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17-Dec-2004
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#1 |
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bonsaiTALK Adept
 
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Concave cutters
We had a discussion today at the nursery concerning concave cutters. A customer wouldn't buy one of the cutters because the cutting edges were not perfectly lined up. We checked others in stock and they were slightly misaligned as well. After calling the distributor we heard that they are supposed to be that way for a clean cut. We were questioning this as I have a pair of cutters that do line up and they work fine.
Can anyone enlighten me on the subject? Thank you.
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Regards, Ed |
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Concave cutters |
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17-Dec-2004
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#2 |
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Bonsai Doer
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Good concave cutters should not come together like wire cutters. Wire cutters cut because they are cutting metal, and the metal actually pushes away from the blades and is almost pushed off the cutting edge at the last moment. It works like a pair of opposing wedges. For cutting plant material, we want a clean cut. We want to cut the branch off, not smash the branch off.The edges should just come together but be slightly offset like an underbite, but the tool should have a stop built in. This underbite gives the tool an almost secatur like cut at the very end rather than crushing the material between two blades.This stop prevents the edges from riding on to one another and springing the edges or tool. This overlap is quite small, less than 1/32 of an inch. Larger than that and the tool is not properly made. This overlap should be parallel all the way down the edge of the tool. If it is not it may have been sprung or is not made properly.
This goes for knob cutters also.. Bonsai-al Regards, Bonsai-al
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I been kidding the last seven years. no.... really! |
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17-Dec-2004
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#3 |
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Tips:5¢ Advice:Free
 
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Yep, another point is if the blades lined up, they would not stay sharp for long.
Regards, Matt There is a little more info at the bottom of this page: http://www.treebay.com/index.html?A=41
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17-Dec-2004
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#4 |
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bonsaiTALK Adept
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Al and Matt:
Thank you for the information. It is very helpful and clears up all my questions.
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Regards, Ed |
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19-Dec-2004
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#5 |
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bonsaiTALK Master Chief
 
Join Date: Sep-2003
Location: Amstelveen
Country: Netherlands
USDA Zone: 8
AHS Heat Zone: 2-3
Posts: 1,607
 
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I read this and thought "damn mine aren't very good then" (20 years old, though they may be).
I used them today and discovered that they do, indeed, not meet at the blades but overlap. Well I never. Jerry Amsterdam
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10-Jan-2005
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#6 |
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bonsaiTALK Artisan
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Mandible cutters
After being in the metal cutting business most of my professional career and selling special HS and Carbide/Diamond cutting tools to the automotive industry, 30yrs ago I got a pair of Masakuni tools.
The first cutter, a Mandible cutter, the #16 standard concave tool was quite interesting. Bonsaial1 is right on target. In fact I've just given up my Masakuni distributor-ship no more than 4~5 yrs ago because of price and availabilty. Now I sell Futaba and they are nearly the same tool. In fact over the years I'd had certain 'ignorant' customers try to '-re-grind' their tools thinking they were faulty. Unfortunatly this voided any warrenty and I had to tell them/show them why. Your #1 trim shear, the scissor type Masakuni also has some 'looseness' in the rivit joint. Hammer it shut and it won't perform. This cutter is a shear cutter. As Bonsaial1 has pointed out it does not crush (like a rose or anvil cutter) but slices thru the materail. Basically ALL cutting tools, no matter how complex they appear act (with the exception of that anvil rose cutter) (Which by the way is NOT a bypass cutter such as a Guillotine) in the same manner, they shear the material away from the blade. In fact fine bonsai tools have two lands. A primary and the secondary. The primary is that very fine edge that appears as a .010~.015" land. This is the shear edge that does the cutting. The primary is the one that we sharpen. However that secondary must be ground flat and parallel to one another in the scissors tool. Regarding fine knives this is sometimes called "hollow ground". It is not flat. The reason: Relief. When cutting the pushing action of the 'blade' is held by friction of the material in the process of removal. Thus, a 'relief' or hollow grind had no material to 'get in the way' thus allowing the blade to soar thru the material. In cutting cast iron, steel, aluminim, that primary changes angle considerably. Thus, the 'correct' angle makes a significant difference in the tools performance. The same is actually true of woody fiberus material. Here we need a shearing action and that is why fine bonsai tools are made from High carbon steel and or fine stainless: They hold the edge that was ground! best, vance hanna
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vance hanna fine bonsai take time |
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