How we got to where we are now:
When I started this project I had 15 years experience as a Journeyman Machinist on both conventional and CNC equipment and had been a CNC Programmer for three years in a furniture factory doing 2D work only. I had very little experience with electronics or building working machines. I also had no money. I did however have a Grizzly X2 Minimill and a 9X20 Jet Lathe and a shop full of woodworking machines.
Two years ago the decision was made to manufacture the worlds largest wooden cameras and accessories. I had a Grizzly minimill and decided to retrofit it with CNC equipment. The money was saved and the orders were placed. The equipment came, woo hoo! A Xylotex 4 axis driver box and four 269 oz/in stepper motors and a set of motor mounts and cheap single trace ball screws from CNC Fusion. The equipment was installed and a one year old relatively fast computer was moved into the one car garage to control it. Two days later when the Z axis dove for the table there was no way to shut it off because the emergency stop buttons had not been wired in yet. The cable from the box to the motor somehow got yanked in the confusion frying the Xylotex board. Saved for and bought a new Xylotex board then two days after receiving it, sent 35 volts into the parallel port on the computer while trying to find the correct power supply for the e-stop buttons frying the mother board. Saved for a new motherboard and installed it but now the computer wanted a replacement of the XP operating system because the motherboard had changed. More saving and got a new operating system. The ball screws were not the good Nook screws, but junk designed to transfer stuff from here to there, not designed to control a precise machine tool. The table was too small for the parts I needed to make anyway. I sold the CNC Fusion kit on ebay and kept the Xylotex box and motors then saved for a larger table from DeWayne Harlow at CNCBridges. After 4 months, 25 broken promises for delivery and an offer for half my money back, I contacted the authorities and received a full refund of my money but none of my four months of waiting were returned to me. All of this was the precursor to this thread. All of this saving, waiting, and getting screwed made me decide to design and build my own CNC milling machine/router/lathe from scratch.
The design phase:
I had built a workbench in my shop while waiting for the CNCBridges XY table. The bench is 72 inches long and 36 inches wide. A very nice sturdy table made from recycled wooden sheet metal pallets. All the joints are mortice and tenon and all of the frame members are solid hardwood. After deciding to make my own mill, using the workbench to set it on was a given. This defined the footprint of the machine. The first photo shows the sketch the bench was built from. This drawing details the joinery. The second photo shows the base of the bench assembled. The end frames are joined together by stringers. Thethird photo shows the base of the bench semi enclosed and waiting for doors. The frame and panel doors were made and hung and the top inlet and the bench was done. So Yay! had a bench.
Now that the footprint was written in stone and as large as my shop would accomodate, it was time to write a specification for the machine. A sort of design guidline of must haves. Because the parts I intend to make are very precise, I needed a machine with .0005 accuracy and .0002 precision. It needed a really long work envelope compared to other machines. More log shaped than cube shaped because more than 95% of what I intend to make will be from a board 1 inch thick or a sheet of brass 1/8 inch thick. The longer the better though because then I would be able to get more parts per blank. The machine has to be rigid because of the length of the X axis. This ruled out aluminum as far as I was concerned. Originally I had wanted to use aluminum, but I bought a heavy aluminum extrusion and tested it for deflection by supporting it at both ends and putting a weight in the middle while measuring deflection with an indicator. Aluminum was definitely out. A heavy wall square steel tube was similarly tested and found to be very much stiffer. The X axis needed to be as long as would fit and had to have a carriage wide enough to mount the Z axis on. Y axis would need to be no more than 12 inches of table travelling 12 inches. Z axis would probably have to be around 8 inches to accomodate long tools and one inch thick materials or the occasional tall job with shorter tools. Z axis turned out to be ten inches because of the geometry surprises that came later on.