@@ -112,4 +112,16 @@ Kevlar string wrapped around stepper axle, tension in string opposed by spindle
- Add second x-axis beam.
- Characterize machine with Kevlar string, if that makes sense.
#### Progress as of 4/27/22
- Kevlar string measured. Creep and hysteresis were below measurement sesitivity on my apparatus. Elastic constant K = 9.5kN. That is, for one meter, dF/dx = 9.5 N/mm.
- With this string, wrapped directly around motor shaft, and using weight of the spindle as the sole downward force, it is possible to mill a reasonable PCB with the conical bit, and wax milling goes well. Measured dF/dz is much higher than before, 120 N/mm.
- The xy stage by itself has dF/dy ~ 40 N/mm. With wax block on table, at the top of the block dF/dy = 30 N/mm. Extra compliance is due to rotation about the single x-beam as a function of sideways flex of bearings.
- Applied kevlar string to the xy stage. Now the stiffness of the stage, dF/dy, has doubled to 80 N/mm. When the table is added, and a wax block attached, the stiffness at the top of the block is still low, about 40 N/mm.
#### Next steps.
- Make a double-beam for the x-axis. This will triple the torque arm for the stage.
- Looks like, with the stiffer string, that the xy compliance is dominated by the stepper motor holding torque. Let's cut the drum radius in half, and increase the holding current to 0.6A
- Once we have a configuration that we like, it would be good to do a more detailed analysis of the compliance budget. Good to use the
