Roger Hill

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About Roger Hill

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  1. No reflections from the edge, the bevel is now set. Take your sacrificial knife to the very fine stones and see how sharp you can actually get it. It won't require much time to get an excellent edge.
  2. Can't help with making wine, but starting at about $15.00/bottle you can find plenty of stuff that I like and would enjoy in prudent quantities at any wedding I'll ever attend. In addition, after about half a bottle, you may find it quite easy to find a violin arch in the shape of the bottle, burgundies in particular..........
  3. Very gently criticizing, doesn't anybody see the geometry of that bridge structure as being approximately the shape of the shell of a violin plate? No one sees the approaches to the bridge as having the same shape of the figure 8 of the top and bottom plates? That the ridge of the violin arch from lower bout, through c bout and into the upper bout has the same shape as da Vinci shows for his bridge? Sheesh!
  4. A biblical reference, explanation from Wikipedia, not intended for you Marty, or for others who respond in genuine interest in what I thought would be obvious. I must be wrong about what is obvious, my bad. What does it mean to cast your pearls before swine? Do not cast your pearls before swine. Do not waste good things on people who will not appreciate them. This proverb is adapted from a saying of Jesus from the Gospels, “Cast not pearls before swine.” Jesus appears to be warning his disciples to preach only before receptive audiences.
  5. What is the "CG" design? I have missed something. What is "LIW"? I've missed something else. If the bridge design is used to cross a creek 50' wide it is pure genius for structural rigidity. The side arch structure will tend to oppose any stresses trying to bend it in a horizontal plane. It can twist along an axis parallel to it's length but not much. Has to be useful in the event of earthquake. Load on the bridge is transferred to the end-supports. The arches at the very ends look much like end-blocks to my eyes. The side arches and end supports look like triangles which would be the equivalent of a modern truss bridge with a triangular cross-section if looked at from the end. More rigidity. The approaches to the center of the structure look like the straight lines seen in some arches, particularly those from Robert Zuger. I'll try to spend more time casting dry flies rather than pearls.........
  6. I assume that means you I admit it, I'm just an ignorant, ill-educated redneck Okie injuneer from near Muskogee who loves curves in all the right places. I find the side arches supporting transverse stress and the end arches supporting compressional stress very stimulating, but I must admit that I am getting old . da Vinci died in about 1520, the Amati's came along in about 1540. Do you know if there was any influence of his work passed to the luthiers of that era? Thanks.
  7. I can't figure out how to get rid of duplicate drawing. I guess That I am doubly impressed
  8. From none other than Leonardo da Vinci. Everywhere I look at this drawing I see similarities to the Cremonese arching structure. Did the Amati family have any access to da Vinci's drawings? They appear 50 years after his death. https://www.livescience.com/da-vinci-bridge-never-made.html
  9. Normal working direction is with the cutting edge pointing into the direction of motion on the stone. At the end of (say) a dozen forward strokes on one side, work the edge back and forth for three or four strokes in a short scrubbing motion. Rotate the knife blade 180 degrees to work the other side in the same manner. A burr is not what you are working toward. You have not yet spent enough time getting the bevel planes to intersect, rather than just enclose, what will become the cutting edge. Also, do this with NO pressure on the stone, otherwise you will be rounding the edge, not sharpening all the way to the edge. Google "razor sharpening bevel setting" and you will probably find better explanations than In am providing.
  10. Adrian, you have now shown what an almost perfectly sharp edge looks like. Note that for a considerable length on the knife, the edge cannot be seen. A little more time on the stones with this one and it will be perfectly sharp. Good illustration that with no surface on the edge that is transverse to the blade, there is no reflected light.
  11. Just so that you understand the geometry I am describing, if you look straight on to the edge of a dull gouge, the light path will be parallel to the axis of the gouge and passing along the hollow of the gouge. If the gouge is dull you will see an arc. If you look straight on to the edge of a knife, if it is dull you will see random segments of a straight line. If sharp, you will not be able to see the edge.
  12. Adrian, you are overlooking the obvious. Look again at your first picture, it shows a reflection from the very edge of the knife. You simply do not have the bevel set. The bevel consists of two planes which intersect in a line. Now, turn off the room lights, hold the knife blade under a light with the plane of the blade vertical, edge more or less horizontal and the light shining more or less equally on both sides of the blade. If you see any reflection from the very edge, then the two edge planes do not intersect in a line. To make this simple to understand, imagine doing this same test with an old dull axe with a badly chipped blade. To restore the axe to sharpness the first thing you might do is run the edge of the axe along the grinding wheel until the very edge is 1/8" wide. Hold this under the light as above. You will see the edge clearly and you know that it is very dull. You would then return to the grinder and grind the plane of the edge on both sides until the both side planes planes in a perfect line, curved to be sure. At that point, you will no longer be able to see the edge under the light. Same with your knife. When the edge can no longer be seen with this test, you polish the edge on the stones to sharpness desired. But you will not get anywhere until the bevel is set. To set the bevel, start with your coarse stone and work the edges until the entire edge passes this test. Then proceed to your finer stones.
  13. Varnish Recipe 2 members active in this conversation (including you) Davide Sora Read: 4 hours ago Roger Hill Read: Just now Roger Hill Started conversation: March 5, 2018 Hi Davide: Enjoy your videos and advise immensely. Thank you for all you contribute. One thing I want to try is your varnish recipe. Where do you get linoxyn? Only idea I've had is to dissolve old linoleum in alcohol, but god knows what harmful contaminants you introduce. Any advice or sources would be appreciated. Thanks, Roger Hill Quote Edit Davide Sora Replied: March 6, 2018 Hi Roger, unfortunately I do not believe that linoxyn can be found for sale in any store, the only option is to make it yourself. It is a rather slow process, but once it is done it will last indefinitely, improving its characteristics with aging. You have to let the linseed oil oxidize and polymerize in thin layer (preferably cooked oil to speed up the process a little) with time it will darken a lot and will naturally become soluble in alcohol and ready to be used in alcohol varnish. To accelerate the process, after the initial polymerization (after a few months, when liquid oil will no longer be present but the linoxyn not yet soluble in alcohol) there is the possibility of saponifying it with sodium carbonate or caustic soda to separate from glycerine, then neutralizing it with an acid to make it coagulate again. The resulting product will be soluble in alcohol and after a short maturing it will be possible to use it. I made mine with the natural process because with the chemical process there is a risk that chemical agents will remain as contaminants inside the linoxyn, and I prefer to avoid this potential problem. I was told that even put the polymerized oil in alcohol for several months might work to make it soluble, I had tried this with a small quantity but it did not work at all..... I am not a chemist so I stick to the natural method, perhaps with better knowledge of chemistry it would be possible to find a faster system to obtain it. Moreover, my idea was to get a product as similar as possible to the one present in very old oil varnishes, which in fact have the characteristic of becoming very sensitive to alcohol. In my opinion the advantage of this varnish is that after a few months it has already completely matured, while the oil ones require a period of many years to become stable, distorting the initial perceptions on the acoustic performance of the instruments a few months from the painting The disadvantage is that the application especially of colored layers is more problematic (like all alcohol varnish) than a "normal" oil varnish..... Quote Roger Hill Replied: March 6, 2018 Thank you, Davide. Was afraid that there would be no sources other than DIY, couldn't find anything with Google searches. Guess I better get started if I am to try it in this lifetime............ Quote Edit Davide Sora Replied: March 6, 2018 I am polymerizing about 400 g of oil right now to experiment and see how much weight increases with oxygen absorption (out of curiosity). This is the starting point, in this case cold pressed oil (not cooked) : First skin that has formed after about two weeks : This is how it looks after about two months, moving the skins that are gradually formed and exposing new oil to the absorption of oxygen, but I did everything in one container only (to record weight accurately), if I spread it in larger surfaces in more container it would take much less time to get to this stage (not yet soluble and with still liquid oil present). But it is a long-term experiment, I'm not in a hurry...... This is the finished product I'm now using in my varnish (30 years old.....) Quote Roger Hill Replied: March 6, 2018 Thank you, Davide. In 30 years, I'll be 106. I'll probably end up trying mine before it is really ready..... Would putting it in the oven occasionally speed things along? I'll try it just to see. Do I need artists grade linseed oil, or will the hardware store product (Contains some dryers, I believe) be worth trying alongside some of the artists product? Thanks again for all the help you provide me and everyone else. Greatly appreciated and better that what can be obtained from any book I have ever seen. Roger Quote Edit Roger Hill Replied: March 6, 2018 What made me wonder about the oven bit was this thread started by Ben Conover years ago. I don't recall you posting back then. You might find it interesting: Quote Edit Davide Sora Replied: March 6, 2018 My actual linoxyn is from artist grade cooked oil, probably some siccative was insìde this oil (I do not know, but it's likely). I keep the containers you see in the photos on a radiator so heating may speed up chemical reaction, not tried an oven but maybe may work if you keep temperature not very high, but do not know how much. You don't really need 30 years, If I remember correctly I start using it after about 5 or 6 years, but I noted that with time it become less sticky and more stable, but the difference from 5 to 30 years is not much in terms of elasticity. Thanks for the links, I missed that topic of Ben Conover but in 2011 I wasn't a "maestronetter" yet..... Quote Roger Hill Replied: March 6, 2018 Thanks again, Davide. I am a classical music lover, retired from science, burning to understand how things work and I am awed by the work I see from you and a half-dozen other makers. Were Stradivari, Joseph Guarneri and a half dozen of their contemporaries with us today, they would be hard pressed to compete with today's living makers making new violins. Incredibly impressive. Quote Edit Davide Sora Replied: March 6, 2018 Perhaps if we had lived in the times of Stradivari we would have been less pressed by the competition among makers in order to emerge and we would not have reached the levels we have today. Nowadays it is certainly more difficult to achieve your own style, but the information we have available is much higher and this is very helpful and a big advantage. Thanks so much for your appreciation.
  14. I had this conversation with Davide via PM about a year ago. If someone can tell me how to make it accessible to everyone, it would save Davide some time and I am guessing that he won't mind, given his incredible generosity.