Grinding thin steel

[Phil705]

I've been a bit disappointed with my flat grind on some 1/16th 440C and A2. In attempting to somewhat replicate the grind on a Global veggie chopper, I find it isn't quite right. It works fine as a medium chef's knife, but not as well as the commercial product at making fine slices of an onion, for example. The Global seems to have a perfect flat grind from the spine to the edge, tapering into a perfect steep "V". The secondary bevel is hardly noticable (I think it is VG 10 steel).

To the eye, mine looks pretty similar, but not in performance.

So, any advice in grinding technique to get that perfect flat grind on thinner steel? It has been hardened to Rc 58-60, but is there anything I can do to improve it at this point?

Picture of my attempt and the Global attached. The handle is stabilized tulip and the steel on this one is A2. I still have some scratches to get out.

 

[Johnny Warner]

When grinding thin steel such as 1/16" for fillet knives I temporary glue/tape a flat piece of pine board to the opposite side I am grinding. This method prevents the blade from flexing while grinding and helps keep the grind straight. Hope this helps!

 

[jim moyer]

When grinding thin steel such as 1/16" for fillet knives I temporary glue/tape a flat piece of pine board to the opposite side I am grinding. This method prevents the blade from flexing while grinding and helps keep the grind straight. Hope this helps!

Thanks for the cool tip.:thumbup::thumbup:

 

[Patrickknives]

Is the surface as rough as it looks?? The last couple of passes on a 50-60 belt is what I use for the final surface befor I start finishing. The surface needs to be free of defects at that point or its get harder to get a smooth flat surface. I slow the ginder down and with a new belt make 2-3 passes very carefully across each side. Then a couple of passes with a 120 and you should have a nice surface for finishing.

On a chef knife the bevel can make alot of difference in performance, the edge needs to be less than 0.04" to allow an angle of 12-15 degrees. Is the blade you are showing really 1/16? seems really thin.

 

[Phil705]

Yes, the knife is 1/16" A2. So when Patrickknives says he goes from a 60 grit, then new belt with 2-3 more passes at 60 grit, then to 120 grit, and it's ready for finishing. I guess I don't understand what you mean by finishing. I just keep using higher and higher grit up to about 800 before HT. The finish has a few scratches, but the picture makes it look rough. It isn't.

Good tips!!

Phil705

 

[galadduin]

To get a perfect V I have a cheat some times I use for big chefs knives. Before HT I scribe the centre with two lines defining the edge thickness. After roughly ground the bevels the the desired thickness I make each bevel perfecly flat by hand sanding on a glass plate.

After HT I grind both sides to almost zero edge and sometimes in fact I do a zero edge. Then I dull the edge a bit by just touching edge on the slack belt before hand sanding. I grind the bevels to 220 then move to handsanding starting from 120. Make the bevels perfectly flat. Remember the edge is almost zero edge. After I go up to 1000 or 2000 handrubbed finish I put a micro-edge by light and gentle passes on 400X belt. Dont use slack belt for chefs knives' edges, use flat platen or a flat stone to put an edge. The convex edge produces more durable edge I know but It doesnt perform good on chefs knives...

 

[Phil705]

To get a perfect V I have a cheat some times I use for big chefs knives. Before HT I scribe the centre with two lines defining the edge thickness. After roughly ground the bevels the the desired thickness I make each bevel perfecly flat by hand sanding on a glass plate.

After HT I grind both sides to almost zero edge and sometimes in fact I do a zero edge. Then I dull the edge a bit by just touching edge on the slack belt before hand sanding. I grind the bevels to 220 then move to handsanding starting from 120. Make the bevels perfectly flat. Remember the edge is almost zero edge. After I go up to 1000 or 2000 handrubbed finish I put a micro-edge by light and gentle passes on 400X belt. Dont use slack belt for chefs knives' edges, use flat platen or a flat stone to put an edge. The convex edge produces more durable edge I know but It doesnt perform good on chefs knives...

Galadduin, great tip! And I love the knives on your web site!

 

[Patrickknives]

120 is the last belt that takes off significant material so I want to be sure the surface is really flat and no gouges or marks, after that I consider finishing and the belts wont do much damage but also wont make much correction. After 320 anymore I go to hand sanding just because it seems easy to me for some reason.

Good tip on the zero edge, next set of chef knifes will go to zero. the last were 0.02 with a 24 degree bevel and they worked well but I felt they could do better on harder vegatables like carrots.

 

[James_Terrio]

What are y'all's thoughts on grinding bevels pre- or post-HT on stock less than 1/8"? It seems most of you do the bulk of your grinding before, but I've read other folks suggest to HT first to prevent warpage.

What RC hardness do you shoot for on a stiff chef's knife, as opposed to a filet knife which should be more flexible? Or is just dependent on how wide the blade is?

I would probably be using CPM154 for thin kitchen/fishing knives, if that makes a difference.

 

[galadduin]

What are y'all's thoughts on grinding bevels pre- or post-HT on stock less than 1/8"? It seems most of you do the bulk of your grinding before, but I've read other folks suggest to HT first to prevent warpage.

What RC hardness do you shoot for on a stiff chef's knife, as opposed to a filet knife which should be more flexible? Or is just dependent on how wide the blade is?

I would probably be using CPM154 for thin kitchen/fishing knives, if that makes a difference.

Some do, youre right but I wouldnt dare it as it is really thin at the edge and it takes a milisecond to burn it. If you are plate quenching warpage is not a big problem...

You want about 60 HRC for stainless alloys but I guess It can be more on carbon steels. Flexibility is about the thickness of blade not about HRC or width. A cefs knife is not so thin at cross section but the width is large therefore the bevel angle is too small, that angle defines the performance. The fillet knives are about 3 times thinner than chefs knives. You shoot less HRC for them not because the flexibility but ability to bend without braking...

 

[Hmathews]

I like to superglue a steel bar to the back of the blade while grinding thin blades like filet knives. I like to grind them after heat treating because the metal comes off slower and the mistakes are smaller.

One thing that can have an effect on the final finish is the condition of the platen. If it is worn and has ripples or imperfections in the surface, these can show up on the blade in the form of irregularities in the finish.