Cheap electric knife sharpeners such as those found on electric can openers grind aggressively but with poor control of angle and depth. I've seen many knives ruined by them and they have given electric sharpeners a bad reputation.  Here are some electric sharpeners worth considering for household use.

The FireStone Diamond Electric sharpener from McGowan is a fast machine that produces a toothy, aggressive edge with just a hint of a burr. I prefer a more refined edge and the FireStone manual sharpener reviewed in slot devices is just the tool to refine it. You may also want to try pulling the knife through the wheels a few times with the machine turned off to align the edge, effectively using it as a manual sharpener.  But this edge, right from the machine, will slice right through a ripe tomato while a fine edge may not.

The manufacturer specifies 23 degree bevels on all their FireStone sharpeners, but I measured 18 to 19 degrees on the electric sharpener and 21 to 22 degrees on the manual sharpeners. The 18 - 19 degree hollow ground edge would be another reason for the aggressive cutting.  The FireStone manual sharpener would hone it to a longer lasting angle.

Note: there is no generally accepted method for measuring bevel angle of hollow ground blades.  I like to measure the wheel diameters and spacing and calculate the angle at the edge by trigonometry.  This manufacturer suggests measuring the average angle of the entire bevel, but that varies with blade thickness.  My low number is the angle at the edge, and my higher number is the average angle for a blade with 0.020 thickness at the back of the bevel, typical of a hunting knife.

The FireStone design features four interleaved, counter rotating wheels like commercial machines, but without the adjustable angles that make the commercial machines so expensive.  The wheels are 220 grit diamond impregnated ceramic.  I found it impossible to sharpen close to the bolster with the FireStone electric sharpener and, because it grinds so fast, you cannot play around much without grinding a swale into the blade.  The instructions say you might need up to 10 passes on a new blade, but I found that every blade I tried was sharpened in a single pass and begin to show loss after only 3 passes.  I suspect that repeated use of this sharpener would reduce knife life or require professional sharpening to re-shape the blade.  I would prefer a sharpener that used finer stones and a slower speed.

McGowan has updated the Firestone electric sharpener. It is now called the DiamondStone and comes with finer stones.  My few uses of it indicate it works as well and the Firestone and produces a better edge.

The Chef'sChoice 110 features three sets of diamond hones, and does a great job of sharpening.
It has since been surpassed by newer models, see below.

EdgeCraft's Chef'sChoice Model 110 uses 3 sets of diamond hones and each sharpens at a different angle. The first stage is very aggressive, grinding even faster than the FireStone (above), but it is only used once to pre-shape the bevel.  From then on you use the second and third stages (sharpening and honing) only.  The final honing is at a very sturdy 25 degrees, which will give very long edge life.  (The Model 310 is similar, but with only the final two stages.)  The model 110 gives an edge that is acceptable for most users, but I have not been able to obtain a shaving sharp edge from it.  The 110 and 310 have been replaced by newer models, below.

EdgeCraft has made a major upgrade with the introduction of the Chef'sChoice Models 120 and 320, which replace the 110 and 310.  Gone are the magnetic guides and the orbital motion hones, replaced by an elastomer spring guide and rotating conical hones.  The spring is more foolproof in holding the angle than the old magnets.  The rotating hone in stage two is more aggressive than the old orbiting system, so fewer passes are needed.  In fact, it set a new edge on the first pass on each of the six knives I tried, so I never used stage one.  The third stage is very interesting.  It uses an abrasive polymer disk, rotating on the shame shaft as the first two stages, to hone the edge.  My 110 always turned out an adequate edge, but one I preferred to touch up a bit on a ceramic steel.  My edge came off the 120 third stage shaving sharp on the first try, no touch up needed.  (The 320 has only the last two stages, but that may be all most people need.)

The latest Chef'sChoice sharpener is the model 130.  It is identical to the 120 except the second stage has been replaced with a steel, giving you the option of having a steeled edge without mastering steeling.  Guides make the task foolproof, and the steel segment is threaded so that as the small section you are using wears out you can turn the screw a notch to a new section.  If you have a CC 110 or 120 and want a bargain upgrade, just buy the Chef'sChoice 470 SteelPro manual sharpener - the manual version of the CC 130 second stage.

Chef'sChoice is my recommendation in this class, with one caution - all electric sharpeners have a tendency to scratch the sides of a blade.  I can't recommend them for collectible knives but they are great for working knives.
 

WET WHEEL SHARPENERS

While hand sharpening meets the needs of most of us, a machine is the way to get the work done. Here are some power sharpeners worth considering if you do a lot of sharpening.

A wet wheel machine is very useful if you have to remove a lot of material, like re-grinding a broken tip. The water prevents over heating the blade and ruining the temper. Sears and Wen sell small wet wheel grinders for about $30. They are only suitable for light use.  The Sears Home Sharpener rest is easy to adjust and can be set from about 10 degrees to 90 degrees.  It is reversible so that you can grind on of off the edge from the same rest setting. 

The wet wheel machines mentioned above have a limited number of guides or fixtures available, mostly for planer and joiner knives and other woodworking tools.   The only wet wheel grinding system with guides and fixtures for all sharpening needs is the expensive Tormek - about $400 for the grinder, then $30 to $60 for each fixture.  You will need at least the regular and large knife fixtures, plus the grading stone and truing tool.

I spent over a year debating between buying a Delta 10" wet wheel grinder or one of the several cheaper imported models, then my wife bought me a Tormek for Christmas. She shares her Father's philosophy of buying the best, and it was the right choice. The wide selection of accessories means that it can sharpen every tool I own, including woodworking tools, and makes a nice wish list for future birthdays and Christmases. I should never outgrow it.  UPDATE: In May 2005 I bought a second Tormek.  It is being used for teaching while the old one remains the market workhorse.

I even sharpened the knife from my chipper/vacuum - a full half inch thick single bevel - on the Tormek.  It took a while, but it did it.  I also sharpened an 18" sword.  By using both knife fixtures placed about 9" apart I was able to sharpen the full length in one smooth, continuous pass.

Changing the grade of the Tormek wheel is a bit of slight-of-hand that I think might work on any of the large wet wheels. The silicon carbide grading stone is much harder than the wheel, and transfers a coarse or fine texture to the wheel rather than actually changing the grit. The coarse texture cuts faster because it contacts only at the high points with greater local pressure, but it also transfers the coarse texture to the edge. The fine texture is flatter and leaves a smoother edge. If someone tried this with another wet wheel, I would like to hear the results.  A little known fact is that the Tormek wheel has a third, faster grinding speed, and that is right after it has been trued with the diamond truing tool and before using the grading stone.  Be careful, it will eat a knife faster than you imagine, but it may be useful when you have a really bad chisel to sharpen.

PAPER WHEELS

If you are comfortable using power tools, try a paper wheel system. Paper wheels are safer than buffing wheels and less likely to catch and throw a knife, but you still work with the wheels moving off the edge, like stropping, for safety.  Paper wheels are often demonstrated at gun and knife shows, and are also available from knife making supply shops and woodworking tool stores. These wheels mount on a grinder or buffer. The sharpening wheel is coated with silicon carbide, and grease is used to cool the blade. Buffing compound is used on the other wheel for honing. Cost is about $25 to $35 for the wheels, plus another $30 to $50 if you have to buy a bench grinder. 

Using paper wheels requires a little skill, but once you get the hang of it, it is very fast. I sharpen twenty knives at a time for my church's kitchen, and I can do them in less than 30 minutes with this system.

The most difficult knives I ever tried to sharpen was an old set of Gerber kitchen knives. They were so hard that natural stones hardly touched them. Diamonds would grind them, but I don't have a diamond stone fine enough for a shaving edge. Paper wheels is the only system that has ever brought these knives to a razor edge.

I use paper wheels a little differently than recommended by the manufacturer. Normally a grinder wheel turns toward the user, and grinding is done on the front, where debris is thrown downward. The instructions for paper wheels say to use this same rotation but sharpen on top, where debris is thrown toward you. This seems inherently unsafe to me.

Here is how to modify a grinder for safer use of paper wheels.

I recommend you buy a dedicated grinder motor for this purpose. Changing the wheels too often can introduce wobble in them. When you buy a grinder make sure it has removable guards, because you are going to take them off. Put a good light over the grinder so you can see the burr as it develops then polishes away.

Mount the grinder so the top of the wheels moves away from you, and sharpen and hone on top of the wheel with the edge away from you. This lets you see better, and debris or anything caught by the wheel is thrown away from you.  Hold the blade level and work near the top for a small angle, down the wheel closer to you for a larger angle.

If you thought trigonometry was something you learned in school but never thought you'd use, think about this. When the blade is horizontal the angle between the blade and the wheel is equal to the angle between the point of contact and vertical (identical triangles). I've marked angles of 0, 15, 20 and 25 degrees on my wheel.  I put zero at the top and position the blade at the angle mark I want to grind before I start the motor.  Then I turn it on and hold the angle steady as I move the knife lengthwise. Practice a little and you will learn to see the burr and where to hold the blade to get the proper angle.

Woodworking catalogs offer a variety of rubberized, nylon and composite buffing wheels for sharpening. These are usually sold industrially for deburring and polishing.  They require skill and practice, and they are expensive. I think paper wheels are the best choice for the home knife sharpener.

Tips for using paper wheels.

Don't store a paper wheel system in a closed car or truck in hot weather, the wheels will de-laminate and split.

If another method like a wet grinder is used for the initial sharpening, the sharpening wheel will last for over 1000 knives before needing a new abrasive coating/

If the sharpening wheel starts sparking, add more wax.  This is first noticeable on carbon steel knives.  If you do not have to wipe the knives after sharpening, you are not using enough wax. 

Wiping off the with paint thinner makes it easier and therefore safer.

Hold folding knives from the back, so that if they accidentally close when being sharpened, it won't be on your fingers.

You can sharpen the serrations of bread knives using the corners, but they will quickly round off.  Good use for a second set.

Add polishing compound to the honing wheel every 4 or 5 knives.  The polishing wheel will turn black from the removed steel.

BELT SANDERS

The belt sander is popular sharpening tool, often seen in knife shops and shows.  The knifemaker’s grinder, basically a powerful variable speed belt sander that takes a 2-in. by 72 in. belt, can be used for sharpening.  Sanders with 1 in. by 30 in. or 1 in. by 42 in. belts allow more maneuvering room.  See field.htm for ideas how one inexpensive belt sander can be modified for use as a sharpener.  The 110 VAC machine's speed is rather high and you have to be careful not to overheat the blade.

The pioneer of this type machine was Loray.  Happily their machine is available once again.  See http://www.freewebs.com/gramparay/  Ray Longbrake has come out of retirement with help from his son John. 

The procedure for using a belt sander is much the same as any sharpening.  As with any abrasive on a flexible or soft backing, the abrasive must move off the edge to avoid the blade catching on the belt.  I start with a 120 grit blue zircona belt for new or very dull knives, and finish with 400 grit.  Some sharpeners like to use a worn 600 grit belt for the final step.  It leaves an edge smoother than a new belt, but with enough tooth to cut fibrous material well.  Proceed to a finer belt or a leather strop if you prefer a polished edge.  One sharpener recommends a 1200 grit Trizact belt.

There are also about a half dozen belt sharpeners sold almost exclusively to the food service industry.  The Hook-Eye sharpener listed below in one.  Use your favorite search engine to search "belt sharpener -squeegee" to find others. 

PROFESSIONAL KNIFE SHARPENERS

Although I think the Chef'sChoice 120 or 130 is as far upscale as I think any household would need, here is a listing of some professional knife sharpeners and their features:

Hantover - really just a grinder with flap wheel sander on one end and felt honing on the other. Creates convex bevel, requires skill and safety glasses. About $250

Ekland - stainless steel knife guides, slow running wheels to avoid overheating, single angle, looks like the Chef'sChoice but works differently. About $250

Chef'sChoice 2000 Commercial - this machine produces a double bevel edge, unlike the triple bevel produced by their home machines.  About $350

Hook-Eye Belt grinder - aluminum oxide belt similar to a knifemaker's belt grinder creates a flat bevel, requires skill and safety glasses. About $450

TruHone - 3" 220 grit counter rotating wheels create a toothy hollow grind edge.  Adjustable angle allows a three angle bevel that offsets the fragility of the small wheel hollow grind.  LC model about $700  Heavy Duty Commercial HCA model about  $1000

The TruHone (LC or HC) is a one trick pony.  It has only one grit of wheel, a limited range of adjustment, and grinds dry.  It is great for a quick re-sharpening of a not-so-dull knife, but will not re-bevel a really dull knife, although people try.  I use mine to deburr the edge after beveling on the Tormek when I want a slicing edge (toothy) rather than a shaving edge (polished).

TruHone makes a line of expensive sharpeners and hollow grinders for the industry, but does not tell you that you should use one of them or another grinder before the LC or HC.

The TruHone does a fairly decent job of sharpening straight knives, considering it does it all on one set of small,  fairly coarse (220 grit) wheels.  It is suited for a kitchen or shop where there are no skilled sharpeners.   The main complaint that I hear is that the wheels wear out of round quickly.  I have not used mine extensively, so I have not had this problem.

Our local gourmet shop uses a TruHone and their customers are beginning to come to me because they are disappointed with the results.  Their knives require a lot of grinding to restore a bevel, just like a very dull knife.  I assume that their machine is not set up right, and/or they have an inexperienced operator.

I would compare the TruHone with the Chef'sChoice 2000 commercial sharpener which costs half as much.  I would rank TruHone below a Tormek for versatility, and below a Tormek in conjunction with paper wheels for versatility and speed.  Cost is about the same.  I would rank TruHone well below the F. Dick SM-111 for professional results and total capacity.  F. Dick makes a sharpener of the same basic design as the TruHone but with two sets of wheels, like having two TruHones.  It is their model RS-150 Duo and costs about $1000, see below

Friedrich Dick RS-75 - machine is normally equipped with Diamond Wheels, but is available with ceramic wheels on special order.   Comparable to a TruHone.  List Price $625  about $500

Friedrich Dick RS-150 Duo  - Two Stage Sharpening and Honing machine suitable for a restaurant or food processing plant.  It is equipped with Diamond and Ceramic Wheels.  An RS-150 Duo is like having two TruHones with different grit wheels all on one machine.   List Price $1320  About $1000

Friedrich Dick SM-110 - special shaped water cooled wheels, one for each side, create flat bevel. Variable angles. Counter rotating honing wheels to remove burr. about $1850  SM-111 adds adjustable honing wheels and a buffing wheel for a more refined edge.  About $2000

  The SM-111 is quite a machine, with grinding, honing and polishing all built into one. It is  the perfect machine for anyone wanting to start a knife sharpening, rental or exchange business.  The dual wet wheel grinder is adjustable from 10 to 20 degrees and has magnetic guides, and the counter-rotating overlapping honing wheels are adjustable from about 20 degrees to over 35 degrees. Right off the honing wheels the edge is ready for kitchen use. The polishing wheel will give an even greater degree of sharpness, but I have rarely used it.

The advertised capacity of 400 to 500 knives a day assumes that the knives have been sharpened before to the right primary angle.  Expect to spend up to 5 minutes the first time with stamped blades, and 10 minutes or more with large forged blades.  For that reason it might not be the best choice for a business where you will never see the same knives twice.  My solution is to charge more for a first sharpening; call it a major sharpening or a pre-sharpening.

The scissor attachment is described for household scissors, and has only one bevel angle for paper cutting scissors.

Friedrich Dick SM-160 T Universal Sharpening Machine is a Belt Grinder, Flap Wheel and Buffing Wheel All on One Machine
It is a favorite of full service sharpening services. An Attachment for Mezzaluna and Circular Knives Available, and are wheels for sharpening Serrated Knives.  220 VAC or 400V 3-phase, 16 Amps Not recommended for mobile service.  Price, about $5000

Updated November 28, 2006
Copyright 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006
Company and product names are trademarks of their respective companies.