Stopping the grind smile

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Randydb

Joined
Sep 27, 2014
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I use a bubble jig when I grind, and everything goes pretty well with the early part of my grinding. But when I get about 3/4 of the way up the blade I wind up getting that smile shape at the plunge side of the blade. I play around and fix it eventually but it is more trial and error than knowing what I did right to fix it or what I did wrong to cause it.

I wonder if I am causing it because I'm not putting the blade dead flat against the platen as I start, or if I am pushing wrong, or?

What is the best way to fix it once I started it? I guess I would like to be a lot more efficient about fixing it.

Thanks,
 
Randydb said:
I use a bubble jig when I grind, and everything goes pretty well with the early part of my grinding. But when I get about 3/4 of the way up the blade I wind up getting that smile shape at the plunge side of the blade. I play around and fix it eventually but it is more trial and error than knowing what I did right to fix it or what I did wrong to cause it.

I wonder if I am causing it because I'm not putting the blade dead flat against the platen as I start, or if I am pushing wrong, or?

What is the best way to fix it once I started it? I guess I would like to be a lot more efficient about fixing it.

Thanks,
Click to expand...
I use a Bubble jig also. I'm not certain what you mean by a smile shape. Are you referring to the arc at the top? Can you post a pic?
 
If I understand you correctly, your grind line moves up toward the spine at the plunge end? If that’s the case, you are starting your grind with your blade too flat, then adjusting it to the correct angle as you progress down the grind toward the tip. If that’s the case, try this. When placing your blade against the belt to start the grind, just kiss the belt with the edge side of the blade. Then push the spine towards the belt until you reach the desired angle. Then pull your blade across the belt to complete the grind. This will keep you from grinding too high into the flats near the plunge.
 
Grind more where it is low.

Also flatness is huge, get a surface plate to fix this on a budget, I consider it essential.
 
These are flat....cut and ground flat by JT.

Yes, my grind line moves up towards the spine at the plunge end. I think the reason it is happening is what blackdirt cowboy said...I think I start with my blade too flat and cause it. I think I do it trying to "lay the blade flat" against the platen...but it makes sense to err to the blade side.

I'm going out to try some more.
 
I do not start the grind at the plunge.

Start at the tip and work your way back.

Then you can work the grind from the plunge region back toward the tip.
 
You control the grind by how much pressure you apply and where you apply it. If you are leaving a fat spot grind more there. If it's a skinny spot grind (apply less pressure) less. Ther ei s no rule that says you have to grind the full length of the edge. Grind where the blade needs.
 
Jesse Latham said:
You control the grind by how much pressure you apply and where you apply it. If you are leaving a fat spot grind more there. If it's a skinny spot grind (apply less pressure) less. Ther ei s no rule that says you have to grind the full length of the edge. Grind where the blade needs.
Click to expand...
I went and watched a number of videos and saw this...as they grind they get the odd fat spot and I noticed them slow down, go back and forth in the area, or start in that area. After grinding 6 blades today I realize that sometimes that it just works itself out as it goes. It is also easy to fix the problem by grinding in the area that needs it. I'm slowly improving at getting the knife on there flat and keeping my pressure even. I'm realizing that things tend to get off when I start to rush, or don't get off it and readjust if something isn't right as I make a pass. It helps to know what I am looking at too and know that it isn't really a problem.
I know things were smoother on the sixth blade so I am sure after 50 blades it will be even better.
 
Geez there is a lot of variables. I'm starting to realize that part of it is going to be experience....I have built about 200 native american flutes now, and when one isn't quite working right experience lets me pinpoint the issue very quickly. I have another 15 blades to grind tomorrow.

Soooo...I started with a brand new 36 grit belt and ground six 3.5" AEBL blades so far. They are already heat treated. How many blades should I grind before I change the belt?
 
Belts can dish out in the middle and cause these problems. Get a cheap coarse diamond file to check and fix. Also check your platen is flat.
 
Randydb said:
How many blades should I grind before I change the belt?
Click to expand...

When you are grinding and you think "This is taking longer then it should". That is a good indicator to put on a new belt.
 
Randydb said:
Geez there is a lot of variables. I'm starting to realize that part of it is going to be experience....I have built about 200 native american flutes now, and when one isn't quite working right experience lets me pinpoint the issue very quickly. I have another 15 blades to grind tomorrow.

Soooo...I started with a brand new 36 grit belt and ground six 3.5" AEBL blades so far. They are already heat treated. How many blades should I grind before I change the belt?
Click to expand...
I get one AEB-L kitchen knife out of a 60 grit belt, if I'm lucky.

When I started making knives last year, I made a few carbon knives with hand tools and then jumped straight into making AEB-L kitchen knives on the grinder. Yesterday, I ground a carbon steel honesuki knife blade, first time grinding heat treated carbon steel on the belt grinder. The sparks really showed where I was grinding and it was easy to slightly adjust so that I got a uniform spark pattern all across the platen. I made a lot fewer mistakes than normal. Maybe it was just an outlier, but I thought the feedback from the sparks was really helpful.
 
The amount of material that is removed depends on pressure and time spent at that point. If you have even pressure and the same time spent at each point of the bevel, your grind will be even. So, if your grind is too tall at the plunge you either are applying more pressure there or you are spending more time there. I grind like AVigil said, start at the tip, work to the plunge, and then work back out to the tip. I am usually pretty quick on the turnaround at the plunge. This is also a good way to get a nice radius at the top of the plunge. It’s also easy to put too much pressure on the tang causing the bevel to only be making contact on the edge of the belt.
 
I ground a fair number of blades yesterday. Definitely got better as things went on. About half the time I used Avigil and Matt suggestion starting at the tip. That worries me because I worry that I will overheat the tip, but it hasn't been an issue yet. I also watch the water on the blade and as I see it disappear I know things are getting hotter and I either lighten my pressure or get the blade off. I only had one "OW! thats hot" moment yesterday.

I have also adjusted where I place my thumb that puts pressure on the blade to a more central spot which I think is helping me maintain equal pressure.
Part of it is experience, part is patience, and part is understanding how to do it right, and also what I am doing when it isn't going right.
I really appreciate all the answers here. It helps me gain knowledge quickly and gives me strategies to develop a lot quicker.

I asked about how many knives could be ground with one belt. I have begun to notice that "it's taking longer than before" piece, and also things started getting hot quicker without cutting as much. Changed belts and suddenly was getting much more ground off in a pass with much less heat.

Final thing for tonight. I know that I press harder when I am holding the handle with my right hand and using my left for pressure because the blade gets warm quicker and it takes less passes to get to the same point on the blade from the other side. It's funny because I am conscious of this happening, but I can't stop doing it yet. I find things go much better and quicker from the other side where I don't press as hard. More controlled it seems like.
 
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