Why is my grind line looking like this?

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Dixieblade57

Joined
Jun 20, 2007
Messages
1,361
OK this is a new learning curve for me as I just finished my KMG clone and before that all bevels were done by file. I know before everyone says it, the trick to getting a good grind line is mostly muscle memory and practice, practice, practice!

I can look at this bevel and see I have got some learning to do and I understand where the practice, practice, practice is going to come into it.

However one thing that is concerning me right now is the fact the grind line is coming out with an arch in it.

In other words I think I am pulling the blade straight across the platen but the resulting grind is not showing that. It archs downward away from the spine of the knife instead of running paralleled to it. (In other words there would need to be more taken from the center area of the grind to make it become straight across)

I hope these pics will show what I am talking about. If you look closely in the third pic you can see the reference line for the grind which runs parallel to the spine of the knife and the arch I am referring to! What ever I am doing wrong to cause the arch in the grind I am consistently doing it from side to side, because the arch is pretty consistent from side to side!

click thumbnails to see large view:










Anyone got any thoughts as to why I am ending up with the arched effect in the grind line?

Is it because I am not pulling the blade straight across?

Or is it more something to do with the pressure?

I think if I can figure that out I can get the rest of the problems out with practice and muscle memory!
 
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If you're referring to the high spot in the grind line near the plunge, I had a similar problem with that when I started out. For me, it was letting the edge of the belt take off too much material as I unconsciously rocked the blade to the right on the platen when approaching the plunge. What I started doing to fix it was to watch where my sparks were coming from until I developed more control. In other words, if you see sparks fly out near the side of the belt, you're actually rocking the blade towards that side of the belt ever so slightly. When paying attention, I noticed that the smiley face grind line with the line higher at the plunge happened when I let the right side of the belt take off too much material, resulting in sparks flying from the right side of the belt near the plunge (I grind edge up, tip to the left). Try and make all your sparks fly from the very center of the belt, especially when approaching the plunge. This ensures your blade is flat against the belt. It will also give you a visual aid to help you develop a feel for grinding and gain control over the subtle movements used when grinding.

As you gain more control and skill, you will learn how and when to rock your blade to correct or avoid mistakes.

However, the one caveat to the above suggestion is to watch out for the dreaded 2-inch line. This happens when you have a blade flat against the platen, and you slow down as you approach the plunge. Typically, there is a very small pause right then before either lifting the blade or reversing the direction of the pull. The line may be brought about as you try to correct your previous mistakes of grinding too deep at the plunge (resulting in your :) grind line). As you try to avoid it, you unconsciously over-correct and actually rock the blade off of flat into the OTHER direction, causing the opposite edge of the belt to dig in 2 inches from the plunge, creating a line.

Practice, keep the blade flat, watch where you sparks are flying. Keep the sparks in the middle until you refine your control.

--nathan
 
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I am going to make a guess here with you are coming into the belt at an angle, flattening out through the middle and pulling the handle out to far at the end

handle is to the right if the screen
you come in like this
one.jpg


start coming across and flatten
two.jpg


and pick up to much at the end
three.jpg


just my guess, that is what I was doing:o

Nathan beat me to it, and yes I now get the 2" line
 
Something that many makers do is to actually touch the bevel gently to the belt away from the plunge, giving yourself a chance to get the bevel flat on the belt, the push into the plunge (keeping things flat), and then draw the bevel across the belt towards the tip staying flat at first and then rocking the handle out as you approach the tip as illustrated above in order to get the line to curve up towards the spine.

If you rock out too far, you'll have too much curve in your grind line towards the tip as Unky suggested. Not far enough, and you grind line will be more flat. Start rocking out too soon, and your grind line will start to curve up too early. Too late...well you get the idea ;).

--nathan
 
I just started really using my grinder a few months ago so all this stuff Dixie is going through is fresh in my mind. I got a few PM tips that said the exact same thing that you just said. I still have a bit of the 2" disease but its getting better with each blade, each pass even.:thumbup:
 
You can create that by using a fine grit belt to start with. Are you using say a 50 or 60 grit? Practice with some inexpensive mild steel. Expect to still be learning abot 75 blades or so later. Frank
 
Another issue could be that you approach the belt at the plunge line and work your way to the tip. This is ok, but try to give equal amount of belt time to the whole blade. Looks like you might grind for longer amounts of time at the plunge and tip than in the middle
 
I am using a 60 grit but it is a well worn belt. Guys that all makes perfect sense now. I am starting at the bevel guide and that is also where I am trying to find the right angle when contacting the platen. This particular knife is a flat grind and trying to hit that correct angle means I am more than likely staying at the starting point longer thus removing slightly more material. And I did see some rocking issues in my grind. OK now I get more about how to make the smile disappear.
Thanks you have definitively given me something to think about now. The sparks is another big clue.
 
It will all come together for you, watch for it on your first pass and start correcting right away while there is still plenty of material to work with and room to over correct and fix that too. Order some fresh belts asap, otherwise you will end up like me:o I have grinding I want to do, but all but a 220 belt is too wont to do anything but heat up the steel:( I gave a bunch of ceramics on the way and should be here mid week though:thumbup:
 
Thanks for the advice unky. You know I use to have an aunt an uncle and we always called them auntie and unky.

I actually have a large number of belts but was trying to do a little learning before I slapped a brand new on there and eat up the whole blade.

You know I ought to know better than that though. I used to a lot of carpentry and furniture work and I know from experience when I first learned to sand with a big 4x24 belt sander you do more damage with an old belt trying to make it do something it won't. A worn belt is good for polishing type work but try one to make it do some serious cutting and you will screw something up in a heart beat.

I still have not ruined the blade I was grinding so will go back and grind out some of the belly in the middle of the grind and then work it all out by file. But I do have a good idea where I was going wrong with this one and hopefully it will get better with the next one. It still beat days of file work to lay in a primary bevel, but I did learn a lot on those first knives doing them that way!:eek::D
 
Remember, with a little patience and a light touch, most grinding mistakes can be corrected. In my experience, a belt worn from typical use often has more grit on the very edge than in the middle, and this exacerbates your troubles. Hope you nail it the next time you fire up the grinder!

--nathan
 
You know your right, that makes a lot of sense but never really thought about it and your right that would make the problem that much worse!
 
Danbo said:
Get new belts. Worn belts only make your work more frustrating.
Click to expand...

Agreed. Use a worn belt and you might as well be angling your blades into your platen as half or part of the belt is probably all that's removing metal at any one time anyhow.
 
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