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Session 10: Post-Processing & Troubleshooting

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Session 10

Post-Processing & Troubleshooting

The Router Never Sees CAM Studio

Verify played your coupon on a model of the board. The router can't run a model. It reads a text file, one line at a time, and does exactly what each line says.

Today you make that file, read it, and fix the one line in it the Genmitsu refuses.

The Post Writes the File

A post-processor turns your toolpaths into the language one controller speaks. In CAM Studio, the machine in your job picks it.

The Post Writes the File

Your template's machine is Inventables X-Carve GRBL. The Genmitsu runs GRBL too, so the post writes G-code, in a file ending .NC.

The ShopBot speaks a different language, and its post writes a different file, ending .sbp.

Same Plate, Two Languages

The top of a Genmitsu file:

G21
G17
( Operation: Button hole )
T1 M6 (D3.175 mm End mill)
S6000 M3
G0 G90 G54 G94 ( Work plane )

Same Plate, Two Languages

The top of a ShopBot file for the same plate:

'UNITS:MM
SA
TR,6000
C6
PAUSE 2

Both say "millimeters, absolute positions, spindle on at 6000 RPM," in completely different words. That's why the post has to match the machine.

Read the Top of Your File

G21
G17
( Operation: Button hole )
T1 M6 (D3.175 mm End mill)
S6000 M3
G0 G90 G54 G94 ( Work plane )

Read the Top of Your File

G21
G17
( Operation: Button hole )
T1 M6 (D3.175 mm End mill)
S6000 M3
G0 G90 G54 G94 ( Work plane )

G21: millimeters. S6000 M3: spindle on, 6000 RPM. G0 G90 G54: fast moves, absolute positions, measured from the zero you set on the machine.

Read the Top of Your File

G21
G17
( Operation: Button hole )
T1 M6 (D3.175 mm End mill)
S6000 M3
G0 G90 G54 G94 ( Work plane )

T1 M6 means "change to tool 1." The Genmitsu has no tool changer. Typed into Candle, it answers error:20: unsupported command.

So every file gets that line deleted before it goes to Candle. The post writes it anyway, every time.

Read the End Too

G0 Z15.
M5
M30

Lift 15 mm above your zero, spindle off, program over. Nothing else.

Read the End Too

It didn't always end that way. The post used to add a return move to the machine's home. On a router that hadn't been homed, that move dragged the bit down through a finished part.

The template's post is fixed. Homing after every connect still isn't optional.

Name It So You Can't Run the Old One

The first real cut in this shop ran in the air: someone loaded an older file with a different zero.

Every file you post gets a version number: coupon-v1, then coupon-v2. The newest number is the only one that goes to the machine.

The Diagnostic Clinic

From here on, problems show up as a symptom first. You work backward to the cause. Every one of these happened, or nearly happened, in this unit.

Symptom: The Whole Job Ran in the Air

Probed Z without typing G10 L20 P1 Z20, so zero sat on top of the 20 mm puck. Or an old file was loaded. Session 4.

Symptom: The Job Froze Halfway

The computer slept, and the router stopped at the last line it was sent. Sleep and screen-off stay off on the Candle computer.

Symptom: The Outline Didn't Cut Through

The model is thinner than the board. CAM Studio measures every depth from the top of your model, so a 12 mm model on an 18 mm board stops more than 6 mm short of the bottom.

Symptom: The Button Won't Fit Its Hole

Offset left at 0.8 mm: a 26.4 mm hole. Session 9.

Symptom: The Plate Came Out 6 mm Small

The side arrow points into the part, so the bit cuts inside the line all the way round. Session 8.

None of Those Show Up in Verify

Every one of them looks fine on screen. They're settings, files, and habits, and the only thing that catches them is checking on purpose.

That's what a pre-cut checklist is for: the things Verify can't see, checked before the spindle starts.

Two Things to Remember

Read the top and the bottom of every file you post.

Delete T1 M6, and make sure it ends with a lift and M30, not a trip somewhere else.

Two Things to Remember

Verify checks the cut. The checklist checks everything else.

A perfect toolpath still fails on an unhomed machine, a sleeping laptop, or last week's file.

Next Up

The Practice Build.

Design a small part, program it, and cut it for real: this whole unit in one small project, with your checklist in hand.

'F' → Fullscreen

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Build

Step 1: Post Your Coupon

  1. Open Session 8 - your name and its CAM Studio tab. Right-click Setup → Regenerate all toolpaths.
  2. Right-click Setup → Post child operations…
  3. Set File name to coupon-v1. Leave Options on Store file in a new tab, and click Export.
  4. A new tab appears at the bottom, named coupon-v1.NC. Open it and click Download.

The file stays in your OnShape document, right beside the design that made it. That's the copy to trust, not whatever is lying in a Downloads folder.

Step 2: Read the Top and the Bottom

Open the downloaded file in a plain text editor: Notepad on Windows, TextEdit on a Mac. On your sheet, write what each of these lines makes the router do:

  • The first line that isn't in parentheses
  • The line with M6 in it
  • The line with M3 in it
  • The last three lines

Step 3: Search the File

Press Ctrl+F and search for each of these.

  1. ( Operation: — write the three operations in the order they appear. That's the order the router cuts them.
  2. Z- followed by your thickness: for a 12 mm board, Z-12. (the dot is part of the number in this file). That's the bottom of your button hole, and the deepest the bit goes in the whole job. Which operation is it under?

If the hole's bottom isn't there, don't guess. Go back to the Button hole's Heights in CAM Studio and compare.

Step 4: Delete the Line the Genmitsu Refuses

  1. Delete the whole T1 M6 line. Delete nothing else.
  2. Save (Ctrl+S). The name must still end in .NC; if your editor offers to add .txt, don't let it.
  3. Check it: search M6, then G28. Both should find nothing.

Step 5: The Diagnostic Clinic

For each symptom, write the likely cause and the fix.

SymptomLikely causeFix
The whole job ran above the board without touching it
The job stopped halfway and the router just sat there
The outline didn't cut all the way through
The arcade button won't fit its hole
The plate came out about 6 mm small both ways
The bit snapped on its first pass

Step 6: Build Your Pre-Cut Checklist

Write the checklist you'll use before every cut in the Practice Build. At least two items in each group:

  • The machine (Session 4): homing, zero, the probe, clamps, the computer
  • The model (Sessions 5 and 9): thickness, sizes, what's in the job
  • The toolpaths (Sessions 8 and 9): side arrow, step-down, offset, depths, order
  • The file (today): name, version, the line you delete

Write each one as something you can check with a yes or no. "Check the depths" isn't one. "The hole's bottom, Z-12., is in the file" is.

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Checkpoint

Before you move on, confirm:

  • Your saved coupon-v1.NC has no T1 M6 line and still ends in .NC
  • You found the operation order and your hole's bottom in the file
  • Your checklist has at least two yes-or-no items for the machine, the model, the toolpaths, and the file
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Reflection

Answer these on your own. Reflections are individual, even when the rest of the session was team work.

  1. The post writes a line the Genmitsu refuses, every time. What does that tell you about trusting a file just because software made it?
  2. Session 11 starts your own practice build — your design, your material, your toolpaths. Name one thing you'll deliberately keep simple, and say what would go wrong if you didn't.
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Submit

Submit your sheet with the lines you read, your depths, the clinic table, your checklist, and your reflection. Keep coupon-v1.NC.

Activity Complete