Thread: wheel speed

I am a new member and would like some opinions on grinding wheel speed on surface grinders. Having just refurbished a small Union surface grinder, which was missing the motor when i bought it, i just fitted 0.75 hp motor i had tucked under the bench. This motor runs at 1,500 rpm which seems a little slow to me but i have some reasonable results with it. I just wondered if there is an optimum speed to run 8" and 6" wheels
Steve

I have a six speed grinder,(step pulley) so I run 8" wheels at 2800 rpm and 7" wheels at 3600 rpm, and occasionally 3400 rpm as I grind dry. That's wheel speed, not motor speed.

The first thing you do with a grinding wheel after checking it for cracks by ringing it it see what the maximum RPM is for the wheel. These are not suggestions, these are not to exceed. Exceeding these speeds could cause the wheel to explode. If you don't know the spindle rpm, calculate it by using the motor speed and ratioing through the pulleys.

Now what is recommended for best cutting? I shoot for 6000 ft/min

Tom

4 pole motor grinders can be very nice to use, especially with a well dressed free cutting wheel on carbon steels. Whilst they lack speed, thats made up for in increased torque and less heat for a given amount of "in-feed" pressure.

How about a VFD.
Be careful at 120 HZ, the motor may come apart and you may have balance (vibration) problems.
Grinders use special balance motors.

You are at 1/2 the normal speed for this size wheel but think about this. Many will use a 8 inch wheel dressed down to 4 inches before they toss the wheel.
One thing I ran into in the past was that "small" used up wheels did a better job grinding the chuck.
We saved small diameter wheels just for this task.

All of my grinders now have a VFD on them.
You can change the apparent hardness of a wheel by changing the RPM (SFM at the wheel actually).
The slower you run, the softer the wheel will seem to be. The change in the way things act can be huge.

Some very special stuff we run down as far as 800 RPM on a 5 inch wheel.
When we build a program we put a comment in the front with the SFM that was used.
RPM is then adjusted depending on the wheel actual size.

What you have will work but having the ability to move the speed around is very useful.
Finish is usually better at high speeds, deep cut plunge and creep feed grinding likes a lot less speed but you are going to run out of HP here.

just my .000002 cents worth, your mileage may vary.
Bob

[QUOTE=CarbideBob;1827261]How about a VFD.
Be careful at 120 HZ, the motor may come apart and you may have balance (vibration) problems.
Grinders use special balance motors

Thanks guys, You have given me some useful info, I do intend to replace the motor, it was really just to get things up and running. It has done several little jobs for me and saved me a heck of a lot of time and i am pleased with the results so far. I do have a three phase single ended grinder motor but as i have just moved and downsized my shop i dont yet have three phase supply. this is causing me several other problems as well as grinding so will have to be addressed fairly soon, meanwhile i still have to earn a living so " needs must" as they say.Once again thanks for your interest and replies.
Steve