Saturday, May 10, 2014

Adze Grinding and Sharpening.


I recently finished up a batch of the adzes that I make and grinding and sharpening all of the blades provided the opportunity to show how I go about creating and maintaining their edge geometry.  My process is specific to my adze, but the techniques could definitely be adapted by a clever person to sharpen other adzes.  If the grinding set up that I use seems overly complex, skip to the bottom for other options.

My adze blades have both interior and exterior bevels.  The exterior bevel is hollow ground and if the hollow has been mostly removed by honing I begin by regrinding the bevel.  My grinding set up is half Rube Goldberg, so  I'll start with a picture of the entire rig and then walk back through the components and hope that it all makes sense in the end.

Adze grinding set up using the Woverine V- arm attachment.

The heart of my setup is the V-arm attachment that comes as part of the Wolverine grinding jig.  I use the V-arm in conjunction with an angled wooden grinding fixture to hold the blade at the desired angle.  It is just like regrinding a turning gouge, rotate the assembly in the V-notch and grind away, with a light touch.  I recently switched to using the 3X 46 grit blue wheels from Tool for Working Wood for on my grinder, which basically takes overheating the edge out of the equation.  If you are in the market for new grinding wheels, or have had trouble overheating other tools, I can't recommend them more highly.

Grinding jig and adze blade.

My adze blades are easily removable from the head and have a flat rear section that can be clamped to the angled ramp of the grinding jig with a small C-clamp.  The overall length of the jig, without the blade, is 12 1/2".

Blade clamped in place.

I visually center the blade on the jig and align the edges of the blade parallel to the edges of the jig.

Blade aligned and clamped.

Well, I get it close any way.

Blade positioned in line with the grinding jig.

The outside of the blade at the edge should be in line with the bottom side of the grinding jig.  The basic theory here is that the outside of the blade at the edge should be in a direct line with the wooden grinding jig, and the shape of the wooden grinding jig where it rests in the V-arm should be approximately the same shape in cross section as the sweep of the adze blade at the edge.  

I had to read that sentence a couple of times to see if it made any sense.  Hopefully the pictures help.

Curvature of grinding jig roughly matches sweep of adze blade.

You can see from the last picture that this doesn't have to be an exact match, but as the difference in curvatures increases, grinding becomes less consistent and more difficult to control.  The end of my grinding jig is 2 1/16" in diameter.  It was the biggest piece of scrap I had on hand.  When the edge is traveling in the same path and turning at the same rate as the part of the jig rotating in the V-arm you get a nice consistent grind.  When the back of the grinding jig is significantly smaller than the sweep of the adze blade, the angle of the grind decreases dramatically as the blade rotates toward the corners.


The ramp that the blade is clamped to is angled at 22 degrees.  There is slight variation of the curvature of the blades, this angle has worked well throughout the range of variation.

Testing the grind angle.

With the blade properly positioned I take the assembly to the grinder and lock the V-arm in position when the bevel appears to be laying flat on the wheel.  Then, with the grinder off, I rub the blade back and forth to confirm that the assembly is properly aligned.  I remove the assembly and check the bevel to see that the scratches from the wheel are centered on the bevel.

Scratches from the grinder are centered on the bevel.

If the scratches are slightly forward or back from the center, I adjust the position of the V-arm to achieve the desired alignment.  

The final adjustment before grinding is to position the assembly at the grinder and swing the blade to either corner and rub it side to side to confirm that the wheel is still striking the center of the bevel at the two most extreme points.  If the alignment is off, usually the scratches will run up to the edge on one side and to the back of the bevel on the other.  If this is the case, I skew the blade on the ramp to compensate.

Skewed blade to adjust for misalignment at the blade corners.

The picture shows a blade that is skewed more than I have ever found necessary, to clearly illustrate the idea.  When the blade is skewed the corner that moves forward, will climb slightly up the face of the grinding wheel, which will move the scratches away from the edge and towards the center of the bevel.  The corner that moves back will slide down the face of the grinding wheel, which will move the scratches from the back of the bevel, toward the center.

I adjust, confirm that the adjustment has aligned the blade properly and then grind.  The grinding is quick and the hollow makes it easy to maintain the performance of the tool.  When regrinding I never grind all the way to the edge.  I always try leave a small polished flat.  I treat the bevel on the outside similar to the way I treat the back of a chisel.  I usually raise a burr by sharpening with coarse abrasives from the inside and only use fine abrasives on the outside to polish and roll the burr back to the inside for removal.  Using this technique extends the amount of time between grinding sessions.

Inside of the blade.

The inside of the blade is microbeveled.  The total included angle of the edge should be around 35 degrees to withstand the rough use that the adze is put to.  It is important that the inside bevel be micro to keep the resistance of the blade as it cuts through the wood low.  A big fat bevel on the inside the blade makes the adze feel sluggish in use.  Keeping the inside bevel small allows the tool to slide right through the wood with a minimum of effort, while the microbevel gives the edge durability.  I learned this from the Yanesha bowl carvers I worked with in Peru.  They spend day after day swinging their adzes and need their tools to cut aggressively and have the edges last as long as possible.

I use a dremel to remove material behind the micro bevel.  In the absence of a handheld rotary tool, coarse sandpaper wrapped around a dowel works well.  This step isn't necessary every time you sharpen the blade, but keeping the microbevel small keeps the tool functioning at a high level.

Diamond paddles and a drill bit wrapped in P600 wet/dry sandpaper.

When the grinding is done on the outside and the material behind the micro bevel has been removed with a rotary tool or coarse abrasives, honing commences.  I use diamond paddles for honing the outside of the tool and a drill bit wrapped in P320 or P600 wet/dry sandpaper for honing the inside.  A dowel wrapped in sandpaper works just as well as the drill bit.

Raising a burr from the inside.

I begin resharpening by forming a burr from the inside with P320 wet/dry sandpaper.  To check the angle I set an angle gauge to 35 degrees and rest one arm of it flat on the exterior bevel.  I position the other arm close to but not touching the interior bevel and check to see that it is parallel to the gauge.  If it is not I focus my attention on the front or back of the bevel to adjust the angle.  Some convexity here is not a problem.  If the angle gets too obtuse, you'll know because it will feel like you are beating the wood apart when you start to use the tool.  It should feel like the blade slices through the wood with little effort.

Honing the bevel.  Be aware of your fingers.

Next, I hone the exterior bevel with a fine diamond paddle.  I press the paddle flat onto the bevel and slide it back and forth.  While doing this it is important to consider where a slight slip of your hand could put your fingers, with the burr raised contact with the edge can leave a fingertip on the floor in a hurry.  I feel confident using the position demonstrated in the photo above, but note the potential danger.  I move the paddle with slow, deliberate motions.

With the outside honed, I switch to P600 paper on the inside to polish the scratches and then alternate between honing the inside and outside to remove as much of the burr as I can before stropping.


I strop the outside using the same technique I use on carving gouges.  I place my fingers on the edges of the blade and rotate the blade side to side as I pull the tool along the strop.

Strops have a bad reputation for rounding over the tool edges.  To minimize the rounding at the edge, I place the bevel flat on the strop and then emphasize the pressure on the back of the bevel.  The leather deforms enough to polish the edge, but with pressure emphasized on the back of the bevel, rounding at the edge is reduced.

The slipstrop I use to polish the inside.

I use the slipstrop I made a few months ago to strop the inside.  It it takes five minutes to make and works brilliantly.

Stropping the inside.

I alternate stropping the inside and outside until all traces of the burr are gone and the blade takes clean shavings from pine endgrain.

I sharpen the blades this way for a couple of reasons.  My grinding jig allows me to controllably grind the same amount of bevel on the outside of each blade and the hollow that it leaves is easy to hone.  I want the tools that I send out to customers to be at peak performance, so that when that person starts using the tool, the way the tool feels becomes the standard of performance for them.  If that person resharpens the tool and some aspect of the performance has changed, they will know that the tool isn't functioning at its full potential.  If they cannot figure out the problem they are welcome to contact me to help them address it.  The key is knowing how the tool should perform.  The hollow grind allows me to repeat the process over and over, and know that I am sending out tools that are working at the highest standards.

That said, if you don't have a grinder, or feel intimidated by the grinding set up and potential risk of overheating the blade, you can get great results from freehand sharpening the exterior bevel on sharpening stones, just as you would a gouge.  I sharpen gouges by rocking them from one corner of the edge to the other as I move the tool lengthwise along the stone.  It is easy to maintain a flat bevel with this technique. blade detaches from the body and it is easy to manage on stones.  Try to mimic the existing bevel angle and keep it as flat as you can.  I have sharpened adzes like this and it is simple and works great.  In fact, for many people this approach probably makes more sense than the approach I outlined above.

Sharpening a gouge.

Choices in sharpening are a matter of preference.  It helps to draw on skills that you have already developed through previous experience.  If you have experience freehand sharpening gouges on stones, then adopting that approach for an adze probably makes sense.  But if you are an avid turner who has extensive experience grinding spindle or bowl turning gouges, then you might prefer to hollow grind and hone the bevels, as I do.


4 comments:

  1. Awesome instructional Tim, thanks for posting!

    ReplyDelete
    Replies
    1. Paul,

      I thought this one would be up your alley.

      Delete
  2. Thank you! Your blog is really helpful and a pleasure to read. Are you now selling your adze? I am interested.

    ReplyDelete
    Replies
    1. I'm glad you like the blog. The adzes are for sale. The wait list has been quite long since Woodworking In America last year, but I am finally getting caught up with it.

      Please email me for more information and I will add you to the wait list.

      Thanks for your interest.

      Delete