New Gear Reducer

[djhazeleger@mindspring.com]

I downloaded the new assembly manual and noticed a gear reducer on the stepper motors. Can this reducer bolt on to the standard motors? What is the ratio? Any advantages over the timing belt system?
Dirk

[Ted Hall, ShopBot]

Hi Dirk,

There is not a gear reducer available for the 187oz motors. However, the issue is a toss up. The gear reducer provides about the same reduction as our timimg belt system ... so gearing is not the issue.

The real issue for us was that we were not able to make the timing belt thrust box as inexpensively as we thought it should be, because of the labor cost involved in putting the whole thing together (even though we were machining the aluminum parts on a ShopBot). I imagine that at some point we will design another thrust box where the design is optimized for assembly and manufacturing. For the moment, we found that we could provide the (very nice) Vexta motor with gearhead for less $ than we could build our belt system.

Here are the advantages of each variation:

1. Because gearing is about the same, there is no difference in overall speed or accuracy with either system.
2. The timing belt absorbs some of the vibration generated by the discrete stepping of the motors, thus the timing belt system is a little less noisy, and maybe a tad smoother.
3. The 187oz motors represent the high end of small motor performance. In particular, because their moving parts are light, they are efficient and carry their power to a high step rate before the power drops off. This means that in practice, you get almost full cutting power up to above 2in/sec.
4. The 300oz motors that you saw mounted on the gearhead version, as noted above, provide the same general resolution and speeds. However, at slow (say 1in sec) speeds they have awsome power (maybe even too much). Yet, they don't have the high end performance of the smaller motors and their power drops off faster, falling below the the 187oz motors around 1400 steps sec (say about 2.75 in/sec). There is also a small amount of backlash in the gearhead.

What this all means is that with the gearhead motors you get more low end and some slow speed rattling and noise from the gears. Going fast, the small motors and thrustbox may give a bit higher top end jog speed.

Note that in either case, we can alter the pinion size in order to produce a gear ratio that optimizes for power and precision -or- for speed.