[harryn]

Hi, I am in the planning stages of my first DIY router / mill project for hobby use on wood / Al. Nominal cutting area size is (hopefully) 30 in x 24 in x 4 in. There are some odd arrangements on my setup, but I think I am working through them.

My goal is to microstep / gear the setup so that 1 step = approx 0.001 - maybe 0.0002 in. , not that the end system will be that accurate of course.

I am estimating the gantry mass at 100 lbs / 50 Kgs, based on the posts of others, and my own parts list.

The plan is to use belt drives run off of stepper motors. On at least 2 axis, I would like to use a stepper motor with 2 shafts, put belt pulleys on each shaft, and drive the belts directly. At least in theory, this would provide a belt on each "side" of the axis drive, and reduce racking of the axis.

The particular stepper motor I am thinking about is this one: http://kelinginc.net/KL34H2120-60-4B.pdf . This is one of the standard Kelling size 34 stepper motors with a shaft from each side. I picked it just based on approx torque, 4 wires (because I don't know any better), length, and in stock. Feel free to suggest an alternative model.

So, now the question - Two each belt drive pulleys directly attached to the motor shaft and pulling the axis around will have considerable side load on the axis. I am not sure how much, but (maybe ?) 10 lbs on each side. I really need to do this calculation. Belt will probably be 25 mm wide AT 10 steel wire reinforced.

Is this OK to do with a stepper motor, or are they exceptionally side load sensitive ?

Most of the stepper motor installations I am seeing use the shaft to drive a coupling with separate bearings / shaft to deal with the side load, but it would of course be very convenient if the stepper motor could eliminate the extra parts.

Thanks in advance for any advice.

[ger21]

The Powermax II nema 23 motors are rated for a maximum radial load of 20lbs. Pacsci nema 34's have a max radial load of 65-110lbs. I'd expect the cheap chinese import motors to be a bit less.

[harryn]

Thanks Gerry

[harryn]

Hi, In case this comes up again, I found some more info.

The basic answer for radial / axial load capability is - it depends.

If you search through these various size 34 stepper motors from Anaheim Automation http://www.anaheimautomation.com/literature.htm

you will quickly see that each motor series (letter type) has its own specs for torque, radial play, axial play (play commonly measured at 1 Lb) AND radial and axial load limits.

The variation is amazing, even from the same company, same size motor, etc. My sense is that these guys offer similar target offerings to Pacific Scientific.

Play specs can be from 0.080 in to 0.0008 in. Radial load specs appears to vary from 1 Lb to 49 lbs. Step accuracy can vary from 1.5% to 5 %.

Anyway, it was eye opening for me, but I suppose a lot of that can be just bearing / shaft quality specs.