Sunday, May 16, 2010

Sharpening sticks - an alternative to stones for razor edges

A recent email ad from Amazon about sharpening gear jogged my memory about documenting my own sharpening systems.

I have a number of sharpening systems I use, and use them based on what I'm sharpening, and how much shaping of the edge is required.
The systems I use for aggressive removal of material from the edge, centre around the typical stones used in most workshops and homes. A friend from wayback taught me to use babyoil on the standard carborundum stones favoured by butchers and handymen. The lighter oil carried away the metal flakes, and did not clog up the stone as it dried. I have a few "inherited" stones which are sticky and almost tar-ry in feeling with old oil soaked into them.
I also have some water stones such as this, which I use from time to time. My first water stones were actual carborundum stones, but instead of using oil on them, I used water as the lubricant. I eventually purchased a few proper water stones, but only use them occasionally.

I also have some diamond plates. I don't like calling them stones since they resemble plastic backed plates of metal, with the diamond material bonded to the metal. I occasionally use them for aggressive removal of metal, but find they can be too aggressive, and leave deep scratches. Admittedly the plates I have aren't as good as the ones in the link above, but they look similar. I think mine were some cheap chinese knockoffs, so the "fine" is more of a "medium", etc. They have their use, but I don't use them for honing an edge.

I used to be heavily involved in model rocketry, and would still be if it weren't for the firebans in this area. One of the tricks I learnt in model rocketry was the concept of mounting disposal scalpel blades into permanent holders, and then resharpening them as required. I cannot recall the webpage which introduced this concept, but from memory it was one of the HO scale sites.
The sharpening method the site used was perfect for such small blades, and I used it every since for all size blades.
The main premise of the system presumes the blade shape is already correct, and all that is required is to refine the cutting edge whilst preserving the angles. A selection of "wet and dry" carborundum paper is obtained in a number of grits - I used 400, 600, 800, 1000, and 1200.
I obtained some timber of size 35x12 (1 1/2" x 1/2") DAR (Dressed All Round) and cut it into lengths of about 350mm (14"). I cut strips from the wet and dry paper, and glued them to the wood strips using rubber cement. The photo below shows a number of these sticks with the size written on them with a permanent marker, and a 3/8" hole drilled through the top for hanging.

The other side of the stick has another size glued and labeled to it... except the stick on the right. An observant reader will notice 2 sticks with 400, and  1200 grit paper attached. Part of this was due to the even number of sides, and the odd number of papers (including the RHS one), but the main reason for the duplication is the heavy work 400 grit gets early in edge refinement, and the regular use 1200 gets for touchups. These two grit sizes get more work than the intermediate sizes, so they are duplicated. I still use the intermediate sizes, so will not give them up.

The right hand stick has a strip of leather glued to it (again with rubber cement). The leather was cut from a discarded belt, and has then had rouge rubbed into it. The rouge was standard cheap Tripoli, nothing fancy. The leather strip becomes a strop to polish away any fine scratches in the sharpened edge, and to remove any burrs or "wires" I recharge the Tripoli every now and then, but the amount is uses is almost negligible.

So how is this system used?...  The tool to be sharpened will need to have it's edge geometry already formed by some other means. I use stones if minor rework is required, if major rework, then it's power tools to the rescue (grinder)
Once the edge geometry is correct, and all deep scratches are removed by use of a stone (or extra fine diamond plate), I will use the 400 grit stick to start sharpening the edge. I usually choose to hold the stick stationary, and move the tool, but sometimes it's easier to move the stick over an edge.

As the appearance of the edge improves, I will switch the sticks to the next grit up, working from 400, through 600, then 800, and to 1000, and then 1200 grit. By the time I've gotten to 1200 grit, the edge is not changing in shape, but merely becoming smoother, and almost "frosted" in appearance.

The photo above shows a cheap garage sale knife on the 1200 grit stick. Lubricants can be used with these sticks since the paper is designed to withstand moisture, and the rubber cement was chosen for the same reason. Eventually the sticks may warp, but since I dry them after use if I wet them, I've never observed any significant warping - these sticks were made over 10 years ago. The only lubricant I've used on these sticks is water.

The photo below shows the mirror finish on the edge of a knife after using the leather strop.

The above knife was one I found laying on the road when walking to the train station several years ago. The tip had been broken away, and the edge bellied out in that area. (I suspect it had been used to twist something open, and the tip broken off as a result.) I reshaped the point using a grinder, and put a tanto style chisel point on the blade. After some work on the stones, the point, and edge of the blade had a useful blade geometry, and fairly pleasing lines. After using the sharpening sticks on it, the cutting edge (with it's mirror finish) extends from point to ricasso in a width of around 2mm (~1/16") As a knife, it's a rough cheapie which suffered a hard life, but now resides in my workshop as a general utility knife and can cut most things I point it at.

I keep mentioning blade and edge geometry. I've got a couple of books I've read which discuss how to sharpen tools, knives, etc. Both books shown below have their strengths and flavour.

The Razor Edge Book of Sharpening by John Juranitch
This book is good at explaining what to do, how to sharpen common tools, and has some good pictures covering methods, and testing an edge. John is quite vocal about how simple sharpening should be, and illustrates the gaining, and protection of edge geometry well.

The Complete Guide to Sharpening by Leonard Lee
Leonard Lee is a name most woodworkers know from the company "Lee Valley Tools". This book covers the finer detail left out of the preceding book (John Juranitch), and discusses some metallurgy, and the effects of edge geometry on certain tasks, and the effects it has on finish, effort etc. The other main appeal of this book is the demonstration of sharpening methods for common, and some "not so common" tools.

To some up, John's book is good for homeowners looking for some skills in sharpening, Leonard's book is for workshop folks looking to understand and maximise the ability of their tools. I cannot recommend one book over the other, and instead took advantage of the bundling deals amazon seems to run when buying both books together.

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