Bridge feet again

[Martin Jonas]

Having read the various advice on bridge fitting at frets.com and here, I've been sanding down my bridge feet (standard rosewood adjustable bridge on a Washburn carved spruce top), using fine sandpaper on the top. The curvature and the fit seem just fine with the strings off and slight finger pressure at the bridge pins; good contact all around. However, with the strings on and tuned up, the string tension slightly deforms the bridge and/or the top and there is light shining through along about the first 2mm on each foot next to the centre gap and about 5mm of light at the other side of each foot. That means the bridge is still in full contact along about 90% of its length, but it doesn't seem quite right. How can I get the bridge to match the shape of the top under tension rather than without? Continuing with sandpaper on the top with the strings off doesn't seem a promising route to get the last bit of light eliminated. Or should I leave well enough alone? Compared to the fit when I got the mandolin (which I think was still the original factory setup), it's already an incomparably better fit and the tone has improved considerably.

I think the root of the current appearance is that the original fit had a large gap in the centre of each foot, as the bridge was clearly pre-cut for a top with a higher arch than mine. As a result, the tension had previously pressed onto the edges of each foot and this seems to have made a permanent slight depression just where I now have the light shining through.

Any advice?

Martin
(feeling my way through mandolin setup...)

[sunburst]

I can think of several possibiulities:

The rosewood bridge may be lacking in stiffness. An ebony one might work better.
The compressed areas of the top from the old bridge fit could be the problem. they might steam out and be better. Steam out (http://www.frets.com/FRETSPages/Luthier/Technique/Finish/SteamOut/steamout1.html)
It might be good enough like it is. How does it sound?

I use little scrapers (old Xacto blades that I can't get anymore) and emory boards to fit bridge feet. you could just cut the centers of the feet a little more.
Many years ago a violin maker taught me to fit violin bridges with a little German carving knife. When I found out I could do that I quit taping sandpaper to mandolin tops. I've never been happy with the results, tho it seems to work for others.

[Martin Jonas]

Thanks Sunburst. I've just picked up the mando again from a local luthier, who checked the setup and recut the bridge and nut slots (and charged a very reasonable 12 Pounds for it). He thought the bridge feet are fine as they are now, so I think I'll leave it for the time being. One thing I'm surprised about is that he cut the e-string notches a good deal deeper than they had been -- he said the saddle had a slight reverse camber that he needed to correct for to bring all string into the same plane. I hadn't noticed that and will have to check with a level when I get home. I'm a bit concerned that the deep notches (they're about 2mm deep and very narrow; no widening towards the top) will constrain the string and stop it from chiming freely. No doubt I'll find out when I get home and try it out.

Martin

[sunburst]

A lot of bridges sag in the center, especially rosewood or anything less stiff than ebony. If the deep notches bother you, shave the top of the saddle down 'til they're normal looking.
Your luthier probably set the action for good string height over the frets and that's what it took. 2 mm is right much, you might benefit from a better bridge.

[Martin Jonas]

Thanks again!

Martin