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ctviolin Super Member
Joined: 07 May 2009 Posts: 961 Location: Roswell
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Posted: Sun Mar 17, 2013 9:13 pm Post subject: |
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actonern wrote: |
Hi John!
Good to see you here...
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Yes, I agree.
Very good to see you here John!
Craig T _________________ Look,
Listen,
Learn. |
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R Mac Member
Joined: 05 Mar 2013 Posts: 80 Location: Near Phily USA
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Posted: Mon Mar 18, 2013 10:42 am Post subject: |
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John,
Thanks for pointing out the underlying math that the computer program conceals. I am afraid it is lost on me, though.
It's remarkable, how different one human brain can be from another. To me, the math is opaque and artificial, and the physical derivation with a rolling disc is beautiful. To you, the disc is a barbarous approximation, and the math is sublime truth.
I sometimes wish I could have the sort of experience that a mathematician has when he sees an elegant proof, or a beautiful derivation; but alas, it seems ever denied to me. Perhaps just a glimpse of it would have kept me from flunking calculus.
Mac |
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John Masters Junior Member
Joined: 13 Mar 2013 Posts: 23
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Posted: Mon Mar 18, 2013 6:30 pm Post subject: |
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R Mac wrote: | John,
Thanks for pointing out the underlying math that the computer program conceals. I am afraid it is lost on me, though.
It's remarkable, how different one human brain can be from another. To me, the math is opaque and artificial, and the physical derivation with a rolling disc is beautiful. To you, the disc is a barbarous approximation, and the math is sublime truth.
I sometimes wish I could have the sort of experience that a mathematician has when he sees an elegant proof, or a beautiful derivation; but alas, it seems ever denied to me. Perhaps just a glimpse of it would have kept me from flunking calculus.
Mac |
I am not a mathematician. I blush at the suggestion. Also, I don't think like one. It is just engineering. I have a computer and one needs only one formula and you can copy it down the page. The computer is such a handy tool, you don't need to understand anything. Cosine and Sine are functions in Excell. Just put in the expression.
I don't dislike the circle (disk with hole), but you need a new one for every point along the longitudinal arch. I am lazy, so I measure these widths and put into the spreadsheet.
All I did was to change variables, I admit that this may be unfamiliar. You have one column in the spreadsheet for widths. Another for the heights. Also Columns for X and Y. You need to enter just one row and copy down the page. It is nice to have a math formula to give the height along the longitudinal arch. Here is where I was lucky to find one that did not involve circles. I was able to adjust this to fit Bruce Carlson's side view of a 1724 Strad. It has a smooth transition in curvature. Tangent circles will not do this.
The easy way is to have something the computer can calculate. My CNC router uses spreadsheets to calculate 200 and something transverse arches each with 101 points. I save all this data as points to cut. The G code is dumped out in about 10 seconds.
I use an old Lotus program (1985) which has never let me down. I cannot do it in Excell, because macros are written in some kind of Basic which, again, I was too lazy to learn. But you can at least copy a column of numbers. |
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actonern Super Member
Joined: 15 Aug 2007 Posts: 444
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Posted: Mon Mar 18, 2013 7:01 pm Post subject: |
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John:
A question about the CNC machine.
I'm guessing the router bit has a profile of some kind where it does the cutting.
When the machine is routing out the arch in the mid bouts, where there is a pretty rapid change in profile, does the outer edge of the bit cut away more than it should? Does the question make sense?
So, for example, if the router bit was 1 inch in diameter at the business end, (extreme example) the outer edge of the bit would be removing stock 1/2 inch away from the centre, which I imagine is what the computer is controlling for in terms of height at any point. in a rapidly rising situation, like the rise from the edge to the centre of the arch, that outer edge of the bit would cut away more than it should? Even if its shaped in a round profile?
Best regards,
Ernie |
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John Masters Junior Member
Joined: 13 Mar 2013 Posts: 23
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Posted: Mon Mar 18, 2013 7:36 pm Post subject: |
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actonern wrote: | John:
A question about the CNC machine.
I'm guessing the router bit has a profile of some kind where it does the cutting.
When the machine is routing out the arch in the mid bouts, where there is a pretty rapid change in profile, does the outer edge of the bit cut away more than it should? Does the question make sense?
So, for example, if the router bit was 1 inch in diameter at the business end, (extreme example) the outer edge of the bit would be removing stock 1/2 inch away from the centre, which I imagine is what the computer is controlling for in terms of height at any point. in a rapidly rising situation, like the rise from the edge to the centre of the arch, that outer edge of the bit would cut away more than it should? Even if its shaped in a round profile?
Best regards,
Ernie |
I use a 1/4" square end every .1 inch for rouging. A 1/8" square end every .05" I find these compress the wood less than larger bullnose. It must be scraped perhaps half a mm. I leave a margin around the edge, as I cut purfling with another tool which uses pattern-followers in lucite.
I call the cutting pattern a 'raster' because it scans just like an old TV.
Between the corners, I made things wider, so that it looks guitar shaped. If the CC is made as short as the actual width, the shape looks chicken-breasted. I experimented (with no theory) to get what I wanted.
Yes, your question makes sense. Any error would be 1/16" times the slope, which is pretty small in the bouts. And I am cutting with the fudged shape in the center portion.
At first, I factored in the slope everywhere but saw so little modification that I ignore it now. |
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actonern Super Member
Joined: 15 Aug 2007 Posts: 444
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Posted: Mon Mar 18, 2013 8:12 pm Post subject: |
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Just curious... with that setup how long does it take to take a full size fiddle back and have it outside arch machine finished, start to stop?
E |
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John Masters Junior Member
Joined: 13 Mar 2013 Posts: 23
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Posted: Tue Mar 19, 2013 2:14 pm Post subject: |
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actonern wrote: | Just curious... with that setup how long does it take to take a full size fiddle back and have it outside arch machine finished, start to stop?
E |
It is NOT intended to be a labor-saving device. Rather, it cuts exactly what I want from the expressions for a CC and also the longitudinal shape.
I suppose an hour to do inside and out. (If I am not lazy) Lots of things can screw up, and I am taking it slow until I have more experience. Inside, I leave a couple of islands to mount patterns for purfling and final outline. I have made one violin with errors. But the arching is very handsome to my eye.
A couple coarse passes and then a finish pass... I don't like to cut deeper than about 4mm. I never timed it, but my transverse cuts move at 100 mm per second. And the coarse has about 130 transverse cuts.
I did not make this to save labor, I already had a pantograph for violins and violas. This had 1" rods as rails. About 25 years ago, I bought rods, linear bearings, and supports and started a cello pantograph which I never finished. The CNC used up all the parts without waste, and of course I had to buy other things also. I would say to allow perhaps $4k to $5k to make what I have. If I did not have the round rods as rails, I would use a different design rail. But this one is very rigid and quite accurate.... for woodworking. It would not be the best design for a metal work lathe to .ooo1" It is probably accurate to .002". I did some experiment to test this.
The real point was to make arches to the shape I wanted. The pantograph used a wooden pattern. I have always had trouble shaping an arch, bumps and hollows etc. And I wanted the inflections to be determined by a math model..
Remember that I have about 15mm margin on the edges. These are easy to finish to shape.. edges and purfling are another issue.
The CNC simulator is Mach-3 which you can look up. It sends pulses at about 25000 times a second to the stepper motors on the axis screws. |
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John Cadd Super Member
Joined: 23 Jul 2009 Posts: 842 Location: Hoylake
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Posted: Mon Jul 26, 2021 10:54 am Post subject: Curtate cycloids |
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Last edited by John Cadd on Mon Aug 30, 2021 7:52 am; edited 1 time in total |
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Michael Darnton Moderator
Joined: 23 Mar 2007 Posts: 1286 Location: Chicago
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Posted: Thu Jul 29, 2021 11:25 am Post subject: |
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The hanging chain fails in the very most important spot of the arch: the recurve. I don't much care what's going on in the middle, where the chain works. Most of the muscle regarding sculpting the behavior and sound of a violin is in controlling the scoop around the edges, and only curtate cycloids absolutely prescribe the shape in that area. Half templates offer the most flexibility in that you can move the scoop around with them while still maintaining the same curves. _________________ new blog at my site! http://darntonviolins.com/blog
my work sites: http://darntonviolins.com and http://darntonhersh.com |
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John Cadd Super Member
Joined: 23 Jul 2009 Posts: 842 Location: Hoylake
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Posted: Fri Jul 30, 2021 10:00 am Post subject: Curtate cycloids |
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Last edited by John Cadd on Mon Aug 30, 2021 7:51 am; edited 1 time in total |
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Michael Darnton Moderator
Joined: 23 Mar 2007 Posts: 1286 Location: Chicago
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Posted: Fri Jul 30, 2021 11:52 am Post subject: |
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The importance of the recurve area is my own understanding after having seen a lot of fine violins that didn't make sense otherwise. Then I realized that my templates fit the edges but often not in the center, and that half templates follow better than full.
I think there is a logical explanation as to how this can work, but it needs a lot of words and drawings. Bear in mind however that the center is thick and inflexible, so central curves logically should matter less there than around the thinner and more flexible edges. Consider also that enforcing a consistent strategy around the perimeter will give a cohesiveness that doing something random or by eye will not. I don't believe that CC curves are the only way to achieve this, but they certainly do fit the original violins well, since it's a natural outgrowth/byproduct that doesn't need to be thought about. With other methods you'd have to be aware of that need, then figure out a way to make it happen, where with cycloids it just happens on its own. _________________ new blog at my site! http://darntonviolins.com/blog
my work sites: http://darntonviolins.com and http://darntonhersh.com |
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John Cadd Super Member
Joined: 23 Jul 2009 Posts: 842 Location: Hoylake
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Posted: Sat Jul 31, 2021 12:23 pm Post subject: curtate cycloids |
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Last edited by John Cadd on Mon Aug 30, 2021 7:50 am; edited 1 time in total |
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Michael Darnton Moderator
Joined: 23 Mar 2007 Posts: 1286 Location: Chicago
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Posted: Sat Jul 31, 2021 12:46 pm Post subject: |
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The robust edges are an obvious thing for people with neophyte eyes to latch onto, but the arching of these instruments is also quite a bit different in ways that really matter, specifically, shallower scoop very much towards the edge. That also forces the center area to be flatter which may be of some smaller importance on the top between the f-holes. This can also be seen in early Brescian violins, some long pattern Strads, and late Guadagnini violins, the tonal characteristics being somewhat similar among all of those groups, to the extent that they are similar (they are all somewhat different in various details, so it's not a 1:1 correspondence). This is a common strategy among some more modern makers, too, and it's a very effective approach in cellos as well. Carried to extremes it leads to a more compressed tonal range and more aggressive behavior that appeals to some modern players. _________________ new blog at my site! http://darntonviolins.com/blog
my work sites: http://darntonviolins.com and http://darntonhersh.com |
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John Cadd Super Member
Joined: 23 Jul 2009 Posts: 842 Location: Hoylake
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Posted: Wed Aug 04, 2021 8:37 am Post subject: curtate cycloids |
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Last edited by John Cadd on Mon Aug 30, 2021 7:49 am; edited 1 time in total |
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John Cadd Super Member
Joined: 23 Jul 2009 Posts: 842 Location: Hoylake
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Posted: Thu Aug 19, 2021 9:08 am Post subject: curtate cycloids |
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Last edited by John Cadd on Mon Aug 30, 2021 7:49 am; edited 1 time in total |
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