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Dennis J

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Everything posted by Dennis J

  1. Well some makers do a very good job replicating examples of past makers' work. And as you say the way tools are used will play a large part in the results. Arching guides can predetermine an arching outcome. Mainly how full or otherwise it is once an inflection point is determined. And they simplify the whole process. Arching does have a definable geometry and I'm absolutely sure early makers knew of it and how to use it. Makers are always asking questions about arching and how important it is because they see very few practical, predictable ways to approach it.
  2. The only thing necessary to construct an arching profile is to locate the position of the inflection point between the upper convex and lower concave curves at any cross-arch location along an arc. And an arc drawn between the widest part of the upper and lower bouts can be used to calculate both its height vertically above the level of the edge and its distance from the edge horizontally. The inflection point is at edge level at both the upper and lower end of the arc, all of the recurve section of the arching is below edge level. So the three-dimensional position of the inflection point can be ascertained from an arc drawn on a sheet of paper. That arc can be drawn from a vertical between points where a double-string-length line crosses the uppermost and lowest cross-arch lines. How ISO lines can be used to draw arching profiles is beyond my understanding. As far as I can see they are a misleading irrelevance as far as trying to draw or make arching guides is concerned. Only geometry that can be used to make arching templates or patterns is of any use.
  3. Dennis J


    I would advise anyone planning to make violins that they study the geometry first. Soundhole placement is covered by that.
  4. Dennis J


    I've tried making inside moulds with basic measurements. And while the results are ok important things like the disposition of and the distance between corners can be a bit problematic. The 4-circles method works on proportionality so everything is balanced and practical whatever the starting measurements, such as the width of the lower bout, are.
  5. Dennis J


    Knowing the geometry of the violin is the only way you can resolve design issues if you want to make your own form/mould. And the 4-circles method described by Kevin Kelly is the best way to go. I have posted arching design methods, the last one is currently on page 57 of the Pegbox. It covers how to make long arches for both the front and back plates which can be used to establish heights for each cross arch as well as how to construct each cross arch profile.
  6. Volcanic pumice deposits are common around the Mediterranean and it is a commonly used sanding grit. I use it loose on a flat granite slab concentrating on the larger end blocks first and then the corner blocks. And I test for overall flatness on the saw table surface. It is a fairly slow process but I find it the only reliable way to get the blocks, lining and rib surfaces flat. In my experience sanding sheets glued to a flat surface always wear the rib/lining surfaces below the level of the block ends. And it is not too hard to imagine why that occurs. I should add that I do that with the inside form still attached.
  7. Of course it does. But I wouldn't think clamping pressure would be particularly significant as far as plates are concerned. I don't think there would be any significant residual stresses left after clamping because the gap being closed is so small. And, as I've said, I don't think clamping would close such a gap anyway. But, as far as stresses are concerned, I think things like installing purfling after the plates are glued to the ribs might be something worth exploring.
  8. I found very early on that checking planing progress with a straight edge was the only way to go. And I found that whatever plane I used the cut was deeper at the end of the stroke. To compensate for that I used a smaller block plane to hollow out the middle of the cut a little and then finished using a larger plane with one long stroke. That often results in the last inch or so still low. In that case I sometimes leave it as is if I have plenty of waste length in the wedges. And after the glue has set a wider glue line is noticeable. So I don't worry about light shining through at one or both ends, only in the central area.
  9. No I'm not a full time maker. However apart from general woodwork I have a lot of experience with woodworking tools as well as making violins and joining plates to know what is necessary to glue violin plates successfully. I work things out for myself, and I'm confident that the often repeated methodology around plate gluing is an unnecessary complication of what should be a simple, straightforward process. Planing a joint surface flat and handling tools is difficult enough for a beginner without making the process even more difficult for no logical reason. The whole concept is just woodworking myth.
  10. How anyone could prove that glue applied to a flat glueing surface distorts that surface is a mystery to me. Saying that surfaces need to be curved and clamped after glueing is tantamount to saying that perfectly matched flat surfaces cannot achieve a perfect glue joint. And that is just baloney.
  11. Wooden planes can be just about as accurately made as steel ones. But old bevel-down versions with tapered irons can have a lot of problems which can make them hard to adjust. Also they have a high centre of gravity which doesn't help. Bevel-up wooden planes can be made more easily and don't have those sort of problems. I don't think it is wise to use anything larger than a number 4 to plane violin centre joints. And I doubt it would be necessary to use anything larger than a number 8 on cellos. Creating anything other than flat glueing surfaces doesn't make sense to me. I doubt that clamping would close up a purposely made gap on a violin let alone a cello.
  12. I think the term micro bevel is misleading. If a chisel or a knife blade is hollow ground with a jig or a Tormek at a certain angle it can be sharpened by hand at the same or slightly higher angle with very fine stones. The small bevel produced will not be perfectly flat, especially after stropping. And that to me is the best general purpose edge to have. Regular light regrinding of the main bevel just makes it easier to sharpen with finer stones. Gouges should not have any sort of rounding at the cutting edge apart from what might result from stropping. Rounding over the edge will mean that the cutting angle of the gouge will have to be raised too high. A gouge should cut or register with the work at a reasonably shallow angle. But the profile of the bevel should be slightly curved so that the gouge will initially dig in to the work and then come out of the cut automatically. So essentially a gouge bevel should be continuous from edge to heel. Light, hollow grinding when resharpening will help maintain the original angle when resharpening. I think gouges need to be ground at not more than 20 degrees. Curving or doming that surface will result in a cutting angle a little over that. Hollow grinding plane blades and sharpening with a jig-produced micro bevel down to about 5000 grit is perfectly fine. The bottom line is that how the tool is ground and sharpened can have a big effect on how it performs.
  13. I've never seen an old Stanley plane with a gap at the centre. The gap is always at each end, either through wear or distortion. Is your straight edge straight? If it is as it looks, the sole of the plane will not make contact with the wood's surface when planing where the blade projects and it will not work properly. Major problem.
  14. It would probably be a major production John. I remember the first time I tried sharpening gouges and the results were not very encouraging. It took me a long time to perfect a method that worked and I've posted how I go about it. The knives I've made recently are another challenge. I've been able to bevel these at an angle of about 15 deg. by hand using a tool rest on my grinder and water stones, but it's not easy. I think a Tormek might be the only way to go. As a matter of interest, what angle do you grind your blades at?
  15. Well I don't use a Tormek, but I've got nothing against them. I've got a 1725 rpm grinder that handles any bevel regrinding. But if I had one I'd still sharpen the cutting edge by hand. If your Tormek has a wheel coarse enough to grind a bevel quickly it won't produce a very good cutting edge unless you refine the edge by hand. I'm not talking about deliberately rounding over cutting edges. Just avoiding flat micro bevels using jigs. Sharpening the cutting edge by hand at a slightly higher angle than the ground bevel doesn't result in that sort of edge. And using a strop or buff to take off a wire edge blurs the edge anyway, just enough to smooth the cutting action. Flat, jig-made micro bevels on plane blades dig into the wood on contact. But planes have two handles to force the blade through the wood. I watched someone recently "carving" a violin top plate with a blunt gouge. Enough said.
  16. Carving gouges should have only one continuous, slightly curving bevel extending smoothly from the cutting edge to the heel. In other words the bevel should be slightly convex or domed. I aim to grind that bevel at less than about 25 degrees. It is important to avoid increasing the cutting edge angle in the final stages of sharpening with finer stones. The whole bevel needs to be reduced to avoid that and it takes time. Shaped like that the gouge will cut with a scooping action. If you use a mallet and hammer a gouge into a piece of wood at the right angle it should cut down and then up out of the cut if the bevel is properly shaped. Chisels, plane blades and knives can be hollow ground close to the cutting edge and sharpened with fine grit stones. The main reason for keeping the sharpening bevel narrow by that way is that wider bevels, say more than 3 mm, don't readily sharpen with stones less than 1000 grit. Especially with steels rated at 62 Rockwell or more. A narrow bevel can be quickly sharpened with 1000 and 4000 grit stones by hand. That bevel will be slightly rounded so that when used bevel down it will cut smoothly. I lightly regrind chisel and plane blade main bevels every few sharpenings to prevent the sharpening bevel getting wider than about 2-3 mm. Only takes a couple of minutes and reduces sharpening time. I also lightly hollow grind gouges before sharpening. It speeds up the sharpening process by reducing the surface area. It doesn't have to be a deep hollow grind. I have chisels and gouges well over 60 Rockwell. It is simply impossible to quickly hand sharpen a chisel blade which might have a bevel 8 mm wide with stones finer than 1000 grit without increasing the sharpening angle. So at each successive sharpening the cutting angle is increased. And grinding regularly will preserve the cutting angle where it needs to be.
  17. To me the term micro-bevel means a small, precise, jig-produced, flat bevel applied after grinding the main bevel. As a general rule it is logical to keep the sharpening bevel narrow. That means lightly regrinding the main bevel regularly before resharpening, especially with plane blades. And using a jig to sharpen those that way should not be a problem. However, all hand-held tools such as chisels, gouges and knives need slightly rounded bevels to work properly. Especially gouges, which should have a smooth, slightly rounded bevel extending back from the cutting edge.
  18. When using a knife with a flat side and a bevelled side it will perform in much the same way, with or without a micro bevel, except a micro bevel provides a bit of clearance to change the cutting angle. The down side is that the knife will tend to dig in and jam either way. So I think it best to sharpen the bevelled side freehand at a slightly higher angle. That will result in a slightly rounded bevel and that will allow more flexibility in the angle of attack when cutting into tight corners and also prevent jamming. And the flat side can be used in situations like cutting purfling channel bee stings. I've just ground a bevel on one of the knives I've made at a little less than 15 degrees. I had previously ground it at a slightly higher angle and sharpened it and the edge held up apart from a tiny overheated spot on the edge. I'm going to resharpen it and see how the edge holds up. I don't know what angle violin knives are generally ground at but I've now come to the conclusion that anything over 20 deg. after hand sharpening is too high, especially used when cutting across the grain.
  19. I remember an article about hooks being found on the top floor of Stradivari's domicile which had large windows or openings. The speculation was that he hung his instruments there so that they were exposed to sunlight.
  20. It's no wonder this topic is sometimes described as the sharpening nuthouse. It's hard to know where to begin. Plane blades and chisels should not be a major problem even for the inexperienced. The most important thing is getting the geometry right. That means deciding what angle the primary bevel should be ground at and a bevel gauge is the only way you can check that. A little under 25 deg. will enable an edge to be sharpened at about 25 deg. which is ok for most uses, but a paring chisel might need something less. Plane blades like the Veritas and Lie Nielsen variety have backs lapped flat and smooth and shouldn't be touched by a stone or anything other than a leather strop or soft buffing wheel. Other blades or chisels which have deep machining marks can be lapped flat or nearly flat and smooth with a bit of effort finishing with diamond paste or fine silicon carbide grit on glass. Grinding a primary bevel with a dry bench grinder can easily cause overheating. I use an 8 inch aluminium wheel running at 1725 rpm and that is too fast when bevelling small, thin blades, which I just found out when bevelling a small knife blade even though I had turned the grinder off and was using it as it slowed down I got a tiny brown spot on the cutting edge. I sharpened it to a really fine edge after relapping the back and taking a bit off the main bevel on a coarse stone. But when I tested it on a bit of spruce the edge where the brown spot was collapsed under the pressure. So a Tormek is one way of safely grinding a bevel. However, if that stone is rated 4000 grit it will be ok to regrind an already ground bevel, but there would be no point in using it until a sharp edge is produced. Just by increasing the angle on a fine stone by hand is all that is needed to produce a sharp edge. The same fundamentals apply to gouges and knife blades but they are far more complicated to manage.
  21. I lap all my stones regularly on a granite slap using silicon carbide grit. I have no problems with my other Shapton stones but I'm skeptical about all the advertising hype and claims made around these sort of things. I've started using a 5000 Shapton I have to finish sharpening the knives I'm making because it seems to be the best choice for that job. Some other stones are faster but they are just too soft for small blades.
  22. I have a white Shapton stone which I no longer use because it just lost its cutting ability. Hard to draw conclusions about what the cause is. As far as sharpening is concerned wide, flat sharpening bevels are not very practical especially when using finer grades of stones.
  23. I've made others before out of different types of recycled steel in various shapes. A few I made from old Stanley plane blades and some of them didn't seem to hold up too well so I decided to make these. I did make one bevelled both sides and it performs ok as well. But it is difficult to bevel both sides at a shallow enough angle to end up with an 18 deg. edge. But I'll probably try when the skin regrows on my fingertips. I'm thinking a curved, single bevel edge might be the way to go. Of course ideally you need a left and right pair for each configuration.
  24. Here a couple of knives I've made using forged carbon steel from old laminated plane blades. One tested at 65 Rockwell and the other would be of similar hardness. They have been ground down to solid hardened steel a bit less than 2 mm thick at the cutting end. The bevels have been ground at about 16 deg. and sharpened at about 18 deg. And, what I think is most important, the backs have been lapped smooth and flat at the cutting end. The smaller one I did using a mixture of 1200 grit silicon carbide and 50,000 diamond paste with water on a piece of plate glass. The larger one was done on an aluminium plate down to 1200 diamond grit. It's not an easy process to lap even a small area such as this on steel this hard but I like the result. I've tested both on some tough spruce and maple and they both show no sign of edge failure. Both were sharpened down to 5000 on a Shapton stone and finished with a cotton buff charged with chrome oxide.
  25. There is no single magic process which will produce a superior steel blade. Nor is there any single magic alloy that will produce a superior wood cutting tool. There are however particular iron ores which are or were used to make the best edge tools. Traditional blacksmiths made high quality edge tools and blades using forges fuelled with charcoal. They had no scientific knowledge of the crystalline structure of steel they just relied on the accumulated knowledge of their trade. Red hot hammer forging refines and smooths out the crystalline structure of steel and has no part in the mass production of modern tools. The industrial production of forged steel was still happening in Sheffield, England up to about 1920 or so.
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