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I have a Collings MT and it's my understanding that the fingerboard has a compound radius. The frets are getting to the point where they will need to be dressed. I've dressed/leveled frets on mandolins with a flat or "single" radius, but never on one with a compound radius. Any advice would be appreciated.
Thanks.
Hi Dave,
Compound radius leveling is slightly more difficult, but not as bad as it seems. Think of the fingerboard as a cone, the point being somewhere north of the nut and the widest part towards the bridge end.
Keep your leveling file or block along the lie of the strings following the shape of the cone as you level. If you go parallel to the center line, you will mess up the radius. You also won't be able to use a radius block to put a radius back in if you take the frets down very far. I suppose you could use short radius blocks of varying radii to put the radius back in if you know what radius is at each point along the fingerboard?
Scott
I just use a 12" or 10" radius sanding block, using a layout marker (glorified Sharpie) on the crowns of the frets to make sure that every three or four swipes, I haven't gotten off track. Using this method, you can mill the frets without risk of losing the compound radius.
As Scott says above, you have to be able to visualize the truncated cone formed by the compound radius and align the sanding block to approximate the surface of that cone. The procedure is really no different than leveling a straight radius fretboard, you just have to be able to understand the geometry and what you're trying to achieve.
Scott has it right... if the conical shape of the fingerboard really does follow the taper of the strings. Sometimes folks just arbitrarily choose two different radii for the fingerboard, small at the nut, big at the bridge end of the fingerboard (and another for the bridge, or even use a flat bridge), and if the radii are not chosen correctly, the strings do not follow a centered path from point of cone to base of cone. I don't know for sure, but knowing the attention to detail that Collings is known for, they probably got it right, and milling along the paths of the strings should do it.
John is on track. I had a mandolin in that gave me fits until I realized the compound radius wasn't. It was some kind of odd mix of who knows what! Wasn't immediately apparent until I marked the frets and tested the shape with a straight edge to scrape the marks. All over the place. I had the truss rod snugged up a bit to get the neck straight, and the contact points along the string paths were just a bit weird. I filed along the cone carefully, making sure the contact point areas were really nicely lined up. Used three radius gauges I made to test. Then crowned and polished. There was a bit of eyeballing involved, but the thing played great. It was more work than usual, but not that much more.
As in most oddball jobs, patience and testing along the way were the keys. Have fun!
This is one of the few specialty tools from Stewmac that I cannot live without.
Along with being a conventional fret re-crowner, a few strokes with this allows for eraser like spot touch-ups on radiused or flat fretboards.
http://www.stewmac.com/shop/Tools/Sp...Fret_File.html
Thanks so much to all of you have so generously offered your advice. I do have two radiused blocks, a 10" and a 12", which I bought from Stew-Mac several years ago. I'm not a pro, just a do-it-yourselfer, but I've done quite a few fret-dressing jobs for myself over the years and they turned out well. I've used the Sharpie marker technique before, although not with a compound radius. Thanks to your advice, I'll feel safe using that method on my Collings. I've been looking at that fancy fret diamond file that Stew-Mac has, but just haven't pulled the trigger on it yet. Maybe it's time!
Thanks again for all the good advice. Long live the Mandolin Cafe!
Keep an eye on what's happening to the tops of the frets as you go. Although things can vary fret-to-fret due to wear or unevenness or whatever: generally if you see the frets getting flatter/wider in the middle of the fret, you're flattening the radius. If you see them looking flatter/wider at the ends of the fret, you're tightening the radius.