How to- First Sharpening After Heat Treat

[JohnCenter]

This is something my search skills have not been able to find a clear 'A-B-C' answer too.  I have some blanks going out for heat treat (stock removal, O1). I am not clear on the steps to get a sharp edge for a scandi or a sabre grind after I get the knives back.

I only have hand tools. I left the edge approximately the thickness of a dime as per the recommendation of the heat treater.

My understanding so far:

1) Soak in vinegar for 24 hours to help remove gunk from heat treat.

2) Finish cleaning with high grit sand paper

3) For Scandi edges: Wrap sandpaper around a file and go back to my filing jig.

4) I figure Scandi's are easy- Sand the edge from dime thickness to zero hopefully ending up around 20-24 degrees inclusive. Right?

But, for a sabre ground, what do I do?
Follow steps 1 & 2, but leave the 'dime thickness' and grind the secondary bevel (approximately 20-25 degress inclusive angle) directly on to it? Or does the edge still need to be reduced first? How much?

 

[Will Wilcox]

Ive never done a Scandi grind, so i will claim no expertise there but this: 

7 hours ago, JohnCenter said:

Follow steps 1 & 2, but leave the 'dime thickness' and grind the secondary bevel (approximately 20-25 degress inclusive angle) directly on to it?

Is what i do for full ground blades. I leave about a dimes thickness and grind in the secondary after heat treat.

[JohnCenter]

Thank you. That makes it straightforward. But now I have to be more careful about actually grinding a dime's thickness since it will be the foundation for my secondary bevel. 

With a scandi there is, dare I say it, more room for error since in the end the edge will be ground to zero...

[Vern Wimmer]

To be a bit of a stickler about it, a proper scandi is nothing more than a high secondary bevel without a primary bevel. As such the goal is still to have the cutting edge basically in the center of the blades thickest point. To do it right takes as much care as a secondary on a flat or sabre grind.

[JohnCenter]

Right, but I would imagine any discrepancies (within reason) on the dime edge for a scandi can be ground out as you work the bevels down.  With the saber, if the dime thick secondary bevel is being used 'as is' for the primary, then anything other than a consistent thickness down the edge will lead to an equally inconsistent primary bevel.

I am just guessing as I've yet to reach and experience this stage in my journey.

[Alex Middleton]

A Scandi grind is probably less forgiving, inconsistencies will show up as waves in the cutting edge.  If you have a measurable edge bevel, minor inconsistencies are somewhat less noticeable (to me anyway). 

Regardless of the style of grind, I typically will stop grinding just shy of complete and finish it out with hard backed sandpaper.  It takes time, but leaves everything nice and straight without having to go farther than you wanted.  I have to believe that a disc grinder would have the same effect, with a lot less effort, I just don't have one.

[Vern Wimmer]

3 hours ago, JohnCenter said:

Right, but I would imagine any discrepancies (within reason) on the dime edge for a scandi can be ground out as you work the bevels down.  With the saber, if the dime thick secondary bevel is being used 'as is' for the primary, then anything other than a consistent thickness down the edge will lead to an equally inconsistent primary bevel.

I am just guessing as I've yet to reach and experience this stage in my journey.

The problem there is that you need the top of the bevels to be equal in height so that they approach the edge or finite point from the same angle. If they are different heights then the angles are not the same. With the large visually exposed surface trying to get them both perfect can be like trying to even up sideburns. " oops, too much off this side, now I have to take more off the other. Oops, too much. Back to the first side." Pretty soon you have white sidewalls and you have to get a crew cut to match.

Trust us folks "what are giving you advice". We might have "been there, done that". 

The BEST advice I can give is to forget about a sabre or a scandi grind and learn to do a flat grind all the way from the spine to a secondary, cutting edge bevel. Really anything else is a "noob" grind and it will be an embarrassing thing later on when you catch on to the whole concept. Low bevels seem like a good idea to start but they are generally less efficient cutters and far more complicated to do correctly. 

[JohnCenter]

7 hours ago, Vern Wimmer said:

Trust us folks "what are giving you advice". We might have "been there, done that".

I do.

Just trying to better understand. Thank you.

[JohnCenter]

Re-reading everything, and with respect to the posts above, is their an actual thickness I should have the primary bevel at before grinding the secondary on it? I referenced 'dime thickness' before, but in reflection I'd rather have a number. 0.030"? 0.025"?

When I measure a dime, it comes out at 0.044". A bit thick I think.

[steven smith]

I usually do a flat grind with a microbevel, it just cuts so much better, a zero edge is okay on some knives but I like to chop things so I rarely go to zero and if I do I still do a microbevel. 

First thing I do is grind a 45 degree edge to establish the centerline and then take it back from there, dont grind all the way to the spine or your grind line, do the last bit by hand. 

If you want to take the edge down grind with the sanding belt coming at the edge, if you want to take down the spine hold the blade so the belt is coming at the spine. If you grind into a 90 degree edge you can strip off your grit, thats another reason to do the 45 degree grind on the blade edge. Move your body at your hips instead of just moving your arms, its much more stable. 

[Brian Dougherty]

The dime rule of thumb is usually used for grinding prior to heat treating.  For most blades, I think you'll find that most grind to a much thinner edge before sharpening.  How things depends on the intended use of the knife.

My last kitchen knife I took down to less than 0.005".  For a hunting knife, I'll shoot for 0.015".

[JohnCenter]

Thank you for the post Steven. I don't have a grinder (maybe I should stop saying, 'grinding'!) I am using only files, but I definitely gleaned some good information from your post. I basically have been doing what you said. Filing a wide angle to my center lines, then pushing the shoulder back to get the angle I want (for scandi) or the depth (for sabre). It has been going well and quite accurate. I have not yet had to 'chase' shoulders from side to side. 

Brian, forgive me your leaving out such important information! Of course the type of knife I am making would dictate the thickness... This knife is a 4" long Bushcraft type knife. 1/8" thick. 1" wide. So, would your advice still be to have it filed down to 0.015" before putting on the secondary bevel/sharpening?

[Brian Dougherty]

0.015" would probably be what I would shoot for.  Opinions will vary greatly on this, so don't treat it as gospel.

[steven smith]

I got a 10" diamond coated file from amazon, just a cheap $10 thing, ill try it on a hardened tempered blade tomorrow. Since you dont have a grinder it could be useful to you.

You can use a grinding wheel from a bench grinder to grind down the blade by hand, im not sure of other rough grit stones. Concrete with sand in it, like a curb or sidewalk should do some rough work but you would be left with deep scratches.

I dont know what kind of rocks you have laying around but you might be able to find a useable stone in a creek, theres not much more than limestone here so no free stones for me, but west of here there is granite and other stuff. Its not ideal, but I got a flattish piece that removes scale pretty good. It has tiny iron crystals and mica in it so it wears away, I think a stone that doesn't wear much will clog with steel more, but I dont know much about rocks. Sandstone could be nice. 

Ill do some research on natural stones.

[JohnCenter]

18 hours ago, Brian Dougherty said:

0.015" would probably be what I would shoot for.  Opinions will vary greatly on this, so don't treat it as gospel.

Very good. Thank you.

[JohnCenter]

What a nightmare!

Finally recived my first batch of knives back from the heat-treater. Being my first batch, I experimented a bit. Also, it goes without saying, my consistency is not that great yet.

Of the four knives I sent, all are 3.50" blades 1/8" thick and 1" wide:

2 are Scandi grinds with one having an edge thickness of 0.010"- 0.15" the other, at 0.020-0.25". I'm pretty happy at how consistent the edge turned out ( as in not too wavy.).

2 are sabre grinds going back 0.75" of the blade. One of the edge's measures between 0.020" to 0.30" thick. The tip and near plunge being thicker and the middle and belly being thinner. Not too bad...

The last is a nightmare at a thickness of 0.040" almost the whole edge. A nightmare because trying to thin out that edge with sandpaper is going to cost me my shoulder and wrist cartilage... Seriosuly. No exaggeration.

So if the key is to get this bevel's edge  down to at least 0.020" (or even 0.015" as advised above) before putting on the primary bevel with my Lansky kit... how do I do it?

I've been going at it with 100 grit sandpaper and making very little progress considering the effort and time I've put in.

 

 

 

 

[Alan Longmire]

Coarse waterstones or diamond stones are about all that will do anything at this point.  That's why you check your edge thickness before hardening, when it's still relatively easy to remove steel.

[JohnCenter]

I've definitly learned that lesson! Wow. 

But I'm also so very confused.... I always read: grind only to 'dime thickness' to avoid warping and cracking when quenching. But dime thickness is about 0.040"  which is way to thick for me to finish once hardened.

So what should I actually be doing? Grinding to 0.015-0.020" before heat treat? Or is that too thin?

 

[Brian Dougherty]

Most people use a belt grinder for the final grind, hence the dime thickness rule of thumb.

Even a cheap 1x30 would be better than trying to hand sand from 0.040" to a sharpenable edge.  For smaller knives like that it would get you by.

[Alan Longmire]

If you aren't having decarb issues 0.020" is fine.  Since you are sending them out rather than doing it yourself, ask your heat treater.

[JohnCenter]

8 hours ago, Brian Dougherty said:

Most people use a belt grinder for the final grind, hence the dime thickness rule of thumb.

Even a cheap 1x30 would be better than trying to hand sand from 0.040" to a sharpenable edge.  For smaller knives like that it would get you by.

So what is the rule of thumb for people hand grinding?

 

when I asked a while back about files vs cheap grinders:

I was told not to waste my money and time and learn to accept abrasives. I've no problem with hand tools, except now they simply don't work and I have metal to remove. I feel misled. And confused...?!

[Alan Longmire]

A coarse waterstone will do it.  I don't mean to confuse people about the utility or not of the cheap sanders, they are barely functional.  What I try to do is keep people from nickle-and-diming themselves out of a better grinder.  The 1" belt sanders are fine for sharpening, but they do not remove metal very fast at all.  The 4x36 sanders are disposables, since the motor and bearings are not sealed.  Under heavy use they last about a year when used on steel.

In the days before belt grinders they used large stones, but more importantly they did not leave the temper as hard as we tend to now.  What hardness did you specify on these?  

[JohnCenter]

60RC. They came back at 59RC.

Alan, sonin line with your advice, would it be wise to purchase a DMT Extra course (4" or 6") stone? I'm thinking I could hook it up to my file jig and to start regrinding the bevel thinner.

And, last question, my next batch should go out at 0.020" or even 0.015", right? Then I can polish them and simply grind on the primary bevel with my Lanky kit... right? Avoid my current nightmare repeating!

 

I apologize if this is getting repetitive. But I want to be clear on how to move forward and not repeat the same mistakes. Hand filing is my only option for now and I want to continue making knives.

[Alan Longmire]

I'd go with the extra coarse 6" stone, take the next batch to 0.020", ask your HT guy if he's running a decarb-free atmosphere, and ask for 57 Rc.  60 Rc is, in my opinion, too hard.  Most people won't be able to hand-sharpen that.  That's just my opinion, though.  

[JohnCenter]

Actually one more question- Since I'm going to pick up the exra course stone, hwo deep of scratches is it going to leave? Will I be able to continue with sandpaper after? Or do I need another grit of stone before I can move to paper?