grinder shaft eccentricity

[Andrew Howe]

Hi all
I picked up a used bench grinder that somebody dropped in it bent very slightly the left shaft approximately 3/1000th inch eccentric. How can I fix it? Bash it with a hammer or grind it out with a stone? Thoughts?

[Peter Gregory]

I would buy a new shaft. The whole machine is no good if it isn't right.

[Ronald Blue]

Did you measure this with an indicator? Is this a typical bench grinder with a wheel on each end? Have you measured the opposite end? .003 is pretty mild for this type of appication. I would try putting a wheel on and truing it with a wheel dresser and see how it runs. On the other hand .030 would be a problem. If it's truly only .003 I don't think it will be an issue. On a surface grinder it would be a different story.

[Myk Rian]

How can I fix it?
Arbor press.

[Jerry Bruette]

If your grinder turns at 3600 rpm, which I'm guessing it does, .003 runout can be a big deal. We have some 3600 rpm 15 and 20 horse motors on our shot blasters at work and if they have more than .0015 run out we throw them away rather than try to rebuild them.

I don't know how you'd get rid of one or two thousandths of runout, but I'm guessing if you don't you'll have a grinder that walks all over your bench or will shake everything off of it.

Jerry

[Ronald Blue]

A shot blaster is nothing like a bench grinder except that it rotates. The wheel on it is heavy and balanced because of it. I suggest he try it before he gets to concerned about it. If after dressing a new wheel he has a vibration problem then he can look for solutions. The wheel will have a couple thousandths clearance in the hole by itself.

[Gary Herrmann]

How did you measure it?

Stick a wheel on it and see how it runs. If it isn't acceptable, I agree that replacing the shaft would be the best bet. I wouldn't have the necessary skill to move something .003 out of round.

[Bruce Page]

I agree, mount the wheels. You will be able to dress the face true but will likely have some side wobble. Depending on what type of grinding you do, a little side wobble might not be a problem.

[Andrew Howe]

Gary
I clamped a dial indicator on the tool rest of the tool, set it to zero and rotated the shaft by hand to measure eccentricity ( zero to 4/1000ths) out. Did the same to the right side and it is no more than 1/1000ths difference. Wobble is noticible. Someone dropped it I was the one that didn't notice it when I grabbed it at the garage sale. Would be nice to salvage. No arbor press to fix how about a big bench vise?

[David Cefai]

The wheels are also going to have some tolerance. It may be worth trying to get the runouts to cancel each other out.

Note that the runout may be caused not only by the shaft bending but also by damage to the bearing. Possibly both.

[Ronald Blue]

Andrew I still think you should try it before getting to concerned. The wheel must be dressed or trued anyway so it will run true. As Bruce said you might notice a side to side wobble but you shouldn't be using the side of the wheel anyway. What size is the shaft? 1/2" or 5/8"?

[Andrew Howe]

It has a 1/2" shaft with variable ask?
speed to 3400 rpm . Why do you

[Ronald Blue]

My thought was possibly using a piece of pipe that fits well when slid over it and use it to tweek it. One note of caution is that you usually have to go beyond the desired point due to the shaft springing. Don't go to far and end up worse off.