Motor shaft questions

[AllenHunt]

I have a pedestal buffer and I think I need to make a new shaft for it because it wants to walk across the floor even with no wheel on the shaft. One end of the 1" shaft has a .0005" runout and the other end has a .0015" runout. If I make a new shaft out of 4140 should I start with annealed or heat treated material? If annealed is the choice, does it need to be heated treated after the machining? I am a newbie with respect to making motor shafts.

Thanks, Allen

 

[Garwood]

end of the 1" shaft has a .0005" runout and the other end has a .0015" runout.

That is is exceptional runout. How did you measure that?

If the shaft is straight have it balanced.

 

[john.k]

Does it need new bearings .......if it has the tapered screw type shaft mounts ,I dont see any degree of precision being helpfull.

 

[Bill D]

I would consider straightening the shaft after replacing the bearings.
Bill D

 

[johansen]

That is is exceptional runout. How did you measure that?

If the shaft is straight have it balanced.

Do you mean its good or terrible?


A 2 hp motor shaft .001" off is nothing.

If the entire internal rotor of the motor is off a few thousandths, it might do what OP describes.

Such a thing might happen if the motor was dropped, but im having trouble imagining how that might happened without also destroying it.

If this is a belt drive pedestal buffer and its 1" diameter shaft off by .0015" is causing it to walk around.. it should be bolted down....

 

[hvnlymachining]

Sounds like a balance issue, but could be a bad rotor too. With those run-outs it's not likely the fault of the shaft.

 

[tnmgcarbide]

i think any motor, on an un-anchored stalk would walk around , 48" above the base.
is there some reason this buffer is not fastened to the floor? have you actually tried buffing something with this machine? buffers can be scary beasts...they can snag and
snap a wrist .....throw the work in your face ...or worse. are you familliar w/ heavy polishing wheels? they are going to find balance with pressure.

at the very least, anchor the thing to the floor or a stable
bench . try it ...wheels on... then decide .

an avg of .001 " runout is excessive ? PUHLEEZE!

 

[AllenHunt]

The buffer is direct drive and the motor shaft is held by bearings that are in the end of cast iron hollow arms and only about 6" of shaft extends beyond the cart iron arms. Maybe the grinder was dropped and the shaft bent a bit in inside the cast housing near the motor. I bought the buffer from a dealer years ago, but I'm just now trying to use it. I'll have to check on that.

Can anyone inform me about using the 4140 annealed or heat treated?

 

[Laverda]

So you think the grinder was dropped and the shaft was bent by 1/2 thousands of an inch? Wow! 1/2 thou on one end and 1 and a half on the other end. Just sell it to me as none of my grinders has this little run out. How did you measure this? My 1HP grinder which has never been dropped will also walk across the floor if not bolted down.

You do realize that making a new shaft with less than .0005" run out will be near impossible? Are you looking for it to have .0000000000" run out? My lathe with expensive precision bearings has .0003" run out at the spindle.

You are falling in to the trap of many new machinists who have this crazy idea that every machine tool should have zero run out and be capable of making parts with zero run out. It is never gonna happen.

Assuming in another universe you could make a perfect shaft with absolutely zero run out, the ball bearings will have more than .0005" run out.

Bolt the grinder to the floor and be done with it.

 

[Flail]

Although your shaft doesn’t seem that crooked, consider the following: do you have the equipment to remove the old shaft from the armature without destroying it? Can you hold that same .0005 tolerance on a shaft you build? Is the old shaft serrated or splined and can you reproduce that? Lastly can you press in your new precision shaft without bending it or wrecking the armature?

 

[john.k]

Generally ,the buffer wheels develop a flat on one side in use ,which gets worse .....so there is more unbalance than any miniscule shaft runout ...........i d be looking at a more rigid mounting for the buffer to the floor.

 

[GregSY]

As noted above, you're dreaming if you think you will remove the old shaft and install a new one without damaging the rest of the rotor. And if somehow you do get the job done, you can be sure you'll have more runout than when you started.

A motor of this size? Toss it and buy a new one if you are convinced the old one has problems. Then...get on with life.

 

[hvnlymachining]

Just to answer your question about 4140 since you are trying to learn.

4140 in the prehard ( cold finished, half hard, around 27-32 Rockwell c hardness) has internal tensions that release during machining and some claim can release for years after. It machines beautifully with carbide tooling and proper feeds and speeds.

Annealed 4140 is soft, relatively low internal stress and machinable with HSS tooling if desired.

The down side to annealed is lower yield and tensile strength and therefore easier to wear and damage.

But for the purpose of a high precision shaft with near zero runout you would be better off to use stress relieved steel, and finish it with a high precision cylindrical grinder, heat treatment would also be advisable between the machining and grinding steps.

Precision can be achieved with less than ideal machines and conditions, but expect labor times to be greatly extended.

 

[GregSY]

A bag of sand would be cheaper

 

[eKretz]

Don't make a new shaft. Either anchor it to the floor, add a good amount of weight to the base, or balance the shaft. Preferably the first. If not, the second. The third will do little once you put a buff on. They are not balanced that well either.

 

[AllenHunt]

Many thanks for the replies. I think bolting it down sounds like a good solution.

 

[rons]

I have a pedestal buffer and I think I need to make a new shaft for it because it wants to walk across the floor even with no wheel on the shaft. One end of the 1" shaft has a .0005" runout and the other end has a .0015" runout.

You should take apart the motor and inspect the inside. Then do a static balance.
For buffing that runout won't matter. If you attach an abrasive wheel and true it the runout won't matter.

I made a pedestal for a 10" buffer/grinder. There is a 6" square column with angle iron at the bottom.
Looking from above the angle iron pieces look like a T. At the top of the T there is wheel on each side.
Tilt the structure and the wheels make contact. Easy to move.

I type in "annealed or heat treated" and Google was suggesting putting 4140 in front. This has already been asked:

4140 annealed or heat treated - Google Search

 

[Doozer]

Ya know, you can bolt a buffer grinder to the wall.
I mean, the switch is kinda underneath instead of
on the front. But no biggie.

-D