How many blades do you get out of a 400 grit belt?

Nathan the Machinist

Nathan the Machinist

KnifeMaker / Machinist / Evil Genius
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Okay, I'm going to jinx my new "Grind Fu" but I've got the hang of grinding (not too bad for a "turn crank"). I can set the KMG up on high (these are four sheave pulleys, so high is high), put on some really thin nitrile coated cotton gloves and can grind the mess out of some knife blanks. They're finally turning out nice in a reasonable amount of time.

I go from the mill to the grinder and start with 120. I get good life out of my 120 and 240, but the 400s don't last long. The sanding belts don't wear out on-off like a light switch, but gradually taper away. I could use one 400 grit per blade or stretch it out over half a dozen. I'm wondering what most folks get out of their 400 grits?

I'm using a Klingsor 309 J flex, they're about $3.00 a pop.
 
Nathan,

I use the cheapest AO belts I can find; as long as they run true.

What sfm are you running the 400's at? You want to slow them down, to a crawl. They load up very quickly when run at the higher speeds.
I run my 50 grit ceramics at 5200 sfm. [flying:eek:]
When I get into the 120 range and below, the speeds should be less than 25percent of the course grit speeds.
I can almost count the revolutions when theres an 800 grit belt on the machine.

Some of the 400 grit belts, around this shop, are as old friends.;)

Fred
 
i have some well used 400 grit belts that still cut fairly well. i use some even older ones for a finer finish if i'm going for a mirror finish in the end. try a 3m belt the next time or get some of the norton belts from tracy mickley. they hold up very well.
 
I use Norax, and can get a couple blades. But keep in mind, I'm using a disc sander in between grits on the Burr King/KMG and that helps a lot.

For hollow grinding, I go from a 60X ceramic to a ~400X Norax and only get about one blade per belt.
 
I am glad you ask this Nate. I have been wondering the same thing. I run my at the same speed as the course ones. I think I will try slowing them down.
 
Mike Stewart of BRKT gave an interesting example comparing A-2 and CPM3V. There was a very LARGE difference ! If you look at the varous types of carbides you'll find differences in grindability. Iron carbide easiest , then Cr .When you get to Mo, V, W you get very difficult to grind in comparison. There's no surprize then that so many tool steels are based on Cr !
To answer , it depends. 1084 long life , S30V short life.
 
When I'm careful about "recharging" the Norax belts frequently, I can get about one knife per belt. But when time really counts, I pretend my belts are free and switch as soon as the steel begins to heat up quickly. It's amazing how much more accurate my grinding is when the belts are very sharp.

But since I throw out the old belts only once a year or so, it's paid off in going back through them when I have a short task and don't want to start a fresh belt.
 
I get one knife out of a 400, sometimes I get one side. The 3M belts tend to last longer for me than other AO belts in that grit. I've been grinding 50, 60 or 80 grit and straight to 400 for a bit now and I've been happy with the results. You have to spend a little more time on the 400, but you cut out using up a 120, 240 and possibly a 320. Sometimes I do like to go to a 120 first.
 
It sounds like:
A. 400 grit belts don't last very long and sometimes getting more than one blade out of one is good.
B. I need to slow it down to extend belt life. 5000 SFM is too fast.

It makes sense the belt life is dictated in a large part by what is being ground. These are fairly small, D2, not hardened. I'm going to shoot for 2-3 blades per belt.

Thanks all for the input, this is a great forum.
 
I get one side out of a 400 grit belt.i honestly treat belts as if they're free!! but,damn it they're not :p if it was'nt for the cost of belts it wouyld be possible to make a few bucks off this knife making thing. i use cheap 240 and 400 grit belts.977 cubitrons for roughing!
 
AcridSaint said:
I get one knife out of a 400, sometimes I get one side. The 3M belts tend to last longer for me than other AO belts in that grit. I've been grinding 50, 60 or 80 grit and straight to 400 for a bit now and I've been happy with the results. You have to spend a little more time on the 400, but you cut out using up a 120, 240 and possibly a 320. Sometimes I do like to go to a 120 first.
Click to expand...

I've tried this too, and sounds like it's how Nick approaches it. I saw the Steve Johnson video, that's how he does it too. I tried it once but used a lot more belts than your experience. I'm probably working it too hard or just too lazy to let the belt work long enough. I'll give this a shot again, as I think it's a very good way to make sure all prior grit's scratches are removed.
 
I slow down my fine grit belts to the point that it wont even spark the steel, and i get a decent good long life out of them, i usually start at 60, then to 120, heat treat, then go straight to 220 and then whatever finishing belt i'm using.
 
I look at belts much like the way gears work in a manual transmission, jumping gears is hard on transmissions, and so it is with belts.

Like shifting, I go through steps in the grind. For the best belt life I work my way up from coarse to fine grits. Starting at 50 or 60 grit, then onto 120, 220,320, 400, then the fine microns like 9 mic and finally onto the polishes.

If I am going to mirror polish then I go through the steps there. After the micron belts, then I use the black compound, followed by the green and then the fine white compound using a separate buffing wheel for each compound before calling the job done.

All these steps seem like alot of work, but actually it reduces the amound of time and work that it takes to do the job.
 
i hog with a 60 blaze belt then go to a 220. And i guess this is where i leave the pack. I hit it with a 400 gater belt. Man these last forever. I bought 5 400 grits and 5 600 grits. And i still have not worn one out. Amazing belts for the money. So then i go over it with my 400 grit j weight belt. I heat treat after the 220 grit belt. Works great.
 
ddavelarsen said:
I've tried this too, and sounds like it's how Nick approaches it. I saw the Steve Johnson video, that's how he does it too. I tried it once but used a lot more belts than your experience. I'm probably working it too hard or just too lazy to let the belt work long enough. I'll give this a shot again, as I think it's a very good way to make sure all prior grit's scratches are removed.
Click to expand...

Hi Dave, I read about this on knet a while back and learned it from Steve Johnson's posts as well. I started doing it just before I watched his video. I've also been using cork belts like he does and follow his directions mostly. I've had the opportunity to handle and examine a few of his knives now and if there was any doubt before, it was all taken away with the first one I picked up.
 
You are a lucky man! Closest I've come to that are some good pictures. :)

Mostly I've tried it with flat grinds, do you suppose this technique works better hollow grinding? I have a project coming up that'll be hollow ground, I'm going to give it a try again. I have the cork belts too, what a great investment those were. I was never sure what they meant by breaking them in - using the flat or an edge of a piece of steel for example, but I've been using them so long now, I'm confident they're "broken in." :D
 
ddavelarsen said:
I've tried this too, and sounds like it's how Nick approaches it. I saw the Steve Johnson video, that's how he does it too. I tried it once but used a lot more belts than your experience. I'm probably working it too hard or just too lazy to let the belt work long enough. I'll give this a shot again, as I think it's a very good way to make sure all prior grit's scratches are removed.
Click to expand...

I had trouble the first few times I tried Mr. Johnson's techniqe but after a few blades it all started to work out alot better.

I sometime use the same 400 grit belt on four knives, and that is going straight from 60 grit heat treated CPM-154 blade.

Give it another try Dave, you'll like it.

Charles
 
One question that keeps occurring to me is wheel diameter between the different belts. The 60 grit and cork belts would have a larger diameter than the 400 grit, has this been a problem for anyone? Naturally not an issue flat grinding, but curious about hollow grinding. Would wheel diameter affect this much? I use a 10" wheel.

Getting four knives out of one 400 belt sounds great! I use Norax (X30, probably more like 500 grit), and its "rechargeable" feature should help that too.

Slightly off topic, can anyone suggest a good source for EDM stones for recharging Norax belts? (I keep hammering Tracy Mickley to stock em, maybe if others started harassing him (Tracy has tons of free time) he'd give them a try. :D)
 
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