Maximum/Minimum grinder speed?

D

David LaFerney

Joined
Feb 4, 2015
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122
What are the maximum and minimum FPS speeds that you usually normally use on your 2x72 grinder. Also if you had to use one speed for everything what would that be?

I'm sure this has all been said, but what I have found has been somewhat conflicting.

Obviously I'm building a grinder. I know, I know - but the thing is I like to build things.
 
You are going to get lots of different opinions. My grinder runs about 4500 sfpm. That is really fast. It's great for profiling and heavy grinding. It's tricky doing fine work. If you can, built a variable speed. Either a 3 phase motor and a vfd or pulleys. If you only want one speed I would shoot for 2000-3000 sfpm.
 
Stacy is right, 5,000 FPS (second) would be screaming fast, even for a pro. I think Beaumont Metal has a good selection with
the KMG, this set-up produces 3 ideal belt speeds of approx: 900, 1800, and 3600 ft/min.
Click to expand...
for most folks, especially hobby knife makers. That is for a step pulley/belt setup. As an occasional hobby maker I've come to really like a VFD drive with 300 SFPM to 4,000 SFPM belt speeds.

Choice of belts speeds will vary with level of proficiency, AND if it's the only grinder available.

Ken H>
 
As a normal procedure, my grinder is run between 500SFPM and 2000SFPM.

corrected to read SFPM, not FPS...dang auto-correct!
 
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Thanks for the responses - even if they are all over the place. And actually I have variable speed capability (treadmill motor and controler) but I still needed to know that speed range to calculate the pulley sizes. The question about the most used single speed is to make sure that I don't give up too much torque where it is most needed in order to achieve a rarely used very high maximum speed. Although the way the controller works it increases voltage under load to maintain a set speed - it might not be a problem. I am having to enclose the motor to keep metal dust out of it, but that's not a very high bar.

So I think I'm going to shoot for a max speed of about 3600 SFPM initially.
 
David - 3600 SFPM will do just fine for profiling. At the lower speeds you don't need much torque at all because the grinding at that speed requires a light touch. At the high speeds where you're hogging off metal is where the torque requirements come in.

Good luck and have fun
 
Modern ceramic belts are built to run at high SFM as well as high pressure. The lower grits, like the 36, 60, 80 are designed for this type of operation. This type of belt tends to round over instead of shear at lower belt speeds. James Poplin of Pop's knife supply told me its not uncommon for production grinders to run @ 7,000 SFM. My main grinder, which is a KMG runs at 5400 SFM powered by a 3 HP motor. These numbers are not an absolute necessity to be able to run ceramic belts, these are numbers to get the optimum performance when using ceramic belts.
 
Fred is right about using ceramic belts - they do like high speed. I've used a couple of ceramic and they just didn't work so good for me as I didn't run them fast enough, nor really put enough pressure on them. With a 36 grit AO belt running 4,000 SFPM you can really throw some sparks and move some metal - hard to imagine how many sparks a 36 grit ceramic at 7,000 SFPM would thru. Lord - I'd hate to get a finger slipped into a belt at that speed!!!

Ken H>
 
The responses in this thread really surprise me. For comparison, the non-variable-speed Burr King 960-272 runs at 5400 SFPM, and can be ordered from the company to run at 4400. Their model 760 runs at 8000 (or special order 4000). Obviously, these are pulley drive machines, so you can change the speed by installing a different pulley combo... but I would never have guessed that you guys are running so slowly. Over on the machinist side, most machine shops I know that use belt grinders really like 7k/8k SFPM -- it makes the work go quick!
 
Catalytic - you're right, "IF" you're wanting to remove a LOT of metal using 36 grit then high speed is certainly the way to go. BUT - in knife making there are places where much finer grits are required. For the person who has 2 or 3 grinders, sure - you'd want one that was set for high speed of 5,000 SFPM or so and one grinder setup for using fine grit down at much slower speeds. As Stacy says, a range of speeds are required for knife making. For a person with only 1 grinder, there is a need to have a slow speed below 1000 SFPM, and I've found since using a VFD I use speeds down around 300 SFPM at times for fitting handles.

It takes a real expert to finish a bevel at 5,000 SFPM. On top of that, a 400 grit belt just doesn't work as well at that speed.

Ken H>
 
not to dig up an old thread, but I figured it would be better to dig this up than to start a new one. So with my setup I'm putting together I've done the math and this is what I'm looking at;
Motor RPM - 3450
4 Step Pulley system
Slow 2:6 - 1150 shaft RPM
Fast 4:3 - 4,600 shaft RPM
4" input wheel yields following SFPM speeds
Slow - 1,204 sfpm
fast - 4,817 sfpm

so here is my question - will the 1200 sfpm speed be slow enough to do fine work and work on a small wheel without problems or should I look to add another step to slow it down further? On the fast side, I think 4800 is more than fast enough and would only be used for hogging.

thanks in advance!
Adam
 
My grinder runs from 300SFPM to 9000SFPM and yes I do use the faster speed. When I profile thick stock I use the rest and crank the speed, even a used blaze belt will remove an amazing amount of material at thoes speeds. But a word of caution it will eat anything you put in its path. The other day I had a belt come off. The belt was causing some vibration and I turned around for a sec and the tracking wheel vibrated and turned and adjusted the belt right off the grinder. I tell you what that belt shot across the shop and up the forge bench and just kept going. Hit the rafters and came back at me. But that being said I normaly do my main grinding between say 2000 and 5000. When I use gator belts I run them slower at around 1500 or even slower depending on what I'm doing.
 
Ken H> said:
Catalytic - you're right, "IF" you're wanting to remove a LOT of metal using 36 grit then high speed is certainly the way to go. BUT - in knife making there are places where much finer grits are required. For the person who has 2 or 3 grinders, sure - you'd want one that was set for high speed of 5,000 SFPM or so and one grinder setup for using fine grit down at much slower speeds. As Stacy says, a range of speeds are required for knife making. For a person with only 1 grinder, there is a need to have a slow speed below 1000 SFPM, and I've found since using a VFD I use speeds down around 300 SFPM at times for fitting handles.

It takes a real expert to finish a bevel at 5,000 SFPM. On top of that, a 400 grit belt just doesn't work as well at that speed.

Ken H>
Click to expand...

For any noobs here I can relay this experience from knife making, Generally, There's that word again! ;)

The Finer of grit belt you are running, the slower you want the machine to spin. I can give you percentages off of my two 2 x 72 machine controllers.

36 Grit, Balls out or 50-100% of throttle, 60Grit around 50% 120Grit 50% or less, A/O 600 Grit 40-10% 1200 Grit/15 Micron 30-5%


To put it in plain speak, Each grit will have a SWEET Spot of speed for you, your belt material choice, Grit and the way you Grind or SCULPT steel, woods & synthetics.
Have fun and stay safe!
 
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