Variable Speed Worth The $$$$ ?

S

Satchmo

Joined
Jan 11, 2005
Messages
56
Hi Everyone
I am a newbie to posting and have been making a few knives for a while.
Hope this has not been posted before, but I need to find out a few things.
First I am planning on purchasing a KMB grinder at the end of the week. Everything I read on the forums, says the variable speed is the way to go, but
I have not read anything saying what the advantages and uses are that would justify spending that much more money on a controller and motor listed on Rob's site. Also, is it that much better to go with the 2 hp..220 V input, has I would have to make up an extension cord to reach to my 220 outlet.
Also, wheel size? is the 10" serrated wheel the way to go?
I had a local person state that 12 or 14 is even better and that I could get a smaller wheel in the future as I definitely interested in learning to do folders later.
Seems like a great bunch of people on this form and I am looking forward to posting in the future. Your thoughts on this are much appreciated
BTW, if anyone in the Central Florida are is willing to share a few things on folder making I would be happy to compesate for their time.
 
Maybe I can help...

Satchmo said:
Hi Everyone
I am a newbie to posting and have been making a few knives for a while.
Hope this has not been posted before, but I need to find out a few things.
First I am planning on purchasing a KMB grinder at the end of the week. Everything I read on the forums, says the variable speed is the way to go, but I have not read anything saying what the advantages and uses are that would justify spending that much more money on a controller and motor listed on Rob's site.

There are many differing ways to go as far as what motor to buy, etc, but know this: Having the ability to slow down your belt speed is priceless. Speed control at your fingertips allows for more concentration to be spent on grinding your work, and not in what pulley groove you have your v-belt in at that particular time. A variable-speed grinder is the quintessential tool of any knifemaker.

Also, is it that much better to go with the 2 hp..220 V input, has I would have to make up an extension cord to reach to my 220 outlet.

It's better, but don't run your extention cord too far, less you'll draw more amps than the rating and then you will be in trouble. Keet the power cord short if you go with a 240v system, and run a new circuit to your grinding bench with a dedicate breaker.

Also, wheel size? is the 10" serrated wheel the way to go?

You'll be happier with the 14"

I had a local person state that 12 or 14 is even better and that I could get a smaller wheel in the future as I definitely interested in learning to do folders later.
Seems like a great bunch of people on this form and I am looking forward to posting in the future. Your thoughts on this are much appreciated
BTW, if anyone in the Central Florida are is willing to share a few things on folder making I would be happy to compesate for their time.
Click to expand...
 
Welcome to Bladeforums!:D


As for using variable speed, it's a bit hard to explain if you haven't used a belt grinder at it's single full speed before.
Being able to slow the belt down when finishing blades, after heat treat is so nice compared to single speed, or three speed pulleys that it just doesn't compare. Many people who have never used one, and don't want to, just won't see the value of it, but those that have used them, won't go back.

You can go DC variable speed, or AC variable frequency drive(just one name).
I have all DC stuff on my grinders, but if the current choice of AC VFD's had been around(or if I'd known anything about them)I would have gone that way. You can get by with less torque loss on the AC system, than the DC.

AC VFD is also less expensive. Here's a link to a place with very good prices. On the front page, look at the one, and two HP units for $299, and $397. I doubt you would need more.
http://www.dealerselectric.com/

Those are complete units. And 220V is a must.
A DC unit complete will run way more than that, new.


Edited to add; I have 8, 10, and 14" solid contact wheels, but if I had to choose just one, I'd get a 10" solid. I do use the 8" quite a bit when grinding, and you will need one too, eventually. I haven't used the 14" yet.
I prefer solid wheels, as I feel I can get a better finish with them, and they don't vibrate as much as serrated, but there are plenty of excellent makers using serrated. It's just your choice.
 
Good info above.
For me it's variable speed all the way, cost more up front but priceless down the road.
Also if I were hollow grinding I would use the largest wheel I could get, even for folders.

Don Hanson lll
 
It won't be worth it if you've never tried one. But once you've had it, you'll thank your lucky stars....




lemme add.....the reason it's so nice to slow down after HT is that a fast moving 400 grit belt can really screw up a nice grind fast. Sure, it takes longer to get it finished, but it's worth it.

Last few knives I did, I had the belt moving at 600-700 rpm....
 
I have been keeping up on things here without posting. Great forum!!!!! But I have to ask a question that I have not seen yet. Does the variable speed motors allow you a slower speed that a three step pulley from Beaumont Metal works on the KMG grinder with a 1725 RPM motor? And if so, how much slower? Also do you loose much horse power at the slower speeds? Thanks for any answers!!!!!
GARY
 
Yes!!!!!!! ;)

You'll never get those micron belts slow enough to do the fine stuff if'n ya can't slow 'em down. :)
 
HOGCAT said:
Does the variable spped motors allow you a slower speed that a three step pulley from Beaumont Metal works on the KMG grinder with a 1725 RPM motor?
Click to expand...
The three step pulley sytem gives you:

700 rpm
1700 rpm
3500 rpm

(according to Rob's website)


I've ground at all three of those speeds and it is perfectly fine for knifemaking. If you're on a budget, it's a great compromise.



I've found that I use these speeds most:


600-700 final finish
1600-1800 general post-HT grinding
2200-2500 general pre-HT grinding
3500-5000 hogging (depending on belt & steel)

Others will certainly have different speeds they like....these are just the ones I'm most comfortable with at my skill level. YMMV
 
HOGCAT said:
Also do you loose much horse power at the slower speeds?
Click to expand...
depends on the motor....

There are many different types. There are certainly motors that keep HP consistent. Others vary with the applied voltage.


Power (HP) = Current (Amps) * Voltage (Volts)

Motors that keep the HP consistent will have to vary the amps as you vary the volts (which is how a VFD works....varying the volts to increase the frequency output of the drive).
 
Hello from another newbie. I said I wouldnt answer questions I wasnt sure about, but I think I can feild this one. Variable. If you are going to make alot of knives, invest in good equipment, and care for it. Fast stock removal as is acheived with a single speed high rpm grinder, belt or whatever, can cause hard spots, which, although removed in the final stages of heat treating, would be best never present. Also, work and in some steels air hardening if left uncorrected with an annealing can be hard (hey, sortof a pun) on your expensive stuff. I should add, I have only my experience to go on, Im sure there others who could give better reasons to go with variable speed. Respectfully, Levi
 
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