Is variable speed on a grinder necessary?

mnavarro

mnavarro

Joined
Nov 21, 2013
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288
I'm in the market for a new grinder. I have weighed all the grinder options. I need to know from you more experience makers if variable speed is necessary? I believe I'm going to pull the trigger on the kmg 2 hp grinder with the 10 in wheel and the flat platen. Any opinions?
Thanks
 
No, it's not necessary. None of my belt grinders are variable speed. I wish they were, though.
I had to learn to grind carefully on a fast-moving belt. Variable speed wasn't an option in the dark ages.
Of course I walked 2 miles to school, too. Uphill. Both ways.
 
No it's not necessary as Bill said, but you will be so much happier you have one later on down the road if you get one. As they say, "Buy once, cry once." I've learned (still learning in fact) the hard way and have cried quite few times now :D lol.. A number of times I've been in too much of a hurry and would just get what I could afford at the time so I could hurry up and "go out and play", and have ended up regretting it later on. However, I didn't have a steady income for most of those things (and very little when I did), so I don't feel too bad, but if you do have an income, just save up a little bit longer if ya need to to afford the variable speed, you will not regret it. :)

BTW, I still don't have variable speed, but I sure wish I did. But I'm glad I at least have a "slower" motor (1750 rpm as opposed to ~3600 rpm) with 3 step pullies, that way I can slow down the grinder down to a "relatively slow speed" compared to single speed direct drive grinders. I'd rather have the lower rpm motor with step pullies, but with variable speed, you get more range with a higher rpm motor.. anyway, just something to think about.

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ETA: Most guys here are saying they mostly use the high speeds for profiling and grinding bevels.. I can understand the high speed for profiling, and maybe for roughing in the bevels, but for getting them crisp, clean and tuned in, I myself still need a ways ta go to be consistant.. so the slower speed is a MUST for me. For some guys, grinding bevels seems to come more naturally after practicing a bit, but for others, not so much, and it can take much longer to get it "down".

I however, usually end up taking too long when it comes to finishing most of my knives, so I pretty much loose most of my muscle memory by the time I start grinding my next ones, so that may be why I am all for the slower speeds you can get with a VFD. But you will shorten your learning curve by starting out with slower speeds so you can better observe what is happening as you grind. Just one more thing ta keep in mind ;) .

~Paul
My YT Channel Lsubslimed
 
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Once you have variable speed you will want it on all your equipment. I don't think I could go back to a fixed speed. Pay a little more and have the option...you will not regret it. Larry
 
I have one variable speed machine in the shop and it is quite useful. That said, I do all my grinding and handle shaping on the highest speed anyway. I rarely use the variable speed machine. YMMV.
 
My machine is 3 step pulley and a 1750 motor. I use all 3 speeds.

A couple knifmaking friends have VFD's on their machines and rarely use it and leave the machine on high.

It really depends on your style of grinding.

I keep thinking I am going to install a VFD on my grinder but just have not found I need to.

Also one of the first parts of using a VFD is not having VFD electrical issues at the more inopportune times.
 
The three speeds on the kmg are more than adequate. I have a three speed kmg and a variable speed little buddy grinder and still do 90 percent of my grinding on the fastest speed on the kmg. When using a small wheel attachment you do need the slower speed.
 
I had a 3 speed pulley setup on my first grinder and didn't feel variable speed was worth the money. A few months ago I built a new grinder with VFD drive and have had to "eat crow" - there is NO comparison. There is too many times I use the 2X72 to grind just a couple of thousandths, and that MUCH be done at a dead slow speed - 500 SFPM or so.

If you've decided on the KMG (great grinder) with 4" drive wheel, buy with no motor, but with the 56C mount. Purchase a 2hp, 3ph motor for $127 shipped, and a cheap Chinese VFD (NEMA 1 - about $130 shipped), either mount in enclosed box or put filters around the inlet to prevent metal dust from entering the drive. Then "IF" the NEMA 1 VFD ever fails, you'll have enough experience with variable speed grinder, spending the $400 for a NEMA 4 drive won't hurt so much!

I just can't imagine the skill level that allows grinding that critical point at 4,000 SFPM - and I've seen some pretty darn good knifemakers and they ALL slowed grinder down for that critical fitting places.

Ken H>
 
If you have only one machine VS makes sense. I have three machines, one is VS the other two are pulley machines. The 3hp pulley machine, which I profile and grind bevels on rarely gets slowed down. The one I use for shaping bone and other handle materials is constantly being adjusted.
With a bevel grinding machine, there is no substitute for speed and HP. A machine used for handles and softer materials there is no substitute for VS.

The solution is: buy two machines :) Just kidding. :)
 
Cliff Parker said:
For sure it is especially if you want any control at all.

Cliff
Click to expand...
Who needs any control? ;)

I profile on a wheel at near full speed, I grind with 36-80 grit belts at near full speed, but moving up to 120-400 grit I damn sure want to slow the belts way down!

But what the hell do I know...
 
After getting my first 2x72 grinder which is variable speed I can't imagine not having it. Actually I can, I had a Craftsman 2x42 before and I hated it. Way too easy for me to screw something up at that speed. I use mine more on the slower speeds than the faster ones now but that's probably because I'm still pretty new to this and I'm sure I'll speed up my grinding eventually. For handles everything I use seems to burn at fast speeds so that just means I had to do most handle work by hand before but now I can do 95% of it on the grinder by slowing it way down.
 
[sarcasm]My first grinder was variable speed. The speed would increase when you first turned it on, and decrease when you flipped the switch off. In-between, it had a single "holy-crap" speed. I remember actually sharpening a knife by flipping it on and off, and sharpening while it slowed down. It's not recommended but it worked.[/sarcasm]

It you're looking to build a grinder, you can always change the speed by changing the drive wheel. You don't have to have a VFD or belt setup to change the speed, and you can always change the motor and add a VFD later.
 
Atlas Knife Company said:
[sarcasm]My first grinder was variable speed. The speed would increase when you first turned it on, and decrease when you flipped the switch off. In-between, it had a single "holy-crap" speed. I remember actually sharpening a knife by flipping it on and off, and sharpening while it slowed down. It's not recommended but it worked.[/sarcasm]

It you're looking to build a grinder, you can always change the speed by changing the drive wheel. You don't have to have a VFD or belt setup to change the speed, and you can always change the motor and add a VFD later.
Click to expand...

I assume you had a foot switch

Cliff
 
IMO the answer is yes, IF you want to slow the belt down to speed up the process of certain tasks, such as shaping wooden handles so as to not burn the wood, or carefully touching up a plunge line, or cleaning up a bevel using a very fine grit belt. Having variable speed makes many tasks easier and or quicker. Variable speed is not however the only way to accomplish these tasks. Just easier and quicker and as others have said, most of my grinding is done at near or full speed.
 
LARRYZ10 said:
Once you have variable speed you will want it on all your equipment. I don't think I could go back to a fixed speed. Pay a little more and have the option...you will not regret it. Larry
Click to expand...

Those were my initial thoughts. Spend a little more up front and have the option available
 
I went from craftsman 2x42 to step pulley 2x72 to VS 2x72. Dramatic improvement at each step. Get the best you can afford. Like somebody up the page said, I'd rather have a VS grinder with a platen than to drop extra money on a 10" wheel.
 
Not only does my new grinder have variable speed - it has reverse!!
Which means I can grind standing on my head. :D

But I think I'll check with Don first.
He's forgot more than I know. :thumbup:
 
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