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dalpets Member
Joined: 13 Jan 2022 Posts: 26 Location: Adelaide, South Australia
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Posted: Thu Jan 27, 2022 7:36 am Post subject: under bars to lift mold blocks |
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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? |
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Michael Darnton Moderator
Joined: 23 Mar 2007 Posts: 1288 Location: Chicago
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dalpets Member
Joined: 13 Jan 2022 Posts: 26 Location: Adelaide, South Australia
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Posted: Thu Jan 27, 2022 11:50 am Post subject: |
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Michael Darnton wrote: | I say your mold is too thick. There's 10 mm of room for 15-16 mm of linings. |
I don't completely understand the maths. Could you please restate another way.
The rib height for the Messiah, I believe, is 31mm.
I thought, all along, that the mold could be any reasonable height and that it in this case it would not interfere with the ribs or the blocks at the time of eventual separation because 31mm for the blocks & ribs is more than the height of the mold.
Also, am I hearing that the standard for all Violin molds is 12 or 15mm & nothing else? |
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Michael Darnton Moderator
Joined: 23 Mar 2007 Posts: 1288 Location: Chicago
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Posted: Thu Jan 27, 2022 2:15 pm Post subject: |
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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. _________________ new blog at my site! http://darntonviolins.com/blog
my work sites: http://darntonviolins.com and http://darntonhersh.com |
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dalpets Member
Joined: 13 Jan 2022 Posts: 26 Location: Adelaide, South Australia
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Posted: Sun Jan 30, 2022 1:08 pm Post subject: |
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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. |
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Michael Darnton Moderator
Joined: 23 Mar 2007 Posts: 1288 Location: Chicago
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Posted: Sun Jan 30, 2022 1:25 pm Post subject: |
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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. _________________ new blog at my site! http://darntonviolins.com/blog
my work sites: http://darntonviolins.com and http://darntonhersh.com |
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dalpets Member
Joined: 13 Jan 2022 Posts: 26 Location: Adelaide, South Australia
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Posted: Mon Jan 31, 2022 9:30 am Post subject: |
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Michael Darnton wrote: |
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. |
I've seen these large sheets of sandpaper being used in Youtube videos but I have not seen them for sale anywhere online, particularly in Australia.
Do you know of any sources that I might try? |
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Michael Darnton Moderator
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dalpets Member
Joined: 13 Jan 2022 Posts: 26 Location: Adelaide, South Australia
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