Natlek - higher speed?

K

Ken H>

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Dec 31, 2011
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Natlek, you might not remember a year or so ago when you were encouraging higher speeds for grinding? At the time my grinder with a 4" drive wheel was max'd out around 4,000 SFPM, and I mentioned I never used over 3,000 SFPM very often. Then I started grinding profiles and start of bevels at 4,000 SFPM and, yea, it was good. Not as hard to control as I expected and for sure went faster. Well, yesterday I put a 5" drive wheel and am now max'd at 5,000 SFPM and I expect to be grinding at that speed some.

See what your pushing for "more speed" grinding has done? It encouraged me to push myself and learn more. Thank you.

Ken H>
 
I'd like to hear your experience. Do you grind pre/post heat treat? What belts and grits work well? Etc.
 
I m glad to hear that higher speed work for you Ken :thumbsup:5000 SFPM are 25 m/s which is probably max. speed will work with free hand grinding . You are still 5 m/s below the minimal recommended speed for carbon and stainless steel ;)
I must find way to make one grinder with less noise on high speed ......on 50 m/s mine sound like F-15 ..........so I can t use that speed in shop , to loud ! I can t wait to finish my big wheel grinder , with somewhere around 40 m/s belt speed , I hope it will be reasonably quiet .
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For grinding blades <1/8" I grind post HT, mostly AEB-L and 14C28N with some carbon steel 'n Damascus. I tend to use VSM XK870/760 belts in 50 to 60 grit.

Natlek, what belts is the chart above for? Do you have the whole page you could send to me as PDF or jpg? sailingtoo at gmail?
 
Ken H> said:
For grinding blades <1/8" I grind post HT, mostly AEB-L and 14C28N with some carbon steel 'n Damascus. I tend to use VSM XK870/760 belts in 50 to 60 grit.

Natlek, what belts is the chart above for? Do you have the whole page you could send to me as PDF or jpg? sailingtoo at gmail?
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I will try to do that , no problem .
Ken , you grind free hand ,right ? Do you ever try belts designed for low pressure ? With free hand grinding i think they would work better and last longer . In essence, the difference is only in the number of grains per square inch , for example .The biggest problem / I think/ with belts durability is glazing due to insufficient pressure...so maybe that belts will last much longer for you ?
Edit to add......what i think is you use as much pressure as you can while free hand grinding with ordinary belts so with new belts that same pressure would be higher . That should somehow be equal with pressure i can put on belt with my jig with regular belts ?
 
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I grind with a mix of freehand and jig.

I've mention that same issue of glazing a number of times, if you're not using high speed and high pressure ceramic belts are a waste of money - they'll just glaze over. Once I get a blade profiled, and the bevels started good I'll move away from ceramic to another belt - perhaps Zirconia or even AO belts for light and lower speed grinding. I've never tried 120 grit ceramic, just seems like 120 grit doesn't use high enough speed or pressure to keep ceramic from glazing?

I also use Ceramic 36 grit for cleaning up a Damascus Billet at as high a speed and as much pressure as I can get. Works really good.
 
any experience grinding wear resistant steels post HT at high speed? like Z wear
I've found that significantly lower speeds is more suitable for a wear resistant steel
 
That's a question for Natlek - I don't use those "high dollar" steels. I have to "get by" with lowly AEB-L type steels :)
 
This is actually an interesting topic for me as I've just changed from a 10-in drive wheel to a 4-in wheel and while I do have better control of the finish I have much less ability to "carve" out the initial shaping of the bevels. With the 10 inch drive wheel and faster belt speeds I could hog in and see where I was going and set the bevels pretty quick. With the 4-in drive wheel it seems I meander around a while waiting for the main bevels to appear and sometimes I just don't have the stamina or patience to wait for the main bevels to arrive.... And while my belts seem to last longer I'm not sure if they really cut any better after a certain point.... I do almost 99% of my grinding pre heat treat
 
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I'm really amazed when I see videos, including some of Natlek's, that show the sparks flying and the steel dust piling up, just hogging into that blade and shaping it out ! Some of the real pros that just go in there and"carve" their blades out in no time! Sometimes I fantasize about a gigantic industrial grinder that I can just barely touch my blades to and they're all ground and a moment!
 
Let me ask this, when grinding high speed, high pressure, are you guys changing the steel's color? I've heard this is not good to do, even before heat treat, especially to the blue range - unless you normalize first. Maybe Larrin Larrin could chime in on this though for some clarification.
 
In the case of overheating annealed steel when grinding typically it is a stress relief that is recommended rather than a normalize.
 
I can't see any harm in turning the blade blue in hard grinding Pre-HT. There is no grain growth or phase transformations at those temperatures. I have made a blade glow red in the area being ground when hogging off steel.

The addition of a Kool-Mist system will help with smoother grinding and belt life as well as eliminate overheated blades.

As Larrin said while I was typing, a simple stress relief of heating to red and letting it cool a couple times will make it fine if you are worried about the structure.
 
Stress relief has to do with reaching the recrystallization point (below critical) and thus letting the disruptions recrystallize and form even and stress free boundaries. It is done by heating to just below the critical point ( heat to around 1100-1200°F/600-650°C) and air cooling. For those doing it by eye in a forge, a dull red is all you want. Some only heat to "Black".
Normalization involves changing the structure to austenite, dissolving the carbides, and then re-forming pearlite as a more even grain size. The grain is not necessarily smaller, just more even. This is done at 1700°F/925°C. This is bright red to the forge HT folks.
Thermal cycling involves forming austenite and dissolving carbides, then forming pearlite. then martensite. This reduces grain and leaves the blade ready for final hardening. This involves steeping down from Normalization temps to just above critical and a final quench. The end result is fine grain martensite. This is done by eye and a magnet if using a forge.
 
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Larrin said:
In the case of overheating annealed steel when grinding typically it is a stress relief that is recommended rather than a normalize.
Click to expand...

Stacy E. Apelt - Bladesmith said:
Stress relief has to do with reaching the recrystallization point (below critical) and thus letting the disruptions recrystallize and form even and stress free boundaries. It is done by heating to just below the critical point ( heat to around 1100-1200°F/600-650°C) and air cooling. For those doing it by eye in a forge, a dull red is all you want. Some only heat to "Black".
Normalization involves changing the structure to austenite, dissolving the carbides, and then re-forming pearlite as a more even grain size. The grain is not necessarily smaller, just more even. This is done at 1700°F/925°C. This is bright red to the forge HT folks.
Thermal cycling involves forming austenite and dissolving carbides, then forming pearlite. then martensite. This reduces grain and leaves the blade ready for final hardening. This involves steeping down from Normalization temps to just above critical and a final quench. The end result is fine grain martensite. This is done by eye and a magnet if using a forge.
Click to expand...

Ahhh thank you both for the explanation... I don't do my own ht yet so haven't learned all the processes. That is some good info!
 
I got much faster at grinding with my 50x2000. It maxes out at 29 m/s and I also grind post HT.
I will run it on 80-100 percent speed for rough grinding, which really helps with large kitchen blades for adding taper and similiar.

I currently use Bora 7 40 - 120 - 180 grit.

120 and 180 will even last quite a bit if you do only last 10-20 percent of the grind with it.
 
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