Cnc router project, part 4

Last weekend I managed to get the last of the mechanical assembly done.I made a fairly rough, but secure, mounting for my rotary tool. Which I mounted to the Z-axis. It took a bit of re-adjustment of the various bearing holding brackets, to try and get things fairly square and straight which is still frustratingly difficult. It is getting easier though, the more assembled it’s become, the easier it is to make adjustments and alignments. But it’s still not perfect.
Here it is with the rotary tool mounted in place, looking very much like a finished thing.

Of course it isn’t finished by a long way. One of the challenges I overcame this time was having a screw thread on the Y-axis that was a little short for me to chuck my drill onto, in order to test. This won’t be a problem once I’m mounting real motors, but was annoying for trying things out. I figured that I was going to need to come up with a way to couple the motor shaft to the threaded rod, so I might as well try first coupling two pieces of threaded rod in order to extend the y-axis and let me use my drill driver to move it.

So I came up with this:

It’s just a block of hardwood, with a hole through the centre, drilled and tapped for teh threaded rod. Then from opposite sides and each end there is a smaller hole drilled into the main through hole. These drilled and tapped for my 5mm bolts. The two threaded rods to be coupled are screwed into each side to meet the middle, and the tightening nuts are then screwed down to hold them in place.

What I discovered was that the tapping in the wood wasn’t really strong enough to get a good grip against the threaded rod on one end. I may have to adjust both sides, but for now the bolt against the main length is holding ok. For the shorter length I decided to drill a hole through the threaded rod itself, and tap that too. So now on that side the holding bolt screws through the wood and right through the threaded rod.

It doesn’t look too pretty, but it appears to be effective. I can now attach my drill driver to the y-axis and drive it back and forth.

As I came to want to test it I had to think about how I would mount working wood securely.  As it happens I had a couple of lengths of mdf which were pretty much exactly the right length to lay between the two sides mounting the x-axis rails. The panels had been from a panelled door I tried to make out of  MDF a few years ago. By screwing these down across the gap I provided a raised surface that I would then be able to just screw into if I needed to hold things down to it.

If you recall from part 1, I considered using a suspended surface when I thought I might want my x-axis driver thread to push on something in the middle. I rejected it on the basis of being simpler and stiffer to work from the real base of the structure. Well here I have basically gone back and put a suspended surface in place again. which does mean I’m not making the most of the z-axis depth I could achieve. but for the moment this was the easiest thing to put in place.

So at last I was ready to make some test cuts. just manually lowering the z-axis and driving the x or y axis with my drill driver to cut straight lines.

Not terribly exiting, but it did reveal an issue, starting or stopping on the x-axis really showed up how much twist there was between the two legs of the gantry. The cutter would start by swinging out to the left, then cut a straight line and settle back to the right by a few mm when you stopped moving forwards. Clearly I needed to reduce the twist.

Now that I have a suspended work surface, the option to connect the base of the two legs had returned, so I decide to just screw a plank between the bottoms of the two legs. This hasn’t completely eliminated the twist, but it seems to have done so enough to stop the cutter from obviously deviating off path. So I was pretty happy.

Similarly the y-axis had a little too much play in the bearings, so I went through another round of loosening, adjusting, tightening. Again I don’t think  I got it perfect, but I did manage to improve matters. So at last I felt I was able to get a nice straight line in both the x and y axis, producing a pretty clean 90 corner.

Of course it’s a little hard to tell how precise things can be, since I’m using a drill driver to wind things and just judging by eye when I realigned to make slightly deeper pass. However I consider this to have been a successful test of the mechanics of my cnc rig.

Now I have no idea how long it will be before I can get the electronics together. I’m going to be very busy with work for the next month at least, and can’t really justify spending the money on electronics right now either. So I think for the moment this will have to do.