Engraving Fret-slot Positions with a V-tip Cutter

A key component of this method for accurately placing and cutting fret slots involves the use of a low-deflection 60° V-tip engraving bit. These tools are specifically designed to scribe lines in hardwoods and composites with very little deflection, even at high chiploads. By scribing a shallow groove into the fingerboard at each fret position, a "guide" channel is created that helps reduce the deflection of the fret-slot cutter. This is especially effective if the engraving pass is made in the opposite direction to the first slotting pass.

Note: When shopping for V-tip tools to be used for fingerboard scribing, make sure that the vendor, or manufacturer, lists the full specifications and tolerances of the cutting flutes. If you do not know the included angle and flat-tip diameter to a reasonable level of precision, it will be very difficult to accurately calculate the feed-rate and depth-of-cut needed to program the cut. The included angle (total angle) should be specified to ±1° and the flat tip to ±0.0005" (0.013 mm).

If this information is not readily available on the vendor's website or printed on the cutter's packaging, find another source.

60° V-tip Details

Scribing fret slots with a V-tip tool is about the easiest operation employed when making a fingerboard. Because of the strength and stiffness of the tool, effective heat conduction from the cutting tip and the efficient shape of the cutting flutes of a properly designed tool, the engraving process is very tolerant to variations in chipload. Basically, you position, plunge and go. Not very exciting, but VERY effective.

Obviously, the v-grooves can be cut as deep and wide as the bit will allow. However, do NOT make them too wide or the studs (barbs) on the fretwire tang will not get enough bite to lock the fretwires into the stots. Typical values for the chamfer width on both sides of the fret slot vary from 0.005" (0.127 mm) to 0.010" (0.254 mm) per side.

EXAMPLE: Assuming

• a 0.023" (0.584 mm) wide fret-slot will be cut
• 0.005" (0.127 mm) chamfers are desired on both sides
• the total width of the "V" slot will be (2 x 0.005") + 0.023" = 0.033" (0.838 mm)
• a 60° v-tip bit with a 0.015" (0.381 mm) flat diameter (as shown) will be used

The bit will need to plunge 0.0156" (0.396 mm) deep for a single pass cut. A minimum feed rate of 80 IPM (2,032 mm/min) at 24 KRPM is recommended. You can probably go faster, but this will be a good starting point.

NOTE: If you are scribing a billet that has been rough planed or radiused, remember to add the thickness of the stock allowance to the depth-of-cut determined. Assuming that the roughing pass left 0.010" (0.127 mm) allowance above the finished surface, the total depth will be (0.0156" + 0.010") = 0.0256" (0.65 mm). If you want to be really picky you can recalculate the feed-rate based on this new depth, but it is not usually necessary.

Oh, what the heck. The new numbers would be: feed-rate = 107 IPM (2,718mm/min) @ 24KRPM with a depth-of-cut of 0.0256".

For more information on the use of V-tip engraving tools and how to easily calculate plunge depths, cutting width and optimum feed rates, go to V-tip Engraving Tools

3D model of 60° scribe line 0.0156" (4 mm) deep


V-scribing Fret-slot Positions
video courtesy of D. Wieland, , Dark Art Guitars