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# Roller Milling

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

![wb](/images/wb-01.jpg)

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

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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.

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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.
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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).

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![one-mill](/images/rob_rct_one.jpg)
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## CAD

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

![bits](/images/little-bits.png)

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

![more bits](/images/multiple-bits.png)

And combined into a complete gantry:

![comb](/images/combined-bits.png)

Here's the back of that:

![allup](/images/backside.png)

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## 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/](/cad/assembly/elements) for kinematic elements, and [cad/assembly](/cad/assembly) for one-machine made with these elements.

Motor and XY Constraint:

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![motor](/images/kunit-motor.png)
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XY Constraints, with preload adjusting and without:

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![xy-adjust](/images/kunit-xy-adjust.png)
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![xy](/images/kunit-xy.png)
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YZ Constraints ('out of plane'):

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![yz](/images/kunit-zy.png)
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**Assembling in Rhino**

![basically](/images/kunits-basic.png)

or

![units xz](/images/kunits-before-form.png)

filling in

![one](/images/kunits-one.png)

![two](/images/kunits-two.png)

![three](/images/kunits-three.png)

![four](/images/kunits-four.png)

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## Hardware Notes

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- 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

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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.

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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

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

## 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:

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![onebar](/images/preload-sim.png)