Finishing Edges with Burnishing Rods

[tstop4me]

<<This post and Replies #1 - 11 comprise a single post.>>

I.  Background

I sharpen my own knives, both with manual whetstones and with a powered sharpener.  The edges are then finished with a steel, commonly referred to as a sharpening (or honing) steel.  A steel is also used to maintain edges between sharpenings with manual whetstones or powered sharpeners.  The sharpening steel typically is a substantially cylindrical rod fabricated from tool steel (some steels have an oval, rather than circular, cross-section).  The surface of some rods are patterned with ridges; the surface of other rods are polished smooth. 

A steel is applied to both sides of a knife edge, typically in an alternating sequence:  one side is swiped along the steel, the other side is swiped along the steel, and the steps are repeated several times.  One day, as I was "steeling" my knives, I had a lightbulb moment:  I should try steeling my figure skate blades.  I did, and I was surprised at the increased sharpness of the edges; even though, with the commercial steel I had on hand, I was able to finish just the exterior sides of the edges (outside the hollow). I've since tried many different commercial steels, but I eventually made my own tools, including ones that could also finish the interior sides of the edges (inside the hollow).  Since my homemade tools are more effective than commercial steels, relatively easy to make, and relatively inexpensive, I'll skip an account of my early trials.  But if anyone is interested in recommendations for commercial steels, please ask.

[tstop4me]

II.  Introduction to Burnishing

Terminology varies with specific industries and with specific applications.  To avoid confusion, I will not use the term "sharpening steel", since the tools that I will describe do not sharpen in the sense typically used in reference to figure skate blades (i.e., grinding a hollow), and they are not fabricated from steel.  I will use the term "burnishing rod".  "Burnishing" itself has various definitions.  The definition I will use is the one in Wikipedia (https://en.wikipedia.org/wiki/Burnishing_(metal)):

"Burnishing is the plastic deformation of a surface due to sliding contact with another object. It smooths the surface and makes it shinier. Burnishing may occur on any sliding surface if the contact stress locally exceeds the yield strength of the material. The phenomenon can occur both unintentionally as a failure mode, and intentionally as part of a metalworking or manufacturing process. It is a squeezing operation under cold working."

[tstop4me]

Ideally, burnishing is a non-abrasive process; i.e., it does not remove material. In practice, depending on a variety of factors, some material is likely removed.  After all, there are instruments that can detect the removal of a single atom (for particular materials under particular circumstances).   Here, I consider burnishing to be a non-abrasive process on the macroscopic level.  If I sharpen a knife edge with an abrasive whetstone, metal particles are readily visible on the whetstone (as long as the whetstone is not black) and on a white (or other light-colored) paper towel or cloth used to wipe the knife edge.  But if I burnish a knife edge with a non-abrasive burnishing rod, generally no metal particles are readily visible on a white (or other light-colored) paper towel or cloth used to wipe the knife edge or the burnishing rod.  If the knife edge is nicked, however, then burnishing can cause stray chips of metal to break off from the damaged nicked regions.

Two key factors are required for burnishing to be successful:  (1) The material of the workpiece (the object being burnished) must plastically deform when the burnishing rod (object doing the burnishing) is applied to the workpiece.  (2) The material of the burnishing rod must be harder than the material of the workpiece.

In our instance, the workpiece is a blade (knife blade or figure skate blade).  If the blade material is too brittle, the edge will likely chip, rather than plastically deform, when a burnishing rod is applied to it.  This is an issue with some knife blades, but not with figure skate blades, since figure skate blades must withstand the impact of stroking, jumps, and landings. 

Commercial burnishing rods are used in woodworking to form the edges of card scrapers.  They are also used in the fabrication and repair of music instruments.  Most commercial burnishing rods are made from tool steel, but at least one is made from tungsten carbide.  The steel in some knife blades may be harder than the steel in some burnishing rods.  But tungsten carbide is harder than any steel used for knife blades or figure skate blades. 

[tstop4me]

III.  Homemade Burnishing Tools

A.  Tungsten Carbide Rods

The cylindrical burnishing rods are fabricated from tungsten carbide; more specifically,  cemented tungsten carbide:  tungsten carbide particles fused with a binder (cement), such as cobalt.  Fig. 1A and Fig. 1B show the unmounted rods as purchased.  Rod A and Rod B are identical except for their diameters.  They each have a length of 2", with one end chamfered and one end as-cut.  The cylindrical surface is highly polished.  The diameter of Rod A is 1/8"; the diameter of Rod B is 1/4".  The diameter of Rod A was the smallest stock diameter I could find.  A small diameter rod is necessary to reach into the hollow to burnish the interior sides of the edges.  The diameter of Rod B is not critical:  I tried several diameters ranging from 3/16" to 3/8"; the 1/4" is purely my personal preference based on how it handled.  The rods themselves are fairly inexpensive (see below); I recommend that you also buy several diameters to try out. 

Successful burnishing depends on sufficient pressure being applied by the burnishing rod on the side of the edge.  The applied force can therefore be reduced by reducing the contact area of the rod by using the smallest diameter rod (1/8") on both exterior and interior sides.  In practice, I found that when I tried to burnish the exterior sides with an 1/8" diameter rod, the rod was prone to slipping. I got better control with a 1/4" diameter rod.  For interior sides, as mentioned above, a small diameter rod is needed to reach into the hollow.  Also, as explained below, when burnishing interior surfaces, the end of the rod is pressed against the hollow, thereby stabilizing the rod and making it less prone to slipping.

[tstop4me]

The supplier I use is Castlebar (https://www.cbar.us/carbide-rods-inches-s/118.htm).  Prices are surprising low:  currently US$0.75 for Rod A and US$2.64 for Rod B.  There is a fairly steep minimum shipping charge, however [currently ~US$(22 – 30)  to the contiguous 48 US states, ~US$128 to Alaska*].  Some items are occasionally sold through Amazon and eBay.  You can check availability and pricing there.  But if you buy direct, it's best to bundle spares and extra items into a single order (see below for some suggestions).

*@supersharp, you should check with the company whether they will ship via USPS instead of UPS.

Most of the stock at Castlebar is Grade 9008 cemented tungsten carbide.  For our purposes, the grade is not critical.  Details on various grades, dimensional tolerances, and surface finish are given on the Castlebar website. Metric sized rods are also available. 

[tstop4me]

B.  Mounted Tools

You will need to mount each rod in a handle.  Fig. 2A and Fig. 2B show my mounted rods.  Each handle comprises a wooden Shaker peg and a wooden ball.  The ball is drilled to accommodate the peg; the peg is attached to the ball with wood glue.  The ball is drilled ~1/2" deep to accommodate the rod; the rod is attached to the ball with steel-filled epoxy.  The as-cut end of the rod is embedded into the ball; the chamfered end of the rod extends ~1-1/2" from the ball.

Fig. 3 shows a mounted rod grasped in my hand.  The material and configuration of the handle are not critical.  You should use whatever you personally prefer.

[tstop4me]

IV.  Burnishing Process

Caution:  If you are not used to working with sharp edges, I would recommend that you wear cut-resistant gloves or finger cots.

A.  Exterior Side

I will first describe burnishing of an exterior side, since it's more straightforward than burnishing an interior side.  Fig. 4A and Fig. 4B show use of Rod B to burnish the exterior side of an edge.  The skate is flipped on its side, supported on a floor or table, and firmly held with one hand (in this instance, my left hand, not shown).  The picks are pointed away from me.  Rod B is grasped in my right hand, and the side of the rod is pressed downwards against the exterior side of the edge.  The process is started with the rod just in back of the drag pick (Fig. 4A); and the rod is pulled along the exterior side of the edge towards the heel of the blade (Fig. 4B) until the rod clears the heel.

B.  Interior Side

Fig. 5A and Fig. 5B show use of Rod A to burnish the interior side of an edge.  The skate is positioned and held as before.  Rod A is grasped in my right hand, the end of the rod is pressed against the hollow, and the side of the rod is pressed downwards against the interior side of the edge.  Again, the process is started with the rod just in back of the drag pick (Fig. 5A); and the rod is pulled along the interior side of the edge towards the heel of the blade (Fig. 5B) until the rod clears the heel. 

[tstop4me]

C.  All Sides

Each blade has two edges; usually referred to as the inside edge and the outside edge. Here, to avoid confusion with excessive designators, I will refer to them simply as Edge 1 and Edge 2.  As discussed above, each edge as two sides, an exterior side (outside the hollow) and an interior side (inside the hollow).  Hence, for each blade, there are 4 sides to be burnished.  Burnishing works best if the burnishing rod is pressed downwards against a side of an edge. 

Fig. 6A – Fig. 6D show the sequence I use. 

Since burnishing the interior sides is a bit more tricky than burnishing the exterior sides, I use Rod A to tackle the interior sides first.  In Fig. 6A, the skate is held with my left hand, and Rod A is grasped with my right hand.  The end of the rod is pressed against the hollow, and the side of the rod is pressed downwards against the interior side of Edge 1.  The process is started with the rod just in back of the drag pick; and the rod is pulled along the interior side of Edge 1 towards the heel of the blade until the rod clears the heel.

In Fig. 6B, the skate is held with my right hand, and Rod A is grasped with my left hand.  The end of the rod is pressed against the hollow, and the side of the rod is pressed downwards against the interior side of Edge 2.  The process is started with the rod just in back of the drag pick; and the rod is pulled along the interior side of Edge 2 towards the heel of the blade until the rod clears the heel.  [In Fig. 6B, for clarity, Rod A is shown near the heel at the end of the process.]

I then use Rod B to burnish the exterior sides.  In Fig. 6C, the skate is held with my left hand, and Rod B is grasped with my right hand.  The side of the rod is pressed downwards against the exterior side of Edge 2.  The process is started with the rod just in back of the drag pick; and the rod is pulled along the exterior side of Edge 2 towards the heel of the blade until the rod clears the heel.

In Fig. 6D, the skate is held with my right hand, and Rod B is grasped with my left hand.  The side of the rod is pressed downwards against the exterior side of Edge 1.  The process is started with the rod just in back of the drag pick; and the rod is pulled along the exterior side of Edge 1 towards the heel of the blade until the rod clears the heel.

[tstop4me]

A typical sequence comprises burnishing each interior side with 3 swipes (toe to heel) of Rod A, followed by burnishing each exterior side with 3 swipes (toe to heel) of Rod B.  When the blades have been freshly sharpened with a commercial sharpener by a tech, I typically carry out a total of 2 or 3 sequences.  For maintenance after each skating session, I typically need only 1 sequence.

Additional sequences may be needed if the blade has been worn.  Multiple local sequences may be used to smooth out minor nicks.

[tstop4me]

D.  Further Discussion

Burnishing does not restore the hollow, it sharpens the apex of an edge.  Eventually, as the edges wear down, standard sharpening will be needed to restore the hollow.  Burnishing, however, creates an initially sharper edge and prolongs edge life between sharpenings.  An advantage of the burnishing rods described above is that they can be used to burnish the entire length of the edges:  from immediately behind the drag pick to the heel.

The burnishing process as described above is a totally manual process:  you need to control angular alignment, pressure, and travel speed of the burnishing rod.  This is no different, however, from a tech using a whetstone to manually deburr edges after sharpening.  I would recommend that you practice on an old pair of blades. Since no material is removed, however, no major damage is incurred if done improperly.  Superficial damage can be undone by subsequent corrective sequences of burnishing.  At worst, a conventional sharpening will restore the edges with little waste of material. 

[tstop4me]

V.  Burnishing the Entire Hollow

I experimented with burnishing the entire hollow.  My radius of hollow (ROH) is a nominal 3/8", which corresponds to a diameter of 3/4".  Fig. 7A shows Rod C next to a Pro-Filer chassis.  Rod C is a stock cemented tungsten carbide cylindrical rod similar to Rod A and Rod B, except the diameter is 3/4" and the length is 3".  The current price is US$32.37.  The Pro-Filer chassis is taken from a 3/8" (also marketed as 7/16") ROH kit:   one roll bar has been removed; the stone has been removed; and one roll bar is left intact.  Fig. 7B shows Rod C inserted into the Pro-Filer chassis.  The as-cut end of the rod is seated against the roll pin; the chamfered end of the rod protrudes about 1/2" from the chassis.  I won't describe any further details, since the ROH of the blade (either created by a Pro-Filer or by a tech with a commercial sharpener) was not a sufficiently close enough match to the radius of the rod (the rod is ground and polished to h6 precision tolerance).  But if you have a commercial sharpener, can control the ROH of the blade precisely, and are concerned with the surface finish of the hollow, you might want to play with this approach.

[tstop4me]

VI.  Addendum (for Knife Blades)

If you sharpen your own knife blades and want the ultimate "sharpening steel", you can purchase a 7/16" diameter X 13" length cemented tungsten carbide rod (current price US$34.66).  Consider adding one of these to your order.  Same specifications as the rods above, except both ends are as-cut.  If you insert about 1" of the rod into a handle, you will have a sharpening steel about 12" long.  It will be far superior to the best polished sharpening steels fabricated from tool steel; these cost over US$100 (with handle).  Fig. 8 shows my mounted rod.

[tstop4me]

<<added in error>>

[Bill_S]

Nice work!

I use hardened steel pins in a fixture to draw an edge on card scrapers for woodworking, but have never considered tungsten carbide for putting an edge on skate blades. It makes perfect sense. This should increase time between sharpenings and extend blade life.

Nice job creating your own wooden handles from common shaker pegs!

[Kaitsu]

Sweet-Stick is also based on the same plastic deformation affect. Basically you roll the steel from the blade side surfaces into the hollow side and it causes foiled edge, which feels extremely sharp. In your case you have reduced this foiled edge affect using stick also on hollow side.

Same affect can reached also with flat whetstone which grit size is example 3000 and it's hard enough. Magnitude of the plastic deformation depends on the pressure you use and angle of the whetstone or round bar you use. Flat burnishing tool requires more force to achieve same steel deformation than round bar.

Personally I would rather use pro-filer which removes material from the hollow than this burnishing rod method to the side surfaces. At least pay attention to the angle of the rod. Example 45 degrees angle to the side surface would be quite extreme, which cause easily so sharp edges that you cannot skate with them.

[Query]

I assume tstop4me wants to increase blade life by removing less steel than an abrasive (like Pro-Filer, or skate sharpening wheels) removes.

I do use a Pro-filer. But I usually (roughly 2/3 of the time) just need to straighten the edge, not re-sharpen, so I just just a few low pressure strokes using the fine (cylindrical) stone. That way a skate blade can last for years, maybe (no record kept) 1000-2000 hours on the ice.

And because I love very sharp foil edges, I use a rather fine grit (5000 grit) flat stone to straighten and polish the sharpening burrs into foil edges. It is possible very fine grit flat stones aren't all that far from being steels. And suspect a rod would be better, because it could polish both sides. I have to be careful not to reshape too far with the flat stone, and I can't polish the sides of the edges that aren't on the sides.

If it is done exactly right by someone with perfectly controlled hands, I suspect tstop4me's way is better, in that it removes less steel. I just haven't tried a steel, and I may lack the near perfect hand control he probably has. And if he is actually creating a micro-bevel (a short narrower angle tip on the edge), rather than just straightening, that may be better than the polishing I do with the flat stone.

BTW, as you both know, Pro-Filers are no longer being made, so supplies will eventually run out.

[AlbaNY]

This is a lot, so I have to wait and read it later. 
I sometimes use an Arkansas stone on my blades.  Not sure how similar that is?

[tstop4me]

This is a lot, so I have to wait and read it later. 
I sometimes use an Arkansas stone on my blades.  Not sure how similar that is?

Arkansas stones are natural stones; so grit size is not as well-controlled as in synthetic stones.  They are generally in the fine grade, equivalent to about 600 grit or finer.  But they are abrasive whetstones, not burnishing tools.  I have some hard Arkansas stones that are greyish-white.  When I use them to hone steel blades, the abraded steel particles are obvious.  Also, unless you custom shape a stone, it's difficult to hone the sides of the edges inside the hollow.

[tstop4me]

I assume tstop4me wants to increase blade life by removing less steel than an abrasive (like Pro-Filer, or skate sharpening wheels) removes.

I do use a Pro-filer. But I usually (roughly 2/3 of the time) just need to straighten the edge, not re-sharpen, so I just just a few low pressure strokes using the fine (cylindrical) stone. That way a skate blade can last for years, maybe (no record kept) 1000-2000 hours on the ice.

And because I love very sharp foil edges, I use a rather fine grit (5000 grit) flat stone to straighten and polish the sharpening burrs into foil edges. It is possible very fine grit flat stones aren't all that far from being steels. And suspect a rod would be better, because it could polish both sides. I have to be careful not to reshape too far with the flat stone, and I can't polish the sides of the edges that aren't on the sides.

If it is done exactly right by someone with perfectly controlled hands, I suspect tstop4me's way is better, in that it removes less steel. I just haven't tried a steel, and I may lack the near perfect hand control he probably has. And if he is actually creating a micro-bevel (a short narrower angle tip on the edge), rather than just straightening, that may be better than the polishing I do with the flat stone.

BTW, as you both know, Pro-Filers are no longer being made, so supplies will eventually run out.

I hardly have perfectly controlled hands.  As I pointed out above, even if a tech uses a power sharpener, the final deburring step is done manually with a whetstone.  Working with burnishing rods requires roughly the same degree of control as working with whetstones. 

[AlbaNY]

Arkansas stones are natural stones; so grit size is not as well-controlled as in synthetic stones.  They are generally in the fine grade, equivalent to about 600 grit or finer.  But they are abrasive whetstones, not burnishing tools.  I have some hard Arkansas stones that are greyish-white.  When I use them to hone steel blades, the abraded steel particles are obvious.  Also, unless you custom shape a stone, it's difficult to hone the sides of the edges inside the hollow.

Ah, okay.  Thanks for the answer. 

I believe mine is the fine sort.  It's what one skate tech used and recommended, so I bought that.