Help with a grind issue

So......my main work in progress thread is in "The Forge" area, but this is a very specific question on the grind issue I have. I'm getting close to giving up because I'm afraid I've stuffed it up something fierce.

http://img.tapatalk.com/ad1867a9-be58-1ad0.jpg
Here's the ground edge. It was wider at the heel and the tip compared to the middle of the edge. However, the faces were sanded completely flat. I filed a little bit off the heel and toe areas only and left the middle alone. I've started re-flattening it down on sandpaper on marble, but it seems I'm going to be doing the same thing all over again. Is this going to end up with the edge wider at the toe and heel again? Am I just chasing my tail? Sorry if this doesn't make much sense, maybe I need to explain it a different way.

Here are the faces partially flattened again.
http://img.tapatalk.com/a6898e33-d006-88e5.jpg
http://img.tapatalk.com/a6898e33-d01c-bb01.jpg
You can see the middle is coming up higher than the ends.

My junior technician has no idea either. Now what?
http://img.tapatalk.com/a6898e33-d06c-5ae1.jpg

Your problem is that because your blade has an arch to it you are getting what basically amounts to a three point contact (at the spine on both ends and the belly or edge in the middle). Your method of sanding/grinding on a surface plate will work but only if the blade is straight and parallel.

Since you have put a smile shape on your blade you are going to have to establish a center line on the edge and carefully draw file to that while maintaining a consistent thickness to your spine. It will take you a little more time but if you are careful and take your time it you will be able to do it.

Ray

It looks normal to me, curved/smiling edges take a bit of work. I tend to go through iterations of establishing the flats, this shows me where I have to grind, then hollowing. Basically set bevel/find flats -> grind away flats till the are only at the edge and the spine.

Charlie

Let me see if I can explain what is happening to you.

Look at the first photo. This wedge is (for the sake of argument) straight and parallel. The way you trying to grind, this type of blade can be done very easily. You grinding flat parallel surfaces on a flat surface. No problem.

http://i287.photobucket.com/albums/l...ver/wedge1.jpg

Look what happens when we put a "smile" on the blade. I exaggerated it here to increase the effect. As you arch curve into the edge of this wedge you are climbing up the taper of the wedge making the leading corners thicker.

http://i287.photobucket.com/albums/l...ver/wedge2.jpg

To correct this effect You need to establish a center line and file toward that center-line to correct the corners. However. You need to keep the spine a consistent thickness across its entire length. You do not want eh spine to taper toward the ends. You will almost have to do this freehand. Your surface plate is not going to help you with this.

http://i287.photobucket.com/albums/l...ver/wedge3.jpg

The autofocus on the camera chose the wrong item so this one is a bit blurry but I think you can still see. Notice how the corrected surface curves up from the edge of the table its not a straight line from the center of the blade.

http://i287.photobucket.com/albums/l...ver/wedge4.jpg

Now if the curve of your spine matches the curve of your edge you should be able to file this in such a way so that ...even though the leading edge curves up away from the table you can take a ruler from the spine to the edge from the centerline of the edges arch and the ruler will lay flat from spine to edge.

Do you intend to go back and hollow grind this on a wheel or belt grinder?

Ray
Ray

That's normal and wil also happen when grinding a straight edge.
Basically the contact wheel of the grinder is not flat across the front. The ends are slightly convex. The middle part of your blade will always be thinner as the toe and heel side if you grind equal and parallel with the same pressure. It's mostly eye and hand coordination as you need to tilt the blade and push into the edges of your contact wheel to grind equal thickness all across your edge.

When I read his post it was my understanding that he was doing this on sandpaper resting a marble surface plate.

If the surface of your contact wheel has an arch to it you need a new contact wheel. Sometimes you will find a little drop off of the edges of your idler wheel. Some manufacturers do that to help belt tracking but your contact wheel you grind on should be dead nuts flat. across its surface.

Ray

I don't think so Ray. The contact wheels are configured that way so that smooth grinds can be achieved without digging the ends of the belt into the steel you are grinding on. We grind usually with 70D wheels. If I have to follow your advise I need to toss my dozen + contact wheels. Grind a few razors and then come back to me with your finding. The toe and heel side will always need more work when grinding.

Maybe your grinder is specifically made to your specs and I'm cool with that.

However every belt grinder I have seen has had flat contact wheels. Mine on my 2x72 grinder are flat. The ones on my fathers are flat. Every knifemakers grinder I have ever seen has had flat contact wheels.

I am new to razors but this aint my first rodeo. I have been making blades since I was about 10 and I'm now 44. I knnow a lot of knifemakers and all the stock removal guys i know use 2" wide flat faced wheel and none of us dig in on longer blades.

I am planning to make a few razors. Maybe I will find your your right and I need a wheel that falls off at the edges but I don't think so. If I do I will certainly admit I was wrong and buy you dinner.:)

That's good cause I'm hungry. My wheels area flat too. I'm talking about the outer edge. I have Bader and KMG wheels. All the same. You will need to compensate to wind up with a straight line across your cutting edge. Been grinding razors long enough to know what I'm talking about.

When I am grinding away on auto pilot, (thinking about dinner or something, it is always food) I tend to grind the heel thick and the the toe thin. I have to make a conscious effort not to grind that way. I think a lot of grinding maladies come from muscle memory and bad habits.

Back on task one thing I forgot to say was, when I establish the flats on a smiling blade. I use a rolling X stroke, just like honing a blade with a big smile.

Charlie

Wow guys! Seven replies in two hours! Quality stuff gentlemen, quality.
Charlie, thanks for letting me know that is normal.
Max, I am indeed making this all by hand. I'm in negotiations with the CEO to buy a 2x42 grinder from Craftsman. Barring that, a 1x30 from Harbor Freight. I am also interested in knives, but I need to get this thing done first and really understand what's happening and why.
Ray, thanks for making the wedge for me. That really, really helps me understand what's happening with the geometry.

I understand now why filing to the middle and then flattening on the plate then filing to the middle and flattening to the plate has me chasing my tail. I can't wait to get back into the shop tonight and try this out!

Any suggestions on finding the center on such a thin, uneven edge? I know, I should have done the center marking on the original blank, but that ship has kind of sailed. Next time I'll do it correctly.

Lay the blade on a flat surface and use a drill bit that is the same diameter to make the scribe line, If it is 1/4 stock use the tip of a 1/4 drill bit to scribe the line. it is not a perfect way but it is good enough for now. Use a sharpie or something to coat the edge before scribing the line.

Charlie

I can try to do that, but I'm not sure how it's going to work on the thin edge. Maybe clamp the piece so the spine is flat and the edge is "suspended" then roll the drill bit? I have a nagging suspicion that my grind may end up being a little off left to right and I may have to improvise a bit.

Is your spine the same thickness all the way across at this point?

If so what I would do is clamp this to your marble surface in such a way that your spine touches all the way across. Hopefully, the flat of your shank will touch too. Clamped like this your edge should be suspended.

Then as Spazola said take a scribe of some kind the same thickness (Drill bit should work fine) as your spine and make the mark along the edge.

If your spine is not parallel or is drifting to one side due to the struggle you were having you may have to just clamp on the shank flats and use that as a reference to realign the rest of the blade. Keep in mind that if you have to re-true your spine (ie making it thinner by straightening it out) you may have to take a little off the edge to keep the proper edge angle range.

Ray

Thanks to everyone for incredibly useful posts.

No kidding, right!? I'm learning a lot, which is why I hang out here!

To answer a previous question, I am planning on leaving it a true wedge. No way to hollow it right now.

The tang is no longer flat. However, the spine is the same thickness all the way across, so if I can clamp it right, I think I'll be able to get the edge up where it needs to be. I'm hoping I haven't screwed the edge up so badly that it isn't mostly straight.

You can probably clamp on the spine but you may need to shim under the bottom bevel to orient everything and keep it solid so it doesn't move while you are marking. Since you no longer have an established "reference flat" you may have to do a little "eyeballing" while shimming it up but if you take your time I'm sure you can get it as close as it needs to be.

Ray

Also, let me make sure I have this right; filing should be perpendicular to the spine at all times.

Not really. You can draw file this. actually it would probably be easier to draw file this.

The point I was trying to make is that if you have all the geometry in order you should be able to take a straight edge and set it anywhere along the spine (perpendicular to it) and the straight edge will touch all the way down from spine to edge. In other words you won't have any spots where your straight edge gets high centered and rocks back and forth when its perpendicular to the spine at any given point.

It would help to keep a bottle of dyekem with you when doing this to re-blue the blade occasionally so you can easily see any high spots as you file.

Ray
Ray

****Update****

I went out and tried to mark the center. It didn't really work, as it was already so thin as to be impossible to get something to mark it reliably.

I think I have it right. The edge is much thinner, and is the same width across what I would consider to be the "cutting edge." I have a few high spots to draw file out, then I'm going to hand sand it up to 800 grit before I send it off for HT.

For next time, I am going to make sure I make the center before I do ANYTHING!

This thing may end up as a "razor shaped object" and nothing more, but it has been a hell of a learning experience.

Do not sweat the center line, just do the same things to both sides it will be close enough. 50 draw files strokes one side then 50 on the other side. Just try to keep it even, your eye is better than you are giving it credit for.

Charlie

I tried to take a picture, but as you can tell, it didn't turn out.

I sighted down the edge several times from both directions. It is as close as I'm going to get it, I fear.

You have a surface plate. Do you also have a precision grinding vice and a height gage? You could clamp spine in vice and use the scribe.

You could also use an angle plate or other "square" block of steel, resting spine on surface plate (so blade points up) and scribe from the square plate and not the surface plate.

Make sense? If not don't sweat the small stuff, eyeball it and call it a learning experience. It will probably turn out better than you think.

Jeff

Quote:

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Originally Posted by TURNMASTER

You have a surface plate. Do you also have a precision grinding vice and a height gage? You could clamp spine in vice and use the scribe.

You could also use an angle plate or other "square" block of steel, resting spine on surface plate (so blade points up) and scribe from the square plate and not the surface plate.

Make sense? If not don't sweat the small stuff, eyeball it and call it a learning experience. It will probably turn out better than you think.

Jeff

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Jeff, I had to laugh at your post, but not because of the content. Its because of my woefully inadequate shop. Yes, I have a surface plate, but it's only a $3 piece of marble from Lowe's. I don't have a basic vise, let alone a precision grinding vise and I'm not even sure what a height gauge is. I will have to post a workshop pic in the main WIP thread.

Your post makes sense, in the sense that I understand what you're saying. However, I just eyeballed it as close as I could. If nothing else, it will indeed be a learning experience.

I thought just maybe. I have a very limited shop at home myself. Hand and basic power tools, with a bench grinder and shopsmith. Anything precision I do at work.

Well, I did the filing. Here are some pictures. Not sure if it's worth getting heat treated or not. I may have messed this up.
Edge, front side up:
http://img.tapatalk.com/ad1867a9-831d-ee3f.jpg

Spine, front side up:
http://img.tapatalk.com/ad1867a9-8366-aab4.jpg

Edge, reverse side up:
http://img.tapatalk.com/ad1867a9-8415-e4f5.jpg

Spine, reverse side up:
http://img.tapatalk.com/ad1867a9-8454-ac55.jpg
You can see where the grind is off on the tip.

I guess I'm stuck now. Shouldn't have tackled a smiling wedge first, the geometry is hell. Scratch it all and make it a western ground kami?http://img.tapatalk.com/ad1867a9-84e9-1b80.jpg
Props provided by Pinky the dolphin, and my daughters. :)

With a smiling blade the plane that spans between the spine and the edge is not a true flat plane, it is more like a section from a sphere A blade with a big smile will not lay flat on flat surface. You have to use some sort of compensating stroke (like the rolling X) to establish the flats on smiling blade.

I think what you have done so far looks good.

Pinky rocks!

Charlie

So the actual grind isn't flat from spine to edge? Like when I lay a straight edge from the edge to perpendicular to the spine, it shouldn't be flat all the way across at every point along the length of the blade? It is really close, along the order of 1 mm in places it's not perfect, but I wasn't sure. I'll just keep plugging along and sanding it up through the grits then. I'm only going to 800 before HT.

Yes the line is flat in between any given two points going from spine perpendicular to the edge. I can not articulate what I want to say. I am trying to say that the edge of a smiling blade will not touch along its length on a flat surface.

Charlie

If your edge looks straight enough to hone, HT it. We never know until we try something new. If it doesn't work, well, we learn more from our failures than our successes. If it was me I would put it to a hone now just see if it is workable. It may take a bit more to hone but it would be worth HT if possible to hone.

Either way you look at it you win.

Jeff

Jeff, it's definitely straight enough to hone. Now, whether it stays that way during HT, who knows. I got the edge a little thin during filing, so we'll see. I have Mike Blue's address, and will be sending it to him tomorrow!

If your edge is smiling, it will NEVER touch the hone from heel to toe. That is how the geometry works out.
What you see is perfectly normal. :)