Thin belts making wobbly grinds?

S

smartanimal

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May 7, 2015
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Has anyone had this problem?

I'll rough grind the bevel at about 60 grit with a Norton Blaze belt. No problems so far, all the small grit lines are unbroken and the bevel looks satisfyingly flat. Repeat process with norton blaze 120, still good.

After i heat treat, i try to bring it up to 220 with a J flex belt and i see the grit lines break up in weird, wavy broken patterns. I'm beginning to hate j flex belts for this reason. usually i put a 320 Bluefire on after this (a thicker belt) and it straightens the bevel noticeably, or at least if i come to that belt with a straight bevel, it maintains it.

Am i using the J-flex at the wrong time in the process? I can feel the seam of the belt bumping under the knife as i push into the platen and i swear it's messing me up and giving me problems when going into the higher grits. I don't know if it's because of the belts im using or if its my technique.

The higher the grit i go, the harder it is to seemingly maintain a flat bevel. Is it just revealing mistakes I'm making earlier on?

Super confused.
 
I use either a 65 or a 220X and I then go to 45,30,16, and a cork belt loaded with green chrome polish.
Frank
 
I avoid that problem by using the structured abrasive "gator" belts.
 
Frank and timos, are you referring to the gator belts with the grooves or the smooth ones? They also have ceramic ones.
 
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I use J flex a lot and it is not your belt but your grinding technique.

Pull that blade smoothly across with a bit of attention in pressure toward the top of the grind and it will smooth out those waves.

Waves in the grind are from technique and how you are apply apply pressure.

The thin belt is not as forgiving as those with thicker backing.
 
I use an old file and rub the grit off the splice area before using the finer grit J flex belts. You can also stretch a belt and put it over the top of another to run two at the same time to give it a little bit of extra give when doing your final finish grind.
 
As the always wise Nathan pointed out, it is the splice that causes those little wormy looking divots and hickeys. The Gator belts solve that problem. Stuff like graphite cloth on the platen can also help, but some say that stuff introduces a new set of issues.
 
Buy better belts. I hate the klingspor j-flex belts; they have a huge bump at the seam. Try the Hermes j-flex belts from Tru-Grit. They are far better. Also the gator structured abrasive belts in a/o are fantastic. My progression is 50 grit Blaze, A160 Gator, A65 Gator, A45 Gator...then 320 EDM stone, 400 EDM stone, 500 grit redline, 800 grit redline, pull on a Scotch-Brite and done. That easy!

Bob
 
I hate J-flex belts also, and almost never use them for blades, although I do use them for handles.


Even the blue j-flexes that have a good splice will cause issues with grinding very thin blades, when they ride unevenly over the platen, due to the crown of the wheels stretching the center of the belt. Guys that don't grind blades thinner than 1/8 never notice this problem because the blade doesn't flex as much and you can put more pressure easily. For pocket knives and super thin kitchen knives, where the belt cups will dish top and bottom of the grind, no matter how much or how even the pressure you apply. The whole "rolling the belt over the edge" to get into plunges is also counterproductive with thin blades like this, as the belt will tend to roll over your plunge shoulders and wash them out.


Personally I buy X weight belts all the way up to 800, in conjunction with j-flexes. I also highly recommend the Norton U936 Ceramic Norax belts. Using these stiffer belts, I can keep super flat, ultra tapered bevels with crisp plunges on super thin blades easily. Can you do it with j-flex belts? Yes, but it's not the right tool for the job and there's no advantage to it IMHO. Although if you're rolling plunges on a 1/4" thick knife, yeah, they're great.


Call Pop, he's got good 3m belts in X weight in 220 and 400 grit, and then some stiff hermes belts in 800, they cost less than the yellow j-flexes, and grind longer.
 
I'm with Javand- Someday I'll get a lesson from someone who gets good results with J-flex, but for now I don't use them much for flats.
Pops has an X-weight Hermes 120 that is just great, and very reasonably priced. It runs much smoother than my 3M 120s- after that, it's the 100m and finer gators (as in, Trizact), and the disk grinder, up to cork and often fine Scotchbrite.
 
Just to add, I highly recommend the 984F and 947A Cubitron II's in 120 grit from Pop. They're both premium ceramics that last a long time, and cut aggressively. The 947As are cheaper but designed for low pressure (i.e. hand pressures, not machine pressure) grinding. The 984F's are better for alloy and hardened steel. I can grind a handful of pocket knife or titanium blades per belt.


Might want to check them out elementfe, they're X weight.
 
Funny, but in my experience, those bluish gray Hermes fine grit belts may the only ones they make that are worth a hoot.
RangerBobTX said:
Buy better belts. I hate the klingspor j-flex belts; they have a huge bump at the seam. Try the Hermes j-flex belts from Tru-Grit. They are far better. Also the gator structured abrasive belts in a/o are fantastic. My progression is 50 grit Blaze, A160 Gator, A65 Gator, A45 Gator...then 320 EDM stone, 400 EDM stone, 500 grit redline, 800 grit redline, pull on a Scotch-Brite and done. That easy!

Bob
Click to expand...
 
After the 120 Blaze I switch over to Norax U264 belts (structured abrasive). I like them because they stay really flat on the platen. I usually grind up to X16 which is about 1200 grit.
 
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