Session 7: Toolpath Types & Profile Offset
Session 7
Toolpath Types & Profile Offset
First: Your Model Has to Move
You modeled in OnShape. You will program toolpaths in Autodesk Fusion. Two different programs, so the part has to cross between them.
STEP: A Neutral Format
Export from OnShape as STEP — a format nearly every CAD and CAM program can read.
- The geometry crosses over intact
- Your design history does not — no sketches, no feature tree, no parameters
Why That Matters
A STEP file is a finished shape, not an editable design. If you need to change a dimension, you change it in OnShape and export again.
Editing the shape in Fusion instead means your two files no longer agree — and the one you cut from is not the one you designed.
You Have a Model. Now What?
Fusion takes your flat panel's shape and turns it into an actual path the router bit follows.
Three Toolpath Types
Two Names for the Same Thing
Those are the industry names. Fusion labels two of them differently in its menus — learn both, because you'll hear the left column and click the right one.
| What it's called | What Fusion calls it |
|---|---|
| Profile | 2D Contour |
| 2D Pocket | |
| Drill | Drill |
Drill Has a Catch
A Drill toolpath plunges the bit straight down. So the hole it makes is exactly one bit wide — no more, no less.
Drill Has a Catch
Need a hole bigger than your bit? A Drill toolpath physically can't do it.
That's a Pocket (clear out the round area) or an interior Profile (cut around the inside of the circle) instead.
Why This Will Matter
Your arcade cabinet needs holes for buttons and joysticks. A standard arcade button wants roughly a 28–30 mm hole.
The biggest bit in the shop is a fraction of that. So none of those holes are Drill toolpaths — and knowing that now saves you a failed job later.
Profile
Cuts along a drawn outline — the toolpath you'll use to cut a panel free from stock.
The Bit Has a Diameter
It's not a mathematical line — it's a spinning cylinder with real width.
Cut exactly on your drawn line, and the bit removes material on both sides of it.
Profile Offset
Cutting a Part: Use Outside
The bit runs outside your line, so the material it removes is all waste — your part comes out full size.
Cutting a Hole: Use Inside
The bit runs inside your line, so the hole ends up exactly the size you drew — not slightly small.
This Is a Tolerance Problem
The wrong offset choice makes a perfectly modeled, in-tolerance part come out of the machine the wrong size.
Same idea as Unit 1 Session 9 — a spec on a screen doesn't guarantee a correct real part.
Two Things to Remember
Ask "am I keeping this or removing it?" before choosing an offset.
That question alone tells you Outside or Inside almost every time.
Two Things to Remember
On-Path is rarely what you actually want.
It ignores the bit's width entirely — both a cut part and a cut hole come out wrong-sized.
Next Time
Session 8: Pockets, Step-Over & Step-Down
Clearing out material instead of just cutting along a line.
'F' → Fullscreen
Build
Step 1: Identify Toolpath Type
For each of the following, name which toolpath type (Profile, Pocket, or Drill) you'd use. For the holes, state what bit diameter you're assuming — it changes the answer.
- Cutting a rectangular panel free from a full sheet
- Clearing a recessed tray area into a panel's face
- A 6 mm mounting hole for a bolt, using a 6 mm bit
- A 28 mm hole for an arcade button, using the same 6 mm bit
Step 2: Choose the Right Offset
For each scenario, decide Outside, Inside, or On-Path, and justify using the "am I keeping this or removing it?" question:
- Cutting your control panel's outer shape free from a sheet
- Cutting a joystick's mounting hole to its exact drawn size
- A test cut where dimensional accuracy genuinely doesn't matter
Step 3: Predict the Error
If you accidentally used Inside offset instead of Outside when cutting a part free from stock, would the part come out too big or too small? Explain using the bit-diameter idea from today.
Checkpoint
Before you move on, confirm you can answer this out loud, in your own words:
Why does the same drawn line need a different offset depending on whether you're cutting a part out or cutting a hole into it?
Reflection
Answer these on your own. Reflections are individual, even when the rest of the session was team work.
- How is today's offset problem the same problem as Unit 1's tolerance work, even though none of the vocabulary matches?
- Session 8 covers pockets. Based on today, what do you expect is different about programming a pocket compared to a profile cut?
Submit
Submit your toolpath identifications, your offset choices with justifications, your error prediction, and your reflection.