Plasma Cutter Gen 2 - Part 11: Z Axis Design and Gantry Improvements
I got to work on my X axis and Z axis today. For the Z axis, I wanted to use a small section of the V rail extrusion that I purchased to use as my X axis, because I figure it will be perfect, and not too expensive. I am using a similar design as I did on my first machine, including the floating head (which I will show later). It has worked well for me, and this design only improves on my first one, which already worked well.
This is the X axis slide, without a Z axis attached yet, though the V bearings are mounted there to accept the Z.
The base is made of 1/4″ thick aluminum, so it is quite rigid, but very light in comparison to steel. Also shown at the bottom of the plate is the bearing support for the lead screw which will be used on the Z axis.
Here is a picture with the Z axis (leftover V rail extrusion) in place and awaiting a motor mount to be mounted on top. Please excuse some of my spacers. The local hardware store only had 3 of each, and I needed 4, so I had to improvise for the time being. I have temporarily clamped a stepper to the X axis plate to add weight for flex testing.
I would LOVE to say that I passed my flex test, however I did not. When I had a vibration in the X direction due to flex at the Y carriages, I had to fix it to reduce the vibration. I am building this machine to be superior to the first machine, so any vibration that I can test for needs to be eliminated. Of course, I am testing the vibrations and flex at extreme speeds (1000 IPM at 80 in/s/s) because I want to be sure there is no vibration translating into the cut.
After doing these tests on this machine, and with how robust I am making this, I cannot believe that some of the commercially available tables on the market would come close to passing this test. Perhaps I am wrong, though…
Anyway, I tested my flex and vibration in the Y direction by quickly jogging the gantry back and forth to try and hit the natural frequency of the whole assembly to see how much I can flex it. I tested it with the X and Z axis assembly near the center of my gantry. I will have to admit that it flexed… a lot. I did not measure it, it was visibly apparent. To try and eliminate the flex, I clamped square tube to my X axis slide to see if it was flex in the X axis plate. This did not change anything. I removed the whole thing, and clamped a big piece of 3″ square tube to the aluminum extruded V rail to see if that was flexing relative to the gantry. It was pretty stiff, but still flexed.
At this point I was scratching my head, and I was quite annoyed, to be honest.
Well, I moved the X and Z axis assembly to the very edge of the gantry near the 0 coordinate in the X direction right next to the Y axis carriage. I repeated the test again, and I saw very small amounts of vibration and shaking.
So, I have concluded that my gantry truss design is twisting under the extreme testing under torsional forces. To fight this torsion, I will be adding more tensile members down the length of the gantry truss. I believe it will eliminate any torsion, though add some extra weight to the gantry assembly. At first I was concerned about the overall weight of the gantry, but since I can currently rapid at 1000 IPM at 80 in/s/s, I am not concerned about gaining another pound or so.
I will report back with the results, and do plan to provide an overall weight of the gantry and the components for reference of others.