Beginner’s Guide to Machining CNC Parts
Deliverable: CNC’d Parts
After all the preparation, we’re finally ready to make some chips and machine a CNC part.
Push the Green Cycle Start Button
Deliverable: Begin executing the G-Code Part Program to make chips for the first time.
The program and setup have been carefully proofed, there is a workpiece in the workholding solution ready to go, and it’s time to make chips. Push the Green Cycle Start button and begin executing the g-code program.
Watch the Part Carefully
Deliverable: Keep an eye on the Part Program until it finishes.
If this is the first time you’ve made this particular part, you probably don’t want to just walk away and leave it. Here are some tips on how to monitor progress to make sure everything is going well:
Tip: Be ready with Feedrate Override and E-Stop or Feed Hold.
If this is the first time cutting chips, it’s still a good idea to be ready with the Feedrate Override and either E-Stop or Feed Hold, depending on which one is better for your machine.
Tip: Be especially mindful as each tool starts cutting.
This is the time to make sure the tool enters the cut cleanly without chipping or undue noise and to make sure that the feeds and speeds are producing a result that looks and sounds good.
Tip: Make sure the coolant, mist, or air blast is aimed to clear the chips.
Be paranoid about chip clearing. Recutting chips is hard on tool life, and in the worst case, the chips can pile up to the point a cutter gets broken. Also, sometimes a chip will get into the plumbing and can block the coolant. That’s a recipe for a broken tool if you don’t catch it.
Tip: Watch for untoward vibration and movement of the workpiece.
The cut should be smooth. If the noise is too loud and especially if you see the workpiece move at all, there may be a problem. You may need to adjust the feeds and speeds or find a way to hold the workpiece more tightly.
E-Stop in Case of Emergencies
Deliverable: Being prepared for emergencies.
Always be ready to E-Stop in case of an emergency!
Deliverable: Inspect the part as much as possible before removing it to make rework easier.
A vise stop can make it easy to put a part back right where it was…
Experienced CNC’ers realize that once a part is removed from the machine, it can be difficult to put it back exactly as it was to permit rework. Re-work is going back to machine away errors in the part. Errors may be due to mistakes in the Part Program or simple things like using a tool that is too worn or that breaks for part of the job. They may even be due to having a customer change their mind about the part’s design midway through manufacturing.
It’s always wise to inspect the part as much as possible to make sure it was machined correctly and meets tolerances before removing it from the machine. Resist the urge to pull it off until you’ve done so, or make provision (as described in the drilldown article) to be able to put the part right back if a problem is discovered.
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