Help with Flat Grinding

Jason thats how my video does it. i will have to try the other way some time and se how it works.
 
Jason Magruder said:
There are two ways to do it. Some guys hold the knife perpendicular to the ground and pull the handle away from the belt as they get towards the tip. I like to go the other way and keep the handle the same distance from the belt but move it down as I get towards the tip. in other words I try to keep the portion of the blade that is in contact with the belt perpendicular to the belt.

Here's a super cheeseball drawing I did in paint to hopefully help show how I do it. I suck at paint :P

http://i267.photobucket.com/albums/ii316/Belstain/1supercornydrawing.jpg

Blue lines are the edges of the belt red is point of contact and yellow is what the spark pattern should look like.
Click to expand...


1supercornydrawing.jpg


That is a good illustration
 
Karl B. Andersen said:
A correctly done flat grind IS completely flat from spine to edge, and ricasso to point.
Click to expand...


How can it go around the belly and maintain an even edge thickness without deviating from a plane?

I tried to visualize your example, but I didn't quite get there. Do you have any pictures of a flat ground blade where the entire bevel could be sat flat on a table including the belly? I don't have any flat ground blades, so I don't know.
 
There are just two planes that are at a cant.
I would think that if a maker was not achieving that, then he is probably rushing the job.
I'm not saying it is easy to do. It takes patience.
Truth be told, I find a flat grind boring and not as strong as a convex grind. Hence, I currently have no flat grinds to photograph.
I find that a well done and symmetrical convex grind is far more appealing.
My current grind that offers me ease of finishing, easily sharpened and a strong profile is a flat grind taken to about 80% completion, and then finished off with a convex grind to a zero edge and up the blade about 30-40% from edge to spine.
All of the blades on this page are finished that way:
Pay close attention to the second one down. It may appear flat - but it's not!
http://www.andersenforge.com/knivesinprogress.html
 
Looks like you need to pull the end of the tang towards you more when you reach the tip. Also, tilt the blade slightly upwards towards the tip.

I'd also recommend grinding fast with a fresh Norton Blaze 60 grit belt, then clean up on slower speeds with a 120, 220, etc.

Hope this helps. Good luck!
 
Nathan the Machinist said:
How can it go around the belly and maintain an even edge thickness without deviating from a plane?

I tried to visualize your example, but I didn't quite get there. Do you have any pictures of a flat ground blade where the entire bevel could be sat flat on a table including the belly? I don't have any flat ground blades, so I don't know.
Click to expand...

If you had previously forged/ground the distal taper in FIRST, this will facilitate that dilemma.
If you are trying to keep the spine at the same thickness, you'll have problems.
 
Nathan the Machinist said:
How can it go around the belly and maintain an even edge thickness without deviating from a plane?

I tried to visualize your example, but I didn't quite get there. Do you have any pictures of a flat ground blade where the entire bevel could be sat flat on a table including the belly? I don't have any flat ground blades, so I don't know.
Click to expand...

Nathan, that's exactly what I couldn't figure out.
- Mitch
 
TekSec said:
Troop,

After reading these today, I went down and really paid attention to what I do. The one thing that may help (newbie here also) is to make sure and watch your spark line. As you move across the platen, the sparks will fly out from where your steel is meeting the belt. If you're only getting sparks on one side or the other, try to flex your pressure until you get a nice even spray the width of the belt. It really does help.
Click to expand...
Erik,
:thumbup: I discovered the even spark thing already (That's the one positive step I took in figuring out how to flat grind.:)) The grind got nice and even, at least on the straight part of the blade, when I watched the sparks fly off evenly on the belt.
Thanks
- Mitch
 
Hey Guys, This is what I'm hoping is true about flat grinding...As long as I make a distal taper from plunge to tip, which, of course, includes the belly, there's really no reason to come off of the flat platen when I'm grinding on the belly, right? I can keep it all on one taper, without lifting, or pulling, the butt away from the grinder away from it's "normal position" to keep the taper, right? On the illustration posted above, it looks like you are, in fact, coming off of the plane of the taper.:confused: Which is it?
Thanks again,
Mitch
 
Karl B. Andersen said:
If you had previously forged/ground the distal taper in FIRST, this will facilitate that dilemma.
If you are trying to keep the spine at the same thickness, you'll have problems.
Click to expand...

Karl, your grinds are really beautiful. I like convex grinds the best, too. But, that's the only grind that I know how to do. Now, what self-respecting Maker can call himself a Maker, without knowing how to flat and hollow grind too, right?
Anyways, as long as I have a distal taper going from plunge to tip, I don't have to worry about moving the blade off of the line of the taper when it comes to the belly, right?
Thanks, Karl.
- Mitch
 
Troop,

The point of the illustration, and the way I hollow grind is the blade stays perpendicular to the platen or wheel at the point of contact. That means you turn it as you get to the belly to keep it perpendicular to the belt at the point of contact. That is what he is talking about and how I do it, but apparently not everybody does it that way.
 
Here. This illustrates the point. This is a hollow ground blade.


blade.jpg



blade_tip.jpg


See how my grind stays perpendicular to the edge and follows the curvature of the belly.

I'm not saying this is the only way to do it. But it is what most of us are talking about.
 
Thanks, Nathan. Hmmm.....If I could do it in a way where I wouldn't have to turn the blade at all at the belly, that would be pretty much a snap for me to do. Maybe with the whole "distal taper concept", I wouldn't have to give any special consideration when I come to the belly.
- Mitch
 
Nathan nailed it with that picture. With a full flat grind doing it just like that will give you some distal taper that gets more pronounced as you get closer to the tip IE loking from the top the spine has a gentle curve from ricasso to tip like an appleseed. If you want to get a straight distal taper you will need to twist the blade slightly also as you move along the length. this usually means that As I get towards the belly I put more pressure towards the spine and less at the edge to make a shallower angle. blade profile has a lot to do with how you twist it. more belly takes more twisting to get distal taper. a blade that looks more like a triangle in profile takes almost none.
 
Ok my newbie answer. when i was working on the first knife which had a flat grind I was told and did the following (To the best of my rememberance) Made a agressive grind near the edge of the blade with the blade going up the grinder. then tipping the edge of the blade out slightly (just a hair or two between the snader and the edge of the blade) and then slowly creeping the grind to where i wanted it to end on the blade. all done on the flat platen of the grinder. I have not made many but that method worked well for me.

The Second Flat Grind I started with a Hollow Grind and then switched over to a flat platen and grinded the hollow grind out. (The blade was to wide for the hollow grind to look right) That also seemed to work well. Hope that helps, (and hope I remember good enough on what I was learning)
 
Mathematical law: the intersection of two planes is a straight line. :)
 
Nathan the Machinist said:
How can it go around the belly and maintain an even edge thickness without deviating from a plane?

I tried to visualize your example, but I didn't quite get there. Do you have any pictures of a flat ground blade where the entire bevel could be sat flat on a table including the belly? I don't have any flat ground blades, so I don't know.
Click to expand...

I believe you're right, Nathan. If my reasoning is correct, I believe you would need edge curvature from beginning to end in order to maintain a constant taper and edge thickness.
By way of illustration, take some rectangular stock roughly the size of the blade portion only. Next, scribe a center line around the entire perimeter and grind your distal taper in. Next, grind the opposing edge down to a pre-sharpening thickness while maintaining constant contact with the platen. This keeps things consistantly flat in both directions. Of course, both grinding operations may be done at the same time, if you desire. I broke them down to add clarity, I hope.
What you should notice is four corners of different thickness. The edge side at the tip will be very thin, if not ground off entirely. It would depend on the size of your stock and final edge thickness.
Now, if you grind the edge in a curve from front to rear, you can establish a constant edge thickness. The curvature should depend on the width:length aspect ratio.
You can achieve consistent flatness/tapering in both planes, but I don't think any of us make our knives in those shapes. You can, however, come very close due to the size of stock we use, so it isn't really that noticeable.

Brett
 
Jason Magruder said:
Nathan nailed it with that picture. With a full flat grind doing it just like that will give you some distal taper that gets more pronounced as you get closer to the tip IE loking from the top the spine has a gentle curve from ricasso to tip like an appleseed. If you want to get a straight distal taper you will need to twist the blade slightly also as you move along the length. this usually means that As I get towards the belly I put more pressure towards the spine and less at the edge to make a shallower angle. blade profile has a lot to do with how you twist it. more belly takes more twisting to get distal taper. a blade that looks more like a triangle in profile takes almost none.
Click to expand...
O.K., Thanks, Jason. Now I get what you guys mean when you "twist" the blade. At first, it didn't make sense to me, with me doing a "flat grind". I guess, like a bunch of guys have already said, a "flat grind" is not really a "flat grind" at all.:)
Thanks,
Mitch
 
fitzo said:
Mathematical law: the intersection of two planes is a straight line. :)
Click to expand...

Mike, you made the light bulb come on with your first "Zen Koan", but this one isn't working (yet):)
The way I see it, the intersection of two planes is a straight line. O.K., I see that. But, with flat grinding, you don't want a straight line, or angle, at the intersection, right? I want a nice, even taper.:confused:
Thanks Mike.
- Mitch
 
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