Machine Design

jake: ctrl+f TODO

Intro

Machines in a week
It's easy, so to speak
In minutia is mayhem

OK, welcome to Machine Week.

If you're reading this, chances are you're about to design a machine, and then build it, and then 'bring it online', and then do something with it. Exciting! There's a great deal of complexity here! I have done this a few times now¹, and every time it's a new adventure.

The type of machine you build is your discretion. Besides making a straightforward 3-axis CNC Machine (a-la Shopbot, as documented in the following guide) - there are a few cool variations you can explore:

5-axis CNC Machine

A Delta Machine (3-axis and neat kinematics)

Scara Arms

Hot-Wire Cutters

Pick and Place

Lathes

etc!

This document will serve as a guide for how to make a 3-axis machine. In linear time, I'm going to run through my design and fabrication processes, including links, resources and asides when relevant. You should read through it as a launching point for your machine. As a default, you are free to use all of the resource here to replicate the machine, and develop an end effector of your own.

!ALERT! ~ This is a design process ~ !ALERT! so please bear with any ambiguities and nonlinearities. When possible, I will take asides to explain my reasoning², but overall, I hope to demystify CNC D&B³. Good luck, have fun!

In this order, we will do:

Design:

• Draw a Layout (Rhino Suggested)
• Detail the Axis
• Detail Interconnects

Manufacturing:

• Do Material Layout in Rhino
• Program CAM in Fusion
• Do the Milling

Assembly:

• Put it together!

Electronics Assembly:

• Plugs, Switches, Power, oh my!

Motion Control

• TinyG with a Big Heart (and second-order acceleration curves!)

Machine Communication

• Chilipeppr
• GCode

End Effectors

• Open Season: Design your own!

Layout

First thing, you'll want to get a hang of what rough sizes / shapes / orientations your machine is going to have. In this case, I'm interested in designing something of an 'everything machine'. I.E it should be useful for a few different processes: 3D Printing, CNC Milling, Flat-Sheet Cutting (a-la the ZUND), and (maybe) eventually Laser Cutting. Normally I would not advise this⁴, but here we are.

I'm going to aim at a roundabout bed-size⁵ of 12x24"⁶ - largely this just feels like a happy medium between large format and small format work. It's a fairly common size for sheet stock, or at least bigger sheet stock can be broken down into these sizes with minimum work. In Europe, sheets also commonly come in 1250x2500mm stock - a factor of 1.025 over the NA 4'x8' standard. I'm going to add 1" to each of these dimensions to account for that, and for general design-fudge-space, and for fixturing. I feel like 5'⁷is a great Z-travel value - this will handle lots of stock, and lots of tools (in milling) - also, this is relative movement, and I plan on making the overall bed height / end-effector mount locations somewhat adjustable.

SO: 13x25x5" moving area.

W/R/T Layout, there are a number of permutations of how to go about adding axis together in order to get 3D motion. I'd like to cover a few of these in examples, and I'll leave a TODO here: - bridgeport x-on-y with beefy-z style, shopbot and laser 'H' machine w/ dual y-drive (note laser BED moves, not head), omax and fablight 'drafting-square' hella-stiffness gantries, ultimaker t-config, corexy, flexural stages. I really like this machine developed by one of Jens' students. I should explain why⁸. OK, enough talk - let's see an example of a machine layout -

I tend to 'work out' from the Z-axis, towards the edges - this way I can keep track of where I need extra offsets (length of travel != length of gantry). Here's the layout with the Z-and-X axis group moved around to the extents.

And the layout as representative of a real machine...

NONLINEARITY ALERT You can tell I already have some sense of what the details in my axis system are like, which has informed (in a big way) how I laid the rest of the machine out. HOWEVER - as this stage, I took no time to carefully align things, set thicknesses, etc. I was simply trying to get a general sense of what-goes-where. This will inform my next spiral, where I detail axis.

Good design is kind of like this - you are starting far away from your desired goal, and in limited time, you approach the destination. Deviations you make early on have big effect on your final location - even though this is when you have the most limited amount of information. It's important, during the early space, to properly explore as much 'design space' as possible - this way you are better off later on - sometimes in categorically better or worse positions. SO: don't jump too early, be curious, be cautious, think as carefully as you can as you make these initial decisions.

Parametric Axis

Jens Dyvik is on some wonderful machine building sprials (link!) and we're going to put them to work this week. In particular, the chamferrail system. Take a look at his documentation to get an overview of the machines!

I'm using his Chamferrail Generator in Rhino and Grasshopper - included in this repo under /cad/axis-generator/ and in Jen's Repo here.

Links to these files are under /cad/axis-generator/ - you can open the Rhino and Grasshopper file there TODO: Link Grasshopper Tutorials and get to work inputting your parameters.

You can make a linear axis:

Or a rotary axis:

Use Grasshopper to adjust the parameters - you'll find them all on the left. There's a huge swath to get through, try experimenting so that you understand the different parameters. Critically, adjust Axis Length, Axis Width, and Axis Type (Rotary or Linear). The Motor Size & Material Thicknesses are set already for the materials we have on hand for machine week, and the Tooth Size variables are set up for the milling capabilities we have in our shops.

Once I have my parameters set up, I use the 'bake' command to pull the geometry out of grasshopper and into Rhino.

I'm going to do this for each of my axis: X, Y and Z - and then bring those into another Rhino File so that I can start composing them into a machine.

• Observations on Build
• Tricky to coordinate X / Z Axis as rails really need to be adjustable
• Setting Z Height and Thicknesses during fab is VERY important! Face your Bed!
• Countersink Bolts for Motor Mount, or bring hole size down so that you can tap
• Bring Motor Flange Hole size ++
• Bring Motor Mount Screws -- to thread
• Get Flat Head SHCS for Motor Mount, do Chamfer

Axis Blocks

OK, I have my axis:

Critically, I coordinated mounting holes (there's an option for 'custom hole pattern' in the Glideblock Geometry Section) so that my X and Z axis would comfortably overlap:

Now I'm going to bring these into my layout:

What I'll do now is compose axis 'from the action-out' ... i.e. I'm going to set up my Z->X relationship up, and then my X->Y relationship up. I'm working 'out' from where we do the business: at the Z axis, with the end effector.

Now is when we start deviating from the parametric axis. I'm going to make on major concession: my Y axis (the long ones) I have split, and I'm going to put one side of the rail on either, and link them with a rigid member along the x axis... I'm also going to bring one of the adjustable-sides of the chamferrail across.

I'm feeling ready to start 'boxing it out' - i.e. adding some structure to these so-far so-flappy axis. Here we go:

And the X-Axis... Stiffness is king! But weight is not your friend...

Starting by linking the two Y-Axis Gantries with a block - this way, I can comfortably constrain these gantries relative eachother - since they are operating on a split rail. TODO: Kinematic Jams

I was having a pretty hard time ironing this out. 'Annealing' the ~ design-space ~ . I printed a screenshot from Rhino^{TODO: note on printing from rhino, to scale} and tried doodling. Design Education gets a +1 pt for this moment... I figured it out pretty quickly! Actually on paper it seemed really obvious. Brains, weird!

This is satisfying: I have a squared-out structure that I feel good about, it's not too heavy...

And putting the X on the Y axis is semi-deconstructable / easy-ish to assemble:

OK. I feel good about this, I'll throw in a few bonus features (like, a bed could be nice?) and call the blocking-out section done.

Here's the bed. I make no claims to elegance, but this will make it easy to load in a sheet of spoilboard. I am largely trying to avoid cutting so much plastic.

Prepping Your Machine

CRITICAL NOTE These linear axis absolutely require you to face off the spoilboard on your milling machine. If the XY Plane that your material rests on is not truly parallel to the XY Plane that your gantry moves along^{TODO: imperfections note} you will have axis whose chamfered-edges vary in width. This will cause some areas on the gantry to jam up, and others to be loose! END CRITICAL NOTE

First thing, I surfaced the bed. We have this big gnarly cutter at the CBA:

I made a tool for this in Fusion (TODO: include in table), it's included in the table below.

And I ripped out a 'face milling' toolpath:

Then I got on the shopbot, and ran the job! I set the Z (in the program, it just faces along Z0.0) such that the machine thought 0.0 was about 0.1" below the surface. I had to run the job twice, bringing it down by 0.1" each time, to get all of the low spots. Nice circular turnaround courtesy of Fusion 360 CAM:

CAM:

Once I'm ready to do some manufacturing, I start by laying the pieces out - grouping them by material. Most things are in HDPE (or ABS - TBD!). The 'rails' are made with Delrin⁹ of a similar thickness, and the pinon is made of thicker Delrin, about 3/4". Here's a chance to optimize your layout for the size of sheet stock you have. Keep in mind you'll want clearance between items for cutout tools, etc.

Now I brought this into Fusion to do some CAM. From Rhino, select the geometry for one material and Export as a .step file. Then you can upload this into Fusion.

I go to the CAM section right away, and setup some stock. First thing, our Shopbots are setup in Inches, so check that in the 'units' in the top of the tree. I'll use a 0" offset on top of the model, 0.05" on the bottom (then we can be sure to cut through later on) and a 0.75" offset on the sides - I want to be sure to clear the screws I'll be using to fixture my HDPE sheet.

For tools, I set up with a 1/8" 'O-Cutter' - as in, one flute. This is going to be my detail workhorse - it'll cut teeth and holes. I also have 1/4" O-Cutter to do profiles and cutouts. My two other tools are a Chamfer Endmill, used for, well, the chamfers, and a 1/16" 2-flute endmill for some detailing on the pinion. Here's a quick table of the tools, and their feeds and speeds. I used the CBA Feeds and Speeds Calculator to ballpark these, and I'll dial them in as I test the first axis.

A note on plastics - TODO heat, why single flute, sharp bits, what chips should look like

HDPE:

Type	Flutes	Diameter	What For	Feed, XY (IPM)	Feed, Plunge (IPM)	Spindle Speed (RPM)
Endmill	1	1/8"	Most Details, Holes	55	25	13500
Endmill	1	1/4"	Cutouts, Grunt	55	25	7000
Endmill	2	1/16"	Pinion Detail	75	25	20000
Chamfer Mill	2	1/2"	Rail Edges	100	50	5000

Acetal:

Type	Flutes	Diameter	What For	Feed, XY (IPM)	Feed, Plunge (IPM)	Spindle Speed (RPM)
Endmill	1	1/8"	Most Details, Holes	55	25	13500
Endmill	1	1/4"	Cutouts, Grunt	55	25	7000
Endmill	2	1/16"	Pinion Detail	75	25	20000
Chamfer Mill	2	1/2"	Rail Edges	100	50	5000

I also have a tool library for Fusion 360, include TODO here.

The quality of your work on the Shopbot will directly influence the quality of work your CNC Machine will do! A few important points:

• Face your Bed!
• The chamferrail system relies on a consistent chamfer size. If your bed is slightly tilted in any direction, the size of the chamfer will change along the length of the cut. This means that along some sections of the rail there will be too much friction, and at others, it will be lose!.
• Carefully Zero the Z!
• Same as above, thicknesses of varying parts are vary (haha) important. Rather than using the shopbot's z-touchoff plate, I like to dial the Z in myself by dropping the height in 0.1 -> 0.01 -> 0.002 increments, while checking if the tip of the bit is scoring an edge on the material.

Assembly

• Careful on Blocks! Trim and Align

Plugging in Motors

• Coils are connected
• One and two
• Link Datasheet from StepperOnline

Configuring TinyG

• https://github.com/synthetos/TinyG/wiki
• Do Power to the board
• Should enumerate on a serial port
• Use https://github.com/synthetos/TinyG/wiki/TinyG-TG-Updater-App to flash new firmware
• Make sure you don't have the serial port open anywhere else
• Now complete setup
• Open in a serial terminal (Arduino has one built in, or see Neil for links) TODO

Chilipepper

• It's Rad
• Like Mods, Chilipeppr uses a local serial server to pass messages from the browser to your serial port.
• Download the Serial Port Json Server after configuring TinyG
• http://chilipeppr.com/tinyg
• Steps / mm
• Acceleration
• Travel, etc

Talking to, loading firmware on, TinyG

• Arduino, I hope?
• Chilipeppr (rad alert!)

Gcode Basics

• may it RIP

Bill of Materials

Controller

• TinyG
• buy on Adafruit

Power Supply

• 24v 14.6A switching PSU

Motors

• 4x NEMA 23 57x57x56 w/ 6.32mm Shaft w/ D w/ 400 Steps / Rev

Tooling

• 1/8" O-Cutter Upcut - https://www.bhid.com/itemdetail/HARVEY%2051908 or Onsrud PN 65-013
• 1/4" O-Cutter Upcut - https://www.bhid.com/itemdetail/HARVEY%2044916 or Onsrud PN 65-023
• 1/2" 90deg Chamfer Endmill - https://www.bhid.com/itemdetail/NIACUT%20N76595
• 1/16" O-Cutter Upcut - https://www.bhid.com/itemdetail/HARVEY%2051162
• M5 Tap (McMaster)

Hardware

• SHCS M5x12 (Motor Mounting) - 91292A125
• SHCS M5x20
• SHCS M5x30 (Rails Mounting) - 91292A192
• Washers M5 - 93475A240
• Set Screws M3x6 (Pinion Safety) - 92605A100

Material

• Rails / Structure etc: 3/8" x 24x36" of HDPE or ABS (TBD)
• Glide Blocks: 3/8" x 12x24" Acetal (Delrin) Sheet
• Pinions: 1" x 2x6" Acetal (Delrin) Bar

End Effector Showdown

• A Router
• A Laser Diode (haute)
• A 3D Print Head (also haute)
• Heated Bed ?
• Ceramic Printer
• Pick-and-place-ish
• Drawing
• Camera / Scanning
• Cutting

Footnotes

1. Five Axis, Metal Laser Cutter, and here, Dual Head 3D Printer, and Ongoing Robot Arm Adventure
2. Asides will be relegated to the footnotes when not strictly necessary.
3. Design and Build
4. Things work very well when they are designed to do only one-thing. For example, vise grips will turn just about anything, but no one would say they are good at turning anything. A building designed for Helsinki may not make so much sense in Dubai. In another example, a laser cutter has a motion system that is optimized for speed, and takes advantage of the fact that it has very little mass to move around (a few mirrors) in order to carry through on this optimization. A milling machine is engineered for stiffness, and trades speed for the mass required to carry through on that optimization. In trying to have one motion system do all of these things, we'll go a little 'soft' in the middle, but we'll also be able to offer a lot of variety in a single system.
5. Relative Scaling: 10^4 of length scale is a common machine, 10^6 is good - lookup slocum ?
6. ~ 305x610mm
7. ~ 127mm
8. So I want an H-style layout, because I want to keep the machine small relative it's total work area. One of the biggest drawbacks with an H-machine is that the two sides of the Y-axis are not always set up parallel. The result is what's called 'racking' - i.e. imagine opening a screen door, and the top or bottom exhibits more friction - the 'jam' that this causes happens in CNC Machines as well. A drawing. By cutting both Y-axis rails out of the same 'frame', Jakob gets around this issue - the parallelness of the two rails is a mirror of the parallelness of the machine which cut them. It makes it a bit bulletproof to novice assemblers. He has also done a really good job of keeping the X-axis loads really close to the Y-axis rails (so, a small structural loop).
9. AKA Acetal, AKA POM

to be linked - dan gelbart talk about resolution vs. accuracy - repeatability vs absolute accuracty - global vs. local resolutions