While cutting aggressively in aluminum, I noticed I was losing some steps, throwing off my job. I grabbed this stepper (referenced in some older posts) as a cheap drop-in upgrade to my X axis to see how it performed:
While doing this, I also noticed that there was visible stretching of my X belt when I pushed against my HDZ. The stepper and its pulley were not moving, but the v-wheels and belt clearly were.
I set up a test where I placed my HDZ’s right idler pulley 400mm from the right edge of my SO3 XL. Belt tension was indirectly measured by placing a dial indicator at 200mm from the right edge and pulling up with 10lbs of force at a point 100mm from the right edge. I then measured X deflection from my Makita’s body (just under the HDZ clamp) when applying force in the X direction to the bottom of the Makita’s body.
9mm stock belt + stock stepper:
Z belt tension: 16.6mm vertical deflection
X stepper breaks free at 18 lbs force with fast jerks, 24 lbs when gradually building up force
X deflection was .53mm per 5 lbs of force
9mm stock belt + stock stepper, tightened:
Z belt tension: 14.5mm
Fast break: 21 lbs, slow break: 24.5 lbs
X deflection: .33mm per 5 lbs of force
9mm steel belt + stock stepper:
Z belt tension: 13mm
Fast break: 18 lbs, slow break: 27 lbs
X deflection: .24mm per 5 lbs of force
9mm steel belt + stock stepper, tightened:
Z belt tension: 11mm
Fast break: 18 lbs, slow break: 27.5 lbs
X deflection: .2mm per 5 lbs of force
10mm steel belt + new stepper, tightened:
Z belt tension: 10.2mm
Fast break: 70 lbs, slow break: 80 lbs
X deflection: .16mm per 5 lbs of force
10mm steel belt + new stepper, extra tight (shortened belt by 1 tooth + extra-long tensioner bolt)
Z belt tension: 8.6mm
X deflection: .14mm per 5 lbs of force
Immediately after releasing tension, the belt retains some stretch. This can be summarized as about 10% of the stretch the belt had when under tension (so .4mm under tension = .04mm stretch after releasing the load). For stretch over .08mm, the belt tends to slowly return to .08mm over time (or back to zero if you tap on the router in the opposite direction to give it an assist). This seemed consistent between the three belts I tested.
Some other measurements with the new X stepper (I didn’t measure with the stock stepper):
SO3 idle power: 39.5 W
XY rapid at 6000 mm/min: 38 - 38.5 W
Y steppers break loose at 40-50 lbs
X+Y diagonal force breaks loose at ~60 lbs
I did a quick test cut and didn’t see any immediately obvious issues with the new stepper - it seems to jog around and handle a medium-duty cut about the same as the old one. I’m guessing this new stepper’s torque curve isn’t as consistent when feed speed (RPM) rises, compared to the stock stepper… the nearly 4x increase in holding torque at close to the same power probably comes at a cost, but hopefully I still come out ahead for speeds that I care about.
At 10lbs of force, the stock belt stretches about .6mm and the steel belts about .3mm. That seems like a lot of deflection?