Whats going on with my grinds?

U

unky_gumbi

Joined
Aug 28, 2009
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7,951
Today I was doing some grinding, everything was going as planned, the grind lines were crisp and even and looking great till I was just shy of where I wanted to stop. When I switched to a finer grit belt,220, (I started at 36 and moved through to 60 and 120) and suddenly my grind line went haywire, no longer crisp and became wavy. The belt was brand new and I can see no visible flaws in the belt or on my grinder, so the problem has to be with me:( or how I run the grinder.

I generally do full flat grinds and have never noticed this before while coming up to the spine. I do the bulk of my grinding with the 36 and 60 grit belts and use the finer belts to clean up my scratch pattern and and arrive at my marks at the same time. I run my grinder at about 90% of max speed till I hit the 220 grit belt, then drop my speed down to 60-70%. I couldn't tell you the exact SFM for those settings, but once I find the formula I will figure it out and update the post.

I ended up taking the grind to a full flat, but I didn't take any pictures of my progress or the mistake so I guess it will be hard to figure out what went wrong, but any suggestions would be helpful because I will be trying again tomorrow with the exact same design and steel. The knife just doesn't look as good as a flat grind so I want to get what I planned.

Thanks
George
 
Any uneveness on your platen or debris on the back of the belt will show iteslf in the finer grits... that much I know. I'll let the "grindmasters" chime in to help troubleshoot. Finish grinding is not my forte.
 
I looked at both the belt, inside and out, and the platen and there was nothing there:(

According to the formulas I found my SFM at 100% would be about 3615, so at 90% it would be around 3254 and when I step down to 60-70% it would be around 2169-2531 if that information helps. Also the steel I am grinding is 5/32 CPM D2, but I don't think that part matters.
 
that's interesting.. I've been kinda wondering myself how often people have to resurface their platen?? mine seems to have a little devit where the rest meets from hogging, not saying this is your problem I was just curious..
 
My first thought was a dull belt that did a little walking on you, could you have come in a little hot with that fresh belt and sheared the bite out of it?
 
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This may be a little off-topic but I'll throw it in anyway... are you grinding edge-up or edge-down? When doing any non-full/sabre grind (which basically means custom order, I much prefer full-flats and full convexes for my own designs) I've found, regardless of goofs or waviness, I get a much crisper grind line when I grind edge up. (belt traveling down, towards the spine) In fact, it's almost stupidly easy to keep the lines clean this way. Whereas, when I've tried to grind edge down, I just cannot keep the dang lines crisp.

I think what's happening is, no matter how steady I think I'm holding the blade, the belt is pulling against it, and if the spine is up that means it's blurring that transition. But the weird thing is, I've noticed the same thing when filing bevels and other features by hand. I mean the difference is pretty remarkable.

Does this make any sense or am I just weird?
 
Possibly a dull belt?

I'd try slowing down the grinder also. I generally rough grind at around 60%.
 
I'm guessing your applying to much pressure on the blade with the higher grit belts. Just let the blade lay against the platen without to much pressure being applied. I normally only grind up to 120 grit before heat treat and do my finish grinds after to clean up the blade, I have found this works much better for me. I also tend to use the edge of platen more with the higher grit belts.
 
GTH11 said:
My first thought was a dull belt that did a little walking on you, could you have come in a little hot with that fresh belt and sheared the bite out of it?
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It was a fairly fresh belt, less than 5 minutes on it. It seemed to be cutting fine, but it is possible that i leaned into it a bit hard and dulled it out

MJV said:
Did you try a different 220 belt?
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No I didn't but I will try a new unused one tomorrow

james terrio said:
This may be a little off-topic but I'll throw it in anyway... are you grinding edge-up or edge-down? When doing any non-full/sabre grind (which basically means custom order, I much prefer full-flats and full convexes for my own designs) I've found, regardless of goofs or waviness, I get a much crisper grind line when I grind edge up. (belt traveling down, towards the spine) In fact, it's almost stupidly easy to keep the lines clean this way. Whereas, when I've tried to grind edge down, I just cannot keep the dang lines crisp.

I think what's happening is, no matter how steady I think I'm holding the blade, the belt is pulling against it, and if the spine is up that means it's blurring that transition. But the weird thing is, I've noticed the same thing when filing bevels and other features by hand. I mean the difference is pretty remarkable.

Does this make any sense or am I just weird?
Click to expand...

I always grind edge up, and its not a weak side strong side thing either, I for got to mention that in my OP:o To be honest what I consider my strong side looked a lot worse than the other side. Thankfully I was able to save the blade and it wont be sitting in the recycle bin at the end of the week

Mitchell Knives said:
Possibly a dull belt?

I'd try slowing down the grinder also. I generally rough grind at around 60%.
Click to expand...

Like I said to GTH11, I may have dulled the belt, but it was barely used and still feels like it has plenty of bite. I will be trying a new belt tomorrow. If I can I will take pictures or video of what I am doing. I still believe it is something I am doing and not the equipment so video of whatI am doing might be a good thing, if I can get the camera set up right to see everything:o
 
Fresh, sharp belts are the best bet in the higher grits. Otherwise, you will have problems in maintaining crisp lines. I never believed it, always trying to reuse a "kind-of" new belt, but when I started using brand new belts on higher grits, I saw the difference.

Also, I've found this to be true: finer grits will show you where you lack control. I find it much easier to get a great looking grind (albeit a very rough finish) from a 36 grit belt. Try doing the same thing on a 220 grit belt, and it becomes a bit harder. J Hoover gave great advice about not trying to hog with high grit belts. Let the flat rest gently against the belt, but still controlled, and let the belt do the cutting. If you have a flat foundation to work from, things will clean up.

--nathan
 
George, take a good, close look at your platen. I suspect the thicker 36 grit belt is masking some uneveness in your platen that the thinner belts are starting to reveal. Just a guess, but if it's not the platen it's either the belt, even though you said it looks ok, or you wavered a touch as you ground. I've had all of these things happen at one time or the other.
 
George,

I see things go south at 220-400 as well some times. Not the grind lines but the flatness of my flat grinds. I thought all my stuff was flat until I put some knives on the disc. I have a much more critical eye now. I bet you do as well. I often find myself stuck between a machine finish and one that wants to be hand rubbed or polished. The problem is that I don't generally want to hand rub or polish. I've seen this problem with new glass on my platen. I think my issue is that I am still experimenting with belts, and I over-grind some stuff. Both new and less than new belts. I tossed 50 belts in the last 3 weeks or so on only 7 knives trying to strike gold.

I'm going to soon try a 120 grit finish on the bevel pre heat treat and get it to 90%. After HT, 120-180, 280-400, medium or fine scotchbrite. I may be crazy, but I am starting to think the less belt time the better! And cheaper. At least for a machine finish.

If all else fails, I will go to my granite slab with rhynowet redline or norton black ice with 3m feathering adhesive to hold it down and get it right.

I do have one trick I came across with those 50 belts that proves promising, but for now, I'm holding on to it. I also have some custom platens on order, I think, he's busy making awesome knives.

Let us know if you nail it down.

EA
 
I will put my straight edge on the platen tomorrow morning when I first get out there to be positive that its not the platen, if it is the problem it looks like I will be buying a new piece of glass in the not so distant future:(

Being that I send my blades out for HT I have always been a little scared of doing any major grinding post HT and wasting the money I spent on the HT:o

Needless to say I will be going over all the mechanical possibilities before starting and using the tips that have been offered to see if I get this solved.
 
If you have another belt, I would start there. I have had some weird grinding experiences that I think were due to a contaminant on the surface of the belt. I one instance I was grinding with my off-hand thumb wrapped in duct tape, and the duct tape turned out to be the culprit (letting the thumb run into the belt at the end of the pass). It dosen't take much to screw up a good grind.
 
Your stock is flat, right?
*pounds head against wall*

-Daizee
 
sykes3170 said:
With all that hair in your face i'm surprised you can see too grind at all:p.
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Thats an old picture from just before getting a haircut so most of that is gone now. I was thinking of using the hair as a natural face mask, but when hot sparks hit it the smell was too much to handle:p

Justin King said:
If you have another belt, I would start there. I have had some weird grinding experiences that I think were due to a contaminant on the surface of the belt. I one instance I was grinding with my off-hand thumb wrapped in duct tape, and the duct tape turned out to be the culprit (letting the thumb run into the belt at the end of the pass). It dosen't take much to screw up a good grind.
Click to expand...

I have a full set of unused belts that I will be breaking out for todays grind session. I use to grind barehanded, but with the numbness from my elbow problems I started wearing mechanics gloves to cut down on the burns I don't feel. The gloves let off a particular scent when they start to get hot, and I smell it long before I would feel the heat if I was barehanded. I wonder if it may be the recent switch to the gloves that is causing the problem:confused: I will have to try barehanded again today as well.

daizee said:
Your stock is flat, right?
*pounds head against wall*

-Daizee
Click to expand...

Yes the stock is as flat as I can get it, and the problem isn't the same as before I started flattening my bar stock. Before I learned about flattening the stock I would get wavy grinds with the other side being a mirror image. This was more of a complete washing out of the grind line, one minute it was nice and sharp and dead straight, the next it was blurred and washed out. We will see how things go in about 2 hours or so, I have a few other things to get out of the way before I start grinding this morning. Thankfully this batch is just practice/inventory knives, but I want to get one really good one that represents what I can do so I can send it out for some hands on testing.
 
OK so on closer inspection there are some very light wear marks on the glass platen, but they are only noticeable in the right light and you can only feel them if you run your fingernail across them, so I don't think that is the culprit. It is other wise flat in all directions, checked with my square and a light source behind it, next is new belts and some grinding once I get the next one cut out and trued up.
 
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