Belt speed rehash

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unky_gumbi

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Aug 28, 2009
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I have been going over older threads about belt speeds for grinders, and it seems that most makers here seem to agree that 5000 sfpm is where you should top out. Well I built my grinder up with a 3450rpm 1.5hp motor and a VFD. Using the formulas I have read and followed links to it seems I top out at 3615sfpm with my 4" drive wheel. Should I look into getting a 6" drive wheel which will bump my top speed up to 5423sfpm or just be happy where I am?

The lowest grit belt I have is a 60 grit zirc right now but on my next order I was planning on going to Norax belts with the lowest grit being U264 X200, supposed to be roughly the same as 75 grit. Does this make any difference in the speeds?

Thanks
George
 
You should be able to increase the speed thru you vfd by adjusting how high your hertz go chuch out you manual. This what I had to do and I have the same rpm motor & drive wheel as you.
 
I'm not too sure about the belt speed but I don't really like the Norax belts for stock removal, to me they are for finishing only. I think you will get the most grinding for the money with ceramic belts, they only cost a bit more than the zirconia and last longer. I really like the Norax belts for their ability to polish without removing stock too quickly, they are good for cleaning up grinds and then scratch removal. The "gator" belts are very similar and I prefer them. Everyone has their own style and I don't have many knives under my belt, this is just an observation I have made by experimenting.
 
Your VFD has a 2x speed adjustment you can do that Wayne has you do if you buy his 1725 RPM 3Ph motor. Not sure about running a 3450 at higher speeds though the 1725 will do 2x speed just fine.
 
Brett Mathews said:
You should be able to increase the speed thru you vfd by adjusting how high your hertz go chuch out you manual. This what I had to do and I have the same rpm motor & drive wheel as you.
Click to expand...

I am not much on the overclocking of things even if they are capable of doing it. I know that my VFD has the ability to up the output, but if the motor is designed to run at X rpm that is pretty much where I will max out at just for the longevity of the motor. If the higher sfpm is needed I would just get the bigger drive wheel.

Daniel Fairly Knives said:
I'm not too sure about the belt speed but I don't really like the Norax belts for stock removal, to me they are for finishing only. I think you will get the most grinding for the money with ceramic belts, they only cost a bit more than the zirconia and last longer. I really like the Norax belts for their ability to polish without removing stock too quickly, they are good for cleaning up grinds and then scratch removal. The "gator" belts are very similar and I prefer them. Everyone has their own style and I don't have many knives under my belt, this is just an observation I have made by experimenting.
Click to expand...

At my source for belts the zirc belts range from $5.25 each to $6.50 each depending on grit, where the ceramic (blaze) belts range from $8.50 to $11.00 depending on grit and the Norax belts are all $7.50 with a grit range from approximately 75 to 3000.
I will admit that I do not have much experience with the grinder and the only thing I have run on it are the zirc belts. They seemed to work fine but the usable life was just a little short. I am on a fairly tight budget right now so in the way of belts I am trying to find that balance of cost and life. The zirc belts work but I can see that the over all cost of them being high because of the shorter life, the blaze belts are close to twice as expensive as the zirc belts but do they last that much longer than the mid priced Norax belts? Then there is the question of how well they cut as you have observed.

But the real question in this thread was belt speed, and the better belt thing is a bit of a side track even if it is helpful information. What it comes down to is the best belt wont work any better than the cheap belt if the speed is off, or so that is how I understand it.
 
Belt choices and speed like everything else in knifemaking are kind of a personal choice. Some belts perform better in certain speed/pressure ranges than others. There are belts people swear by that I despise and I love some belts that others hate even though we grind at similar speeds. I'd guess it has something to do with pressures and how we "feel" the blade against the platen or wheel. Using Blaze belts took me a while to learn because of the feel compared to 3M products.

I only ran my VS grinders near high speeds when profiling, flattening tangs or knocking scale off. Flat grinding bevels is a medium to low speed operation and finishing handles is a low speed operation (getting pin/tubing hot will leave scorch rings in the handle material.)

A high quality belt will outperform and out last a cheap belt, it's up to you to find out if the price difference is worth it. I only used high end belts because I never seemed to have good luck with cheaper belts. I usually wound up wearing them around my neck, guess the pressure I grind at pops the joint.

Proper speed and proper use will extend the life of belts also.... grinding a small starter bevel with a worn belt before you flat grind to prevent shearing off the abrasive helps. Using worn belts to knock scale down and for some of the grunt profiling will extend the life.
 
I understand that I is all a preference but the question still stands, do I need to up the speed of my grinder so it can reach that magical 5000sfpm? It seemed to work fine at about 80% of my current max speed, but I have never tried the higher speeds because my set up only hits 3600sfpm.

A 6" drive wheel cost about $90 plus shipping so not a huge investment. I could also sell my current drive wheel and off set the price some more. Still would that 1400sfpm make a huge difference in how well a lower grit belt cuts?

I probably have a couple more weeks before I get things set up so I can start grinding again so there is plenty of time for debate on the subject so I think we should be able to get this down to about 25-30 distinct opinions with a good dozen or so overlapping ones:p
 
I did some research and my KMG runs at 3500 ft/min at high speed. I do 90% of my grinding at the 1750 ft/min medium speed. For profiling the 3500 fpm seems fast enough to me and is really too fast for much more in my opinion.

Do belts have an optimal speed for performance or is it a user preference thing? I'm thinking preference but I don't know. I have never heard of 5000 fpm being a goal.
 
The belt manufactures have speed recommendations but those are more for industrial applications and not knife making. The magical 5000 number I got from reading older threads but its was a case of lower grits requiring more speed than higher grits.

I think the recommended speeds are just a starting point and you fine tune from there to suit your style and preference, much like the recommended air pressures on the forks for my mountain bikes. The manufacturer feels that their fork work best at pressure X for weight Y. I start there but have yet to agree with them, to the point that I ride with a shock pump for the first month to tune the suspension to my liking. After that if I know the area and terrain I just check my pressures before a ride, if its a new area its back to tweaking to make it work right.

In comparison I can think of the belt speed as the air pressure and the belt and steel as the terrain. The speed can be tweaked to match the other variables.
 
I think that the 5000 ft. per min. is'nt necessary. I don't believe that getting there is going to mean getting better belt use or being able to do a better grind job. I run a slow machine and go slower at times. It's a Bee and goes a great job with a few make overs I gave it and the clone I built goes very well for hollow grinding at slower speeds. Both are variable speed. Sure its not what you have but then it's a quality machine that gives quality results even at slower speeds as I'm sure your's will. Learn to use what you have and I believe you will be very satisfied with the speed you now can call for. Frank
 
I built up the Grinder in a Box with a 1.5hp leeson TEFC motor and a KBAC-27D drive. This is the video of it on its maiden running. I had just finished wiring it up, that is why the bench is a little messy
[video=youtube;tZ_rTozj8sI]http://www.youtube.com/watch?v=tZ_rTozj8sI[/video]

But that was while I was still in Winnipeg, right now the grinder is in Toronto waiting for me to collect the money to pay the movers to deliver all my stuff. I am sure that it will run the same, I packed it well in a wooden crate and used carriage bolts to bolt it into the crate.
 
I've questioned this too but from the other side

I have a 6" wheel and have considered going down


A vfd controlled motor that is not TENV inverter rated loses torque at lower speeds.
running a smaller wheel would keep motor speed up and also torque up at the lowest speeds

an issue? i don't know
i have learned to use a light touch- especially at low speeds

the other reason to go bigger and faster is that the new superduper ceramic and what not belts work best at high speeds - so far I use AO and it's not an issue.

as frank said until I can figure out a real advantage either way i['m going to run what i brung
 
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