Have been busy this past week:
1. Finished the X axis ways by clamping the pipes against the MDF bed/pipe holder – used cut off pipe clamps to screw them to bed. Checked the pipes and they are parallel and level - hurray.
2. Finished the gantry. The lower assembly is a torsion box that is 3 inches high. It has plywood ribs and sides, and MDF top and bottom. The top of the lower assembly also acts as one side of the slide for the adjustable bearing. A piece of MDF screwed to the inside of the gantry wall acts as the other side of the slide. This is a bit simpler than other designs I have seen.
3. I made the Y axis ways by using two pieces of 6 inch by 24-3/16 cabinet plywood, with the long sides cut at 45 degrees. These pieces were glued and screwed together so that the 45’s would form a valley in the top and the bottom of the long sides. I installed the pipes in these valleys so that they are parallel and in the same plane. The gantry sides are double layer, with plywood on the outside and MDF on the inside. Individual pieces of MDF form a pocket for the Y axis ways assembly. The fastener of choice for the gantry was deck screws.
4. The Y carriage presented more of a challenge to me. I wanted to keep it as simple as possible, but the first time it did not come out square, so I trashed it and started over. I used the bearing adjustment ideas from Joe’s CNC and Steve Palm, and they worked well (thanks, guys). The more I get into this project the more I am impressed by the thinking of the earlier builders who shared their ideas on this forum - thanks to you all.
5. The gantry and the Y carriage roll smoothly. I keep tweaking the bearing adjustment for laughs, but it seems to be fine at a range of adjustments. I do like those skate bearings. I am also pleased that I could adjust the Y carriage to be square to the machine bed. This is before any router proves me wrong, of course.
6. The Z axis did stop me cold – I wanted to use the skate bearings again (I bought a 100 of them – they were such a good deal). But all the later designs were showing cold rolled steel and polymer bushings. So I went back to the trusty JGRO design for the Z axis. Of course I am using a different size pipe (1 inch EMT, 1.157 inch o.d.)…and I used 1 inch aluminum angle for the bearing assemblies, instead of 1-1/4…just to keep it interesting.
7. My only addition to the art (?) was to use a cotter key in the top of the pipes to keep them from falling through before you tighten up the adjustment screws. That really bugged me the first couple of times they fell out, so I was happy with this simple idea. As you can see, I made the adjustment blocks from oak to give stronger screw threads.
8. So here is the whole assembly so far. Amazingly, all the axes roll well, and they are square.
9. I have ordered ½ bore bearings and set collars to hold the lead screws. I think at this point, I will use ½-13 all thread to hold the initial costs down. Presuming I can really get this thing to work, I can upgrade to double start acme super duper lead screws later, I hope. I will probably bite the bullet and buy Lovejoy couplings, but I am still looking for cheaper alternatives.
10. The electrical/electronics part of this project scares me a little, because I have zero expertise in this area. So I am reading a lot. Right now I am thinking about driver boards and am pondering between inexpensive (HobbyCNC) and the BMW version (Gecko 540). As I understand things, the steppers that are bipolar can give more torque, and these will not work with the HobbyCNC driver, right? But how do I hide a $299 charge on my credit card bill for the Gecko?