Replies

1. 
   pauld | Apr 18, 2003 04:07am | #1

   Sljester,

   There is definitely a correlation between the diameter of the wheel you are using and the speed "seen" by the tools you're grinding: a 6" diameter wheel mounted on a grinder with a nominal speed of 3,450 rpm has a surface speed of 5,416 feet per minute, while a ten inch wheel running at 1,725 rpm has a surface speed of 4,516 fpm. You can easily do the math and see how easy it would be to overheat a tool and remove its temper using a large wheel on a 3,450 rpm grinder.

   That's probably why I grind my chisels and plane irons using a ten inch wheel on a 700 rpm grinder (Tormek). Delta makes a similar model for about $150. From what I've heard from folks using the Delta low-speed grinder, it works well, but their 10" wheel is supposed to wear fairly quickly - a 10" replacement wheel for the Tormek cost almost $150 by itself.

   I reserve my old 3,450 rpm grinder for utilitarian chores where neither the tools nor I are likely to lose our tempers.

   Good luck,

   Paul

1. 
   JeffKurtz | Apr 18, 2003 04:41am | #2

   Stay away from the Delta wet/dry sharpening centers.  Had a thread on these some months ago, and most of us who had them had very poor experiences.  (Wet wheel out of round, tool rests don't function properly....)

   Looked at Tormek but way too rich for my blood.

   Now I use a Garrett Wade slow speed grinder and sandpaper.  Very happy with the results.

   Jeff 

2. 
   PelhamPete | Apr 18, 2003 04:52pm | #3

   Hi Steve,

   You wrote:

   << Also, I'm wondering if there is any advantage of say an 8" over a 6" wheel. From my research one size (and pretty much brands too) seems to be just as good as another, but then I could be seriously wrong.  >>

   Only addressing wheel size as it relates to resultant edge geometry, and ignoring the VERY important issues of rim-speed of wheel, wet vs. dry grinding, etc ...

   It is substantially my understanding that, roughly speaking, the larger the wheel the better, with an infinite radius wheel (i.e., a flat surface) giving you the best (i.e., strongest, most resistant to deflection) edge.  Of course it also requires the removal of the most material.  This assumes that you are trying to sharpen the blade, and not merely hollow grind for subsequent sharpening. 

   However even for hollowing grinding the same holds true; if you are, say, trying to remove a strip of material equal to 50% (or whatever) of the bevel's surface- a smaller wheel is going to create a deeper hollow than would a larger wheel and therefore leave less material to support the edge.  This is one of the reasons that I went for the large-wheeled Tormek ... it starts at 250mm (a little under 10 inches).  They actually recommend replacing the wheel when it reaches a diameter of 180-190mm (7 to 7 and a half inches).  This is larger than the diameter of grinding wheels (when first purchased) on the market.

   As far as I can tell- the only real advantage to hollow-grinding is that it speeds up the final sharpening/honing.  It doesn't necessarily improve edge geometry.

   I would LOVE to hear other folks' opinions on this particular aspect of the issue.

   -Peter T. 

3. 
   Thom1 | Apr 18, 2003 10:20pm | #4

   Consider on of the 1/42" sharpening systems, better in a lot of ways.  cooler, more agessive.  They can hog steel for tool making so forth.

1. 
   SparrowHawk | Apr 19, 2003 01:22pm | #5

   I guess I'm pretty much old school on sharpening, but I do it all by hand with stones. Having been a carver for a number of years I've tried lots of different techniques but have found water stones seem to work the best and fastest for me. With the Veritas sharpening system I can put a razor edge on an iron in just a few minutes without having to worry about overheating and the primary and secondary angles are as close to exact as hand work can achieve.