Ejholmgren, Welcome.
Winter project huh? I see you are in Minneapolis, so you have about eleven months to finish this. (I grew up in Northfield so I know how long the winters are up there.)
As far as leadscrew pitch; 200 steps per rev x 8 microsteps x 10 tpi will give you 16000 steps per inch. Do you really need more resolution than that (or even that)? Adding belts and an offset motor will probably add more backlash (the slop you get when you reverse direction) than that. You need to look at the system as a whole; speed, accuracy, backlash, flex, and a whole bunch more.
You get more torque from a stepper if you keep the rpms down in the hundreds, maybe up to 1K. Not sure what kind of speed you are looking for but when cutting plastics you can not stay in one place too long without melting. Don’t make this machine too slow while worrying about accuracy. Cut something with your dremel or router by hand and notice how fast you are moving it (time it). You probably move it faster than you first thought. My recommendation would be to go with 8 turn 2 start ACME (4tpi). It is more efficient than standard ACME, you will more than double your speed, and keep the rpms of the screw down which will reduce whip and keep the motor in the higher portion of the torque curve. The 1/2” version is cheap at Enco.
You are alluding to sleeve bearings running on shafts. Seriously consider supporting those shafts. The flex in unsupported rails will make the above steps per inch accuracy inconsequential. Maybe look at split bearings running on shafts that are attached to a support that runs the length of the shaft. The cost will not be much more, but they will be a bit more of a challenge to incorporate.
Lots to think about,
Stay warm,
Steve  |