Blade Sharpening, a Professional Approach

[Ralf1e]

On 27/08/2018 at 16:27, Christine said:

Please forgive the ostentatious title, some of you will remember a discussion a while ago regarding tool sharpening and my insistence that sharpening jigs are not needed; well I was asked to write this about how edge tools are sharpened in a professional cabinet making shop. Now please don't try and compare how a jobbing chippy sharpens his or her tools on site that is a different story but cabinetry and Luthiery have a similar need for tools that are precisely sharp as opposed to being sharp enough.

I will honestly say the one machine/power tool I would not do without is a wet grinder, I would rather rip boards up with a ripsaw and plane them flat and to size by hand than do without that and have done in the past. Why you may ask? Well when you are trying to do fine work in wood the single most important thing you need is control and with cutting tools the only way you can get that control is with very sharp tools, not almost sharp or even sharp enough, to get precise cuts first time and every time they need to be sharper than that razor you shave with each morning and kept that way. It is a job that can be tedious if you let it be, the trick is to let it not be and to do that it needs to be quick and easy then it can be seen as a way of releiving your mind from the concentration levels of doing careful work for long periods.

Lets have a look at my sharpening area

 

What you see is a wetstone grinder, a tub of water and two Japanese water stones which a are wedged into wooden blocks to keep them from sliding in use; they are then kept in the tub of water when not being used. Above these I have a variety of gadgets that are associated with sharpening various tools but there is only one of note, the grinding angle gauge

 

 

The wetstone grinder is used to give a hollow grind to the edge on a the cutting tool at a set angle which is determined by a little gauge. Mine is a 25 degree gauge which is a good all round angle for many tools giving a nice balance between durability and sharpness. The blade is clamped into a sliding carriage at the correct angle like this

Then it is simply a matter of switching on and moving the blade from side to side until you have a fully ground hollow edge that is square. I've tried to illustrate that with these photos as best I can

You can just make it out but notice that ragged burr on the edge. All we have done is to prepare our blade for the real sharpening:

In days gone by various types of oilstones were the way to go, when I was an apprentice I had a prized set of Arkansas stones but things thankfully have moved on some since then, we have the waterstones, diamond impregnated tiles, ceramic stones.... My own favourites are the waterstones and I'll explain why. Waterstones are a man made brick for want of a better term, made of precisely graded grits, they are bound together quite loosely so they actually wear quite quickly in comparison to other types but that to me is an advantage. When you sharpen a tool you abbraide it's surface so tiny particles are removed, these can become embedded quite firmly in the stone and cause something called glazing which reduces it's efficiency. Waterstones on the other hand break up very slowly so the particles are freed stopping that glazing. The downside of that of course is that the stone can quickly wear out of true, thankfully it is so easy to flatten unlike the old Arkansas stones that needed taking to a stone mason. To flatten a waterstone just get a strip of 80 grit sandpaper taped to a flat surface and give the stone half a dozen rubs on that and the job is done, easy. Another great advantage is that water is used a s a lubricant so rather than having oily hands after sharpening they are merely wet and the stones can just be put back in the tub with not further cleaning or drying needed.

I have two stones, the large red one which is a 1000 grit stone and the yellow one which is a 6000 grit, I use one at a time, they are both out above just for illustration. I don't have photos of the actual procedure but it is easy to understand. To start sharpening you stand in front of the stone (1000 grit), one foot in front of the other (important). You take the blade in both hands with some fingers from each hand on top of the blade to give it full support. Place the blade on the stone and feel for that hollow grind, there is a point where it sits flat and stable. Now you can either sharpen at that or as I do lift the blade a tiny amount so I only grind the front edge. Lock your elbows tight into your rib cage to lock your arms rigid, then rock backwards using your legs, so weight shifting from the front foot to the back foot, that stops the blade rocking. Do that four times and you should be left with a tiny shiny flat across the whole front edge of your blade. If you look closely mine isn't even, my stone needs flattening (OOPS!) but looking closely notice the burr

Change the stone to the 6000 grit and do the same again, remember this must only be done backwards never forwards, the stones are too soft. So four times then flip the blade over and place it flat on the stone, slide the blade over the stone backwards four times. Repeat that two or three more times until when you examine the edge there is absolutely no sign of any burr and the back face should be almost a mirror finish. That should give you a wholly flat edge, for a bench plane you may want to give that edge a slight curve, to do this I use an extra pass over the 6000 stone with pressure on one outside edge then the other and that will be enough to give you a nice edge for a plane

And that is it, just give the blade a quick dry on a towel along with your hands and back to work but be careful, that blade will be sharp and i mean sharp. The grinding procedure isn't done every time, just when the sharpening procedure starts taking longer as the flats get bigger; typically I sharpen four times then regrind. Even with regrinding a single blade can be processed within a couple of minutes. I keep four to six plane blades above my bench and sharpen all of them at once, that way I am less likely to be tempted to use a dulling iron when it is so easy to quickly change and it is quicker to sharpen six once then one six times.

I hope you can see the logic in that method, every cabinet shop I have been into uses that exact method so I assume that it is probably the best and easiest way of doing it, being quick and easy you are more likely to want to do it and the more likely your work will improve.

One last thing and this is actually the very first thing with any flat blade. The back face of a cutting tool needs to be flat, when you buy it it won't be, not even close. The first job with any new chisel or plane blade is to flatten it; how depends on how bad it is. Sometimes 10 minutes on a 1000 grit stone will do it flattening the stone a couple of times, if it is really bad then some 80 grit carborundum powder and a piece of glass it the way to go. Once it's flat then it will stay flat as long as you keep your stones flat but that back face MUST be flat to get the best out of your tools. Very briefly the reason why: A chisel is used mostly but supporting the back edge on work that has previously been cut, either to the side or behind the cutting edge. The back of the chisel is used as a rest and as a guide for progression, if your blade isn't flat then it will either dig in (blade concave) or ride up (blade convex) and that will never ever let you produce good work. Plane blades Other than you wont be able to sharpen properly a bade that is hollow along it's length one of the most important pasts of a bench plane is the cap iron, unless that is in intimate contact with the blade face it will clog up and even with the sharpest blade in the world that plane will not work or certainly won't be capable of quality work but more on that again.

 

Love this post. Very informative. My weapon of choice is a Tormek T7

[chrisba]

Well worth a watch. How a busy wooden boat builder sharpens his chisels and plane irons.

In fact, the whole series ( 120+ episodes so far ) is worth a watch if you've got a couple of years to spare. Exemplary woodworking, albeit on a larger scale.