Post by germanguitars on Dec 10, 2019 14:30:53 GMT -5
I'd like some advice for avoiding tear-out in a specific job. I'm refining my process for machining guitar fretboards. Ebony is very chippy, and fretboards need sharp corners. I may need to rearrange my order of operations to get a better edge on this particular corner:
Here is my current strategy in 3 cuts:
Should I do the cutout step first, then radius and fret slots?
Should I make the perimeter passes a mere 0.005" from final? Or even 0.003"?
Should I break up the cut so that instead of making two inside-corner turns, I cut the nut line first and then the sides, plunging in the excess wood?
Edit to add-
I just cut out the same strategy as original except that I did the cutout 0.005" from final, then did the final cut 0.002" proud. I used some quartered redwood that has been drying for over 40 years, so although it is soft, it is more chip-prone than anything else in my shop. Seems to have worked:
Here is my current strategy in 3 cuts:
- Radius cut: 4-flute 1/2" ball nose solid carbide bit. 0.025" step-over at 120 in/min, 18,000 RPM. The stock is thinned down to near final thickness so I'm not hogging off much wood when I carve a radius along the top.
- Fret slots: 3-flute 0.023" end mill. 0.025" DOC at 23 in/min, 24,000 RPM. This step has to happen after the radius cut since the bit follows the curvature.
- Cutout: Onsrud finishing bit 3 flutes 1/4" with slight up-shear. 100 in/min, 24,000 RPM. I climb cut the perimeter 0.015" outside the final surface with 0.0625 DOC passes. This goes well at the corner, but leaves lines that need to be erased. For the final pass I remove that remaining 0.015 at full depth, and the corner sometimes chips out.
Should I do the cutout step first, then radius and fret slots?
Should I make the perimeter passes a mere 0.005" from final? Or even 0.003"?
Should I break up the cut so that instead of making two inside-corner turns, I cut the nut line first and then the sides, plunging in the excess wood?
Edit to add-
I just cut out the same strategy as original except that I did the cutout 0.005" from final, then did the final cut 0.002" proud. I used some quartered redwood that has been drying for over 40 years, so although it is soft, it is more chip-prone than anything else in my shop. Seems to have worked: