How to - distal taper

[awestib]

I am not even sure at all if it makes sense to ask this question here on the forum since I believe that it has to be shown in practice - but I thought I try it anyway and am hoping for some advice.

I have a knife that is too thick behind the edge for my purposes but it also has a distal taper so the issue therefore is less towards the belly and tip. I have a simple belt sander with a flat platen that I'd like to use for this reprofiling project. My question, how do I remove more metal where needed and less towards the tip? Is it just a matter of pressure applied? I move the knife's flat against the platen from heel (ricasso) to tip as the basic movement. I understand that I can determine where I remove more metal from spine to edge by pressure points (either near the spine or near the edge) but how do I do it lengthwise?

Any advice appreciated!

Thanks, Andy

 

[i4Marc]

Ok, it seems like you have the right idea of the mechanics of taking material off where you want. First thing I would suggest is practice on scrap until you are a bit more comfortable working on a knife you care about. You are correct. More pressure at the spine removes material there, same at the edge. To control pressure lengthwise lock your elbows at your sides and use your legs to shuttle your upper body side to side. Many times, because of the distal taper and curve towards the tip, the side movement may include bringing the tang towards you slightly as you near the tip so as to follow the curvature at the tip. Since you don't want to remove any more material at the tip be sure to draw the blade bevel straight across and off the belt. Lighten your pressure against the belt as you move towards the tip and gently lift off the belt before the tip runs off the edge of the belt. Practicing on scrap will quickly give you a better feel for that motion.

 

[Salem Straub]

I second all of that. I'd add make sure to use a new belt for best results, especially on hardened steel.

 

[i4Marc]

I second all of that. I'd add make sure to use a new belt for best results, especially on hardened steel.

I second that.

 

[Grease]

Yup... even if the belt still looks/feels "new", the grits can be dull and that'll make the work go slow.

Also, dont try to grind too much at once. You'll heat the blade too much. Be especially careful around the tip, as it can heat up quick.

 

[Stacy E. Apelt - Bladesmith]

Remember this adage:
"Use belts like they were free.....or they will cost you!"

First off, it may go without saying, but I'll say it anyway - grind the edge back to a flat surface. You don't have to grind back far, but you need both a flat reference and you don't ever want to grind on a sharp knife.

You have the right idea on grinding a distally tapered knife. Grind slower and with heavier pressure toward the ricasso, moving the blade faster with lighter pressure toward the tip. At all cost, avoid sweeping the blade in an arc as you move it across the belt by rotating your body. Move it absolutely straight from right to left ( or left to right), moving your arms only, or you will overgrind the tip. Examine the edge and bevels after every few passes. Also, remember that you will change the belt to a finer one after the initial grind....leave a little extra to take off on that belt.

 

[Brian Avila]

I agree with everything that has been said already, but would like to point out that the design and geometry of the knife will also help with providing distal taper and even grinds. But even pressure and how you are holding the knife and where you apply the pressure is really important.

 

[awestib]

Thanks for all that great advice!

First off, it may go without saying, but I'll say it anyway - grind the edge back to a flat surface. You don't have to grind back far, but you need both a flat reference and you don't ever want to grind on a sharp knife.

You have the right idea on grinding a distally tapered knife. Grind slower and with heavier pressure toward the ricasso, moving the blade faster with lighter pressure toward the tip. At all cost, avoid sweeping the blade in an arc as you move it across the belt by rotating your body. Move it absolutely straight from right to left ( or left to right), moving your arms only, or you will overgrind the tip. Examine the edge and bevels after every few passes.

Thanks, I actually did not flatten the edge but I will most certainly do it now before the next session. I have to admit I just forgot. I remember a post from you saying to draw the edge flat across a piece of 400 grit sandpaper to make sure the edge is smooth, flat, and even!

As far as avoiding the sweeping motion (and again I think this is difficult in theory) - if I don't bring the handle towards my body a bit in the belly/tip area, how can I ever get the belt to match/touch that grind there?

 

[Brian Avila]

Thanks for all that great advice!



Thanks, I actually did not flatten the edge but I will most certainly do it now before the next session. I have to admit I just forgot. I remember a post from you saying to draw the edge flat across a piece of 400 grit sandpaper to make sure the edge is smooth, flat, and even!

As far as avoiding the sweeping motion (and again I think this is difficult in theory) - if I don't bring the handle towards my body a bit in the belly/tip area, how can I ever get the belt to match/touch that grind there?

All my distal taper and flat grinds are straight and I get the distal taper by the pressure applied by my finger either pressing the spine edge towards the platen or the edge towards the platen, while my figures on the free hand are applying even pressure to the rest of the blade. I hope that helps...

 

[logem]

All my distal taper and flat grinds are straight and I get the distal taper by the pressure applied by my finger either pressing the spine edge towards the platen or the edge towards the platen, while my figures on the free hand are applying even pressure to the rest of the blade. I hope that helps...

This is in line with video by Harvey Dean about flat grinding. There is a bit of "rotational pressure" that must be applied while sweeping the length of the blade across the platen in order to selectively remove material from the blade surface nearest to the spine edge or the cutting edge. This can be controlled by how closely you position your thumb (or pressure bearing finger) to the spine or the cutting edge.

As Stacy mentioned, you should "Grind slower and with heavier pressure toward the ricasso, moving the blade faster with lighter pressure toward the tip."

In the end, you want make sure that the bevel is flat after the material removal.

 

[Brian Avila]

This is in line with video by Harvey Dean about flat grinding. There is a bit of "rotational pressure" that must be applied while sweeping the length of the blade across the platen in order to selectively remove material from the blade surface nearest to the spine edge or the cutting edge. This can be controlled by how closely you position your thumb (or pressure bearing finger) to the spine or the cutting edge.

As Stacy mentioned, you should "Grind slower and with heavier pressure toward the ricasso, moving the blade faster with lighter pressure toward the tip."

In the end, you want make sure that the bevel is flat after the material removal.

"Rotational pressure" is a good way to put it. However, after getting a grinder that has slower speeds, I don't pull really fast compared to what it sounds like what Stacy is saying. There is lighter pressure at the tip though, because you can screw that up really fast. I think even pressure across the bevel and then slightly lighter pressure at the tip is how I do it.

I view it as walking the grind up to the spine. You can slowly do it and everything is even if you do it right. Otherwise you have different lines that you have to practice evening out and make it all one flat grind.

 

[Stacy E. Apelt - Bladesmith]

Yes, it is a bit hard to describe in words, but simple once your hands and brain figure it out. What I was cautioning against is accidentally using an arcing sweep.

Taking some bars of plain steel to the grinder and trying different things might help.

There is a twisting pressure that makes the grinder cut more from the edge than the spine. There is the speed and pressure used from side to side on the whole flat bevel that keeps the blade straight and flat from ricasso to tip. These two have to combine to get the grinding pass to make a flat surface with two tapers ( bevel and distal).

BTW, I grind in the distal taper before the bevel in some cases (mainly on large blades). On smaller blades, it just happens on its own.
As a final truing-up once the bevels and tapers are all ground ( when the blade shape allows), I place the blade vertical on the flat platen and flatten the entire surface as a whole. This will show ( and hopefully remove) any high or low spots and assure a completely flat surface. This requires a deft hand and a slow speed. The same thing can be done by hand on a granite surface plate with sandpaper placed on it. That is slower, but much safer to avoid ruining a blade. Whatever method you use - get the entire blade surface on the same plane. Any dips and bumps left in the blade will show up later on in finish sanding and polishing as horrible looking places.