Hidden design features

Hidden design features

A list of features

  1. The unit sits on the leadscrew and everything is in line and concentric. The drive can be coupled solidly to the screw shaft instead of a flexible coupling. Any misalignment that does exist is allowed by the flexure of the anti-rotation mounts
  2. The drive coupler is a cylindrical part that has shoulders for the gear location and bearing diameter machined in one operation making the gear spin concentric with the ball bearing to a high degree of accuracy. The result is a very smooth gear mesh with no variation as it rotates. The same part has the bore that slides over the leadscrew shaft so everything spins in line with the screw. This is important because any slight binding will be the limit to how fast the motors can turn.
  3. The traditional way to mount a motor is to make a bracket that gets bolted to the machine and the motor is bolted to the bracket. To prevent binding, a flexible coupling goes in between the motor and the leadscrew. If a belt drive is used, the motor sits off to the side pointing into the machine or sticking out. A larger bracket is made with tension adjustment for the belt. In many cases the brackets may require holes to be drilled into the machine. My design doesn’t need a mounting bracket at all. It mounts to the leadscrew. The standoffs appear to be what mounts the drive but they only stop rotation.
  4. The stepper motor shaft and leadscrew shaft are mounted fairly close together thanks to the gear drive. This raises the motor for the Y-axis high enough to clear the lip of the coolant pan common with the sheetmetal stands the mills often sit atop. The motor for the Y is turned around so it points inward instead of out. There is a limited amount of room for the motor to fit before the rear runs into the base casting. The gear reduction makes it possible to use motors that fit.
  5. The X-axis motors are close up underneath the X table. They need to clear the base casting or travel would be limited. Again, the use of gears tucks the motor in close but not so close it won’t fit under the table. This lets the rear of the motor point towards the machine and clears everything that would limit travel.
  6. The Z-axis shaft is the end of a worm gear that sticks out from a casting on the side. The stepper motor must fit in the area over the casting but not so high it hits a boss projecting out the side of the head. Once again the 2.2” center to center spacing of the gears puts the motor in between with little more than ¼” to spare.
  7. All three drive assemblies stick out by just an inch more and none of the motors protrude into the work area. Travel is not affected in any axis.
  8. The machine can be operated manually with little change after the conversion. The dial graduations remain visible and the handles are in the same place.
  9. The single piece coupler has a fake leadscrew shaft on one end and a hole for the leadscrew and drive lugs on the other so it directly drives the leadscrew shaft which will absorb manual loads instead of passing them through the motor drive system
  10. The design is ideal for use with ballscrews. A standard coupler used in the Z-axis unit has a ½” bore and an inch deep. When used for X and Y you would bore out the hole to fit the end of the ballscrew shaft then tighten the set screws.
  11. It is dirt simple. That is hard to do and when it’s done, it doesn’t look like you’ve done much.
  12. A drive can be removed in 5 seconds if the tool is handy. A special narrow band hose clamp fixes the drive to the mill. No holes or other permanent modifications to the mill are needed.
  13. The drives are easily modified to match custom applications. You just need to match a shaft diameter for mounting and adjust the length of the anti-rotation legs as needed to reach a sold part of the mill.
  14. The gearing produces 500 full steps per revolution of the big gear. When the motor is near top speed, the rapid traverse rate is good for this application. The 2.5 to one gear ratio provides 0.0002” resolution with full steps. Typical driver settings used for this application uses 40,000 steps per inch or 0.000025” per step


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