Grinding help needed plz!

G

Grussing_Custom_Knives

Well-Known Member
I know i asked this before but i need some more answers. So when i grind with free hand or with a jig the part closest to the handle is low then it goes up up till it hits 2 inches away then it gets lower after 2 inches from the plunge cut. And with the edge the part closest to the handle the handle is thick then it gets thinner thinner till the 2 inch mark then it gets thicker. Keep in mind tho this is with a free hand or using a jig. Thanks for looking and i would appreciate it if i could get some help!
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I'd say it could be that you're not holding the blade flat on the platen when you're starting a pass and not maintaining even pressure. If I'm right a simple fix would be to start a pass by lightly placing the midsection of the blade on the platen to ensure flatness and then sweeping to the ricasso and then out toward the tip. Hope that made sense and helps.
 
J Rosa's advice is great. Just for giggles though, have you put a straight edge on your platen? Platens aren't always as flat and square as you think they are.


*Your platen is sticking out just a hair PAST the idler rollers, right? If it's not, you're effectively grinding on a slack belt and it's eating the center of your grind.

How new is the belt? Belts will almost always get dished out in the center first, and the effect is that you'll have high and low across your grind, just like you have in the picture. It's usually not that pronounced because for longer blades you will begin your grind and then draw the blade across the platen. Usually you see a wavy grind, or a deeper than expected trench where you begin the grind because the edge of the belt is effectively a high spot. Again, usually the edges are prouder than the center of the belt after just a little bit of use.

Third- was the blade blank actually flat when you started, or does it have some bow or cup in it?

What kind of belts are you using? How much pressure are you using? Is the belt tension high enough? Any of these things could be your belt bunching up as it contacts your edge. A bunched up belt is obviously going to give you a bad grind.


The first mechanical things I'd chase (after you address J. Rosa's question) is the platen placement, flatness of the platen, and belt tension (with all new belts).
 
I second checking your platen but just as likely, it's a pressure and torque issue. Those are two things that are important to keep in mind when grinding. And everyone has a stronger/weaker hand, either right or left.

Heavier pressure near the ricasso/plunge line area will eat more metal causing your grind to go up higher there. It's easier to put more pressure there as it's closer to your hand than out near the tip, where you have to intentionally focus to apply an equal amount of pressure there.

Likewise torque, or what I'm calling torque, will play a role equally in how high or low your grind line is. For example, if you grind cutting edge up on your platen with the spine down towards the floor, you can have the whole flat of your bevel touching the belt but if you have the blade torqued up slightly, you will take metal off your edge. Conversely, if you have the blade torqued downward slightly, you will leave the edge steel alone and take your grind higher up the blade.

Now, throw a belly or a recurve portion to the edge in the mix and you should be able to see why it's important to understand the two concepts. Keeping the edge in the belly area of the blade the same thickness as everywhere else is a nice balancing dance between pressure and torque at the same time. A lot of it comes down to practice.

I hope that didn't confuse you more.
 
ReCap from everyone's input:
1. Is your knife blank flat and true on all sides and edges?
2. Is your platen flat and true?
3. Is torgue the problem- I wouldn't think so, if you are doing all you grinding the same direction.
4. Are you using consistent pressure against the belt?
5. Could your belt be worn unevenly? That's a new one on me, but you can bet I'll be watching for that in the future!)

Then:
6. Are you keeping your angle of grind consistent all the way across? That wouldn't seem to be the problem, since you have the same problem using a jig (is the jig trustworthy?).
7. Is your speed of movement across the belt consistent- might you be spending more time in some areas than others? If/when I see my grind-line wandering, the first thing I do is look at my scribe mark to determine if I didn't keep my angle right, or if I just spent too much time grinding in one area. You can probably determine that by checking your 'thickness' along the center scribe-line at the cutting edge (or comparing to the un-sharpened side if it's a chisel-grind knife).

All else considered, I would suspect that those grind lines could be trued up by spending more time in the areas where the grind-line is low (and/or using more pressure in those areas).

But, it's tough not being there, not holding the knife, not seeing the cutting edge.
Maybe this is one of those times when you need to walk away for awhile then come back fresh :mad: (probly been there done that, tho?).
Disclaimer- I'm still a newbie myself. Keep playing with it- you'll get it! Then you will have moved up a level!
Bill
 
1. Yes 2. Yes 3. It isnt 4. Trying too 5. Its fairly new 6. Free hand yes all my free hands are hollow grinds if that matters and the jig is a dd work rest jig so yes its reliable 7. Yep


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