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Post by Rob on May 6, 2014 13:30:00 GMT
and someone please put me out of my misery on something. A hollow ground tool edge (say plane iron at 25 degrees) is necessarily weaker than a straight ground one right? Because (though only a tiny amount) there is less metal supporting the edge due to the scoop taken out by the arc of the grinding wheel.
Also every single scoop taken out by any grinder in any edge tool is always symmetrically distributed across the grind with top dead centre being the "highest" point of the scoop?
Having a discussion on the forum and I'm second guessing my own answers!!
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Post by Jeff Farris on May 6, 2014 15:04:52 GMT
The only advantage to a hollow ground edge is in honing on bench stones. When you drop a hollow ground edge down onto a bench stone, it is quite easy to feel the contact of the heel and the edge if you rock it back and forth. Also, with two small contact points honing is quick.
The downside is just as you've said...the hollow weakens the edge. The more pronounced the hollow, the weaker the edge.
Finishing on a buff, rather than a bench stone, there's no advantage to the hollow.
Not sure where you're going on the scoop symmetry???
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Post by Rob on May 6, 2014 15:18:23 GMT
I'm not sure either :-) But you gave me the answer needed which was that the edge is weaker. Thanks Jeff.
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Post by Graham on May 6, 2014 16:09:57 GMT
In turning, riding the bevel must be a lot easier with full bevel contact rather than two 'ridges', top and bottom
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Post by Jeff Farris on May 6, 2014 16:42:30 GMT
In turning, riding the bevel must be a lot easier with full bevel contact rather than two 'ridges', top and bottom There's an argument to be made both ways, and at the end of the day, it is sort of like debating the number of angels that can dance on the head of a pin. If the diameter of the turning is less than the diameter of the the grinding wheel, theoretically you're riding the inside of the curve, which should be very good. If the turning is greater than the diameter of grinding wheel, you're balancing on two points...less than ideal. To be honest, having used a flat bevel off the ProEdge and a large diameter hollow off the Tormek, I don't find much of a difference in terms of the "feel" of finding the bevel while turning when using most gouges. Where the difference becomes more apparent is on thicker tools, where the curve of the stone really starts showing up. For example, I don't like parting tools sharpened on a curved stone at all.
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Post by Graham on May 7, 2014 8:55:57 GMT
In truth I am new to all this and have never used a wheel type grinder but what you say makes perfect sense. Iust sort of glad that I went straight for the Pro Edge
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Post by Rob on May 7, 2014 9:16:30 GMT
believe me Graham, you jumped into the game at a good time in terms of lathe, tool (chisels) and sharpening technology. All have boomed over the last 20 years with some fabulous innovations. The pro-edge is a classic example of British (Sheffield) over engineered, sturdy as heck, good old fashioned common sense. Just the look of ot reminds me of some of the tooling my Dad owned when I was a nipper. Coronet was strong in those days. He was a teacher, then headmaster, then education adviser and used to get cheap/free 2nd hand kit from schools because few domestic budgets could afford that kind of kit.
They were all solid cast iron, weighed a ton and smelt of Sheffield steel :-)
The Sorby is carrying on that tradition rather nicely to some extent.
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Post by Graham on May 7, 2014 10:07:44 GMT
Ahhh, thats what the smell was !!
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paulm
New Member
Posts: 18
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Post by paulm on May 9, 2014 13:58:56 GMT
Fair comment above Jeff on the times sharpening the edge may be preferable to lapping the larger surface.
Think I'll stick with the ceramic and zirc belts for a while, I've got a few to get through and don't really find a need for anything finer than 240 at the moment, but good to know the trizac are available if needed !
Cheers, Paul
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Post by jimcarroll on May 27, 2014 9:16:38 GMT
When you recieve these replacement cutters the square edge is very rough.
They are designed as a roughing tool with the long type cutters but the other cutters are designed for cleaning up your turnings not a hogging out tool.
The best way to use them is with a very sharp edge, but if you look at the cutting edge it is very rough so need cleaning up first with a diamond lap or flat stone.
Once you get a smooth edge then you can place the flat top onto the diamond plate or other sharpening surface, even wet and dry stuck to a sheet of glass.
This cuts so much easier and cleaner
There is a school of thought that you need a bur rto cut cleanly and you are creating this when you run them over the flat plate , the burr is down not up as some want.
With regards to normal tuning tools I use the ceramic for shaping but the 240g aluminium oxide for touching up, when needed.
Have used the 600g trizac for the shear scraper, gives a nicely polished edge and as indicated only for shear scraping.
One of the things I like about the tormek setup is the jig for sharpening skew chisels, easily controlled.
I find the robert sorby skew jig getting held to the flat plate awkward to control as the jig does not move cleanly across the plate and can cause the tool to move up and down the belt so not getting as clean an edge as I would like, anyone else come across this problem.
Now trying to adapt the tormek jigs to work on the sorby tool but one problem is that the tormek use a 12mm bar and the sorby is 1/2"
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Post by Rob on May 27, 2014 9:41:46 GMT
I must say the skew was the very first tool I couldn't wait to dump the Tormek for. I found the Pro-Edge infinitely superior for skew sharpening and even better for shaping with the 60g ceramic. The Tormek is hopelessly incapable of approaching anything like fast steel removal and as such is redundant for shaping. I had two old skews from my Dad's turning kit and they had been butchered by hand in the 1970's. Multiple facets and the 15 degree was way off.
I literally couldn't face doing the shaping on the Tormek so they had been left for several years. When I bought the PE, they were as good as new within 15 minutes of me starting and that just blew me away. That was my introduction to Linisher style steel removal. Loved it :-)
I know exactly what you mean by the slipping up the belt syndrome and I've figured out a holding method that defeats it. My leading hand is held quite some way up the shaft of the tool and is pressing down (towards the belt) and slightly in (keeping alignment with the jig). My trailing hand is holding the back of the shaft down so it remains flat on the platen and a little pressure in to the jig, but not much. I think the critical issue with the skew is to ensure your belt hasn't run out steam. The tendency when the belt has really gone past its best is to push harder to abrade the edge and that's when it tends to ride upwards. If the belt is cutting correctly, only pretty light pressure is needed. That leading hand is also really helping to keep downward pressure on the tip, also preventing slippage.
HTH
Edit: I should add that I don't move the tool from right to left during skew sharpening, its just still in one spot. As long as the belt is cutting this works fine.
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Post by Jeff Farris on May 27, 2014 12:56:22 GMT
I'm glad Rob added that edited bit at the end. Movement side to side while sharpening is something ingrained in us from dry grinders. It's neither necessary nor helpful when sharpening on a ProEdge. I feed in until it just touches, then, when I want to change position on the belt, I pull the tool back, move the jig and the tool, and then feed back into the belt carefully.
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Post by phoneman on Dec 29, 2018 21:55:03 GMT
The only advantage to a hollow ground edge is in honing on bench stones. When you drop a hollow ground edge down onto a bench stone, it is quite easy to feel the contact of the heel and the edge if you rock it back and forth. Also, with two small contact points honing is quick. The downside is just as you've said...the hollow weakens the edge. The more pronounced the hollow, the weaker the edge. Finishing on a buff, rather than a bench stone, there's no advantage to the hollow. Not sure where you're going on the scoop symmetry??? This comment by Jeff Farris, and his two later replies in this topic are the most useful statements I have ever found on flat vs hollow grinding, particularly as it applies to the Pro Edge and the Tormek. It appears that Jeff no longer posts here, which is most unfortunate. He probably knows more about sharpening with both the Pro Edge and the Tormek than anyone else on the planet. I have not encountered anyone who can take his place. phoneman
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Post by Pete on Dec 30, 2018 0:57:43 GMT
The only advantage to a hollow ground edge is in honing on bench stones. When you drop a hollow ground edge down onto a bench stone, it is quite easy to feel the contact of the heel and the edge if you rock it back and forth. Also, with two small contact points honing is quick. The downside is just as you've said...the hollow weakens the edge. The more pronounced the hollow, the weaker the edge. Finishing on a buff, rather than a bench stone, there's no advantage to the hollow. Not sure where you're going on the scoop symmetry??? This comment by Jeff Farris, and his two later replies in this topic are the most useful statements I have ever found on flat vs hollow grinding, particularly as it applies to the Pro Edge and the Tormek. It appears that Jeff no longer posts here, which is most unfortunate. He probably knows more about sharpening with both the Pro Edge and the Tormek than anyone else on the planet. I have not encountered anyone who can take his place. phoneman Shame Rob isn't still active too, he always had good insight. Good plan to bury the spam posting above, I have reported it but it's better that it isn't the most recent! While I am here, at this auspicious time of the year. may I wish you, and all the woodturning and carving fraternity that use this site a very happy and productive new year, hope you are often up to your knees in woodshavings, and you judge the wall thickness at that center of the bowl just right more often than not. Pete
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