Top 3 Hacks for Building a Guitar with your Desktop CNC Machine
Hey future guitar builder! So, you've got this awesome idea of making your electric guitar using a desktop CNC machine. Here are three tricks that I wish I would have known before building my first guitar on a desktop CNC machine.
1. Make It Smooth with Finishing Passes:
A finishing pass is the last operation that a CNC machine performs on a workpiece after the roughing and intermediate passes. Unlike roughing passes, which remove large amounts of material quickly, and intermediate passes, which refine the shape, a finishing pass is focused on achieving a high-quality surface finish and precise dimensions.
Here's why a finishing pass is essential for obtaining a better-finished product:
Tight Tolerances:
This is the big one. Finishing passes help achieve tight tolerances and accurate dimensions. By taking smaller and more controlled cuts, the CNC machine ensures that the final dimensions closely match the intended design. This is crucial for parts that require precise fits, e.g., the neck joint.
Better Surface Quality:
A finishing pass uses a smaller stepover (the distance between each pass of the tool) and a shallower depth of cut, resulting in a smoother surface. This minimizes visible tool marks and enhances the overall aesthetic of the wood. This is less important when building a guitar because you generally will do at least some light sanding of any piece that comes off the machine, but this allows you to start with a much higher grit. Which brings us to our next point…
Reduced Sanding Time:
Since a finishing pass produces a smoother surface, it reduces the need for extensive manual sanding. This not only saves time in the post-processing phase but also helps ensure that your finished product is consistent with your 3D model. The more manual sanding you have to do, the more likely you are to deviate from your original design. Deviations (happy accidents) can be fun, but if you’re looking for consistency, best to limit the room for human error.
Pro Tip: Free software like Fusion 360 make adding finishing passes a piece of cake.
2. Build a Body That Fits the Neck... Not a Neck That Fits the Body:
Here's a game-changing idea—start with the guitar neck instead of the body. This way, you can make tiny adjustments to the neck pocket until it fits snug, giving you a guitar that has good resonance, sustain, and looks professional… no one wants to see any nasty gaps in between the neck and the neck pocket.
Having done it both ways, we can say with certainty that it is much, much, much easier to adjust your neck pocket to fit the neck than it is to adjust your neck to fit the neck pocket.
Pro Tip: When milling out the neck, start conservatively, i.e., use the “stock to leave” function to leave some material on the inside walls of the neck pocket. Once the operation has finished, check to see if your neck will fit in the pocket. If not, re-run your neck pocket finishing pass with reduced stock to leave. Re-check the neck fit and repeat this process until the neck fits snuggly.
3. Calibrate Your Machine Before You Start.
Calibrating a desktop CNC machine is a crucial step to ensure accurate and precise machining. Calibration involves adjusting various parameters of the machine to align its movements with the intended design. Here's a general guide on how to calibrate a desktop CNC Machine like the Shapeoko 3 XL (the machine we use):
1. Check Mechanical Components:
Ensure that all mechanical components, such as V wheels, are properly tightened. Loose components will lead to inaccuracies during machining.
2. Verify Belt Tension:
Check the tension of the timing belts. This is a Goldilocks & the Three Bears situation. If the belts are too loose, they will start missing steps which hurts your precision. If the belts are too tight, the can snap or damage your motors.
Pro Tip: Watch this video to see how to check those timing belts like a pro.
3. Square the Machine:
Use a square to check that the X-axis and Y-axis are perpendicular to each other. This ensures that the machine moves accurately in both dimensions.
4. Run a Circle-Diamond-Square Test:
This test helps identify any irregularities in the machine's movement. Create a program that instructs the CNC machine to cut a circle, a diamond, and a square. Inspect the cuts for accuracy and adjust the machine as needed.
Pro Tip: Watch this video to see a Circle Diamond Square test being performed.
5. Calibrate Steps per Millimeter:
In short, when you tell your machine to go +100 mm on the X axis, you want it to actually travel +100 mm on the X axis, not +98, +102, or any other number.
Steps per millimeter represent how many steps the motors need to take to move the machine by one millimeter. Adjusting this value ensures that the machine moves the correct distance according to the design.
Measure a known distance (e.g., 100 mm) and compare it to the actual movement of the machine. Adjust the steps per millimeter until the machine moves the correct distance.
Pro Tip. Watch this video for a great explanation on how to calibrate your steps (as well as other helpful calibration and tramming tips).
6. Test Homing and Limit Switches:
Ensure that homing and limit switches are working correctly. Homing allows the machine to find its reference position accurately, while limit switches prevent the machine from moving beyond its physical limits.
7. Verify Spindle/Router Alignment:
Ensure your spindle/router is properly aligned. An off-center router can result in inaccuracies, especially during tool changes.
Get Machining
These three tricks—finishing passes for smoothness, starting with the neck, and tuning up your machine—are like having special powers in your guitar-building toolkit. Each step will help you make a guitar that not only looks cool but plays like a dream. Now go have a blast building! 🎸
