Nev,
It all depends on how fast you are going & what you hit...Steppers lose torque as speed increases & it is not unreasonable for a tool to lose steps after an unexpected collision. FYI - most of us from the early PRT days prefer to leave dust collection off on the newer tools when doing 3D. I leave it on to rough out & take it off when doing the 3D finishing pass. Most of the time, there really isn't enough material coming off of the bit to justify using dust collection anyway...Plus, the savings in wear & tear on your DC is a good idea.
Sheldon,
In most cases you will not notice any difference in arc smoothness between a PRS Standard and an PRS Alpha. Early PRT Alpha and pre-4G Standard tools occassionally had issues with arc 'chatter' on certain materials. Many of the issues with so called chatter stem from poor maintenance (read: dry & worn pinions). ShopBot has resolved/relieved many of these issues by some software and hardware enhancements. The Standards are now microstepping (2000 steps/rev) compared to a PRT 1G-3G 1/4 stepping drivers (state of the art at the time) at 800 steps/rev. PRS Alpha tools use 7.2:1 gearbox motors with at least 2X the torque and resolution, while maintaining a high top speed. PRT Alphas used 1:1 motors and didn't have quite as much torque or resolution of the newer PRS tools. The PRT Alphas also used 20T pinions, which had a tendency to wear very quickly and introduced some cogging (which attributes to chatter), as the pinion began to wear. PRS Alphas use 30T pinions which engages more teeth in the rack than a 20T and has much less wear...and increased smoothness. Sorry so long winded...I figured I'd give you the complete answer.
-B
