Grinding tips too thin

ashwinearl

ashwinearl

Joined
Nov 9, 2006
Messages
521
Hi,
I am having issues over grinding the tips. I am free hand grinding with a 10" Wheel and flat grinding on steel platen. At first, it seems that I am not grinding enough on the tip and have to focus on pressuring the tip more or pulling the tang outwards a hair as I shift from left to right or visa versa.Sometimes I use Dykem blue between each grit to ensure that I am removing previous scratches.

In the end, I end up over grinding. The tip has broken off a few times and end up regrinding the edge back down to 0.30 or 0.20 which was the original goal.

Any suggestions would be appreciated. Below are some pictures. 15N20 steel pre heat treat

NAltt2R.jpg

PvPBJXd.jpg

3ilZZGi.jpg
 
Im not the best at grinding by any means but ill see if i can help out. Could be a couple of things. As your blade comes accross the belt and you rock your body to the side you could be rotating your torso (like a baseball swing) and that's causing more pressure at the tip, or your thumb is pressing to much. Either way there is too much pressure when grinding. Hope this helps
 
A guy (I wish I could remember his name) at Ashokan this year gave me this tip: Grind the tip FIRST. That way, you can grind it without it flexing and you grinding more to overcompensate. I now grind all my kitchen knives this way, and some other blades (like your blade, that doesn't have a lot of meat at the tip) as well. I also find I'm less likely to burn them since i am using the freshest blade possible and also, perhaps (just my conjecture here) because there is more steel in the rest of the blade to soak up the heat. Maybe this will work for you.
 
Rethink the problem and then grind the tip last...

What I mean is leave lots of meat behind the tip, meaning it is a blunt point, and once you have your blade ground and the edge and finish like you want it, finish the profile by grinding the extra meat away from behind the tip to your final profile shape. This will make it grind at the same rate as the rest of the blade and also help you maintain crisp geometry there rather than the mushed up mess you sometimes see.

I think it's crazy that everybody grinds their profile to finished shape first and then grinds their bevels (and then their points suck) when a simple reordering of operations can fix the problem with no extra effort.

A walk around the Blade show ever year shows me that most makers struggle with this. And in my opinion the answer is so simple...
 
Nathan the Machinist said:
Rethink the problem and then grind the tip last...

What I mean is leave lots of meat behind the tip, meaning it is a blunt point, and once you have your blade ground and the edge and finish like you want it, finish the profile by grinding the extra meat away from behind the tip to your final profile shape. This will make it grind at the same rate as the rest of the blade and also help you maintain crisp geometry there rather than the mushed up mess you sometimes see.

I think it's crazy that everybody grinds their profile to finished shape first and then grinds their bevels (and then their points suck) when a simple reordering of operations can fix the problem with no extra effort.

A walk around the Blade show ever year shows me that most makers struggle with this. And in my opinion the answer is so simple...
Click to expand...

so are you saying that you grind the bevels with the end of your blank still squared off? or if its a drop point you grind the drop last?
 
There was a maker here a few years ago (sorry the name escapes me) who left a tab about 1/4" high by 1/2" long on the spine side of the tip when profiling. I tried it a few times and could see the reasoning for it. The tab gives a little more resistance to grinding away the tip.
 
thegardner said:
so are you saying that you grind the bevels with the end of your blank still squared off? or if its a drop point you grind the drop last?
Click to expand...
Yea man I didn't quite get what he is saying either. His statement wasn't very clear and somewhat contradicted itself.
 
jphillipsknives said:
Yea man I didn't quite get what he is saying either. His statement wasn't very clear and somewhat contradicted itself.
Click to expand...
Yes that's what he is saying. Don't grind the profile to shape at the tip leave it blunt rather than pointy, it doesnt have to be completely square but don't fully profile it. Then you have more mass to soak heat, hold on to, etc. Then when the bevel is ground, finish the profile. Iirc Don Nguyen does this, that's who Jesse was referring to.
 
I do the same. Leave extra tip sticking out of the profile. Then as I grind, I remove the excess. After the basic bevels are done, refine the tip profile and give the blade a few final passes to smooth the tip. I get a firmer tip this way.
 
I haven't had too many problems at the tip, but if I mess a little up, I just reprofile the spine a little to get rid of the mistake.
I grind thin, with added distal taper so the tip is crazy thin. If you taper first, you don't need to bevel the tip as much as the rest of the blade. Since it is both thinner and shorter there, the bevel angle for a full flat grind is a hair shallower than the rest of the blade. That means you don't have to grind as much there.

Since the tip and the heel are the most sensitive parts to grind, I tend to start many of my passes int the middle and blend outward. While it is thick, just do heel to tip passes. As it gets thinner, start in a middle area that needs more removed and gently blend out.
 
Ive been meaning to try the "tab at the tip" idea (ithink it was weo ?) who mentioned it to me. For long knives it should also help stabilize the tip, as you can hold onto the tab instead of putting fingertips directly behind the thin tip.

Regarding heating ... i have found (at least for me) that there is a temptation to draw the tip across the entire width of the belt. Bad idea - as that is just too much heating. Instead what i do (now at least) is as i draw the blade across the belt and approach the tip, i pull the blade away from the belt just as the tip starts to contact the belt. Not a perfect solution, but it helps prevent the tip from experiencing that instant burn from prolonged contact.

Gotta try that tab thing...
 
I also leave the TBE on the tip thicker and thin it at the end, when the rest of the grind is done. I needed long to figure out that I can finish the grind (heightwise) and then thin towards the edge as necessary.
 
Back when I wasn't very good at grinding bevels (probably up until a couple days ago), I used to cut out only blade edge profile from my bar of steel and then grind that until I had what I felt were acceptable bevels both sides and only then would I grab a sharpie and draw the outline of the blade and handle based off of those bevels. I figured why waste time cutting out a profile drilling holes and all of that if I didn't have the ability to at least create acceptable bevels. I encourage people to try that, just grind out perfect bevels on your rectangular bar of steel and once you've created excellent bevels then cut out the overall profile of the knife and see where it goes it's an interesting experiment that I think everyone could learn from.
 
eric brinkerhoff said:
Back when I wasn't very good at grinding bevels (probably up until a couple days ago), I used to cut out only blade edge profile from my bar of steel and then grind that until I had what I felt were acceptable bevels both sides and only then would I grab a sharpie and draw the outline of the blade and handle based off of those bevels. I figured why waste time cutting out a profile drilling holes and all of that if I didn't have the ability to at least create acceptable bevels. I encourage people to try that, just grind out perfect bevels on your rectangular bar of steel and once you've created excellent bevels then cut out the overall profile of the knife and see where it goes it's an interesting experiment that I think everyone could learn from.
Click to expand...
think I'ma try that:thumbsup:
 
I'm no pro, but I find that if I just grind away without thinking too much about the tip, it actually ends up a little thicker than the rest of the bevel edge.
Sometimes I leave it a little thicker there and sometimes I focus on thinning it a little.
I just rough ground this one in magnacut the other day before heat treat. It is a 10" hollow, first one on my new grinder.
The tip is right about where I want it as I hope that finishing the grind will bring it right in and make a needle with the swedge.
My biggest focus here was the plunge and how squared up or rounded I was getting it at the top.
JrnzuQy.jpg
 
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