Point grinding problem: help needed.

Alarion

Alarion

Joined
Nov 26, 2001
Messages
1,375
Ok. I seem to have this problem grinding decent points.
I grind the blade all good, and when I come to the point, the grind goes to hell, and the point comes out all wobbly and irregular. The height of the grind is also reduced...
What am I doing wrong?:confused:
 
Can't help you with the details but remember that it's easy to overheat the tip when heat treating or grinding. That leads to brittle tips which break off.
 
I know. But the problem is long before HT, it's in getting a decently ground point.
 
practice practice Alarion :) Are you using a scribed line on the edge to guide you ? Are you pulling the tip into the wheel/platen when grinding ? As simple as it may look Alarion grinding really is an art. I'm just starting to get comfortable on my grinder and I've made a couple hundred knives to date. It takes time brother, patience and persistance will fix the tip ;) Slow down and really look at what is happening and what your body is doing when grinding. I think it was R.J.Martin that said you have to see it in your mind cause you can't actually see what is going on between the blade and belt. R.J. ?? (he can help you better than I can) ;)
 
if it makes you feel better. this weekend i was beveling a blade with my grinder, and had the point almost perfect when i accidentally went too far with the grinder and suddenly my knife was 5mm shorter!
 
I was reading a similar thread a few months ago on this forum.The maker was having the same problem,as was I.
One of the fine knife makers on this site(who I cant remember) gave him great advise.
He said,when grinding bevels,try not to pull the point all the way across the 2 inch wide belt.Instead release your presure when the point gets half way across the belt and ease away.
It helped me alot,and I hope it helps you as well.
I am not very good at explaining things so I hope you get what I am trying to say.:p
 
Pay attention to the pressure applied while grinding, and your angle of the blade in relation to the grinding wheel. Keep your knife flat on the wheel and ease up on the pressure as you reach the point. Avoid pulling the point across the wheel as this applies uneven pressure, as well as exessive pressure at the point. This will result in an uneven grind and too much material being removed from the point area of the knife causing the point to get too thin too soon.

Also keep the blade moving as you grind. Fluid movement will help prevent dimples from forming on the blade.

Check your grind often, each time the knife makes a pass on the wheel, check the blade in the light. That way it is easy to catch problems before they become too big to fix. You can grind it off, but once its gone it cannot be put back on the blade.
Practice, practice, and more.......................................
 
Thanks a lot guys.
So, when I reach the curved part of the blade at the tip, I should ease pressure, and pull the blade into the wheel (down for edge down grinding, or up for edge upp grinding) so that the grind follows the curve in the blade, correct?
 
Also you may want to slow your grinder down a bit if it's going too fast. I don't know how fast yours is going so this may not apply.
 
"If in doubt, use a hand tool"

I'm not suggesting foregoing the grinder, but it might be good to use a big 12 inch file for a few knives to get a feel for how the pressure changes and angle changes matter. I can't speak for anyone else, but it's doing wonders for my feel on knives.
 
I may be called a heretic, but I grind a 45o angle down the spine to establish the distal taper boundaries all the way to the point. Then grind the sides of the blade to meet my edge boundary, already established with a 45o, and the spine boundary, but leave the point area a tad thick until last. I carefully rough in the point holding the blade horizonal. then switch to vertical, point up, to finish. Usualy have to go back and forth with this, until the grind meets both boundaries.
 
Just as I have in golf (swing thoughts), in knife grinding I have (grinding thoughts) that I keep in my head. When I keep these rules in my head, as I grind, I usually do a better job.

  • Don't force the steel into the blade, but instead, let the belt take what it wants to take on each pass.
  • Lock your elbows into your sides and move the knife across the belt by rocking your body back and forth. This promotes a steady, supported and fluid motion.
  • As you approach the point of the blade, let up even more on the pressure and let the belt have less steel to take off. Bring the steel off of the belt just as the tip reaches the center of the belt.
  • Grind with bare hands (don't wear gloves). You'll be able to feel the heat generated and avoid overheating the blade. In addition, a loose thread from a glove can get pulled into a grinder resulting in serious injury.
  • Develop a habit of steps that you follow. Make a pass on the blade, dip it in cold water, look at it carefully, make another pass.
  • Switch from one side of the blade to the other frequently, taking the material off evenly from both sides.
  • Wear a respirator and safety glasses. A full face shield is also a good idea.
  • And lastly, but not least, Have Fun!

This is more than you asked for, but it's the things that I try to follow when I'm grinding. Good luck.

Ickie
 
Jared Stenoien said:
Also you may want to slow your grinder down a bit if it's going too fast. I don't know how fast yours is going so this may not apply.
Click to expand...


Exactly!! This is where variable speed grinders really shine. You will get your own method from taking the advice of the people here, but however you end up grinding it, leave lots of material for finish grinding at slow speed with finer belts after heat treat.
If you grind your point to finish before, you're kind of screwed after.;)

Edited to add: If you're making small knives, profile and drill everything first, then have it heat treated like that. Just grind it after HT being careful not to overheat. It can be easier that way, at times.:eek:
 
I am by no means a talented grinder but I am learning on my own.A few things that helped me get better are

1. Slow down...everything
2. only grind in one direction IE: from ricasso to tip
3. follow the grind you can get with your weak side and match it with your good side(My left handed anything is useless)
4.I try to follow the belt as if I was sharpening on a stone,keep the edge square throughout the curve.
5.reading 100's of posts all say the same thing practice makes perfect,Rome wasnt built in a day :) (neither was anyones masterpeice)
Hope this helps.
 
Try turning your blade the other way. If you are grinding edge down (I'll bet you are) turn it up. Seeing the edge is very helpful when doing the tip. The worst thing ever to do is grind it edge up on side A and flip it edge down for side B. If you are to become good at grinding, you have to become nearly ambidexturous at pulling the blade either left or right....AND DO BOTH IDENTICALLY. Practise, practise, practise.

Stacy
 
Ok this may be considered a bit sacriligious to most readers but here goes: This is what I have done on my first attempts and it worked out well:
1. Use a vernier to measure the thickness before you start grinding (lets assume it is 4mm)
2. decide how thick you want it at the cutting edge when finished with the primary grind. (say 1mm). This would mean you are going to take off 1.5 mm on each side.
3. Grind only one side and keep measuring the thickness of the blank along the cutting edge, using the uncut edge as a 'datum'. Measure along a few points on the edge to ensure everything is running parallel and consistently. (if you alternate between grinding both sides at the same time you lose that very simple reference plane) In this case we would be targeting a thickness of 2.5mm from uncut side to grind surface, along the edge.
4. Do the same now on the other side, regularly checking that the working grind surface and the grind surface on the other side are parallel along the edge.
5. Once your measurement reaches 1mm, your entire blade edge should be straight and consistent from handle to tip.

Hope that helps, and hope my advice doesnt contravene any knifemaking codes!

Lang
 
langchop said:
Ok this may be considered a bit sacriligious to most readers but here goes: This is what I have done on my first attempts and it worked out well:
1. Use a vernier to measure the thickness before you start grinding (lets assume it is 4mm)
2. decide how thick you want it at the cutting edge when finished with the primary grind. (say 1mm). This would mean you are going to take off 1.5 mm on each side.
3. Grind only one side and keep measuring the thickness of the blank along the cutting edge, using the uncut edge as a 'datum'. Measure along a few points on the edge to ensure everything is running parallel and consistently. (if you alternate between grinding both sides at the same time you lose that very simple reference plane) In this case we would be targeting a thickness of 2.5mm from uncut side to grind surface, along the edge.
4. Do the same now on the other side, regularly checking that the working grind surface and the grind surface on the other side are parallel along the edge.
5. Once your measurement reaches 1mm, your entire blade edge should be straight and consistent from handle to tip.

Hope that helps, and hope my advice doesnt contravene any knifemaking codes!

Lang
Click to expand...

A drawback to grinding all of the material off of one side, then turning it over to grind the other side is that it puts stresses into the steel. As you grind material off, the blade heats up slightly altering the microstructure of the steel. If you remove it all from one side and then flip it over, you alter the microstructure unevenly. As we grind, the blade gets nearly too hot to hold, so we dunk it in water. Heat and quench is a heat treating process, even at these relatively lower temperatures, as compared to hardening temperatures. As we continually cycle the steel through this heating and quenching, the steel changes crystalline structure enough to try and pull the blade in one direction or another. The result is a blade that is more likely to warp during heat treat.

When I first started I ground them your way, and even noticed blades warping during normalizing cycles prior to heat treat. Since I've gone to grinding evenly from both sides, I've noticed a decrease in warped blades during heat treat. I prefer to not have to worry much about straightening blades during my heat treating processes, if I can avoid it. It's not difficult to straighten them, it's just a hassle that I prefer not to deal with.

With practice, you'll be proficient at grinding from both sides evenly. Practice, practice, practice. You'll be surprises at how good you'll eventually get.

A way to keep your reference line is use Dykem metal marking compound to mark the cutting edge and back spine of the blade prior to grinding. I have a little jig that I can set to any depth. It's just a gage block with a hole and set screw that allows me to slide it up and down a small shaft. At the end of the shaft is a small scribing awl that is screwed into the shaft and locked in with all thread. It allows me to scribe lines a precise distance from a reference surface in the Dykem marking compound. I set it to the width of steel I want to remove from the edge and then grind down to the line on both sides of the blade. If the blade has distal taper it's a little more difficult to mark the back spine of the blade and I haven't figured out a way to do that with a jig yet. To mark a blade with a distal taper, I scribe a centerline down the middle of the spine. I then determine where the distal taper will begin and use a flexible plastic ruler (like those you get with a Franklin Day Planner) and line up the ruler with the start of the distal taper where the spine meets the face of the blade down to the centerline at the tip. I mark it with a hand held awl. I repeat this procedure for the other side of the blade.

This will give you reference lines to work with as you grind the blade, allowing you to work material off of both sides evenly. I've attached a picture of my jig. There pretty easy to make. I think you can also buy them from Knifemaking Supply companies.

I hope this is helpful.

Ickie
 
scottickes said:
A way to keep your reference line is use Dykem metal marking compound to mark the cutting edge and back spine of the blade prior to grinding. I have a little jig that I can set to any depth. It's just a gage block with a hole and set screw that allows me to slide it up and down a small shaft. At the end of the shaft is a small scribing awl that is screwed into the shaft and locked in with all thread. It allows me to scribe lines a precise distance from a reference surface in the Dykem marking compound. I set it to the width of steel I want to remove from the edge and then grind down to the line on both sides of the blade. If the blade has distal taper it's a little more difficult to mark the back spine of the blade and I haven't figured out a way to do that with a jig yet. To mark a blade with a distal taper, I scribe a centerline down the middle of the spine. I then determine where the distal taper will begin and use a flexible plastic ruler (like those you get with a Franklin Day Planner) and line up the ruler with the start of the distal taper where the spine meets the face of the blade down to the centerline at the tip. I mark it with a hand held awl. I repeat this procedure for the other side of the blade.

This will give you reference lines to work with as you grind the blade, allowing you to work material off of both sides evenly. I've attached a picture of my jig. There pretty easy to make. I think you can also buy them from Knifemaking Supply companies.

I hope this is helpful.

Ickie
Click to expand...

The plastic ruler is known as a batten in boatbuilding and is the best way to get a flowing curve in most cases. Excellent idea, I hadn't applied it to knifemaking yet. The real trick is to get a batten with flexibility that's the same over the length. (the degree of flexibility is obviously choosable with material and thickness). I'll probably make myself a few of varying thicknesses of steel or aluminum.

It probably seems counter intuitive to more modern thinking about machining, though.

That jig looks nice....
 
Thanks Ickie... thats the big picture that us newbies dont think about.. Im going to have to normalise good and proper to try and avoid warpage.

Lang
 
Thanks again. I've stopped the grinder for some time as I'm building myself a smaller charcoal forge for small pieces (it's the old brake drum design).
When I'm finished I'll restart trying.
Having just a few weekends to do this makes everything more difficult.
 
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