How do you sharpen a blank freehand to get even dual bevels?

[DavidL41]

Hypothetically when sharpening a rectangular blank w/ no bevel yet what is the method to get the bevels freehand to be level. Is it like how hand planes go over wood multiple passes to flatten? How accurate can you achieve both bevels to be 15 degrees for example?

How would this be done if someone was to hand you a blade with with multiple different angles and is unusable. Would you sharpen to the lowest angle to level the bevel?

 

[Obsessed with Edges]

At some point a few years ago, I'd seen a post or two here about grinding edges from blanks. A clever means to start, according to the posts I'd seen, was to measure the thickness of the blank, then use a drill bit at exactly to half that thickness (or as close as possible), as a reference gauge laid alonside the blank's edge, to mark a centerline with a scribe. Then grind each side to meet at that marked centerline. To the best of my memory, I think that's what I'd read.

Per your 2nd question, if attempting to fix or regrind a very asymmetric edge (multiple bevels, etc), I'd just start with a very coarse stone and take each side down to the primary grind, i.e., to behind all the ugly stuff at the edge, and establish a clean apex that way. If need be, grinding a flat at the ugly edge and marking a centerline (referenced to the overall thickness of the blade, i.e., spine thickness) as with the blank method above, might be an option if you're still concerned about doing it as symmetrically as possible.


David

 

[TravisH]

Off-hand, I wouldn't think you could get accurate, even bevels freehand starting from a squared blank.

Doesn't freehand sharpening require some kind of bevel that can be felt? Can a freehander hold a blank at a customer's desired angle accurately? Say one blank at 18°, another at 22°?

Edges are ground prior to heat treatment when the steel is relatively soft. Jigs and/or guides are typically used to accurately set the grind and edges.

 

[DavidHoback]

A skilled freehand sharpener can maintain a very consistent angle. Perfect angle? Of course not! No human can achieve perfection. But inconsistency in angle, of a skillfuly prepared bevel, will be very difficult to see. And it certainly would not affect performance. Now, I personally use guides. I make jigs to set my initial primary bevel, or "Grind". And I use my own guided sharpener with Edge Pro style stones. For me, it is necessary, as I have use of only one arm/hand.(my left is paralyzed). But having two, I believe I would work to develope more freehand prowess.

 

[Obsessed with Edges]

Below is an example, in concept, similar to what I'd mentioned earlier. Quoted from a knifemaker and BF member/moderator:

(quoted from thread --> : http://www.bladeforums.com/threads/newbie-grind-and-hone-angles.1178676/ )

You don't have to get them "correct". If you scribe the centerline on the blade edge area of the profiled knife, you just grind the bevels from spine to the scribed lines.


Now, if you don't know how to scribe the centerline, here is how:
You can buy a edge scribe tool for $20-50...but a cheap drill set will do the same thing.
First, sand the blade edge area of the profiled knife blank smooth with 220 grit paper so it isn't scratched up. It should be smooth and fairly flat. It doesn't hurt to sand and scribe the spine, too.
Take a drill bit that is about .040" smaller than the metal thickness and clamp it to something flat and smooth. A piece of steel, a scrap of countertop, a granite surface plate, or even a flat piece of hardwood will do.
Lay the knife blank on the flat surface and scrape the edge along the drill bit tip. It will scribe a line just below the center. Flip over the blade and scribe again. You now have two parallel lines on each side of the center which are about .040 apart. You will file/grind the bevel until it meets these lines. By picking a drill bit the right size, you can make the spacing what you want.

Example - For 1/8" steel, use a #44 bit ( .086") and the lines will be just about exactly .040" apart.

Once the filing reaches the lines, switch to sandpaper backed with a hard and flat backing block. Aluminum, steel, or hard wood will work as a backer.After sanding, the edge should be about .030"...which is jus righ for HT. It can be a tad narrower, but don't go below .020" on carbon steel ( stainless can be .010 without problem)

David

 

[HeavyHanded]

You would scribe the edge side of the blank at the midpoint. Then scribe the faces where the primary is going to stop. Take a file and hog out a flat between these two points or just shy on the edge side so you can grind the cutting bevel without loss of blade width. Finish with a draw file.

I cannot imagine doing it to a heat treated blank, but if the stock were flat and really thin you could do it on a stone. Scribe or Sharpie the width of the bevel and work from shoulder to edge, correcting as you go. Not a whole lot different from putting a real edge on an off-the-shelf machete or hatchet.

 

[HeavyHanded]

Hypothetically when sharpening a rectangular blank w/ no bevel yet what is the method to get the bevels freehand to be level. Is it like how hand planes go over wood multiple passes to flatten? How accurate can you achieve both bevels to be 15 degrees for example?

How would this be done if someone was to hand you a blade with with multiple different angles and is unusable. Would you sharpen to the lowest angle to level the bevel?

Pick an angle= to the lowest existing and work from that shoulder to the edge, swapping sides often. You have to work the edge evenly as it closes in on the centerline.

If that angle is too acute you pick a midpoint and work out from there in both directions toward the spine and edge at the same time - this would be tougher than working from the existing shoulder but not bad once the new bevel is established enough to feel it on the stone.

 

[DavidL41]

Off-hand, I wouldn't think you could get accurate, even bevels freehand starting from a squared blank.



Edges are ground prior to heat treatment when the steel is relatively soft. Jigs and/or guides are typically used to accurately set the grind and edges.

That is what I imagine it to be but many do it free hand on a belt sander with good results

 

[DavidL41]

At some point a few years ago, I'd seen a post or two here about grinding edges from blanks. A clever means to start, according to the posts I'd seen, was to measure the thickness of the blank, then use a drill bit at exactly to half that thickness (or as close as possible), as a reference gauge laid alonside the blank's edge, to mark a centerline with a scribe. Then grind each side to meet at that marked centerline. To the best of my memory, I think that's what I'd read.

Per your 2nd question, if attempting to fix or regrind a very asymmetric edge (multiple bevels, etc), I'd just start with a very coarse stone and take each side down to the primary grind, i.e., to behind all the ugly stuff at the edge, and establish a clean apex that way. If need be, grinding a flat at the ugly edge and marking a centerline (referenced to the overall thickness of the blade, i.e., spine thickness) as with the blank method above, might be an option if you're still concerned about doing it as symmetrically as possible.


David

How would you distinguish if you managed to mess up your edges, one side is 15 degrees and the other side 13 degrees. It would be very difficult to see this from the spine? There seems like there would be a tool to measure this on every type of bevel.

Perhaps measuring the distance from the end of the bevel (shoulder) to the spine to be equal on both sides is an indicator it is even provide that the steel was like a squared rectangle before it the bevels are ground in.

 

[DavidL41]

You would scribe the edge side of the blank at the midpoint. Then scribe the faces where the primary is going to stop. Take a file and hog out a flat between these two points or just shy on the edge side so you can grind the cutting bevel without loss of blade width. Finish with a draw file.

What is the method to keep the angle constant around curves or on edges larger than the width of the belt sander belts? It is a bit like hand planes on wood where you need to find the high spots and take them out as you create them.

 

[Obsessed with Edges]

How would you distinguish if you managed to mess up your edges, one side is 15 degrees and the other side 13 degrees. It would be very difficult to see this from the spine? There seems like there would be a tool to measure this on every type of bevel.

Perhaps measuring the distance from the end of the bevel (shoulder) to the spine to be equal on both sides is an indicator it is even provide that the steel was like a squared rectangle before it the bevels are ground in.

If the blank is truly square, flat and of even thickness along it's full length, a variation in the angle ground from each side would be seen in the differing widths of the bevels on each side. On the lower-angled side, the bevel will become wider, relative to the other side ground at a higher angle. This is relatively simple to see on most any knife blade, when reprofiling or doing major grinding work at the edge. To avoid too much variation in bevel width, do a little grinding from each side at a time, alternating back & forth and focusing on keeping the bevel widths relatively matched up as you approach the centerline (edge). As you get closer to the edge apex, switch back & forth more frequently (after fewer passes on each side), as each pass will begin to show a more obvious change in bevel width, relative to the opposite side. This method is what I've used, when reprofiling edges on blades.


David

 

[HeavyHanded]

What is the method to keep the angle constant around curves or on edges larger than the width of the belt sander belts? It is a bit like hand planes on wood where you need to find the high spots and take them out as you create them.

Ideally you change your attack angle so the largest surface area is making contact. With a file you'd (I'd) use about a 45° angle across the bevel area to hog it off. Once it was more or less established I switch to a draw file technique and flatten the whole thing out - so yes, similar to using a shorter jack plane to rough it and move to longer planes to flatten it out.

You also have to be realistic about how well it is going to turn out without a jig, or even with one. Nearly every single knife blade, even expensive ones, have inconsistencies in the grind. From the factory is the worst. Once you get into a regrind, especially by hand, you realize just how uneven the surface really is.

If you have two reference points like a scribe mark 1/4" from the spine and another 1/8" or 3/32 from the edge, you can get pretty darn flat between them using files and a straight edge. Takes time though, and you still have to use some artistry at the plunge line.

Once the steel is hardened you can't readily use a file unless its low Rockwell, so on to belts and you lose a little precision but still plenty accurate overall.

 

[DavidL41]

If the blank is truly square, flat and of even thickness along it's full length, a variation in the angle ground from each side would be seen in the differing widths of the bevels on each side. On the lower-angled side, the bevel will become wider, relative to the other side ground at a higher angle. This is relatively simple to see on most any knife blade, when reprofiling or doing major grinding work at the edge. To avoid too much variation in bevel width, do a little grinding from each side at a time, alternating back & forth and focusing on keeping the bevel widths relatively matched up as you approach the centerline (edge). As you get closer to the edge apex, switch back & forth more frequently (after fewer passes on each side), as each pass will begin to show a more obvious change in bevel width, relative to the opposite side. This method is what I've used, when reprofiling edges on blades.


David

There is a lot to it to get every style of blade done right. Say for a knife that is thinner tip (looking at the spine of the blade it is a triangle shape) you almost have to get the tip done last because you can't gauge the width of the bevel there since the steel is thinner at the tip.

I will have to just attempt it more.

 

[Obsessed with Edges]

There is a lot to it to get every style of blade done right. Say for a knife that is thinner tip (looking at the spine of the blade it is a triangle shape) you almost have to get the tip done last because you can't gauge the width of the bevel there since the steel is thinner at the tip.

I will have to just attempt it more.

That's basically why it's probably most straightforward to just focus on keeping the bevels looking relatively even from side to side, while doing your best to hit your target angle. For a knife blade, as opposed to a blank, it's going to be difficult or impossible to gauge ahead of time how wide the bevels will be (or should be) for a given sharpening angle, due to the varying thickness of the blade. As you grind on different sections of the edge, the variation in thickness will become more obvious, as you'll see it in a variation of the bevel widths.

The tips of many blades will surprise you, as they'll actually be thicker near the cutting edge, and the bevels wider there at a given angle, due to the cutting edge being closer to the spine of the blade, which is normally thicker steel. This is more easily seen when using a guided system to sharpen the blade, which more steadily maintains the angle throughout the full length of the edge.


David