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Double Bass shaping a new bridge

#4
Hi.

swamprocker said:
if I am shaping a new bridge, and if it is adjustable, can i use the feet off the old bridge? then only have to size the top?
Click to expand...

Yes, theoretically, but unless both the new and the old bridge are exactly the same, You still have to shape the feet as well.
It's not likely that the feet will flex the same either.

The spreader is easy enough to make if that's what worries You.

I have only experience about a few bridge shapings, but the feet were the best part IMHO. Perhaps the sense of accomplishment or something like that ;).

Regards
Sam
 
#7
360guy said:
Try this: put the warped, old bridge upper part into some boiling water for about 15-20 minutes. It will straighten back. Let it dry 24 hrs. It should be good to go. At the very least you' ll have a back up bridge.
Click to expand...

Thanks!! i will give that a try. the bridge i tried to order is out of stock and i need to have a fix by new years. \m/

after i boil it, should i clamp it between some straight wood??
 
#8
What is the "secret" to shaping bridge feet? I tried a few years back by placing sand paper on the top and rubbing the bridge against it (before installing adjusters) but the result was less than optimum. I ended up letting a pro properly shape it for me.
 
#11
360guy said:
Try this: put the warped, old bridge upper part into some boiling water for about 15-20 minutes. It will straighten back. Let it dry 24 hrs. It should be good to go. At the very least you' ll have a back up bridge.
Click to expand...

While this is a good temporary fix, it will soften the maple and the warping will come back quicker the second time around. You still need to be ready to replace it.
 
#14
bssist said:
What is the "secret" to shaping bridge feet? I tried a few years back by placing sand paper on the top and rubbing the bridge against it (before installing adjusters) but the result was less than optimum. I ended up letting a pro properly shape it for me.
Click to expand...

Sandpaper fitting is generally considered a poor method. Pros use some kind of crayon or something to mark the top. Then you carefully shave the feet where the crayon transfers. Start with a knife or a chisel and move to a scraper as the fit gets closer.
 
#15
Hi.

bssist said:
What is the "secret" to shaping bridge feet? I tried a few years back by placing sand paper on the top and rubbing the bridge against it (before installing adjusters) but the result was less than optimum. I ended up letting a pro properly shape it for me.
Click to expand...

There's really no secret, just a tool.

Called a leg spreader :D. ( aren't all DB's just that)

Since I'm not a luthier, mine is just a long M6 (1/4) nut with carriage bolts on both ends. One nut and 2 sets of bolts are enough to cover the entire range from 1/8 to 5/4 bass bridges.

A rigging screw type would be much better, obviously, just haven't gotten around to make one. Yet ;).

The method I use, is that I rough shape the feet without the spreader, string the bass up to tune, install the spreader so it is snug, and shape the feet to match the contours of the top.

If the feet flex a lot, or if the top is very soft, it's a good precaution to place thin, flat strips of wood between the top and the pre-shaped legs when stringing up to tune. Otherwise the inside edges of the feet may dig into the top. NOT RECOMMENDED.

BUT, I feel the need to stress this once again: I AM NOT a luthier, just a DIYholic with very inexpensive basses, so do take my advice keeping that in mind.

Regards
Sam
 
#16
Shaping the feet to the top: doesn't anybody lightly tape sandpaper, grit up, to the top with something like painter's low-tack masking tape (so it won't do anything to the finish), and then rub the bridge feet fore and aft (fingerboard to bridge, about an inch each way from the f-hole notches - NOT across soundhole to soundhole) to conform the feet to the top?
 
#17
Some shops do, but this results in the feet becoming slightly rounded. It will look like a perfect fit, but you will be able to rock the bridge back and forth slightly with the strings off. A sign of a really well fitted bridge is one that does not rock at all.
 
#19
The compression stress on the top of the bridge results in the feet spreading apart a little bit (~ 3mm?). If you fit the feet without taking that into consideration, the feet will not feet once the strings are under tension. So we use a tool called a bridge leg spreader that pre-stresses the bridge to approximate the position they will take under load. Then we fit the feet.

You can either buy them or make them. I made mine out of a small turnbuckle, so that I could simply twist the middle, and both ends would move in or out.

Does that help?
 
#20
Hi.

iiipopes said:
Shaping the feet to the top: doesn't anybody lightly tape sandpaper, grit up, to the top with something like painter's low-tack masking tape (so it won't do anything to the finish), and then rub the bridge feet fore and aft (fingerboard to bridge, about an inch each way from the f-hole notche - NOT across soundhole to soundhole) to conform the feet to the top?
Click to expand...

Yep, as the "rough" mating, before and after using the spreader.

But, after that it's very easy and quick job to carve the feet to match the top exactly. That takes only a few minutes IMLE, so why on earth would anybody skip that important part of the mating?

Regards
Sam
 

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