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Engelmann violin top

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Hi
This time I wonder how I will work my new violin top since this is my first time with Engelmann spruce. 
Seems to be very light and of a fine grain
Any recomendation about?

Thanks in advance

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What's the SG on the top?  A light top <0.34 may need a higher arch to add strength.  That should be enough blood in the water for the sharks to come in and give you more detailed and possibly contradictory advise. :)

-Jim

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18 minutes ago, Jim Bress said:

What's the SG on the top?  A light top <0.34 may need a higher arch to add strength.  That should be enough blood in the water for the sharks to come in and give you more detailed and possibly contradictory advise. :)

-Jim

I try to understand some basic rules of physics one of which is:

"For every expert opinion there is an equal and opposite expert opinion"

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24 minutes ago, Marty Kasprzyk said:

I try to understand some basic rules of physics one of which is:

"For every expert opinion there is an equal and opposite expert opinion"

Action always equals reaction, so there's the logic :) More basic rules: when 2 luthiers agree, one of them is lying (or maybe both) and when asked a question to 5 luthiers, you might get 10 expert opinions .. 

 

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56 minutes ago, Marty Kasprzyk said:

I try to understand some basic rules of physics one of which is:

"For every expert opinion there is an equal and opposite expert opinion"

I'm no expert. But I have used Englemann, and I did make one out of .29 or so Englemann that is very easy to play.  It has a humongous arch of about 20 mm.  Yes, it rises very much on the ends, but that was carved in, because that is the way the poster had it. 

The back is very stiff, .68 or so flamed birch.

I do the arches somewhat different now, but I would make that model out of Englemann.  I wouldn't make it out of something stiffer.

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The things we really need to know is if it was cut on the full moon, waning moon or new moon?

Was a chainsaw used, with or without ethanol in the fuel,,, or

Was it felled with a two man saw? Did both men have two arms,, or finally was it felled with an axe,,, how sharp was it?

Was it blocked and quartered on the spot or was it skidded out with an old fordson? Did a group of boy scouts urinate upon it at any time? and Did any one ever drive a nail in to its virgin grain to hang a lantern upon while they were camping, did a bear ever scratch upon it?

 

Ok funs over,,,,,,,,,

If it's light, then make no curvy lines going to the neck and end blocks, keep it full to the channels with straight lines and no bulging in the ends. A circle with a radius of 48 to 50 inches is good length wise from corner block to corner block then blend gracefully into a straight line going into the end blocks, with a slightly flatter spot in the bridge area, this general Idea  is the least likely to get a neck drop and later distortion,,, which is the bane, or the curse of real light wood.

!6mm is a good all around arch height for light Engelmann, or a bit lower,,,,,

Make the arch 1.5 to 2 mm higher at the widest part of the lower bout, than the upper bout. And the same at the corner blocks, 1.5 to 2 mm higher at the lower corners, and the arch will be lower at the upper corners. At the upper corners start the transition to the straight line,, which should be from 70 to 90 mm long, starting from the purfling and transitioning as it reaches the upper corner blocks. The straight line at the lower block is much shorter .When it's done right it is all very subtle and not obvious, it all flows together smoothly but it is the underlying principle of strength that matters. The straight lines will not always be straight as the years roll by, they will roll with the years. And the upper arch will rise with time. But if it's done just right it can last a long time, but I guess everything's relative isn't it!

 

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2 hours ago, lpr5184 said:

I'm shopping around for some Engleman now so I'm interested in what densities others are using.

I have used from .31 to .40 densities, with the lower ones used on violas.  My wood is torrefied, and started out 5% higher density.  Density isn't the only thing; I have had low-density wood ranging from 5800 m/s to 4800 m/s (unprocessed), so it matters a lot how stiff it is, rather than just density.

I think it is necessary to have some experience database to work from first, before deciding how a different wood should be used.  If the wood is good low-density Engelmann, I would watch the weight and taptones, generally ending up lighter and higher frequency than "usual".  As for arching, I don't know... there are opinions on both sides that make some sense, although lower arching seems to make the most sense to me (and thicker than "usual").  

One other item that makes sense:

29 minutes ago, Evan Smith said:

If it's light, then make no curvy lines going to the neck and end blocks...

This is more important for the neck block, where there is more going on, and if anything moves, it's really bad.  I would also avoid steep angles near the neck block, and I would avoid graduating thinly around the block area as well.  Now that I think about it, these rules apply to everything, not just low-density.

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Evan and Don,  Thanks. I'm going to buy some Engleman from Kevin Prestwich when he gets back home. I was thinking in the .36 range. I'm sure he can pick out something good for me. All of my remaining wood is .40 and over.

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1 hour ago, lpr5184 said:

I'm going to buy some Engleman from Kevin Prestwich when he gets back home. I was thinking in the .36 range. I'm sure he can pick out something good for me. 

Log 1601 or1704 I think would be good, or maybe he has found something new recently.  Finding wood with good properties is hard enough, but then trying to find wood that also has good-looking, even grain, no twist, and the worms haven't eaten is a real effort.

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Hi all


Thanks all for advices.


My thought is:

Light weight - a little more arched and thiniest than heavy weight. Then the ears drive me.

Top finished must sound F or F#. That is all my science.

If I remember well, the SG (¿peso específico in spanish?) is .36. But I must calculate for sure. The halves are glued so it will be difficult to do. School is very far (60 years old)
 

Evan.
Special thanks for archings advices it will be apply.

 

Regards

Tango
 

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4 hours ago, Don Noon said:

This is more important for the neck block, where there is more going on, and if anything moves, it's really bad.  I would also avoid steep angles near the neck block, and I would avoid graduating thinly around the block area as well.  Now that I think about it, these rules apply to everything, not just low-density.

does this also apply for the back plate?

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Ok,help me out here!! You all are mentioning "SG" and "SD" etc. yadda yadda. What I would appreciate knowing is how these sets of numbers are arrived at.

Any clarifications would be greatly appreciated as I am notable a very unscientific luthier!

Fred the violguy

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7 hours ago, Jim Bress said:

What's the SG on the top?  A light top <0.34 may need a higher arch to add strength.  That should be enough blood in the water for the sharks to come in and give you more detailed and possibly contradictory advise. :)

-Jim

On one of the other recent posts about wood, I lamented the lack of a glossary to explain key terms to the uninitiated.

what is SG?  And how is it important?

and SD also.

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SG is specific gravity is in short the density of wood made dimensionless (by comparing to water). Density is weight to volume, for instance grams per cubic centimeter or g/cm3. Spruce has a density ranging from usually 0.35 - 0.45 g/cm3 or as SG: 0.35 to 0.45 (this time no units/dimensions), maple is more like 0.55 to 0.65. When the SG is greater than 1 it will sink in water, think of ebony or heavy pernambuco.

Not sure what SD exactly means but probably Specific Density or simply density (weight per volume).

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7 hours ago, Emilg said:

does this also apply for the back plate?

Yes, but not as much, for several reasons.  The stress on the back is less than the top, particularly near the neck block.  Maple doesn't have such a large difference between longitudinal and tangential stiffness, so shouldn't be as sensitive to arching steepness.  And backs usually are less curvy out at the endblocks anyway.

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2 hours ago, Don Noon said:

Yes, but not as much, for several reasons.  The stress on the back is less than the top, particularly near the neck block.  Maple doesn't have such a large difference between longitudinal and tangential stiffness, so shouldn't be as sensitive to arching steepness.  And backs usually are less curvy out at the endblocks anyway.

thanks..good to know

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20 hours ago, Emilg said:

Action always equals reaction, so there's the logic :) More basic rules: when 2 luthiers agree, one of them is lying (or maybe both) and when asked a question to 5 luthiers, you might get 10 expert opinions .. 

 

Very nice ! Particularly the first part of the basic rule :)

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3 minutes ago, Danube Fiddler said:

Very nice ! Particularly the first part of the basic rule :)

I would take credit for that but that Newton guy beat me to it in his 3rd law of motion ;) but Marty made a nice link to human behaviour as well ..

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20 hours ago, Emilg said:

SG is specific gravity is in short the density of wood made dimensionless (by comparing to water). Density is weight to volume, for instance grams per cubic centimeter or g/cm3. Spruce has a density ranging from usually 0.35 - 0.45 g/cm3 or as SG: 0.35 to 0.45 (this time no units/dimensions), maple is more like 0.55 to 0.65. When the SG is greater than 1 it will sink in water, think of ebony or heavy pernambuco.

Not sure what SD exactly means but probably Specific Density or simply density (weight per volume).

Emilg,thank you for your attempt to clear-up my confusion!

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18 minutes ago, violguy said:

Emilg,thank you for your attempt to clear-up my confusion!

Ha ok, sounds like i did not fully succeed :) ... density and specific gravity are merely measures for how heavy (or light) the wood is.

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