Grinding Tips

Grinding with Speed, Power              

I'd say the most important factor is having a powerful, quality belt grinder.  I have two main grinders in my grinding room, both are 2x72 size.  One is an old Square Wheel grinder, and the other I built myself, using elements of Bader and KMG design.  Both are variable speed, the first is 2 hp. and the one I built is 3 hp.   

Another important trick for grinding fast is to use a push stick.  It's just a flat piece of wood with a step down cut in one end, so that it supports the blade from below a the spine, and can be used to push the work hard into the belt.  I mostly grind steel before hardening it, so no need to worry about over heating the work.  The push stick will start to char sometimes before I dip the metal in the spark bucket.  I use one almost all the time, unless I'm at a finish/polish stage.

Don't be afraid to use an aggressive roughing belt and really lean into the grinder.  See "belt selection" and "grinder stance."

Push stick preparation.

The notch holds the spine.

Aaannd... press the steel into the belt.  Shown with flat blade and 12" wheel
for purposes of confusion.

Belt Selection

Belt selection is also important.  Cheap belts, or the wrong belts for an application, will wear out quickly and will take much more time and effort, and that tends to produce a blade that doesn't look very good.

For rough grinding metal, I use Norton SG Blaze ceramic belts, in 36 and 50 grit.  With 3 hp. behind them, they just rip the steel right off the blade.  I use 3M Gator Grit belts in 220, 400, and 600 to finish metal.  (The technical name for those is 3M Trizact CF belts, in grits A65, A45, and A30.)  They stay sharp WAY longer than anything else I've tried.

I buy decent quality, but cheaper J-flex belts in 220 and 400 for handle work, as well as some 60 grit cheap aluminum oxide belts for roughing handles.  I go through them fairly fast, but they are cheaper to replace and the good metal belts just clog up on this stuff.

Grinder Stance
This is a huge deal, I learned it in person from Ken Onion, who is a master grinder.  Once I started applying it diligently, my grinds improved a whole lot and my speed increased as well.  This is the gateway to grinding beautiful lines and plunges.

Stand with your feet fairly widely set, but in a position that's comfortable to you.  You don't want any strain entering your grinding.  The wider stance gives more stability.  Make sure your grinder is at a good height, I like to grind at just about navel height, that's where my arms rest when I lock them to my sides; more or less riding on my hip bones.  The platen or wheel height should be centered about here.

he technique is to lock your elbows and grind evenly by sliding to the left or right with your hips, not your arms.  This can also be described as shifting your weight. It really helps. Try to act like the carriage in a grinding machine- a perfectly even slide to left and right.  It may help when rough grinding to be aware of the spark pattern- if the entire width of the belt is not throwing sparks, you may have the blade unevenly applied to the belt.

Hold the tang firmly with your left hand.  Don't let it twist or the angle wander.  Locked elbows helps.

Establish bevels, primary bevels 101

Grind the edge with a 45-degree bevel almost down to the desired edge thickness, nice and straight.  Use an older, worn out roughing belt.  This can be done after scribing the edge line(s) for stock removal guys, or after forging for hammer-heads.  This gives you a witness line to grind down to, establishes a straight and even edge from the start, and helps keep your new, sharp belts from getting all the abrasive stripped off by edge-grinding.

Don't "poke and look" a lot. Try to take a full length, even, fairly light pass from plunge to point, and then observe the results.
Once you get a good flat pass established by adjusting your angle, bring the blade to the belt every time with a somewhat "loose" grip so that the blade instantly self adjusts to the flat you already have established.  Doing this so that the edge is very slightly leaned into the belt when you first make contact will save the spine side of the grind (which is much harder to correct) from a lot of dings and grinding mistakes. 

With intermediate flats work the grind up towards the spine, and toward the plunge cuts.

Bevels 102

The process of beginning a flat bevel, then working it up toward the spine to the desired height, can be described as "grinding progressively upward."   Each major pass or series of passes with the belt will overlap the previous grind height, and gradually make the grind angle more shallow until the spine is reached.  If done with care, this can be faster than trying to just "hog" out the main bevels all at one angle to start with. 

I'm going to stop trying explain this myself, and direct you to a forum thread which I feel does a good job of documenting this technique.  The thread is by bladesmith Fred Rowe, and while he is the maker of the "Bubble Jig" grinding aid, I feel that everything in the thread can be applied to grinding totally freehand as well.  Although from what I hear, the Jig is a really good thing to have, as well.

Lastly, I'll add that I find this way of flat grinding nicely effective for wide flats, such as tall thin kitchen knives.  Here's the link:

Plunge Cuts 101

If you are having trouble with these, here are some questions for you:

What are the platen/contact wheel edges like on your grinder? Can you use them to fold a J-flex belt around?  Is your grinder single speed, high S.F.P.M so that the screaming speed of the grinder is not conducive to such a technique?  What grind lines do you have a problem with, the plunges, the grind line along the top of a partial height flat or hollow grind, or both? 

It is an enormous help to have strong, adjustable light on both sides of your grinder.  I use goose-neck lamps.  You have to be able to see what's going on.

My setup with lights.  Yes, I need to clean up in there.

It is a big help to take a fine marker and mark under the ricasso where the plunges need to go, and also to mark the plunges out on the blade.  Having that mark underneath gives a solid reference for when they are even.

I always rough grind at least 1/16" short of where I want my finished plunge cut to be, it gives room to even them up with each other, etc.  So rough grind your plunges in and leave a little room for cleaning them up with a finer belt, grind most of the blade and then you can push your plunges back a little with a sharp 220 belt, also working on keeping them even and shaping the radius at the top corners of the plunges/grind line. 
This works best with a flexible belt such as a J-Flex, which you can track over the edge of the platen a little so that it folds around the edge.  It helps this process a little to break in the edge of the belt a bit by applying the corner of an old file or something to the edge of the belt while it is running.   If you need this spelled out more explicitly, the following photo and paragraphs may be useful.

Flex the belt over the platen edge.  The rough ground plunge will do this.

So, the platen would be the flat surface that the belt rides over. The edge of the platen would be, well, the edge. Where you do your plunge cuts. I ask what the edges are like because you want to use them as a grinding surface. It's nice if the platen is flat all the way to the edge, with a good 90 degree corner radiused very slightly (if it's kind of a sharp edge, just round it lightly with a fine file, then some 220 grit paper.) Why is this important?

                 A common technique for refining your plunge cuts is as follows: take a flexible belt, a common choice would be a J-flex (J weight cloth backing, flexible belt) aluminum oxide at 220 grit, Tru Grit or USA Knifemaker Supply probably have some for you. Track the belt over so that approximately 1/8 - 3/16" is riding past the edge of the platen, on whichever side you are cutting the plunge with, take a piece of scrap metal, and bend the belt around the edge of the platen where it overlaps. This is to make sure the edge of the belt is used to curling around the platen edge at speed, and can help break the belt edge down a bit softer if you don't have a real flexible belt.
               You take your blade, apply it nice and flat to the belt, edge up, and grind toward your plunge cut, so that when you get there the belt rides over the platen edge and is actually grinding lightly on the flat and lightly on the inside of the plunge cut. You're then grinding the plunge face sideways toward the ricasso. It will take some practice and feel to be able to do this evenly and to your satisfaction.
               This all applies more or less to hollow grinding, as well.  Your grinder may prove to be a limiting factor.
Plunge Cuts 102

If a sweeping plunge cut/ grind line is what you are after, I'm with you 100%.  It is an art, and properly done can look great.

A rough ground sweeping plunge at 50 grit.

I rough grind as usual, making sure to stop short of where I plan the grind line to be.  Not by much though; I use 50 grit blaze to grind it almost to a finished look, then refine with Gator A65.

I find the most important part is to have a firm, controllable grip on the knife, and to watch what you're doing as it's happening.  I do this by aiming strong light right at the edge of the platen from behind it, and looking down at the side of the blade from the inside as it comes off the belt.  I can then minutely remove material in a controllable way.

Looking at the grinding action from above, behind.

Go slow.  Turn the grinder down to 1/2 speed or less.

To me, this is not about folding a flex belt around the edge.  I just overlap the belt 1/16" or so, since it is a stiff belt it won't flex around much.  I use the corner of the belt to carve away at the steel.  This holds true from Blaze 50 all the way up to Gator A30.
I'm going to do a few drawings about swept plunges here, I find it hard to explain with text (or at all) and hard to take pics of.  I have a point of discernment between what I call "fully swept" and "semi swept" plunges. I like both, but find the fully swept plunge more challenging and ultimately more appealing. I also suspect it may be a bit stronger, although I find the degree to which people focus on things like that to be a bit ridiculous.  A disclaimer: I'm no draftsman, view drawings at your own risk.

            Practice hard, develop your own techniques and feel for this.  Some things you can't explain- it's muscle memory and instinct distilled by practice that will allow you to consistently get the results you're looking for.

There's nothing wrong with filing in plunges or using jigs, they're smart ideas, but it's really worthwhile to develop good freehand grinding skills and don't be discouraged if you make mistakes while learning.  It's unavoidable.  Hope any of this helped.