After much pondering (variations on that phrase get used a lot around here), I have decided to go with the simplest (relatively) solution for propelling the traverser, a single lead screw. It was always one of the options and after chatting with Trevor Marshall and Ryan Mendell at lunch, it was decided. Ryan deals professionally with assorted ad hoc projects and he tells me that lots of people try belt drives and fail to consider the tension required to get them to work properly. Since I have no desire to see if the traverser baseboard will bend under sustained tension, lead screws are the best alternative.
I conflate ball screw with lead screw in my thinking but I understand a lead screw is better for my applications since there is not requirement to handle heavy loads or avoid backlash of a couple of thousandths of an inch. My concern with this option was that aligning the screw, table and baseboard would be tricky and prone to binding. Ryan suggested attaching the nut (brass bit in the picture) so that it floats a bit. I thought about it and I have a plan to do that.
So, the alternatives considered:
- single lead screw
- single belt drive: two pulleys doing the same job as the lead screw but avoiding fine alignment challenges
- two sychronized steppers with two lead screws or two belts attached to each end of the table.
- one belt attached to each end of the table belts driven by pulleys mounted on a common shaft attached to a single stepper.
- one belt routed so that it was attached at each end of the table. This is a simplified version of how printers are designed.
As you can see, I have been looking at all kinds of fun approaches. I still like the single last one but, besides the tensioning challenge, it represents a substantial increase in required hardware with an estimated 5 idler pulleys in addition to the driver pulley as well as roughly 8 feet of belt. None of that is especially expensive on a per unit basis but the total adds up. At that point, I am would be investing in additional entertainment value.
I ordered an 8mm lead screw, nut, flexible coupler and bearing combo of the required length (sadly not available locally as far as I could discover) and it arrived yesterday. Actual installation work will wait on vacation and the right mood.