Grinder Speed.

Diomedes Industries

Diomedes Industries

Joined
Mar 19, 2007
Messages
7,437
When I make a knife - I start at 36 grit and about 50 percent power on my 2HP Brodbeck grinder. Each belt progression I turn the grinder down a little ending around 30% speed.

I have seen people run FAR faster than me.

Can you all give me the lowdown on speeds and the theory of how fast to run?

Thanks
 
Most ceramic belts need speed and pressure to hog steel. Run low grit ceramics fast. Slow down when you switch to zirc and AO belts. The finer the grit the slower the speed. By 400 grit the speed should be about half what it started at.

The starting speed depends on the grinder setup and the person grinding, as well as what material you are grinding and what condition it is in ( HTed or un-HTed).

Some grinders will run so fast it scares me to watch them. Others are much slower. Find the fastest speed you are comfortable working at and make that your hogging speed.

Adding a Kool-Mist system to the grinder will really improve the speed and eliminate a lot of slower speeds.
 
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I run most belts at 100%. Most of these abrasives are designed to run at high speed. I generally lighten the pressure as I go up in grit. I run Scotchbrites at 60% and my sharpening belts at 20%.
 
Running a 2hp Ameribrade that goes from 1-11 on the VFD.

I run my VSM 36 grit ceramic at 7 (4,200 sfm) with a carbide flat platen. This is a nice speed for fast metal removal but it also lets me control how much I’m taking off quite well. Depending on the knife I’ll do 80-90% of my grinding here.

I step up to a 60 grit and run the grinder at 6 (3,600 sfm) and when I get to 120 grit I run at 5 (3,000 sfm).

After 120 I switch to a rotary platen that has a hard platen backing. It’s recommended to not run that fast than 5. I usually run it at 3 (1800 SFM) for my finishing passes regardless of grit.

If I’m profiling blades or handle material I’ll run 8-10 on the speed.
 
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Am I the only one using "slow" speed?

I grind post heat treat. I start at 60 grit around 30%. Then 120 grit around 20%, and usually stay there till I am happy.

This takes me quite awhile...am I too slow?...lol!
 
I still consider myself a rookie so keep that in mind. Just this moment finished profiling 6 steak knives with 24 grit Norton R980P at full speed. The remainder of my work is much slower for several reasons. Mistakes are smaller and heat are the 2 main reasons for slow speed, for me.
 
AbLonewolf said:
Am I the only one using "slow" speed?

I grind post heat treat. I start at 60 grit around 30%. Then 120 grit around 20%, and usually stay there till I am happy.

This takes me quite awhile...am I too slow?...lol!
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I the world of machining there are optimal feeds and speeds and I would imagine they play a role in grinding as well.

Too fast and you’re burning up belts to slow and you’re wasting time and not taking advantage of abrasive properties.

The biggest factor between makers is the hands doing the work. I’ve gotten a pretty good system down where I can go from no bevel to finished bevel in about 20 min. I’ve also gotten a system down where I can grind usually 5 3 inch magancut blades (64 Hrc) on one 36 grit belt. I know other makers that use the same belts and it takes them longer or more belts to do a similar amount of work.
 
Lets not forget that the position of the knob on the vfd does not dictate the speed of the belt. The RPM of the motor, whether or not the VFD is double sped and the diameter of the drive wheel determine the belt speed. So comparing the position of the knob when you're grinding to the position of the knob when someone else grinds is comparing apples to oranges. It isn't relative unless all else is equal.

If we want to compare we need to be talking in surface footage of the belt.
 
Contender Machine said:
Lets not forget that the position of the knob on the vfd does not dictate the speed of the belt. The RPM of the motor, whether or not the VFD is double sped and the diameter of the drive wheel determine the belt speed. So comparing the position of the knob when you're grinding to the position of the knob when someone else grinds is comparing apples to oranges. It isn't relative unless all else is equal.

If we want to compare we need to be talking in surface footage of the belt.
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Updating my response with the SFM
 
AbLonewolf said:
Am I the only one using "slow" speed?

I grind post heat treat. I start at 60 grit around 30%. Then 120 grit around 20%, and usually stay there till I am happy.

This takes me quite awhile...am I too slow?...lol!
Click to expand...
don't worry, i grind slower speed as well, post heat treat
 
All of this makes sense and something to take into consideration.

Stacey - I added my mister today and ran it. That really changes my higher grit speed idea for sure.
 
This post demonstrates why there is no correct answer to "Which belt is best?". Every grinder is different, and everyone grinds a little differently with different pressure and speeds. I have my favorite belts, but will still try new ones and even retry ones I've dismissed in the past.
 
When grinding soft material with a 10”wheel (NRT grinder), and 50 grit blaze I run about 80% most of the time. Once I get close to what I’m looking for I turn it down to 50-60. Next 120 ceramic I run at 50-60. 220 ceramic down to 40 maybe less. This is as far as I go pre heat treat. Post, fresh 50grit at 60%. Then 120 ceramic at 50 followed by 220 ceramic. Then 220 ceramic at 35.
If I’m doing a regrind, 60-80 on fresh Blaze, dunking every pass. Followed by same as above.
Rotary with radial platen, I never go above 50% and rarely go below 120 grit. All I grind 95 % of the time is 3v. As stated above everyone and all machines are different. Find what is comfortable
 
I'm always messing with the vfd. Full tilt on the Ameribrade for hogging with 24-80 grit if I am up to it... all the way down to just barely moving for delicate swedges. I do go slower as the grits go up. I ground about 5k knives on my KMG 3 speed and now that I have a VFD I will never go back.

I profiled 400 knives the other day on full tilt with one 80 grit belt. They were already at final shape but if I ran at 50% I bet I would have only done 50 or so before the belt glazed over. I don't like using carbide to unglaze a belt either, it messes up the belt too much at least for bevel grinds.
 
I went 4500 sfpm (full speed with my set up) comparing 2 belts on 64hrc cruwear when rough grinding. I could get 1 belt per blade with both the actirox and the vsm 885Y (both of which are 36 grit). I was reminded of the importance of pre-grinding bevels on larger batches of thick fixed blades (.200")😅1000006537.jpg
 
X% on the VFD is not really a useful measure here. It'll depend on the output frequency of the VFD, the specific motor, and drive wheel size, plus possible belt slippage
I have a 4 pole 1440RPM motor that i usually run at full power on a 60hz output (i think), for about 13.6m/s (2680 feet per minute?). So my 100% is slower than others partial output. If i switched to a 2 pole motor it be around twice as fast.

(also why do you lot specify distance here in units per minute? at least m/s are the base units)
 
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