Nic Westermann shares his simple two-point approach to sharpening curved spoon blades and scorps.
In my previous introductory article on sharpening I explained how to cut a bowl or concave surface – the bevel of the blade must be a mirror image of the form it will cut. The bevel needs to be convex – only slightly convex, but convex nevertheless. When you bend a strip of steel to make a spoon blade the outside will take on a concave from edge to spine. This is really unfortunate as it is the precise opposite of the desired convex bevel form, and does make manufacture of these blades problematic.
Edge geometry for efficient carving
The first rule of sharpening is to cut the bevels to the correct form and it is of then the case that spoon knives do not have the optimum bevel form when purchased.
Fig 1 shows an example of a basic flat, bevelled blade. It will not cut well on a curved form as the edge will tend to dig in and then be forced out of the wood by the next point of contact, which is where the back of the bevel meets the blade body, causing chatter. There will be no contact at the spine of the blade so relieving this area is not necessary.
There is, however, a trade-off with the final form you choose. A blade that excels at deep forms will be more convex and will not provide much bevel support on shallow forms so will not be so controllable or efficient.
How much convex is required?
It is hard to know how much of a convex you need, so try this. Test your blade in a form you are likely to revisit. I know this is a bit chicken and egg – how do you hollow out a form with a blade that needs sharpening? All blades will hollow to some degree, as will gouges, burrs, even sandpaper at a pinch. So, once you have dug out your form use a marker pen to draw a series of lines on your blade from edge to spine and cut, just once – you should see the pen wiped off from the areas that need removing. When all the pen is wiped of your job is done. Note that the blade doesn’t need to be that sharp at this stage – it is the points of contact we are looking at.
Admittedly making these changes is not easy. I would recommend starting with wet or dry on a block, in the 360-600 grit range. This is slow going but you will be unlikely to take too much off as opposed to powered grinding or sanding. You may prefer to have the hone on the bench and work the knife though.
Remember that you are aiming to remove steel from the back of the bevel to make the convex, not the edge – leave that alone or you will dramatically alter the effective cutting angle of the blade. If you like to push cut on the spine of your blade then it makes sense to round this slightly for comfort.
Hopefully not much will be needed in terms of shaping on the inside as this should be largely flat, but I would advise refining the surface and removing any grinding marks. I would suggest grits in the 800-1200 range for this.
Refining the edge
Once the bevels are set, then to finish sharpening we need to follow the second rule – which is to refine the edge by working down through the grits. If you have reshaped the outside bevel you will need to work down through the grits to blend everything in. Don’t worry about getting a perfect, scratch-free finish over the entire surface, it is only the edge that really matters.
Even if you haven’t had to recut the outside bevel the edge may well need some touching up, so try to refine this. Go slowly. While being careful not to round the edge at this stage, I can’t emphasise how important this is. As you will see later you will only have to do this once so take your time. I would finish the outside to 3000 grit.
As you will now be painfully aware the outside bevel curves in both directions, which makes sharpening very difficult. Conversely, the inside of a blade should be flat, and thus will only curve in one plane making it an easier option to sharpen. In a situation where one bevel is noticeably easier to sharpen than the other, I always recommend concentrating on the easier one and just removing the burr from option to sharpen.
In a situation where one bevel is noticeably easier to sharpen than the other, I always recommend concentrating on the easier one and just removing the burr from the other side – why make life more difficult than it needs to be? At this point we have a blade with the outside bevel virtually finished, and now all sharpening and resharpenings can be taken care of on the ‘easy’ inside.
Adjustment and stropping
On the spoon blades I designed and refined over the years I use a hollow inside bevel – this makes sharpening easier and quicker than a flat inside bevel, but the overall technique is the same. Self-adhesive wet or dry paper on a wooden dowel is the easiest, but you can wrap or glue paper on. Make sure you are working away from the edge. You should raise a burr quite quickly – this can be felt on the outside bevel.
If you have a blade with a flat inside bevel colour it in with a marker pen to show you where you are working – it is effectively a bevel the entire width of the blade, so it makes sense to know when you are hitting the edge. As ever, be careful not to round this bevel – aim to keep it dead flat. Strop of the burr on the outside – the one in the image could actually be wiped of with my thumb. I just use a fine polishing compound rubbed into suede to polish this off. In a typical resharpening sequence there is no need to use anything else on the tricky outside bevel.
Shortcut
Finally, a shortcut. I often make test cuts before I have finished sharpening at the 1200 grit stage – the wood will show up any discrepancies in the edge very clearly. I then tend to mark the of fending section of blade so I know which areas to concentrate on. This technique is also really useful if you have a ding in an otherwise sharp blade but can’t track it down. Sure, there is an argument that to maintain a straight edge you should sharpen all of it evenly, but if you want to get back to carving quickly this tip can save a lot of time.
Further reading
PHOTOGRAPHS BY NIC WESTERMANN