What RPM do you grind at?

BenR.T.

BenR.T.

Tanto grinder & High performance blade peddler
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I have been doing all my grinding on a 1.5HP Baldor 3600 rpm 2x48 grinder.
At that speed I have a hard time keeping nice, clean, and flat grinds. which means more hand sanding!:barf:
Is it just me, or would running with a VFD at slower speeds be helpful and more controllable?
 
If you are belt sanding dont you want to measure in FPS? (feet per second) The speed of the belt is determined by the wheel size as much as the motor speed.

I tend to like grinding on the slower speeds, especially with wood and plastic as they burn.

You have to be careful what type of speed control you use with larger AC motors, you cant use the cheap router control style devices as they can damage the motor. The speed control devices for larger AC motors are supposed to be very expensive.
 
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eyeeatingfish said:
If you are belt sanding dont you want to measure in FPS? (feet per second) The speed of the belt is determined by the belt size as much as the motor speed.

I tend to like grinding on the slower speeds, especially with wood and plastic as they burn.

You have to be careful what type of speed control you use with larger AC motors, you cant use the cheap router control style devices as they can damage the motor. The speed control devices for larger AC motors are supposed to be very expensive.
Click to expand...


Could you please explain why belt size would effect belt speed? I can see where pulley size would effect it, but not belt size.
 
Drive wheel size along with motor rpm and pulley size are the controlling factors in belt speed.

Surface feet per minute is the accepted measure when discussing belt speed.

I believe people with minimum grinding experience, find it easier to practice grinding at slower belt speeds. After gaining some experience, increasing the speed of the belt is the norm.
Modern ceramic belts are designed for high belt speeds and are much more efficient when run at these speeds. Speed and pressure is the combination that works for ceramics. This is true for rough grinding blades in the 36 to 80 grit range. When running 120 and up, grit belts it makes seance to lower the speed of the belt. Finishing belts should be run at very low speeds.
The machine we use for rough grinding runs @ 5400 sfm.

Most important of all, have fun, Fred
 
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How do you tell what speed your grinder is running at? With a VFD how do you convert that to feet per minute?
 
For my first 5 yrs making knives I've been relying on my Grizzly 2" x 72" grinder http://www.grizzly.com/products/Knife-Belt-Sander-Buffer/G1015 as you can see it is a fixed speed grinder. I recently acquired a Wilton Square Wheel grinder, it too is a fixed speed model.

I will be purchasing the KMG variable speed 2" x 72" grinder in a few months. I already have the 2" x 48" Horizontal Grinder from KMG with the variable speed option. It is in my shop still in the box. I am limited for space and will be re-foot printing everything once I get the other KMG....probably early next year.

All that being said......I will always have a fond place in my heart for my initial 2" x 72" Grizzly. I already have plans to move it into my forging area. It will be dedicated to slag removal, profiling, and other similar tasks. It has served me well over the first part of my knife making career. It was relatively in-expensive and after a little modification produced very nice results.
 
Mooseyard said:
How do you tell what speed yourth grinder is running at? With a VFD how do you convert that to feet per minute?
Click to expand...

I use a magic marker to place a mark on the edge of the platen as well as the edge of the belt at the same spot. I place a mark on the pulley face at the motor along with a reference. Turn the motor one complete revolution until the mark is at the same position. Measure the distance between the mark on the belt and the mark on the edge of the platen.
Multiply this by the motor speed [1725 or 3450 rpm] this will give you surface feet per minute, of the belt at that setting. This is the caveman way but it does works.
 
The more I grind the faster I like it. I started out with my 3 speed KMG on low, then medium, now I'm getting used to high speed grinding. I'm still pretty new to all this.

I find faster just faster... screwups happen faster and good grinds also get done faster. I find belt quality has a lot to do with my grinds looking good, if I have a worn out belt they get funky fast. I think my ceramic belts do last longer at higher speeds.
 
So it seems I am running at 5645
3450 RPM
2.5 motor pulley
2.0 drive pulley feeding
5.0 drive wheel


No wonder I burn up G10 and wood.:barf:
 
Carl_First_Timer said:
No wonder I burn up G10 and wood.:barf:
Click to expand...

Yeah, you really have to apply a light touch when using a fast machine. I've scorched G10 so bad I had to grind off another 1/16" to get past the blackened ugly part. :mad: That will make you say bad words if you're close to your final dimension.
 
It seems I have to be too touchy though. Like almost tapping the belt with the stuff. I can not get a feel for the material. I'm going to switch around my pulleys.
 
Fred.Rowe said:
I use a magic marker to place a mark on the edge of the platen as well as the edge of the belt at the same spot. I place a mark on the pulley face at the motor along with a reference. Turn the motor one complete revolution until the mark is at the same position. Measure the distance between the mark on the belt and the mark on the edge of the platen.
Multiply this by the motor speed [1725 or 3450 rpm] this will give you surface feet per minute, of the belt at that setting. This is the caveman way but it does works.
Click to expand...

My grinder is a fixed speed, direct drive baldor. with about 7" drive wheel, using that math I come up with 81,000. the grinder runs at 3600rpms and the mark travels 22.5".:confused:
 
3600x7= 25,200 divided by 3.82= 6,596

The following was cut and pasted from a link I did above....

SUPER FAST!

Motor RPM x pulley diameter, divided by 3.82= SFM

(SFM=Surface Feet Per Minute)

This is from memory. I'll look it up tomorrow and confirm it.


NOTE:

This formula is correct, according to the Machinery Handbook, 25th edition.
 
Carl_First_Timer said:
So it seems I am running at 5645
3450 RPM
2.5 motor pulley
2.0 drive pulley feeding
5.0 drive wheel


No wonder I burn up G10 and wood.:barf:
Click to expand...

Oh my Changed the pulley's and getting a smooth 3600 is FPM.

Handle material is going down this weekend. Oh man. I have had to shape and finish handles manually up til now. Oh boy. Weekend come faster.
 
BenR.T. said:
My grinder is a fixed speed, direct drive baldor. with about 7" drive wheel, using that math I come up with 81,000. the grinder runs at 3600rpms and the mark travels 22.5".:confused:
Click to expand...

Change the inches to feet: 22.5" = 1.87' times 3600 = 6,732 SFM. The formula posted by fluidsteel is more accurate I'm sure.


Whether you are running at 6,600 or 6,700 that is fast. Its not too fast according to the belt manufacturers. 7,000 ft is not out of hand.

I should have been more clear when I posted, Fred
 
I started grinding on a "Grizzly" which runs approximately twice the speed of light. About 4 years ago, I bought myself a variable speed KMG. I babied it for a while, but now I grind just as fast and hard as that thing will run..........UNTIL I do post heat-treat grinding. Then I slow her down quite a bit.

When I am doing handle materials on the rotary platen, I run at about 50% speed depending on the materials. Some materials will burn easier, so I slow things down a bit.

I'm impatient and I love to see both metal dust and handle dust fly.:D

Robert
 
Robert Dark said:
I started grinding on a "Grizzly" which runs approximately twice the speed of light. About 4 years ago, I bought myself a variable speed KMG. I babied it for a while, but now I grind just as fast and hard as that thing will run..........UNTIL I do post heat-treat grinding. Then I slow her down quite a bit.

When I am doing handle materials on the rotary platen, I run at about 50% speed depending on the materials. Some materials will burn easier, so I slow things down a bit.

I'm impatient and I love to see both metal dust and handle dust fly.:D

Robert
Click to expand...

Man, I am glad to hear that. Someone told me you were getting so old you were grinding at 6 surface feet an hour. I was getting ready to send you a grinding crutch.:D
Good to hear you still got that machine smokinnnnnn! :thumbup:

Regards, Fred
 
I run a 2hp 1800 r.p.m motor at 2x speed thru my VFD. For hogging and profileing I run my VFD at about 70-80%. So far for roughing bevels I have run around 60%. When I first set my machine up I used a digital tachometer to take some readings, but forget what they are now. I will take a few more readings next week and post my S.F.M. compared to my VFD setting.
 
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