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Don Noon's bench

Don Noon

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Inside form of one of my new models (first of 3) is done.  It's complicated to allow gluing the garland to the back plate with the form and all linings in place, and still be able to get the form out. Photo shows it with the fence clamps for clamping blocks and counterforms.  And the spoilboard used to fabricate the form.  Now I have to fabricate the counterforms.  The CNC is a fun plaything, and can do amazingly accurate work, too.



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Some more counterform fabrication on the CNC.   

C-bout clamping has been an unsatisfying operation in the past, as the common method of pressing on the edges of the rib didn't put enough pressure into the corner blocks, and then there wasn't enough room to add features to clamp into the corner blocks.  Often I would have to re-soften the glue at the corners with water and heat, and re-clamp them.

Thus the new idea of a somewhat flexy C-bout counterform.  Hopefully there is enough flex so that there will be extra pressure on the corner blocks when clamping.  I won't know until later if it works; right now, it seems like it might be a bit too stiff.


There's also an issue with uneven surfaces of the counterforms, which are stacked up from 3 shorter pieces.  There's some variation, not sure if it's from flexing of the pieces as they're being routed out, or geometry variations at different areas on the CNC, but it bothers me enough so I wanted to even things out.  Doing it by hand on the spindle sander would wreck the precision of the shape, and commercial sanding arbors with the rubber core are horrid for runout, thus the custom-made super-precision arbor for CNC sanding...

The arbor is turned on a lathe (hand-crank, not CNC) between centers, so there's no runout.  The main part is a snug fit, and then there's  a silicone o-ring that's squeezed against a ramp to keep the sleeve from spinning.  Still a long way to go before the first of the new line violins rolls off the line.


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1 hour ago, Nick Allen said:

Are you sure putting a sanding sleeve that is meant for a relatively low rpm drill press into a router motor/spindle is not going to cause it to unravel in a spectacular fashion?

Based on 3" spindle sanding sleeves that run at 3600 RPM and 1/2" Dremel sleeves that run at 35,000 RPM, I figure my 1" sleeve should be fine somewhere from 10,800 - 17,500 RPM.  Plus, I have a monster variable speed spindle motor that weighs nearly 12 pounds and can put out a decent amount of torque at low RPM, if I want to run it slower than that, which I probably will.

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  • 4 weeks later...

Over the last month I have been continuing to design and fabricate tooling, which naturally required designing the instrument they're meant for.  The sanding arbor I made worked great, after I got a real collet to fit it instead of the CSO (Collet Shaped Object) from the cheapo set of collets I got originally.

Here's the pile of forms so far... two sizes of violin, and two viola forms from the exact same pattern (I have orders for 2 violas, so I'd like to run them in parallel).  And the pile of debris left over from making all those parts.  The spoilboards could be hung on the wall as an abstract work of art.252559997_1903011.JPG.b6e06c4cf5536a4a2ddc27d76f9ea937.JPG


I have a little bit of finish work to go on one of the viola forms, and then I can start on the fabrication of the last violin form.  After that is another major effort to figure out how to design the plates, and what the tooling should be.  Up until now, this has been all 2-D work.  And it has been quite a LOT of work.  I really want to get back to making instruments, but there's still a lot more to do before that happens.

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Your forms look like they should be a significant improvement over traditional clamping, or at least take you there within a couple iterations.  Impressive!

Since you’ve designed plates many times (by carving them), I’m assuming you’re talking about the challenge of translating those designs into a form your CNC machine can understand and execute on.  Is that what you meant by “major effort to figure out how to design the plates”?

My undergraduate degree was in naval architecture and marine engineering, so I know how to describe a three dimensional form, but that was in a pre-digital age (pencil, eraser, plastic curves, and battens).  I designed a violin plate (or guitar body) the same way I would design a ship — by establishing a series of sections in both longitudinal and transverse directions (& vertical, for ships), then adjusting both sets to describe the same surface (more challenging than it might seem).  The plan would then be to make templates from the drawn sections and use those to carve the plate.  Time consuming.

When I (superficially) looked into CAD software, I could not determine if it would accurately interpolate the surface between the sections I had drawn (scanned into the software).   Mastering the software seemed like it would take more time than building just a few instruments the old-fashioned way, and without an immediate pressing need, I never got into it further.  

The other approach I considered would be to carve a plate manually and use a digital scanner to create a data set the CNC machine could read.  But the cost of a scanner with the necessary precision amortized over a few different plates would likely be excessive. 

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9 hours ago, Chris Llana said:

Since you’ve designed plates many times (by carving them), I’m assuming you’re talking about the challenge of translating those designs into a form your CNC machine can understand and execute on.  Is that what you meant by “major effort to figure out how to design the plates”?

There are several parts to the "major effort". 

One is that I have never done 3D shell designs on any software, and this software is still somewhat new to me.  I'm good on the 2D now, but I don't know what's ahead.  It might be complicated.  Or not.

Another is sheer quantity.  I have 4 different instrument designs, which means at least 8 different plate designs.

And, as usual, I have some fancy ideas for tooling to hold the work on the machine.

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Hey Don, to move you forward and save you from 3D for a bit longer, :) why not rough it out with your 2D expertise?  Get some contour maps like Sacconi's, draw the lines in 2D for every 1-2mm or so of height difference, and you will quickly remove a lot of material.  Just a thought.


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  • 2 weeks later...

Needing a break from all this CNC work...

In playing my #27 violin, there has been this irritating metalic ringing noise, and I thought I'd try to chase it down.  It was most noticeable with a short, sharp bow stroke on the open A string, where there was a metallic after-ring.  Damping the E string eliminated it... so obviously bowing the A excited the overtones of the E.  FFT analysis confirmed that the E overtones in the 4 - 7 kHz range was the cause (comparing damped and undamped E when bowing the A).   Now the problem was how to fix it.

For reference, the as-is bridge weighed 1.95g, and I measured modes with the feet clamped in a vise at:  3054Hz rocking, 687Hz bending (fore/aft), and 5561Hz vertical (bounce).  The legs on this bridge blank were on the spindly  side, and ended up at ~4.7mm tall.  

First idea was to reduce the rocking mode, and try to isolate the high frequencies.  There seemed to be some opinions in that direction, and makes some sense.  However, thinning out the waist to 14.2mm, with reduction in rocking frequency down to 2749 Hz (and down to 1.89g mass) did nothing my ears could tell.

Second thought was that the vertical bounce was allowing bridge movement that would transfer energy to the E string around the annoying range.  The unusually thin legs would (I think) give a very low-damped resonance, since bending of the legs would be a long-grain flex of the maple.  So I used a different blank, with much thicker legs, and thinned them as little as possible, finished at 6mm+ tall.  I suspect this blank was lower density as well, since I did almost no thinning or enlarging of anything, but still came out slightly lighter than the old bridge.  Final numbers:

1.92g, 3206Hz rocking mode, 707Hz bending (fore/aft), and 5709 vertical (bounce).

The improvement was immediately apparent on playing, and the impact response plots show a huge reduction in the frequency range of the annoying noise.  So I think "tuning" the bridge mode frequencies looks pretty pointless, but getting the dimensions and mass distribution right makes the difference.  Full disclosure:  the bowed response plots don't show such an obvious result... but my ears hear it.


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1 hour ago, Fiddlemaker5224 said:

Don, what software are you currently using for the plates?

I assume this is a CNC question, where I am attempting to get (con)Fusion360 to work in modelling and fabricating the plates.  I'll let you know when I am successful.  If it is an acoustic question, then the answer is Audacity.

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20 hours ago, Fiddlemaker5224 said:

This was a CNC question. As I just upgraded to Aspire 9.5, and I have been successful in Modeling the Arching for a Violin.

First test run is cutting now.

You modeled with a probe from what I remember. Unless I am mistaken Don is talking about modeling by "drawing" In the fusion 360 software. This involves inputting contours and letting the software render the points in between. Easier said than done...

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On 3/11/2019 at 3:29 PM, Chris Llana said:

Would it be inconvenient to post photos of the two bridges, Don?  Thanks.

Old one on the left.  I decided to go retro on my bridge logo, just traditional name and city, with old-school font.

The old one has had a last-ditch waist thinning to see if that would help (didn't); it wasn't that narrow when I first cut it.  The legs on the new bridge were intentionally left as fat as possible; I may trim them slightly to look a little more refined.


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