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Post by Lukas MG (chenessfan) on Dec 20, 2015 19:06:21 GMT
Something for my fellow blade makers: I tinkered a bit with fuller depth and width. This correlation is good to know so when you design a sword and decide on a certain fuller width, you can set the depth accordingly. This only works when grinding the fuller in the blade while it is still rectangular and of the same thickness throughout. The width of the final fuller will of course change depending on how you grind in the distal taper and the bevels but it's a starting point. Using a stop on the table, it is possible to set the depth of how far the belt will grind into the steel (or wood, as in my experiment). With a 50mm wheel, the resulting numbers are like this: depth: width: 0.5mm 1,2cm 1mm 1,6cm 1.5mm 1,8cm 2mm 2cm 2.5mm 2,3cm Since I measured by hand with a ruler and a caliper, these numbers are more ballpark estimates but they are close enough to work with. In the end, it doesn't matter if the fuller is 1.5 or 1.7mm deep / 1.8 or 2cm wide, as long as it's even and the same on both sides. I will do the same for my 40mm wheel once it gets here and maybe also for the big 150mm wheel.
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Post by Timo Nieminen on Dec 20, 2015 20:47:20 GMT
The geometry problem is easy enough. For a grinding/sanding wheel of radius R (note that a 50mm wheel will usually have a diameter of 50mm, and a radius of 25mm), the width of a fuller will be W = 2*R*sin(theta) where theta is the half-angle subtended by the fuller. The depth will be D = 1 - R*cos(theta). So, for a desired fuller width, set the depth to D = 1 - R*cos(arcsin(W/(2*R))). Choosing R=1, we get The disagreement between the measurements and the geometric calculation suggests that if you want to get a fuller of a particular width, you'd better do a test grind on a piece of wood. Things move, and wheels + belt aren't necessarily the same size as the specified wheel size. But the maths will let you see approximately what kind of depth you'll get from a particular wheel size.
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Post by Lukas MG (chenessfan) on Dec 20, 2015 21:35:46 GMT
Thanks for the calculation. I've seen this done by someone else as well and the math is sound of course but as you say, these things don't happen in a vacuum. Practical tests are necessary to have reliable enough information. And everybody should do these himself as every set up is somewhat different and other variables play a role.
One thing screwing with the math is belt thickness which varies depending on grit and manufacturer. Theoretically that could be accounted for by measuring the belts but who wants to go through that trouble ;) Also, belt thickness changes as the belt is worn down.
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