Taptones, weight, and thickness. A quick question.

[Crimson0087]

So currently my top plate weighs 98g. The m5 tone is 398 and the m2 is 170. Most places are around 3mm thick with a few as low as 2.8. How thin should I be willing to go before I should stop regardless of taptones ...I mean obviously I shouldn't then to 1mm just to get a tap tone where I want it....but what is the lower threshold? What's the weight range to shoot for?

[Shunyata]

This is a loaded question.  
 

The bottom line is that we take a lot of measurements that are only somewhat related to the outcome and there is no consistent pattern that leads to good results.  

That being said, you don’t want to be wildly far from typical values.  98g is wildly too high.

Before you start thinning anything too much, what are your thicknesses at the top and bottom, and around the edges both in the upper and lower bouts and the c bouts? 

[Don Noon]

17 minutes ago, Shunyata said:

98g is wildly too high.

Yes... and combined with the thicknesses that seem reasonable, one can conclude that the wood density is extremely high.  Either that, or we're talking about a small viola.  It helps to know the wood properties you're working with.

I woud continue thinning to get 80g or less, cut the F's (if not done already) and see where things are.  With extremely dense wood, you might be entering the Strad zone of 2mm thickness in spots.

[Crimson0087]

I havent thinned a lot along the edges of the top and bottom bc I read that those would raise m5 and I need to lower it...I'll take measurements tonight and post them 

[Don Noon]

I wouldn't worry about M5 until first getting the weight down closer to an acceptable level.  Even then, I wouldn't do anything specifically to diddle with the M5, but only use it as a rough guideline for when to stop thinning.

[Crimson0087]

Thanks Don,

 

I will continue thinning starting with the areas along the edge...here are my measurements if you can make out my handwriting. But back to my original question....as I'm thinning to drop weight...at what point is it so thin that you would stop regt of weight. Would you think to 2mm? Where should I stop and just say "this is as light as it's gonna get"?

[Marty Kasprzyk]

17 minutes ago, Crimson0087 said:

Thanks Don,

 

I will continue thinning starting with the areas along the edge...here are my measurements if you can make out my handwriting. But back to my original question....as I'm thinning to drop weight...at what point is it so thin that you would stop regt of weight. Would you think to 2mm? Where should I stop and just say "this is as light as it's gonna get"?

If you add up all these thickness measurements and take and average I believe it should be around 2.7-2.8mm which is subject to great arguments.

[Shunyata]

For now…

Do not take the edges at the c bouts below 3.5  Take everything else down to 3.0  See where this gets you and check back in.

Past that point, you need to consider multiple factors including stiffness/flexibility of the plate.  Don’t just aim for weight or tap tones.

As a general note, it isn’t typical for the bass side to be thinner than the treble side.  (At least that is my amateur understanding.)

In general, you may want a little more “methodical” approach to graduating.  I do it in steps: take everything down to 5mm; then take everything but the c bout edges down to 3.0+; then do the final shaping.  This approach helps you avoid biting too much wood out of vulnerable areas.

[Don Noon]

2 hours ago, Crimson0087 said:

...at what point is it so thin that you would stop regt of weight. Would you think to 2mm? 

I would begin to worry somewhere around Titian graduations... but I'd worry more about having a weight above 70g.  For me, I'd say no thinner than 1.7mm (assuming the weight stays high), keeping the grad map proportional to the Titian.  Or stop if the weight gets down to 60g first.  Or if M5 drops below 300 Hz with F''s cut, no bar.  I don't use any particular formula; it's more of a "comfort zone" thing.

[fscotte]

I wouldn't necessarily worry thin plates.

Consider for a moment that violins that are 400 years old, have top plates that are 2 mm thick and less, and they're still working.

Unless you want your particular violin the last 500 years, I wouldn't worry about how thin it goes.

[FiddleMkr]

3 hours ago, Crimson0087 said:

Thanks Don,

 

I will continue thinning starting with the areas along the edge...here are my measurements if you can make out my handwriting. But back to my original question....as I'm thinning to drop weight...at what point is it so thin that you would stop regt of weight. Would you think to 2mm? Where should I stop and just say "this is as light as it's gonna get"?

My plans for the top thickness in the Center bout is 2.8 except at the sound post where it is 3mm. In the upper and lower bouts 2.8mm, except the edges of 2.5mm. 
       A simpler way to think of it is; the thickness is 2.8mm over the entire plate with 2 exceptions. The sound post area is 3mm, and the edges of upper and lower bouts are 2.5mm.
       I try to make the plate thicknesses (within their particular areas) as uniform as possible. [no differences between bass and treble sides.] More experienced folks on here may disagree. 
       The luthier that I rely on most says don’t go below 2mm if you can help it (if you have to go thinner than the targets). This will guard against cracking. 
        You should reach your desired weight and tap tones within these parameters. 

Edited January 3 by FiddleMkr
Inserted paragraph and clarification

[Peter K-G]

I have never understood how anyone can talk about and recommend thicknesses without knowing density of the wood.

The thinnest top I have made had small areas 1.8 mm in upper bout. That particular top wood's density was 0.5/0.51

[catnip]

You are probably using high density spruce.  I would circle any potential low spots ie your 2.8 mm around the center left and 3.0 center bottom so that you don't touch these areas until the final stages.  This is where you might finish at.  Also I would not go lower than 3.3 mm around the edges. What is the density of your wood?  Are you using a pencil gauge?

Spruce can vary from 0.32 gm/cc to 0.42 gm/cc.  You can do some rough ballpark estimates if you have recorded finished weights and densities.  If you have a spruce  top at 0.34 gm/cc and that top finished at 60 gm with no f holes and has the proper flexibility then with same graduation a spruce top with 0.42 gm/cc density would finish at approximately 0.08/0.34 * 60 gm heavier (14 gm heavier) or at 74 gm.

If your average thickness is 3.6 mm and your goal is 3.0 mm then  again you can estimate the weight reduction by 0.6/3.6 * 89 which is around 15 gm.  This is will put you in the 75 gm range.  I would not make tap tones my goal.

[Crimson0087]

I'm not sure what a pencil gauge is

[TZEENTCHAU]

In regards to density, how much variation should be within 1 piece of timber? I measured the density of my first violin bit of timber at .205, but on carving got down to 2mm at points (otherwise similar to the titan above) with a weight of 76g (which would indicate a much higher density than my initial calculation). Apologies if this is taking the topic on a tangent. 

[Crimson0087]

So is it better to have less dense or more dense wood? I assume this means dense wood will be thinner and less dense thicker?

[Don Noon]

5 hours ago, TZEENTCHAU said:

In regards to density, how much variation should be within 1 piece of timber? I measured the density of my first violin bit of timber at .205, but on carving got down to 2mm at points (otherwise similar to the titan above) with a weight of 76g (which would indicate a much higher density than my initial calculation). Apologies if this is taking the topic on a tangent. 

I have sliced up some Sitka spruce that had visibly different grain, and found some significant variability on the order of +/- 5% in density.  For uniform-looking grain, I wouldn't expect anywhere near that.  For .205 g/cc, either you accidentally picked up a piece of balsa, or something was very wrong with your measurement.

1 hour ago, Crimson0087 said:

So is it better to have less dense or more dense wood? I assume this means dense wood will be thinner and less dense thicker?

Violins evolved based on a reasonable range of (say) .35 - .40 density wood, or maybe slightly more.  Lower than .35 risks accidental damage and dents, higher than .40 (or so) loses the advantage of a light soundboard unless you go scary thin.

[TZEENTCHAU]

Thanks Don

[Andreas Preuss]

20 hours ago, Crimson0087 said:

Thanks Don,

 

I will continue thinning starting with the areas along the edge...here are my measurements if you can make out my handwriting. But back to my original question....as I'm thinning to drop weight...at what point is it so thin that you would stop regt of weight. Would you think to 2mm? Where should I stop and just say "this is as light as it's gonna get"?

Arching shape and total arching height are also an important factor. 
 

I think it is useless to compare thicknesses to those of Antonio Stradivari unless you use wood of the same density and work with the same arching shape. 
 

I would first scan through the thickness for irregularities and thin down the edge from the outside. From the figures on your picture I’d say reduczing 10g shouldn’t be a problem with cautiousness maybe another 5-10g. The grain of the wood looks pretty coarse (almost like pine) and I don’t think you can produce miracles. 
 

Lesson learned: Selecting the right material is very important and saves many worries thereafter.

[Don Noon]

From what I see, I'd guess you could comfortably get down to 75g or less for the final plate with F's cut and edges rounded.  Unless you have already fluted the F wing zone, it looks like you might have taken too much off there.  I'd cut the F-holes and do the fluting at this point... or preferably before, if you have a time machine.  Maybe you could go lighter, but I'd get to 75 first and see how things are.

[Crimson0087]

I've gotten it down to 84.5 grams...it's 3.0mm most places with a few as thin as 2.7....I took 30 random measures and the average thickness is 3.08. I know some said don't worry about tap tones....but m2 is 164 and m5 is 375. At this point should I conti to thin it or should I call this as good as it gets for a first violin

[David Stiles]

If it was mine, I would definitely be getting the weight down some more.   The M5 indicates that plate is still fairly stiff & it is not too thin, so there is scope.     

[Don Noon]

Are the F-holes cut yet?  I always cut them early in the process and get the outer wings fluted.  If you wait too long, you won't have enought wood left for this aesthetic.

84 g is heavier than any student regrad I have ever done, an also heavier than my 15 3/4" viola tops.  Way too heavy for a violin. 

I'd say to cut and flute the F's, get it down to 75 g and see how things are.

[Andreas Preuss]

4 hours ago, Crimson0087 said:

I've gotten it down to 84.5 grams...it's 3.0mm most places with a few as thin as 2.7....I took 30 random measures and the average thickness is 3.08. I know some said don't worry about tap tones....but m2 is 164 and m5 is 375. At this point should I conti to thin it or should I call this as good as it gets for a first violin

The decision to make is: 1. Believe in tap tones (and leave it as is) 2. Believe in weight (and continue to thin down)

If you continue it wouldn’t be a bad idea to cut f holes now as Don suggests. It is also advisable to circle a small area around the soundpost to be not touched any further. I see no problem in going down to a thickness of 2.7 all over which would bring you in the 70-80g weight range.

For a useful exercise you could also start a new top with different wood, better arching and the goal to hit 70g or lower. 

[Don Noon]

I would suggest looking at Curtin's survey of weights and taptones of Old Italian violins, where Table 2 shows an average of 60.4g and 314 Hz for M5, without the bass bar and presumably with varnish.  My personal average of 27 violins is 58.5g and 322 Hz... although I use torrefied wood, and this is without varnish (or bass bar).

To use any of this as a guideline, you need to have the F's cut.  To be a bit conservative, consider stopping if you get M5 around 330 Hz or 65g, whichever you get first.  Personally, I'd allow M5 to get down to 300 Hz if the weight was on the high side.  I wouldn't worry too much about getting too thin as long as the weight and taptones are decent.