MadVac engraving on aluminium Y axis cover plate

Y axis

Space is at a premium here so that everything can be compact but also reachable and maintainable. The plumber block elevation and lateral position was adjusted from below and the back side with four 10-32 thumb screws so that the travel of the nut was centered and parallel to the linear slides along the whole length of travel. Then, epoxy was cast under the block and in the space of the top and lower metal tabs. Notice the welded tabs behind the plumber block. The block is fastened by 4 M8 screws through the tabs. The motor side tabs are permanently welded as you can see and the far side tabs are removable so that the screw can be inserted and removed. Since everything is steel, I was not concerned with thermal expansion and screw buckling between the tab mounts. The fun part is masking, damming and mold releasing all the separate parts in preparation for the epoxy injections. The final fit is always perfect!
The most time consuming part of the Y gantry design was to consider the length and centering of all the components so that both Y and W axis would have largest usable range over the work table and at the same time the slides would provide a collision buffer before the ball nut would hit the plumber block at the ends of the travel (without wasting usable length of both components). The limit switches (not mounted yet) are about 4" in front of the plumber blocks mounted on an adjustable/sliding tab. Again, this is important so that you get the maximum usable axis travel without the limit switches imposing constraints. The switches are operated by a "ramp/cam" welded to the Y nut yoke. All switch wiring is routed inside the lower Y tubing.
Mounting of the motor is pretty much the same as the X axis.

Note the tapered pins between the end plate screws. This is to guarantee that the parts will always assemble back together accurately. The pins are made from soft steel and are disposable after each assembly/ disassembly.
The Y nut yoke still without the Z axis plate mounting flange. It is removable from the nut and mounts on the "backside" of the nut flange. This is generally the mounting side of the ball nut (precision ground for that purpose). The face of the yoke had to be done like this since the ball recirculation mechanism on the nut must be on top of the nut otherwise the bearing balls will not circulate properly.
The preload in the nut is achieved by half of the ball grooves in the nut being ground "offset" so that the balls are compressed against the screw towards the center of the nut (lengthwise).

Grease - I am using LG-2 Shell Alvania lithium based grease for all the linear slides, bearings and screws. I called Shell and got a case of 12 large grease tubes for $20 (lifetime supply). This stuff is fairly good. It is thixotropic and more solid when it sits for a while. After the machine warm-up movements, it is has far thinner and oily consistency which is great since it reduces the rolling friction of the bearings considerably. You can see the difference in the motor stalling at high speeds before and after warm-up.
Final adjustments of the far-end block mounting.
Mounting Y yoke.

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Last page update: 19 October 2004