Sharpening a Drawknife
I have not had much reason to use a drawknife, until recently. Spokeshaves are another matter – they are old friends … but drawknives are fairly new to me. I’ve this yen to build a few Windsor chairs, you see. Plus I am looking to a drawknife to help in the waste removal and rough shaping of the back of the Wegner chair I am building.
I’ve acquired a couple of vintage drawknives off eBay: a 6” Jennings carvers drawknife, an 8” curved Pexto, and a 7” straight Witherby. All are in decent condition, the Pexto especially so, and interesting all were described by the sellers as “sharp” – but, of course, are not what we expect of sharp. And this brings us to the point of this article: how to sharpen a drawknife …
I looked around the Internet for articles and found a few, but not one provided a clear pictorial with a method I thought reliable to replicate. And this is why I decided to write one. Of all the videos available, the best in my opinion is the pair by Curtis Buchanan - Part 1 and Part 2. Curtis is one of the doyens of Windsor chairmakers, and if you are seeking “how to” advice then there is no one better to emulate. This article simply takes his method and provides a pictorial for those who want a quick reference.
Tools
I used an 8” half-speed grinder with a 46 grit white Norton wheel. Then there was a Coarse DMT diamond plate, and 1000/6000/13000 waterstones. Feel free to substitute your own equivalents here.
The Victim is this Pexto 8” curved drawknife. As seen below, it is in excellent condition, without any rust …
The back of the blade is in similarly good condition, and looks flat.
On closer inspection, the bevel has some file marks, and has become rounded as a result of honing the flat bevel.
Below: the drawknife will cut hardwood face grain. Just. There is no way it will slice end grain. It is not “working sharp”.
Step 1: ensure that the top of the drawknife is smooth and fair.
I used a fine diamond stone to ensure that it was free of nicks and the curve was even. The reason will be clear later.
Step 2: flatten the back (sort of ..)
Sharpening a drawknife is no different from sharpening a chisel or a plane blade. It all begins with a flat back to the blade. In actuality one does not want the back to be perfectly flat, but instead have a very, very slight camber. Very slight. I find that this aids in releasing the cut, where a flat back can cause the blade to dig in. Flatten first, and add the slight camber at the end.
I began this process by running the back over a 1000 grit Shapton Pro waterstone. Keep the blade flat with fingertips over the stone, not hands on the handles. Watch that the blade does not rock.
Below you can see that the back looks quite flat. This is deceiving. The important area is the leading edge of the back, and here this is rounded. This is seen by the light reflecting off the edge.
Continuing with the 1000 grit is going to take a long time. Ironically, the more one flattens the steel, the more work it will take to flatten the remainder. This is because there is a broader area to flatten. Consequently, I switched to a DMT Coarse diamond stone, and this completed the flattening process reasonably quickly …
Once this was done, it was time to use the waterstones, moving through the grits to 13000.
This time I worked the diamond stone on the steel, largely as it was possible to use the expanse of the waterstone more evenly.
Make sure that you keep your finger high up on the stones and well out of reach of the blade! Only push forward, and never pull the stone back towards the blade!!
Step 3: Build the jig
This is the jig described by Curtis. It is simply a block of wood with a small ledge. The ledge is to rest the blade and the back of the blade will guide the blade (hence the top of the drawknife needs also to be smooth and fair). Use wax for added smoothness.
The jig is clamped to the grinder rest.
For reference, the front of my grinder wheel is curved, not straight.
Step 4: setting up and using the jig
The distance of the jig from the wheel is determined by the angle at which the bevel will be hollow ground. In this case I aimed for 25 degrees.
The existing bevel is roughly 25 degrees. With the power off, roll the wheel around and rub the bevel. It is at the correct angle when the scratches are at the centre of the bevel.
Once the bevel angle is set, start the grinder spinning and draw the blade along the wheel. I suggest starting at one end and pulling it the full length. Use light pressure – let the wheel do the cutting – and an even, moderately fast blade slide.
The long movement of the blade along the wheel, along with light pressure, keeps it relatively cool. It was possible to do three or four grinds before cooling the blade in water. Even then it was warm in the hand, not hot.
Below is an example of how the hollow began to shape up after several light runs.
The aim is to take the hollow to about 1mm from the edge. This is achieved below …
Once the hollow is completed, it is time to begin grinding and polishing a micro bevel.
I work directly on the hollow, with the blade face up, and moving the stones over the hollow, in the same method mentioned earlier. Again, only push forward, never pull the stones back toward the edge!
The process involved a progression through 1000, 6000 and 13000 grits. As with plane and chisel blades, the most important grit is the 1000, and it must create a wire edge at the rear of the bevel before moving to a higher grit. Similarly, all scratches from the previous grit must be removed by successive grits.
Above: the completed sharpening.
Below: testing the drawknife on Radiata Pine end grain. A good result on some really difficult wood.
The same process was completed with the little 6” Jennings carving drawknife, and then tested on the same piece of Radiata Pine. Looks good enough for me.
Hope this helps with your drawknives ..
Regards from Perth
Derek
June 2014