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UG Fiddlesmith

Bass Bar Fitting

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I recently opened a violin with the intent of shortening the ribs as they were hanging off the back edge only to find the bass bar about 50% loose from the top-some attempt had been made in the past to reglue this bar but apparently there was too much spring to overcome.  It took only a few minutes to remove the bar in one piece. I proceeded to shorten the ribs and then started on the bass bar.  I planed it to thickness, cut it to rough length, layed out its position and tack glued it in place pretty well following Weishaar & Shipman and Johnson and Courtnal.  After drying I used my handy little washer to scribe the curved shape of the bar, then removed the bar and trimmed with a knife to the scribed line then fitted 5 cleats to keep it in place while chalk fitting.  The purpose of this thread is to describe how I kept up with the time I spent starting with a stopwatch to determine how much time it took to place the bar on the top and get some chalk transfer then remove the chalk.  It takes me about a minute to do one repetition. I tallied each repepition until I was satisfied with the fit.  I started with a small straight thumb place and did six repetitions then switched to a scraper to remove the chalk for 20 more repetitions for a total of 26 reps.  I have done this experiment before and had a lot more reps but I am finding that the less I use the plane and the more I use the scraper the better it works and I think that is because the plane removes too much material which requires some correction.  By timing myself I am sure I have improved my efficiency and thus my costs.  I have spent over 5 hours installing a bar in the past.  Now I need to figure out how to trim the bar and get predictable results. 

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That's cool that you're keeping track of how many reps it takes you to fit a bass bar. Do find 5 cleats are necessary? I've never used more than 3. Does that speed up your process too?

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I need to figure out how to trim the bar and get predictable results. 

 

 

This is what Michael Darnton posted when I had profile questions:

 

 

I use a simple plan that is based on something I got from the Carl Becker shop, who gets full credit for it. The basic idea is to measure the bar height including the top thickness, with a graduating caliper. Divide the bar into eighths (nine pencil marks, including the ends) and the thickness of top plus bar is 5.0mm, 7.6, 10.2, 12.8, 14, 12.8, 10.2, 7.6, 5.0, from one end to the other at each mark. 

 

It's simple, gives exactly the right profile, and compensates for top thickness. I start the bar 40mm from both ends, and it's 5.5mm wide, 1mm inside the outside foot of the bridge, and 12mm from the center of the upper bout and 15mm from the center of the lower bout. 

 

That's all there is to it, and for smaller instruments multiply by .925 for each successive size downward.

 

 

 

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Yes, this is the Becker method that Chris Germain demonstrated at the Atlantic City VSA. However, Chris used a lower bass bar height than Darnton. 

 

The underlying bass bar geometry is to adjust a triangle to fit your plate contour.

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I've been following Michael Darnton's measurements for a while and gotten very good results. I glue blocks in place (3 usually does it), eyeball the fit for a couple of passes, removing wood with a small flat finger plane. When I get to the chalk part of the program I do something a bit different. Instead of using a metal scraper I use a small piece (approx. 1" x 2") of freshly cut glass, cut slightly convex. It removes wood as well or better than a metal scraper but with the added bonus of being able to look through the scraper and pin point the spot being scraped. I also have found the glass scrapers to work well on fingerboard dressings, neck to fingerboard fittings and especially on the final fit of cello or bass bridge feet. An added plus is that when the glass scraper gets dull there's no need (or way) to sharpen it. Just snap off a new sharp piece. The glass will have one dull edge (the edge contacted by the glass cutter), and one sharp edge. Glass is not for every scraping application but for the ones mentioned above it really works well.

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I use a sharp knife as a scraper.  I’ve used broken window glass in the past (for other things) but the irregular edge can cause scratches and gouges.  I agree that planing after the rough fit can undo a lot of careful work!  :(

 

Re: height, 14mm minus 3mm for the top gives 11mm, which is a pretty standard height, IIRC.

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That's cool that you're keeping track of how many reps it takes you to fit a bass bar. Do find 5 cleats are necessary? I've never used more than 3. Does that speed up your process too?

I put one cleat at the neck end, two on one side and one on the other then it seems I need one more to tighten up the bar so it will barely move; I slide it no more than .5 mm.  Someday I am going to count reps on a soundpost patch-I might need a bigger sheet of paper.

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I fit the bar only with a small plane, very sharp, and with a narrow throat. I rarely need to use a knife, and never a scraper. It's very quick and accurate, I can't imagine how scraping would help.

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