CAD/CAM & CNC Machining

A Kaern Schools course, taught on cycleCNC — the browser-based CAM + CNC toolpath and simulation environment from the cycleX project family. In this room we don't just learn theory; we cut real parts for cycleWASH bicycle-washing machines.

Your tutor: Mill — twenty-odd years of swarf under the fingernails, a soft spot for a well-tuned chip, and zero tolerance for crashing into a vise.

How this course works

Seven modules, each building on the last. We start where the metal meets reality — fundamentals and materials — and we finish at the inspection bench with a part you can measure and be proud of. Every module gives you Mill talking through the why, a worked example on a genuine cycleWASH part, a hands-on job you'll build and simulate in cycleCNC, the three mistakes everyone makes, and a couple of questions to check you've actually got it.

The running thread is real: cycleWASH machines need brackets, manifolds, nozzle blocks, pump mounts, and panels. We'll machine versions of each. By the capstone you'll take a part from a sketch to a verified, simulated, post-processed program.

A note on units: cycleCNC speaks millimetres by default (the cycleWASH shop is metric). I'll give imperial equivalents when it helps your intuition.

Module 1 — Machining Fundamentals & Materials

Learning objectives

• Explain how a cutting edge actually removes material, and what a "chip" tells you about your process.
• Distinguish the common cycleWASH shop materials (6082-T6 aluminium, 304/316 stainless, mild steel, acetal/POM) by machinability and application.
• Read a basic engineering drawing: datums, tolerances, surface finish callouts.
• Describe the CAD → CAM → G-code → machine → part pipeline and where cycleCNC sits in it.
• Make a sane stock-and-material decision for a given cycleWASH component.

Lesson 1.1 — What cutting really is

Teaching script (Mill): "Right, hands off the keyboard for a second and look at this. A cutting tool doesn't grind metal away — it shears it. The edge wedges under a thin layer, the metal yields along a shear plane, and it curls off as a chip. That chip is the most honest report you'll ever get from your process. A nice tight blue-brown 6 on stainless? You're in the zone. Long stringy silver birds-nests wrapping the tool? You're rubbing, not cutting — wrong feed, dull edge, or no chip load. Dust instead of chips? You're burning. So before we touch a single line of code, I want you thinking like the chip. Everything we do — speeds, feeds, tool choice — exists to make a good chip and get it out of the cut. Why does that matter for cycleWASH? Because a 316 stainless nozzle block that work-hardens because you dwelled too long becomes a scrap block, and scrap is just money you set on fire. The machine is dumb; it does exactly what you tell it. Your job is to tell it something the metal agrees with. So — when you next see a chip come off, what's the first thing it's telling you?"

Worked example — reading a cycleWASH bracket drawing in cycleCNC: Open the sample part pump-mount-bracket.step in cycleCNC's model view. It's a 6082-T6 aluminium L-bracket, 120 × 80 × 8 mm, with two M6 mounting holes and a 40 mm bore for the pump spigot. In the Inspector panel, hover the bore: cycleCNC reports the modelled diameter (40.00) and the drawing's tolerance band (H7, +0.025/0). Note the surface-finish flag on the bore face: Ra 1.6. Mill's read: aluminium, generous tolerances except that one H7 bore — so the bore gets a finishing pass and probably a reamer or boring head, everything else can be roughed and finished in one go.

Hands-on exercise: In cycleCNC, load pump-mount-bracket.step. Use the Measure tool to confirm overall dimensions and the bore diameter. In the Material dropdown, set stock to 6082-T6 and define a rectangular stock block of 124 × 84 × 10 mm (oversize for clamping/facing). Write a one-paragraph "process intent" note in the project notes field: which features get roughed, which get finished, and which need tight control. No toolpaths yet — just the plan.

Common mistakes:

1. Ignoring the surface-finish callout and treating every face the same — the Ra 1.6 bore needs its own strategy.
2. Choosing stock the exact size of the part, leaving nothing to face or grip.
3. Reading the H7 as "about 40 mm" — tolerance is the whole job here.

Check for understanding:

1. What three things can a bad chip tell you about your cut?
2. Why did we make the stock 124 × 84 × 10 instead of 120 × 80 × 8?
3. Which single feature on this bracket will demand the most care, and why?

Lesson 1.2 — Materials and machinability

Teaching script (Mill): "Materials are personalities, and you've got to learn who you're dealing with. 6082-T6 aluminium — that's your friendly apprentice. Cuts fast, loves high spindle speed, gives gorgeous finishes, forgives a lot. 304 and 316 stainless? Stubborn, proud, and they hold a grudge — they work-harden, meaning if you let the tool rub instead of cut, the surface goes glassy hard and now you're fighting a material you created. The rule with stainless is: commit to the cut, keep the feed up, never dwell. Mild steel sits in the middle — predictable, a bit gummy, wants coolant. And acetal, POM — that's plastic, machines like a dream but melts if you cook it, so sharp tools and don't let chips re-cut. Here's why this matters for us: a cycleWASH machine sprays water at pressure all day. The wet, sprayed parts are 316 because it shrugs off corrosion. The dry structural bits are 6082 because it's light and cheap. So the material is chosen by the function, and the material then chooses your machining strategy. You don't get to fight that. So tell me — if I hand you a part that's going to live in a constant high-pressure spray, what material am I almost certainly going to specify, and what's the one machining sin I must not commit?"

Worked example: In cycleCNC open the material library and compare three entries side by side: 6082-T6, 304 stainless, POM. The library lists recommended surface speed (Vc) ranges — roughly 250–400 m/min for aluminium, 60–100 m/min for 304, and 300+ m/min for POM. Mill points out: the same 10 mm part takes wildly different spindle RPM in each material to hit the right cutting speed. We'll do that maths properly in Module 4 — for now, see that the software already encodes hard-won shop knowledge.

Hands-on exercise: Build a one-page comparison table in your project notes for the four shop materials (6082-T6, 304, 316, POM): typical cycleWASH use, relative machinability (easy/medium/hard), key risk, and recommended coolant approach. Pull the Vc numbers from the cycleCNC material library.

Common mistakes:

1. Treating stainless like steel and dwelling in the cut — instant work-hardening.
2. Running plastic too slow with a dull tool — melted, re-welded chips.
3. Assuming "harder material = slower everything" — it's about cutting speed, not just being timid.

Check for understanding:

1. Why is 316 chosen for the wet parts of a cycleWASH machine?
2. What is work-hardening and how do you avoid causing it?
3. Two parts of the same size, one aluminium one stainless — which spins faster and roughly by what factor?