After trying a number of different solutions to speed up the stepper that is used on the drive screw:

1. changing the mode from SINGLE to DOUBLE
2. experimenting with the speed settings
3. trying a different motor drive board version

I’ve come to the conclusion that the the current 20 tpi 1/4″ drive rod approach isn’t going to be fast enough 😦 . So I’ve ordered a timing gear and a timing belt – these have little teeth on them – to try using a direct drive approach. This also means that the screw drive rod is replaced with a 8mm linear rail, and the 2 nuts I was using on the threaded rod are replaced with a “linear bearing”. As near as I can tell, the motor speed (around 60rpm is as fast as I think it’s running in my routines) will be able to direct drive the drill platform plenty fast. In fact, I may be able to drop back to MICROSTEP as the mode to really put some fine control on the distance being traveled.

 Adafruit pieces parts!

 

 

 

 

 

The other changes I’m looking at for the next revision include:

1. use of interrupts to detect the start/end position switches, rather than polling for the settings.
2. possibly using interrupts to check on button status changes (again rather than polling) although this may mean I need to move from the Arduino UNO to an Arduino Mega.
3. Changing the way the start/end switches work

I want to move the start/end switches from a “permanent” mount (extents), to be on an adjustable arm, that you manually use to set them to the start and end of the pen blank. That way we don’t have to digitally set the start and end points, and can just use brute strength settings to move things around. (The fact that the steppers can “slip” under certain conditions means I can’t rely on the positions the way I originally planned to).

At any rate, I’ve got to start work on a 2nd assembly carriage because I want to hold on to the first one for further experiments. (Also, I’m a hopeless packrat!)

Update: I did just start modifying the old carriage. I’ll need to take measurements and experiment with how the timing belt holes need to be placed.