Review Sharp maker cubic Boron nitride: how much pressure?

B

Bo-dacious

Joined
Aug 13, 2016
Messages
408
Hey guys, Im using my sharp maker and I find it's not sharpening certain knives because they're too dull or need reprofiling. So I bought some cbn rods. I was told to use only 5 grams of pressure or the particles will fall off. I tried it on a scale and it's Impossoble for me to get that low pressure (I can't get below 10 grams).
Is that the actual recommendation? If not, how much pressure should I use?

Also, I heard you can wrap them in sand paper as an alternative. I was going to do this in addition to the cbn to get the very dullest knives sharp. What grit should I use, with the knowledge that I'm still going to use the cbn rod? What's the next lowest grit I should use? I tried with a 120 grit but it kind of digs Into and catches the sand paper. Would 180 grit be better?

Thanks guys,

Bo
 
Bo...as was mentioned in your previous thread, try posting your sharpening questions in the “Maintenance, Tinkering & Embellishment” sub forum here. You will likely get better answers there than in “General Knife Discussion”.
 
I can’t help ya with those rods or sandpaper ideas but I’d suggest the Spyderco diamond rods if you have heavy removal jobs or if you are re-setting sharpening angles. You can get faster removal using the corners of the medium Sharpmaker rods too but the diamond rods work fastest.
 
Also, will the rod remove much material at 5 grams of pressure? It seems like it wouldn't.

Thanks,

Bo
 
Bill seigle: do you mean rods other than the cbn rods? That sucks I ordered the cbn ones, are they going to do a decent job though? Like a lot more than the brown ones it comes with?
Why do they have diamond rods AND cbn rods? What purpose does each serve?

Bilbo: ok but this is a maintenance question so I thought I should put it here. Oh well.

Thanks guys,

Bo
 
Just enough pressure to hold the knife steady. More pressure means more chance of plowing out grit, I've ruined a few diamond plates like that.
 
diamonds and cbn are expensive, let them do the work. Go easy, or you will wear them out way too soon.
Those two options really open up some possibilities, use them with care.
Russ
 
Bo-dacious said:
Hey guys, Im using my sharp maker and I find it's not sharpening certain knives because they're too dull or need reprofiling. So I bought some cbn rods. I was told to use only 5 grams of pressure or the particles will fall off. I tried it on a scale and it's Impossoble for me to get that low pressure (I can't get below 10 grams).
Is that the actual recommendation? If not, how much pressure should I use?

Also, I heard you can wrap them in sand paper as an alternative. I was going to do this in addition to the cbn to get the very dullest knives sharp. What grit should I use, with the knowledge that I'm still going to use the cbn rod? What's the next lowest grit I should use? I tried with a 120 grit but it kind of digs Into and catches the sand paper. Would 180 grit be better?

Thanks guys,

Bo
Click to expand...
I don’t want to hijack the thread but in woodworking, users of diamond plates do not worry about stripping diamonds. I use appreciable pressure on the plate with Windex to remove the slurry. While the plate feels less grabby after a while, it continues to cut well. CBN wheels for hollow grinding spin at 3500 rpm, giving off sparks without any tactile change in their grittiness. I have to question either the construction of these rods or the instructions for use.
 
Okay but how can they remove much material if I'm using that little pressure?
And I'm not going to risk ruining these expensive rods, but I agree that it seems suspect that you have to use THAT little pressure.

Thanks,

Bo
 
The problem with pressure on the SM's rods is more about the setup of the device and the narrowness of the available contact area. More so on the rod corners, which will focus pressure both against the blade's edge and also back against the abrasive grit and it's bond to the rod. There's very little total grit available along the narrow corner's edge, so protecting the bond of the grit that's there places a greater premium on keeping the touch light.

A diamond plate, being fully flat in the area of contact, won't focus pressure as much. And a few grains of abrasive grit being scrubbed away from it won't immediately degrade it's working performance, nor for a very long time, for that matter.

The vertical setup of the SM's rods also inhibits how much pressure is used, as the base itself will be too unstable to do heavy grinding without a complete loss of control. One could clamp it down in place, on the table. But there's still the worry of focusing too much pressure anyway, which is never any good for the blade's edge or for the nickel plating holding the grit to the rod. It's counterproductive anyway, so heavy pressure won't be of any advantage, at all. Using the flats only, of the diamond or cbn rods for the SM, will allow a somewhat firmer touch if the base is held down by clamps or whatever. But the increased pressure should still be kept only moderately firm, for the sake of results obtained, if for no other reason.
 
Last edited:
OK thanks obsessed. That was helpful too. My cbn rods should be here any day, can't wait to try them.

Bo
 
Bo-dacious said:
Hey guys, Im using my sharp maker and I find it's not sharpening certain knives because they're too dull or need reprofiling. So I bought some cbn rods. I was told to use only 5 grams of pressure or the particles will fall off. I tried it on a scale and it's Impossoble for me to get that low pressure (I can't get below 10 grams).
Is that the actual recommendation? If not, how much pressure should I use?
Click to expand...
Hi,
Who told you 5 grams?

It is weird how the stone makers avoid useful numbers .

I've used 5-10 grams on my harbor freight diamond block with the tip of a knife and didn't scrape anything off that I could see.
I've also used ... 2-3 pounds (? definitely more than 1, unsure, accident ) with a tip and scraped everything to bare steel (nickel+diamonds gone).
Think about that 2lbf/square mm to pounds/square inch = 1290 psi compared to
5 grams/square mm to pounds/square inch = ~7psi

Make it a more dull tip 2mmx2mm = 322psi

If your edge bevel is 2mm wide, .5lb on a 2inch stone is about 3psi. half inch is 12psi and quarter inch is 25 psi

If you use lube (water) and keep the force under 1/2 lb (or 226.8 grams ) cbn/diamond stones should last forever

see CBN Rods - Page 7 - Spyderco Forums
Diamond rods inferior to CBN rods? - Spyderco Forums

update: a quote light force, 1/2 lbs but small contact area meant the pressure was high 10-20 psi this translates to 226.8 grams , this is on the flats not the corners of triangles


BruceMack said:
I don’t want to hijack the thread but in woodworking, users of diamond plates do not worry about stripping diamonds. I use appreciable pressure on the plate with Windex to remove the slurry. While the plate feels less grabby after a while, it continues to cut well. CBN wheels for hollow grinding spin at 3500 rpm, giving off sparks without any tactile change in their grittiness. I have to question either the construction of these rods or the instructions for use.
Click to expand...
Hi,
Hmm, 3500 rpm versus "apperciable pressure" ... hmm, in woodworking, are rulers marked yay long , so long...? :D

10lb/2inch stone wide * 1 inch chisel wide to psi = 5 psi , 20lb is 10 psi, 30lb is 15psi


dot dot dot
 
My bad. I should have said "a lot of pressure". We woodworkers aren't precise, observing the adage "wood moves". Thanks for the specifics.
 
Bucketstove: an eBay seller told me he got 5 grams from the manufacturer. I don't see how it can be true.
So I just wet it and use it til it's dry?

Thanks guys,

Bo
 
You must log in or register to reply here.
Back
Top