Thursday, June 27, 2013

Carving Axe Part 4: Shifting The Balance

As soon as I had the new handle fitted into the axe I started chopping up every piece of scrap within reach to find out what the tool was made of and decide if I needed to change the angle of the bevels.  The tool performed well, but it didn't have the right feel.  This gets tricky to put words to, but as I swung and chopped, the axe felt sluggish in my hand.

I stopped to look at it between bursts of chopping and had a thought.

Photo by Peter Follansbee

During a spoon and bowl carving class taught by Jogge Sundvist at Country Workshops.  I got to play around with a Viking Axe made by Stefan Ronnqvist.  These axes are things of beauty and intuitive to use.  In short, they are everything you want a tool to be.  They feel light and nimble in use, but with enough mass to really go to work.

It was that nimble feeling in the hand that I was looking for and I knew exactly how to get it.

Notice in the photo above how much material there is in front of the eye of the Viking axe.  This forward mass gives the axe that wonderful balance.  As soon as you pick it up it feels ready to go to work.

So I cut the hammer head from the back of my shingle axe, and it was transformed.  I picked it up and it had that light, nimble feel.  The new forward balance of the tool gave it the feeling of being ready to do whatever I asked of it, and it backed up that feeling by delivering greater control when put to use.

I couldn't just leave the sawed off, ugly nub behind the handle so I set up my grinder and went to work.

Grinding the chamfers.

I had to use both wheels to grind the chamfers on the back so that the handle wouldn't interfere.  This could also easily be done with files, maybe more easily.

Shaping the rear profile.

If I had had even a glimmer of an idea that I was going to do this I would have done this grinding before fitting the handle.

Top view.

You can see that my axe has more mass behind and around the eye than the Viking axe.  I could tell that it was going to start looking funny if I removed much more material.

The chamfer on the back edge flows right into the octagonal handle.

This process got me thinking a lot more about the balance of an axe and what handle shapes would translate to the most intuitive use.  I'm sure I'll get another opportunity to play around with those ideas in the future.

And when you can buy one of these axe heads at a flea market for $8.00, why not play around a little?

Carving Axe Part 3: Fitting the Handle

Before diving into fitting the handle to the head of the axe there is one important detail about grinding that I forgot to mention in the last post.  If you are grinding an axe head with the handle still in the head you can still use the method I described.  The single difference is that you will have to grind one bevel on the right hand wheel of the grinder and the other bevel on the left hand wheel.  By switching wheels, you can keep the handle to the outside of the grinder, where it will not interfere with the motor and foul everything up.

I've been storing my handle in the kiln since I shaped it a couple of weeks ago.  I let the blank air dry for three days and then thinned out the section that will go into the eye before it went into the kiln.

Removing the bulk of the wood that will go into the eye while the wood is still green is easier.  The smaller dimensions of that section of the handle will also dry more quickly, if you are in a rush.

Tracing the eye.
Trace the shape of the eye onto the top of the handle blank.  Make sure the pencil lead is tight against the inside of the eye so the marking is accurate.

I do all of the fitting of the handle with the drawknife.  If you have always considered the drawknife a tool for coarse work, prepare to be amazed.   A sharp drawknife easily takes fine, controlled shavings from wherever your heart truly desires.  I like to scoop the material out just below where the eye of the axe will sit.  This scooping allows the handle to be full thickness and comfortable in the hand all the way to the head.  

Shape the handle close to the traced pencil line.  At this point the handle should be a little oversize, a little.

Shape of the eye roughed out.
 I also chamfer the top edge of the handle so it will start into the eye.

Marking the end of the handle.
With the axe head locked in the vise, orient the handle and tap it a few times.  Make sure the center of your handle is aligned with the bit of the axe and that your handle is going in straight.  I find that starting this process at the vise helps me get the alignment right.

End of handle marked.
As a result of the tapping, the axe head scribes its shape on the end of the handle.  Back to the shaving horse to remove the wood that is preventing the handle from sliding further on.  Repeat the process of tapping the handle into the eye and removing small amounts of interfering material.  

Once I got the handle started with proper alignment, I switched to driving the handle into the head over a solid surface instead of in the vise.  It takes some oomph.

The fit of the handle to the eye should be very tight.  This means that the head will get stuck on the handle each time you drive it further on. I use my froe club to persuade it off. Tap the underside of the bit and the section of the head behind the handle alternately to remove the head.  This will take some force.  Once the head is loose, I wiggle it the rest of the way off.

Removing the axe head.

More progress.

Quite a way to go.
Check for alignment.

Check your handle alignment as you progress.  Notice how the section of the handle going into the eye is straight and in line with the bottom of the handle.  Check frequently so you can make minor adjustments to the alignment and avoid major ones.

Getting close.
As the head of the axe approaches its final position on the handle, the scooped out portion becomes a tight radius.  At this point I switch from the drawknife to a carving knife to remove the remaining material.  The carving knife makes the transition from the scooped area of the handle to the flat section that passes into the eye more easily than the drawknife.  The final position of the axe head should be about 1/4" above the line created by the scooped out section.

A little knife work.
When the handle seats down to its final position, remove it, and then saw the slot for the wedge.

Sawing the slot.

Handle complete.
With the handle complete, all that is lacking is the wedge.  My wedge was 2 1/2" long and tapered from 1/8" to nothing.

Driving the wedge.
Handle wedged in place.

With the wedge driven in, saw the remaining wedge and the top of the handle off.  I like to leave about 1/8" of the handle protruding.

Now that the handle is in place, it is a good time to check and see if the angle that you ground the edge at is robust enough for your axe.  I picked up a dry piece of hickory and chopped away at it for a while.  Then I ran my fingernail along the edge to feel for nicks.  If you feel any nicks in the cutting edge at this point it means your grinding angle is too acute.  Grind the short bevel a little steeper to compensate and then resharpen.  My 32 degree included angle held up admirably.

But then...

an idea.

Thursday, June 20, 2013

Carving Axe Part 2: Edge Geometry and Grinding

The defining feature of a carving axe is its edge geometry which gives it greater control in use than standard hatchets.  Carving axes can have flat symmetrical bevels but I prefer grinding them with asymmetrical bevels.  In use the wide bevel faces the workpiece and rides against it, supporting the cut, and enhancing control of the tool.  The comparatively low angle grind of the wide bevel, gives the axe an aggressive feel in use that most conventionally sharpened axes lack.  The short bevel deflects the chip and is ground at an angle that gives the edge durability.  I have found the necessary included angle of the edge varies from axe to axe, depending on the quality of the steel and its heat treatment.

Top view of asymmetrical bevels.
"Inside" bevel.
"Outside" bevel.
I spent February of 2011 and January of 2012 in the Palcazu Valley of Peru working with the sustainable forestry organization GreenWood and our Peruvian partner organization PaTS.  We were working with a group of artisans who primarily carve large wooden bowls.  One tree from their forest sold to loggers generates on average $50 in the local economy.  The same tree when carved into bowls and sold in Lima or exported for sale brings in close to $2,500 into the community.  Can't beat that.
Lucy Peña measuring a finished bowl.

On my second trip I wanted to bring a bunch of carving axes for the artisans to try.  Most of them carve the outside of their bowls with fairly light adzes or machetes and I thought a heavier tool might increase efficiency.  I rounded up six decent hatchets and went to work tuning and sharpening them.  This is the method I developed for reshaping the bevels.

Axe grinding.
The vee-arm grinder tool rest and a pivot stick clamped to the blade enable you to pivot the axe head to the left and right and get a very consistent hollow grind.  I follow this up by honing the bevels with diamond paddles.  The hollow grind is easy to resharpen and when honed results in a very flat bevel which makes the tool easy to control.  The vee-arm tool rest that I use is part of the Wolverine tool rest system.  I find these grinding tool rests invaluable.  With a little ingenuity they can be adapted to grind seemingly anything.

With that brief overview out of the way, back to the project axe.

Removing the handle.
The first step was to remove the old handle.  It is not always a graceful process.  I sawed the handle off close to the head and then drilled out as much material as I could from the part of the handle that remained in the eye.  This is a perfect job for those drill bits that you probably should have thrown away a few months ago.  You are likely to hit the metal wedge that secures the handle on most old hatchets.

My axe was fairly straight at the edge and I wanted it to have a little bit more curvature.  I drew a curve that looked good to my eye.  Next, I created that curve by setting the grinding platform perpendicular to the wheel and grinding material directly from the edge.  This operation creates a flat at the edge of the tool, which can be a useful reference point in the following steps.  When I measured the curve later, it was close to an arc of a circle with an 11" radius.


The heart of my grinding technique is the pivot stick.  I made mine so that the point that sits in the vee-arm was 11" from the edge of the axe when the axe head was clamped in place.  This distance approximates the radius of the curve that I drew onto the head and then ground to shape in the previous step.  If the curve of your axe has an 8" radius then the distance from the edge of your axe to the point should be close to eight inches.  There is some room for fudging here, so don't get too crazy figuring out the exact curvature and radius.

Pivot stick top view.
Pivot stick side view.
My pivot stick is 9" long, 1 1/2" wide, and 1/2" thick.  It tapers to a 3/16" square at the pointy end and the front is beveled to provide clearance for the grinder wheel.

Complete set up.
A small c-clamp completes the arrangement.  I centered the pivot stick in relation to the curve at the edge of the axe.  The pivot stick must be set back from the edge of the axe to clear the wheel of the grinder.

Setting the angle for grinding.
Moving the vee-arm tool rest in and out sets the angle for grinding.  At this point I actually don't think much about the angle, and instead focus on the width of bevel that I want.  I was aiming for the wide bevel to be about 1/2" wide.  This axe head had fairly wide, convex bevels.  My hunch was that by grinding in the middle of the existing bevel, I would get a result close to my target.

Checking the set up.
With my grinding jig in the vee-arm I move the axe head back and forth on the wheel (grinder off) to see if the wheel is touching where I want it to grind.  The wheel leaves scratches where it is touching.  Notice how the scratches run parallel to the curve of the edge.  If they taper off to one side try adjusting the alignment or length of the pivot stick.  My initial set up looked good, so I proceeded to grind.

Proceed with caution!  Note the profusion of white multi-tailed sparks produced by grinding.  This type of spark is an indication of good quality steel in this particular axe head.  When I bought this axe a few months ago, the first thing I did was touch it to the grindstone to see what type of sparks it produced and decide whether or not it was worth tuning up.  Fewer, more orange colored sparks with shorter, fewer sunburst tails coming off the individual sparks indicate lower quality steel.  What you can't see in these pictures is that I am wearing ear protection, safety glasses, and a respirator.  After seeing the river of white sparks flowing onto my hand in the pictures I have decided to also wear a thin pair of leather gloves the next time I grind an axe.

As I move the axe back and forth I slightly raise the corner of the axe that is not in contact with the wheel.  I do this to clear the grinder motor, but it also seems to keep the bevel aligned properly.  Remove the assembly from the tool rest and check your progress regularly.  If the axe is not properly aligned the bevel will not be a consistent width.  Light tapping of the head to adjust its alignment with the pivot stick can usually remedy this problem.

Wide bevel ground.
Estimating the narrow bevel.
With the wide bevel complete, I used an angle gauge to get a feel for how to grind the short bevel.  The protractor is set to 32 degrees.  My sense from the types of sparks this steel produced and the feel of the hardness of the head against the grindstone is that this is an appropriate included angle for this axe head.  I will test and adjust that later, if need be.

Short bevel complete.
Grinding the shorter bevel follows the same process as grinding the wide one.  Adjust the vee-arm to get the angle that you desire, and then grind away.  I kept my protractor close to make sure that I was grinding the edge at the angle I wanted.  Make adjustments to the angle by moving the vee-arm as necessary.

As I grind both bevels I frequently check the flat left from grinding the edge to a curve.  I try to keep the flat straight and even in width.  In the picture above, note the inconsistencies in the width of the flat.  When I return to the grinder I remove more material from the areas where the flat is thicker and avoid grinding in the areas that are thinner.  As you can see, the corner of the blade in the left of the picture above has no flat at the edge, which means the bevels are meeting there.  When I returned to the grinder after taking this picture I made sure not to grind that corner any more.  A word of caution, the thinner that flat gets, the more likely you are to overheat the edge on the grinder.  I use a light touch and I keep a bucket of water near to cool the axe head as needed.

Sharpening the axe.

Even without the handle in the head I couldn't resist sharpening the edge.  I used diamond paddles to hone the hollow grind, and then finished it off with some careful stropping.  It was slicing through pine endgrain beautifully in under five minutes.  The hollow grind is quick to sharpen and makes maintaining flat bevels a simple matter.

In the next post I'll cover fitting the handle to the eye and making adjustments to the included angle of the edge.