Dennis J

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About Dennis J

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    Adelaide, South Australia
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  1. I have seen the video by Rob Cosman and I wouldn't argue with his conclusions. But there is no analysis of how the apparent high area is produced. Looking at your photos I would say that the gap only shows up at the end of the join. That does not suggest it is the result of a convex surface on one or both of the wedges because if that was the case the gap would extend further along the join toward the centre. Anyway, however it comes about, taking a few short strokes in the middle before using a full length finishing stroke fixes the problem.
  2. I don't know how you are getting convex surfaces. I find putting the plane in the vice can sometimes be awkward but it should not make any difference. I counteract what seems to happen when I plane is to take a couple of short starting cuts occasionally before the full length cuts. I've found that the same thing happens when using a shooting board. But I don't bother doing that when planing violin plate wedges. I can't see how a plane with a flat sole and a sharp blade can do what you say. The only way a blade can come out of a cut is if it is blunt and won't cut to its full depth. The only anomaly I've noticed is the one I mentioned. All I can think about that is that the blade doesn't quite cut at its full depth at the very start of each cut. If the blade is very sharp it will clamp the sole of the plane to the wood's surface during the stroke. It cannot come out of the cut. It took me a while to notice the end of stroke dip I was talking about. Going by my straight edge I first thought it was caused by a high area in the middle. And it seems to be only about .2 or .3 mm. Anyway to deal with that dip with the last couple of wedges I've done I planed full-length strokes with a number 4 set to a medium depth cut, checked with the straight edge, then made a couple of strokes only in the middle with a small block plane set with a fine depth of cut, and then finished with one long pass with the number 4. I've then checked with the straight edge. And that seems to be a formula that works. So I'm doing much the same as you but I have finished with a long stroke after making a couple of very fine cuts in the middle. I really don't agree that there is any benefit planing edges hollow, no matter how slight, especially when doing rubbed joints.
  3. What happens when planing a length of timber a little narrower than the plane's blade? I've found that, starting with a squared up piece of wood exactly the same width and depth end to end a couple of things invariably happen. After a few passes of the plane, measurements taken at each end show a difference indicating the plane has taken off more at the end of the stroke than at the beginning. This becomes quite pronounced as planing continues. Also about 3-4 cm from the end of the pass the cut dips down slightly. Only the dip at the end of the cut has any relevance to planing plate wedges. However I've found planes behave quite predictably and that they do what they're supposed to do. And that is to produce surfaces which are straight and flat.
  4. I should have been more specific about what I mean. I'm not saying that planing the edge results in convexity although it can look that way when testing with a straight edge. What I have found is that the plane tends to cut deeper at the end of the stroke, perhaps 3 or 4 cm from the end at most. And going by your pics that seems to be exactly what has happened. I don't think varying downward pressure affects the depth of cut at all. With a sharp blade the depth of cut will always equal the projection of the blade. The increased depth of cut at the end of the stroke seems to be caused by the toe of the plane passing over the end of the board thereby losing some forward support. I refer to my low angle block plane as a number 4 because it is the same length as a number 4 bench plane or smooth plane if you like. And as I have said it has a significantly lower centre of gravity. As far as blade angle is concerned I think that a low angle block blade bed is 12 deg. With an edge sharpened at 25 deg. the cutting angle is 37 deg. OK for end grain work but a bit low for general work. It's not hard to sharpen a higher angle bevel. I have blades sharpened at 25 deg. and others much higher to suit the job. The acuteness of the honed angle does not affect the planing ability of a low angle block plane. A blade sharpened at 33 deg. for a bevel-up block will cut just as easily a bevel-down blade sharpened at 45 deg.
  5. I doubt that winding sticks would be of much use with such a small gap. I've come to the conclusion that a number 4 low angle block plane is about the best plane to use as long as it has been sharpened at a high enough angle to avoid tearout. Its main advantage is its low centre of gravity. I've found that planes tend to cut more deeply at the last few centimetres of the pass. I don't know why that is but I've found that to be the case by routinely using a straight edge when checking for flatness.
  6. The obvious cause of the end gaps is that one or both boards were not planed flat. And checking for gaps by holding two planed edges together in front of a bright light will not necessarily show that gap, especially if you are holding the boards off centre. It is difficult to check both ends at once. To plane such a long narrow edge flat is, not surprisingly, problematic. In my experience the only way to get a perfect fit without using clamps is to use a straight edge to check each planed edge. I've found that planing each board slightly hollow using a smaller plane and then finishing with one long stroke is the best way to go. And I agree that a rubbed joint should be all that is necessary.
  7. Regrinding a primary bevel usually requires removing a fair bit of metal and I think doing it fast can create too much heat. I find the soft aluminium oxide wheels safe enough but I usually cool the blade in water every five seconds or so just to make sure. I think a Tormek is probably the best way to go for gouges, but I manage pretty well without it so I haven't bothered to put my hand in my pocket yet.
  8. I don't hollow grind chisels and gouges for any reason other than to reduce the width of the honing bevel. If I had a flat honing disc or belt sander to produce a primary bevel quickly, as long as it didn't leave deep scratches at the cutting edge, I'd probably use that, especially in the case of gouges. I like to start honing them with a fine stone because coarser stones can easily cut through the curve and distort the cutting edge.
  9. Here's the 1725 r.p.m. grinder I use. It takes an 8 inch x 1 5/16 inch soft aluminium oxide wheel. But the wheel is now at about 6.5 inches and I'll be buying a new one soon. I wouldn't want to use a smaller wheel. I only see hollow grinding as helpful in speeding up the honing process, just as with chisels. I've found that even hollow grinding very close to the cutting edge it still takes quite a while to develop a burr with a 1000 grit water stone, at least with Addis gouges. I sometimes start honing with a medium/worn diamond plate to smooth the edge before switching to the water stone because the ground edge can sometimes dig into water stones.
  10. I find hollow grinding just about a necessity when sharpening gouges and I'm careful to avoid overheating. But I do use a grinder with 8 inch aluminium oxide wheels running at 1725 r.p.m. so I don't have any trouble. And that could be more of a problem using a grinder running at 3000 r.p.m. But it should be manageable. The main thing to avoid is to keep away from the intended cutting edge a little and repeatedly cool the gouge in water. Before regrinding a gouge bevel I use a fine diamond stone to square off the cutting edge and hollow grind as close as possible to it without breaking through. I then use a jig to hone the edge with a mainly side-to-side motion. I adjust the jig so that the gouge is making good contact at the cutting edge and just touching the back edge of the hollow grind. As soon as I get a burr developing on the inside surface I switch to a 4000 grit water stone to finish honing, followed with a cotton buff charged with chrome oxide or rouge to remove the burr. I would add that the hollow grind will disappear after a couple of honings so you will end up with a flat surface anyway and the back edge can be rounded over as well to assist the cutting action. Hollow grinding is just a way of keeping the honing surface to a minimum width and only needs doing occasionally.
  11. Maybe you are right. Given the top centre of the arch, a low point or line for the recurve, the end of the arching figure at the edge crest, and most importantly the inflection point, it is possible to draw freehand an arch profile. Of course the inflection point has to be in a realistic position. I've done it numerous times. If you check your drawn line against french curves, one for the upper convex part and one for the concave lower part, you will realise just how accurately it can be done.
  12. It seems to me to be at odds with the idea of an arch. I think it results from working methods commonly used to shape violin plates and has come to be the norm. If there is not a clear transition between the upper arching and the scoop at the inflection point a flat area results. Very difficult to avoid and I don't think it enhances the arching visually.
  13. I don't know why you would want any straightening in that area. I see that as something to be avoided, as I have just posted. It tends to result in a narrower upper arch. But it shows how a little difference in the arching profile can result in a fairly significant difference in the arching shape. I would point out that any pronounced narrowing of the upper arching at the bridge position might compromise how well the bridge feet fit.
  14. I wouldn't speculate about possible tonal outcomes in relation to arching because I simply don't know. For all I know arching has no bearing. But I strongly suspect it does because it can vary in height and shape so much. One thing I think important is that everything above the inflection line is convex and everything below is concave. No flat areas. Particularly at the upper and lower bouts. The widest arch at the lower bout fits that criteria. It is a very shallow convex curve. I use french curves to mark the upper and lower parts of the arching when marking out the aluminium template blanks. And filing them to shape after sawing close to the line requires a lot of care, but is not difficult. However, I know that replicating that very subtle compound curve when shaping a plate just using shadows would result in something much less precise.
  15. Well that is interesting. That's the one at the bridge position and the same width. But how do the other arching positions compare? Keep in mind the system I've produced is meant to produce a coordinated set of guides. What do you mean by the read lines?