalls I'd appreciate you pointing them out. Comments and concerns are welcome, I would love to discuss this build.