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Step 14: Y-Axis Rails and Transmission Nut
Y axis lead screw (1/4
This tutorial is dated, if you are considering a CNC for your personal use, we would highly recommend purchasing a kit that is very stable from our wide range of machines available. Instead of using allthread for the lead screw and a standard nut, consider using a 5 start lead screw and anti-backlash nut. It will keep you from pulling out your hair by running much smoother and faster. Trudging along... We are at the y-axis rails and transmission nut. We did a lot with the y-axis assembly and rail support, but we haven't cut the rails yet. Previously I used a couple of scrap aluminum angles to test the mechanism. Now we can cut the correct length since we have the gantry sides in place. See... we didn't know what the length would be until now.

To cut the correct length, simply place an aluminum angle next to the gantry sides with one on the inside dimension of one side. Mark the other side a smidgen smaller than the length. We don't want the angle to bow and the y/z axis assembly will squeeze it together enough to press the angle into those beautiful chamfers we made earlier. Do two of these, one for the top and one for the bottom of the y-axis rail support piece.

Ok, now onto the transmission nut. We will have the challenge to doing some precise drilling here. Like with the z-axis lead screw, the y-axis screw is pretty much the same. All of the holes must align somewhat perfectly. If you screw up... pun... too bad, don't worry, MDF only costs about nine bucks a pop. I know, it's hard to go back and do it all over again. Well, this will give you motivation to do it right the first time. If you are as good at drilling as I am at grammar and spelling, well, get your pocketbook ready! Oh yeah, you might get some splitting as you can see in the image. It might be a good idea to use some glue for reinforcement.

The process is pretty straight forward. Draw a line where the y-axis lower support meets the gantry sides. Measure up the thickness of the board (3/8"). Find a spot that will not interfere with the z-axis lead screw or the bearings. You will be screwing all the way through the lower y-axis bearing support. Once that is done, drill a slightly smaller hole than the diameter of the nut, this is of course with the understanding that the nut is much smaller than the thickness of the wood. If it isn't and your way mechanically superior to what I'm demonstrating (anti-backlash nut, ballscrew nut, etc.), then you will have to use the y-axis lower support as a place to mount the other type of nut. It's not difficult, but measurements will have to relocate the holes in the gantry to compensate for this.

At this point, I can tell you that it is possible to build an entire CNC routing machine in less than one week, if you don't have a family. Good luck to the ones that do!