Violin Forum/Message Board

[dalpets]

I have seen some recommendations for the thickness of bars underneath a mold prior to gluing viz.,
for 12mm thick mold, bar thickness 9.5mm
for 15 " " " " " 6.0-7.0mm

At first glance these figures looks suspiciously precious. My mold is 20mm, so if I suspect a formulaic relationship is being used I get 7.6mm for my bar thicknesses. (ribs approx 31mm)

Is it necessary to go to these seemingly ridiculous lengths, or it just in the eye of the holder?

What do you say my under bar thickness should be?

[Michael Darnton]

I say your mold is too thick. There's 10 mm of room for 15-16 mm of linings.
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[dalpets]

[Michael Darnton]

Linings go on before the mold comes out, to maintain precise shape. So you need space above and below the mold for gluing the linings. Linings are 7.5 mm, figure an extra mm one either side so they aren't smack down against the mold is 17 mm for linings and space, half on either side. 13 mm mold thickness, with 8.5 mm supporting sticks works.

Standard Strad rib heights are 30 mm at the top block and 32mm at every other block. A 15 mm mold would be a tight squeeze. You need wiggle room to get the ribs off.
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[dalpets]

Thanks for your tips re linings (purfling).

My strad poster shows rib heights & edge thicknesses for the treble & base sides of the ribs. The measurements for both vary along their total lengths.
There are numerous measurements shown & they are of random sizes.

I didn't expect that!

How in the heck does one achieve all of those variations ? if I am interpreting things correctly it seems like it would be an extraordinarily time consuming exercise to try to do so.

Also, I'm not exactly sure which 'edge thicknesses' the poster is referring to.
If it is the ribs I purchased they are 2mm thick. How does that square with the aforementioned requirement for variations?

You say 'Standard Strad rib heights are 30 mm at the top block and 32mm at every other block' How is that adjustment achieved?

Some help please.

[Michael Darnton]

Ribs need to be planed and scraped down to 1 mm or a bit more in thickness.

On old violins the rib heights vary a lot through shrinkage and careless top removal and replacement. There is no need to copy that.

Edge thickness refers to the thickness around the edges of top and back. Usually around 4 mm new and wearing to less over time. There are additional nuances that you don't need to think about at this point--slightly thicker corners, button and c bouts, but the changes are tiny. A new violin would be consistent but an old worn one all over the place

Some modern makers achieve rib heights by gluing a large sheet of sandpaper to a flat surface and rubbing the ribs on that to put it all in the same plane. Then reducing to the upper block is a matter of finesse with the same tool.
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[dalpets]

[Michael Darnton]

Floor sander belt, cut.
_________________
new blog at my site! http://darntonviolins.com/blog
my work sites: http://darntonviolins.com and http://darntonhersh.com

[dalpets]

I was thinking more along the lines ot this;

https://www.youtube.com/watch?v=dLyeYeZM26Q
@7.20 t0 8.52