Tuesday, March 30, 2021

Jacobus Stainer in Absam prope Oenipontum 16, pt 3

 With the cracks glued and cleated as I thought needed, time to fit the new bass bar.

First, layout in pencil.  We want the bass bar to be under the foot of the bridge, 'east to west',  in a sense as measured from center-line, or from the edge of the f-hole, or some place to hook the tape-measure, as it were.  I also don't want it to overlap the upper terminal hole of the f-hole.  With these two constraints, there is usually not much choice.  We also want it angled relative to the spruce grain, for strength purposes.  Lining the bass bar along the grain is a great way to crack the top.

The problem with old tops is that they are not always normal.  

Here are some of my pencil marks.  The line connecting the notches of the two f-holes is nominally where the bridge would sit.  But you might see that this line is not perpendicular to the center line, meaning at least one of the notches is not in the right place.  What's the right place?  A normal stop length, these days, is 195 mm.  The line below the line connecting the two notches is at 195 mm.  So in some sense, neither one of the notches is where we would think they should be.  

And yes, the top is normal size.  14 inches.  Mixed measurement units, it's how we do things in the US.

Unfortunately, the notches are convenient and easy to see from the outside, when positioning the bridge.  Or repositioning some time in the future when it comes off or is replaced.  

I'm not sure where the bridge will end up on this fiddle.  But with a ruler, I can put it at 195 mm if I want to, even if it doesn't line up with the notches.  And with an inspection mirror, I will be able to see the pencil lines inside, to help with soundpost adjustments, that sort of thing.

For placement, right now I don't really care where the bridge sits.  I can work with that later.  On the other hand, we think we should know where the bridge is so we know how long to make the bass-bar, how far it extends from the bridge both north (towards the neck) and south (towards the end-block).  

Pencil, calculations, guess, and make a couple marks.  

Next to plane some spruce down to thickness, with the growth lines vertical to the top, again for strength.  

With the thickness correct, I cut it a bit longer than my carefully calculated length.

Next, rough-fit the bottom, and when that is close, temporarily glue in a few cleats to help place the bar in the same place for final fitting.  It needs to fit extremely close the entire length.  And that will take longer than what I've done here.

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