Monday, 6 February 2012

The Daily Grind

We left off with a flat back and a decent polish and it is now time to grind the bevel and then we almost have a sharp edge.

The key to getting a sharp edges is to create an intersection of two polished flat planes, the back and the bevel (haha the back and the bevel sounds like a new Disney Movie (note to self write better jokes, So two guys walk into a bar...)).

A good polished bevel is harder to achieve then a polished back.  The the angle is important and maintaining a consistent angle can be a challenge.  Working on a smaller surface while less work is tricky because it is harder to see what is happening and can be ruined faster.  Finally maintenance of the bevel is also important; the back of a chisel or plane blade once flat and polished should not need any work in the future.  A bevel will need work in the future to maintain the sharpness of the edge.

When sharpening a bevel the first thing to determine is the angle of the bevel.  Edge tools can have many different bevel angles.  Bevel down planes with a 45 degree frog will typically have a 25 degree bevel on the iron.  Bevel down planes with higher frog angles may have higher bevel angles.  On my #4 smoother and my #6 fore plane both with 45 degree frogs I use a 30 degree bevel.  The important thing to note is that with bevel down planes the cutting angle is determined by the frog angle, so while my bevel angle is 30 degrees the cutting edge is actually at 45 degrees to the work piece.  The only way to change this on a bevel down plane is to change the frog or use a back bevel (which I NEVER SUGGEST DOING).

Bevel up tools ,such as chisels and bevel up planes can have there cutting action changed easily by changing the angle of the bevel.  I have a variety of bevel up A2 blades for my Veritas bevel up planes.  These planes have a 12 degree bed angle, so with a 25 degree bevel iron that results in a 37 degree cutting angle (great for general work, most smoothing and amazing for endgrain) and with a 50 degree bevel a cutting angle of 62 degrees (used for tricky grain when smoothing).

I have two sets of chisels (or will when this sharpening saga comes to an end).  The first set has all the bevels at 25 degrees.  This angle is great for end grain pairing and light pairing actions.  The set of chisels I am working on now I am grinding to have a 30 degree bevel.  Much better for heavier pair actions and heavy chopping work such as mortising.

Something to keep in mind is that the lower a bevel angle the weaker it is.  Lower angles have less support behind the cutting edge so it can damage easier which means they dull faster.  I have sharpened my A2  50 degree plane iron once and my 25 degree A2 iron at least 3 times and both see almost the same amount of work.

OK so enough talking on to sharpening.  Once you have picked the angle you want for your Bevel you either have to establish the angle (change from an existing angle to a new angle, can be a lot of work) or begin honing the angle.  For the chisel I am working I am establishing a new angle (going from 25 degrees to 30).

To establish the new angle I am starting on a 220 grit water stone.

OK so I have to talk about something else now instead of actually sharpening.  There are a lot of ways to sharpen a bevel: water stones (my pick) oilstones, sandpaper on a flat surface, diamond plates, honing oils on a flat surface.  All work, all have advantages, and all have disadvantages.  I like water stones; they cut quickly and produce a great edge in my opinion.  The big draw back is they dish (go out out of flat) and as I said before a good edge is the intersection of two flat polished planes, so if you do not have a flat stone you cannot achieve a flat bevel.  You can flatten a stone a lot of ways; I use a 200 diamond plate, and you can either flatten after you use a stone or before you use a stone so long as when you use the stone to sharpen it is flat.  When I go to flatten the stone I put a couple pencil marks and rub the diamond plate on the stone until all the marks are gone.

Diamond Lapping Plate

OK so now finally with stone flat and the angle picked you can go about grinding away...WAIT WAIT WAIT.  Sorry totally forgot one more thing.  There is the whole matter of using a jig for sharpening or free hand.  I would love to free hand sharpen and I do practise on occasion; it is a more efficient way to sharpen as you do not have to worry about setting up any jigs to work the blade.  I however am not good at it yet and I find I can get great consistent results using a jig; I use the MK.2 Honing Guide a great jig (a little more expensive then other jigs but it is amazing).  So now with the chisel I am about to work in the jig and the jig set to the right angle and the stone nice and flat yes I can finally ...wait for brain to make sure I am not forgetting any thing else... start grinding the bevel (one final side note; using a 220 grit stone is very rough work and I refer to it as grinding not honing, honing comes after grinding).

The Veritas MK. 2 Honing Guide

Something to keep in mind is that only the front most edge is used grinding the whole bevel is not neccesary; however if you are a little OCD (CDO alphabetical order damn it)  like myself establishing the whole bevel is the way to go.

Grinding the bevel on the 220 stone

Now just like when flattening the back you are looking for a consistent scratch pattern across the bevel.  A good trick to help see where material is and isn't getting removed is to colour the bevel with a sharpy and then draw the chisel and jig back once.  If you still see sharpy on a part of the blade you know that is a low spot.

Ground Bevel 

Finally after grinding the new bevel onto the chisel I have a consistent angle that is now ready to hone, but that will be for next month I have already typed to much and if anyone actually read everything I have written here then congratulations you have a lot of time on your hands, and I apologise for all the bad jokes.

Hans Christopher

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