Monday, January 27, 2014

Tuning Up and Re-handling Old Chisels.

In the last five years I have been fortunate to inherit two boxes of tools that belonged to my great grandfather.  He was trained as a boat builder in Cornwall, England, but eventually moved to the states where he became a house carpenter.  Most of his tools are fairly common; socket chisels, a few gouges, layout tools, a backsaw, etc.  There are a couple of real gems from his boatbuilding days though.  Every couple of months I get some inspiration up and tune one of his tools to replace some of my less cherished modern, plastic handled equivalents.  Lately I have been cleaning up a couple of his chisels.

1/2" chisel with a hump across its width.

I start tuning up a chisel by lapping the back on a granite plate with 150 grit sandpaper adhered to it.  I am no fan of lapping and I will do pretty much anything I can to minimize the number of monotonous hours in my life spent making things flat by rubbing them back and forth on a stone.  The picture above shows the results of lapping one of these chisels 20-50 times.  This chisel had a hump that ran down the middle of the back from the edge to the socket, probably from years of sharpening on dished out oil stones.  In my experience this is pretty common with old chisels.  A couple of months ago I found that I could use my bench grinder to reduce my hours of lapping misery.

Hollow ground back of a 1" chisel.

By lightly grinding the center section of the back I create a concave surface that references easily on my stones.  It also reduces the total surface area that I am abrading and quickens the flattening.  The grinding is only a couple of thousandths of an inch deep and will lap out from repeated honing over time.  In my experience, it is easy to flatten concave surfaces, and a little squirrely trying to flatten convex surfaces.  This is true whether I am flattening a wide board with a handplane or the sole of the handplane with abrasive paper mounted on a granite reference plate.  In most situations flattening begins, for me, with creating a slight concavity.

Setting up for grinding.

This is the position that I use for grinding the hollow in the back.  In the photo the grinder is off. The tool rest is moved close to the grinding wheel and angled steeply.  The chisel then rides in the vee shaped gap between the top edge of the tool rest and the grinding wheel.  The chisel is angled somewhat down.  I eyeball to see that the center of the back is touching the wheel, move the chisel in and out, and then check the scratches from the wheel to see that it is touching where I want it to be.

Scratches right along the center.

Then I take the chisel back to the grinder and practice the motion one more time, memorizing in my body the angle that I am holding the back in reference to the wheel and the downward angle that I am sliding the chisel.  All that is left is firing up the wheel and repeating the motions that I have just practiced.  A light touch is key to success.


Above are the results straight from the grinder.  You can see that I got quite close to the left edge, closer than I would like.  This is the narrowest chisel that I have ground like this.  Wider is much easier.  To the granite plate.

Twenty strokes on the reference plate and the first inch of the blade is flattened at the cutting edge and down the sides.  I think I gave this one a couple more licks before moving up through the grits.

Polished to P600.

That entire process took under twenty minutes.  I have a great way to grind short stubby chisels like the one inch chisel pictured above and below, which I will save for another time.  For now I will just say that I prefer to hollow grind my chisels, with some exceptions for particular tasks or specialty chisels.  I find hollow ground chisels very easy to maintain so they are always sharp when I reach for them.

Long paring handle on another vintage chisel.

Above is another 1 1/4" socket chisel from my great grandfather with a replacement handle that I made.  The handle is 12 inches long.  I think of this tool as a miniature slick.  It hangs on the wall right next to my bench and I use it constantly.  If you have never turned replacement handles for socket chisels, you are missing out big time.  I think it is the most instant gratification woodworking that is possible.  It is also a great use for scraps of exceptional wood that are too small for anything else.  The handle above is ribbon mahogany that was a stair tread that I pulled out of a dumpster.

Where socket joins handle.

I like to leave a 1/8" gap where the taper that fits into the socket continues before stepping up the diameter of the handle to match the outside diameter of the socket.  This gap allows for the handle to slide further into the socket without butting up against the shoulder as the handle size shifts with the relative humidity of the seasons.

Handle blank chucked in the lathe

Roughed down to 1".

I wanted a short handle for the one inch chisel that I tuned up.  I had a macassar ebony offcut that was badly checked.  I was just able to get a piece big enough to get a one inch diameter handle out of it.  The piece was a just over five inches long.  I started by roughing down the blank to one inch diameter.

Test fitting the taper.

Next I created the taper that fits into the socket.  I started by measuring the depth of the socket with a narrow ruler.  I transferred that measurement to my handle blank while it was spinning.  Next, I measured the inside diameter of the socket at the opening and used a parting tool to size the top of the tapered section of my handle.  Then I guessed at the dimension of the narrow portion of the socket and parted the narrow end of the handle to that dimension.  Back at the lathe I connected the dots with a spindle gouge and then tested the fit in the socket.

Look for the shiny spots where the socket is rubbing.

During the test fit I try to wiggle the handle to tell whether the taper is too big at the bottom or top.  I also spin the socket around the handle and when I remove it I look for the spots on the handle that were rubbing.  These are the high spots and I remove incremental amounts of material from the high spots before re-testing the fit.  In the above picture, notice the high spots at the narrow end of the handle and also a ring of contact towards the top.  There was a burr on the top edge of the socket that was preventing the rest of the taper from seating properly.  I ground the burr away and then tested the fit again.

A couple rounds of test fitting later...

After a few more trial and errors I had the fit that I wanted and the chisel slid to its final position on the handle.  I like chisel handles to be a straight one inch diameter that taper over the last two inches to a diameter that is continuous with the outer diameter of the socket.  To create this shape I part the point of the working part of the handle nearest to the socket to a dimension slightly larger than the outer dimension of the socket.  Then I mark a point with a pencil two inches from the shoulder of the handle and fair the shape from the one inch diameter portion of the handle to the parted diameter adjacent to the shoulder.

Sanded.  Chamfered.  Finished.

Once the basic shape is there I sand the handle to 600 grit.  To get rid of the marks from the drive center, I part the last 1/8" of the handle to a diameter just larger than the drive center.  Then I skew a chamfer onto what will be the butt of the handle.  I like applying finish to anything that I can while it is spinning in the lathe.  I apply finish, let it sit for 30 seconds or so.  Then wipe off, generating heat with the cloth.  For this handle I used three coats of tru-oil applied one after the other.  This left a nice satiny finish.  The last thing I do is to saw off the nub on the end of the handle and clean up the end with another chisel.  Then I fit the chisel to the handle and rap the butt of the handle with a hammer to seat the handle in the socket.

The grip portion of the handle is four inches long.  The macassar ebony feels amazing.  It is so smooth.  I reach out many times each day just to touch it.  I want to make everything out of macassar ebony.  I don't use hoops on socket chisel handles to prevent the ends from splitting.  I do strike them with steel hammers.  Sometimes they break.  They are very easy to replace.

One of the things that I love about using antique tools is that they remind me that I am on a continuum of woodworkers reaching far into the past. The tools that I have inherited through my family give me that feeling plus ten.  I am glad to have them in my care for this time.  Hopefully their next owner won't wonder, "What kind of bonehead ground out the backs of these chisels?"

Sunday, January 5, 2014

A little bit more about the adze.

The adze is finally out of prototype phase and swinging into production.  I've been delaying writing more about it until everything was finalized, which it finally is.  I got a lot of great feedback about the tool at Woodworking in America, and Pete Galbert and I went back to the drawing board to make a few design tweaks that have really upped the performance of the tool, mostly the result of a subtle change to the curvature of the blade and the degree of external bevel.  The first batch of twelve tools is in production, so I thought this would be a good time to provide a few more specifics about the adze.

The main structure of the tool is a steam bent hickory handle joined to an East Indian Rosewood head.  The tenon on the end of the handle is tapered at the bottom of the joint, flared and double wedged from the top, and assembled with epoxy.  It's like a chair joint on steroids; rugged, and it has to be to take the abuse this tool is subjected to.

A batch of adze blades awaiting heat treatment with a couple of un-forged steel blanks.

The blades are forged from 1/4" O1 tool steel,  flared out at the cutting edge (1 3/4" from point to point after it is bent).  The sweep of the edge is a two inch radius, enough curve to keep the corners from digging into the work and flat enough to be able to leave a surface that is relatively smooth and quick to clean up with the inshave or travisher.  The blades are drilled and countersunk for a hex flathead machine screw that secures them to the rosewood head.

An allen wrench loosens the blade.

Blade removed for grinding or sharpening.

The machine screw threads into a cross dowel which is inset into the side of the head.  When I assemble the blade and the head, I ever so slightly offset the machine screw hole in the head toward the shoulder that the back of the blade rests against.  As the machine screw tightens down into the countersink, the blade is forced tight against this shoulder, similar to the way a drawbored pin draws a tenons shoulders tight.  This eliminates any tendency of the blade to twist in use.  I remove the blade for grinding and coarse sharpening, like removing nicks from the edge.  For minor touch ups, I leave the blade in place.

This adze is lighter than most adzes of European descent, closer in weight to the elbow adzes of the Pacific Northwest.  Weight and balance of the tool was a major design consideration and one of the reasons for the mountain of adze prototypes that I made.  I inserted weights into different portions of the head to experiment with the total weight of the tool and the amount of weight in front of and behind the handle.  The final version has a thicker blade than my prototypes which eliminated the need for added weight.  The thicker blade also gave the tool the forward balance that I knew I wanted as a result of my prototyping.  Forward balance makes the tool track more intuitively in the cut and also puts all the weight right where the tool is working.

The action of the adze changes dramatically depending on where and how the handle is gripped.  As a rule of thumb the closer to the head the handle is gripped, the more aggressively the tool will dig into the wood.  The closer to the end of the handle the tool is gripped, the less the tool bites and the more easily it clears chips.  Each user's sweet spot to hold the handle will be slightly different, corresponding to differences in forearm length, style of swing, height of work surface, and the desired cutting action.  The red rubber band on the handle slides up and down and functions as a reference point for repeated hand placement.  This is especially helpful when learning to use the adze.  Does that rubber band look familiar to anyone?

North Atlantic Lobster bands.  Welcome to Maine.

To use the adze most effectively, a relaxed grip is essential.  This allows the tool to pivot in the hand at the end of the stroke, which helps to clear chips instead of digging, digging, digging in.  There are times that you want to dig in, but that's another blog post.  I start my grip by wrapping the thumb and index finger at the top edge of the band.  I also wrap my middle finger around the tool, while my ring and pinky fingers remain relaxed.

The following pictures show how much this grip allows the tool to pivot in the hand.

Adze pivoted back in the hand.
Pivoted forward.

Please note that the my wrist position is the same in both of these photos.  The main portion of the swing comes from the elbow joint which generates power and provides gross movement of the adze along an arc.  Imagine if the tool was gripped tightly and there was no movement in the wrist.  In this scenario, the adze would only be able to cut along that one arc, with a radius originating at the elbow joint.  Allowing the tool to pivot in the hand slightly allows the user to adjust the arc on which the tool is traveling to cut a wider or tighter curvature, as desired.  Allowing the tool to pivot also seems to increase power.  I'm going to have to do a video about this!

Roughing out a complex shape like a windsor chair seat requires several types of cuts with the adze and different grips for more power or control.  I do plan to venture into video soon to better illustrate this and other techniques with the adze.  More to come.