speeding up the KMG...?

rfrink

rfrink

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Aug 1, 2000
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Recently I've had several knifemakers contact me about speeding up thier KMG's upwards of the 5200fpm that the Baders run. The inquiries came from guys who replaced thier Baders with KMG's and were used to the higher speeds. Since the KMG was designed for knifemaking..it has slower speeds than the other belt grinders.

The question is: Do you want faster speeds?

It is a simple fix....in the past, I've made a 6" diameter drive pulley to replace std 4". This increases the typical belt speed from about 3400 ft/min to 5200 ft/min. If there is enough interest for the faster speeds...I'll stock the shelf with 6" wheels.


Whattaya think...?

Rob
 
I'm more than happy where it is now, and don't use the high speed that much anyway.
 
Rob,

I don't use a KMG, but it will be the next grinder I buy. I run my current grinder at about 5450fpm and have recently been considering upping that speed, I like the grinding to go quickly, and I can grind most things well with a light touch. I do have a DC motor on mine, and technically could slow it down pretty easily (I've actually got all the speed control components, just haven't wired it all up) but speed is king in my shop!

I'm used to running a fast grinder, and when I use slow grinders I feel handicapped by the lower speed.

Tony
 
Please correct me if I'm wrong (or using bad formulas)...I'm kinda stabbing in the dark here...couldn't find any info after a few searches...


I am running a 2:1 ratio. 5" pulley on the motor, 2.5" pulley on the drive shaft. So that would mean that my 1725 rpm motor spinning at 100% speed is spinning the drive shaft at 3450 rpm. (so far so good?) Then on the other side of the drive shaft is a 4" wheel which (using 3.14 * Diameter * RPM / 12 inches) gives me about 3600 fpm. Is that correct?





Anyway...more speed can't hurt - you could always slow it down, it doesn't affect the ability to have slow speeds. Honestly, I would have purchased a 6" or 7" pulley if I had thought more about it.
 
I can see where the speed would hurry along production but would that reduce control for the average maker? Could you make a larger pully system similar to the 3 step pully I have?
 
Rob,I hog fast and would not mind it being faster but I only use speed for the hogging part when I get into the touchy parts of my grinding I really slow it down....You could make a larger drive wheel like you are thinking and let it up to the person what size wheel they would like for there type of grinding...
 
Rob,
Besides grinding faster, some of the ceramic belts need the extra speed to be able to get the full potential from them. As soon as they are available, I will get one. If it works out like I think it will, I will probably convert my single speed with step pulleys over to variable. Bill
 
Hi Guys,
I understand the need for surface speed but surely it effects the heat build up and the belt life too?
I do not have a variable speed setup and I actually slowed my home made grinder down by making a smaller pulley.(8" down to 7")
True, I am by no means a good grinder yet so I find it more comforatable when things are moving a little slower, especially with the difficult parts.
Just wondering.

Mike
 
My VFD will allow me to go up to 80hz, meaning a 25% overspeed of the motor. At that speed I figure I'd be getting 4250sfpm. The 36 grit Cubitrons seem to hog 01 better at that speed than at 60hz/3400sfpm. I'm not sure I'd want to go any faster as one slip and I could lose a knuckle!
 
Just have to watch out on the motor....the bushings are sized according to the maximum rpm. On some motors, that can be a real problem.
 
Yeah, It's a 2HP Leeson I don't want to ruin. When I first tried it, I noticed the motor warmed up a bit. These days I'll bring a small fan in to blow on the motor and it seems to run nice and cool. Besides, I'm not usually hogging for too long at that speed!
 
I started making them. The material was delivered yesterday and I was able to get the CNC set-up and programmed for the 1st operation. If things run smoothly I should be able to set-up the final operation this afternoon and will have the wheels ready to ship. They will cost $74 ea.

I am running a 2:1 ratio. 5" pulley on the motor, 2.5" pulley on the drive shaft. So that would mean that my 1725 rpm motor spinning at 100% speed is spinning the drive shaft at 3450 rpm. (so far so good?) Then on the other side of the drive shaft is a 4" wheel which (using 3.14 * Diameter * RPM / 12 inches) gives me about 3600 fpm. Is that correct?
Click to expand...

Yes!! that is correct. A 4" wheel is about 1 foot in circumference... the belt speed is the same as the RPM of the drive wheel. so if you spin the drive shaft at 100revs per min....your belt speed is 100ft per min.

With a 6" wheel your belt speed faster by 6/4...or (6/4) X RPM

So if the drive shaft is 100 rev per min...the belt speed is (6/4) X 100 = 150 feet per min. ...and so on.

Fun with math!!!

Gotta go..I'm making wheels today.
 
I'm for the slower speeds! Maybe I'm just getting to be a old fart, and am slowing down, but I worked for a lot of years on a factory square wheel that ran 4,600 sfpm before I got enough sense to put a slow down pulley on it.

Now a days I have the KMG set up with variable speed, and rarely every have the controller set past 60%. Belts last longer, mistakes are minimized, and there certianly not as much wear and tear on the machine.

Just my thoughts..
 
All done! I just finished a batch of 6" drive wheels and put them on the shelf ready to ship. As with all of my stuff.....if you don't like it....please return it to me for a full refund.
 
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