Australian/New Zealand Luthiers Forum

There are actually two tools needed: a cutting gage and a scraping gage. Well, make it five tools if you count in a chisel, plus a knife and needle file for clean-up). Time required to cut all channels: about one hour after having gotten familiar with the process.



The chisel-shaped scraping blade can be ground from a cheap square needle file. It needs sharpening and honing, a bevel angle of about 45° works fine for me (different scraping action depending on scraping direction).

First, using the cutting gage the borders of the channel must be cut to a depth of about 0.7 to 1.0 mm. Then the scraping gage cuts the rest of the depth in the sides, respectively 1 mm deep into the top and back, right adjacent to the cuts made with the cutting gage.




Then, again using the cutting gage the rest of the remaining material in the channel gets cut away:




The narrower the scraping-chisel is, the faster the channel will be cut to its whole depth. My blade is about 2 mm wide, which is on the wide side. 1 - 1.5 mm would be better, but the blade's shaft where it gets clamped should be thicker, unless a more sophisticated clamping mechanism is made (this square blade sits in a round hole in the wood, thus gets bent when clamped, so over-clamping could be fatal for the blade).

Here's another view of the scraping tool, showing more of the blade clamping mechanism:

Nice job Markus.You could grind your blades out of round High Speed Steel to fit the hole.
Here are some photos of my version.
Finished cutters Like this to cut the top Like this for around the sides.Note the cutter needs rolling over in this photo to get the bevel on the right side.This was just for photos.

Localele wrote:Nice job Markus.You could grind your blades out of round High Speed Steel to fit the hole.

Thank you Micheal. It is actually not a real issue with the square blade in the round hole, I only mentioned the possibility of over-tightening to prevent someone could put the blame on me if he breaks the blade for behaving like an elephant. In fact, a square blade (shaft) in a round hole has the advantage to require a minimum of clamping force to hold it firmly in position.

Localele wrote:Here are some photos of my version.

Beautiful tools. Too bad I am not equipped to do proper metalworking - which may be the main reason why I'm not so fond of it. I prefer to grind a needle file to shape than an 8mm thick HSS rod.

The tolerance and fit of "real metalworking" are addictive.Using a milling machine with a DRO for measurements making fret scales really makes it easy and fun.Same for drilling bridges for string spacings.You soon realise the need then for a small precision lathe to make the other parts to the same standard.
All this can take you away from woodwork a bit though as you move over to making your own metal parts.I like to think it is a logical positive step and enjoy it immensely.
Turning knobs for my Rosette Cutters

I am more on the handmade lane. For me, tolerances serve a purpose, not an addiction.