Background:
I’ve always subscribed to the mantra “If it’s worth doing, it’s worth overdoing”. My now named XSV-Carve is excessive in design, excessive in cost, and excessive in the amount of time I’ve spent fiddling with it compared to the time I’ve actually spent carving stuff. That said, I enjoy the engineering aspect and problem solving challenge.
Like many of you I replaced the original X-carve Z-axis with something lead screw based off of E-bay. However I found the there was still too much flex on the X direction and on a really long carve with lots of Z movement, I’d gradually lose height due to backlash on the lead screw.
After throwing my toys out of the cot on the last carve I decided some over-engineering was called for.
Z-Axis:
This is the Misumi Linear Excellence LX-30, precision grade. Self lubricating Ball screw with 5mm lead, machined out of solid carbon steel. It does not have any play at all.
Accuracy is measure in Microns. Yes, it’s total overkill for an X-carve.
Mounted to the X-Carriage:
To reduce flex in the X-carriage V-wheels, I changed them to use long stainless steel bolts as ‘axles’ along with twin locking nuts to make sure the eccentric spacers stay put.
Quite some time ago I’d replaced my belts with 9mm GT2. The smooth idlers I got from Openbuilds have a nylon spacer, but over time they’d compressed. So when I tried to tighten them, I found they pulled the bearing centres in, making the bearings run rough and grind. For smooth operation I had to loosen them so much the idlers would flex. I replaced them with Aluminium spacers 13mm OD, 5mm ID, 3.2mm thickness (+/- 0.01). This allowed me to tighten the smooth idlers right up, removing that play.
Steppers:
While I had the XSV-Carve in pieces I also replaced the stepper motors with 0.9 degree 5A versions. The X-controller is now set for max 4A and on X/Y Microstepping has been reduced to 4 (ie, same resolution but exchanging some micro steps for real steps and reducing torque loss). Microstepping is still 2 on the Z.
To accurately fix the stepper motor bracket, there’s a machined jig to make sure it is dead centre.
I used an NBK XHW-C twin disc flexible coupler - very high rotational stiffness, zero backlash, max 3.00Nm of torque.
Results:
I haven’t carved anything yet, but the spindle is now super rigid in place, where as before I could flex the Z-axis left and right quite easily. Flex along the Y axis is also reduced. I calibrated the Z last night to get the new steps/mm and accuracy and repeatability are what you’d expect them to be - way better than the old lead screw Z-axis. I suspect my digital calipers lack the accuracy to do it justice, as they only go to 0.01mm. Accuracy was 0.00 +/- 0.01 over 80mm Z travel.
I’ll post some details later of the new wasteboard, 50kg of Aluminium comprising 15mm T-slot top on 40mm frame1200x1000mm
-Ant.