Roller Milling

Spent some time working this out on the whiteboard today, and threw together some rhino sketches.

I'm going for simple, strong-enough, and easy to build. Using rollers and pulleys, or, just as easily, rack and pinion or leadscrew-type actuation.

Next up, getting into fusion to get through the details, then fabbing one axis... designing a simple 3axis machine, and fabbing that.

I pulled this off with a simple set of flat-milled parts - I was trying to work with the constraints present in the set of FREP and Milling tools in MODS, to see if we could finish end-to-end gantry generation and milling.

The result is OK, it'll certainly do - there's a line to toe between being kinematically wicked and loosing complexity. This is a bit of a midpoint - all of the axis of constraint have 'tuneability' in that their preloads can be adjusted, but all are over-constrained. There's enough (lots) flex in HDPE that this will be OK. There's a version which (not actually existing yet) is dead simple and totally constrained, and a version which is perfect motion-wise.

Overall, it's a bit bulky. There's some detailing left out before it is complete. But I think in terms of an all-arounder axis, this is pretty OK, and certainly OK for being millable from one sheet of HDPE (or alu, whatever).

CAD

Available Here: https://a360.co/2qQf6wf

password is rollercoaster

The gantry is built with a set of 'kinematic elements' - a Motor / Pulley Unit, Lateral (into the gantry) and Cross (across the gantry) supports:

These can be jimmied around to make a full set of constraints:

And combined into a complete gantry:

Here's the back of that:

Kinematic Bits

Currently the set assumes 3/8" HDPE, 8x22x7mm bearings, NEMA23 Motors and 9mm Wide GT2 Belts

Version for 1/4" HDPE, 5x11x4mm bearings, NEMA17 Motors and 6mm Wide GT2 Belts.

See cad/assembly/elements/ for kinematic elements, and cad/assembly for one-machine made with these elements.

Motor and XY Constraint:

XY Constraints, with preload adjusting and without:

YZ Constraints ('out of plane'):

Assembling in Rhino

or

filling in

Hardware Notes

• needs more clearance on belt-side
• belt tensioning?
• when rounding corner, teeth must at some point disengage b/c different lengths
• same size M3 tensioning

Motor Idlers / Topside Way Bearings mount on M5 SHCS with washers on both sides and washers used as bearing shims. Use 3DP bushing (or purchased?) in axel. Important for carrying some moment to plate.

Clearances here for pulley to be mounted / tensioned! Consider order of assembly, tensioning.

M5 Nuts 93625A200 M5 SHCS (length not selected) 91292A128 M5 Washers 93475A240

also uses long M3's for tuning, nuts, washers. Length to be selected.

Egregious Errors

• bottom rail extremely unhappy, should be smooth and sideways ways should be clear

Minor Errors

• missed a few holes in CAM, double check!
• y block internal boxing has co-dependent assy
• bearing bushings not satisfactory
• on double rollers, accomodate washer in between
• motor collar coule be +0.05mm in diameter
• need long M5 for motor -> bearing
• need bigger wall on captive nut for tuning
• need channel in side of motor collet for screw turning
• XZ situation has lots of unaddressed assembly issues
• add clamping features, hole access for final beam -> gantry assembly
• have to watch where bolt heads, bolts are - should include those in kinematic units modules
• y gantries should include two rollers in xy space (machine space) constraints

Some Simulation

It occured to me in class today (Rob Hart fabricated the below component!) that the two-bar flexure I had intended was acting much more like a one-link flexure. Whoops, all well. Still does its job. Here's an image of that in any case:

ooooh