[jackholman]

I have an 8-year old Unisaw with a 3hp motor. I notice excessive vibration in the blade. The saw is on a slab, and level. I know the bearings are sealed for a lifetime. So--any suggestions on how to minimize this vibration?

 

[Shop_Rat]

1. Run it without the blade. Does it settle down?
2. Run it with a different blade. Any difference?
3. Remove the belt and run just the motor.
4. Unplug the saw and grab the motor shaft. Pull up and down and push in and out. If you can detect movement in either direction (without a dial indicator) something is wrong.
5. Spin the motor. Any rough spots, or smooth as silk?
6. Remove the blade. Grab the arbor and do the same exercise as with the motor. Any play?
7. Spin the arbor. Any rough spots?
8. Change the belt. Many tools that sit develop a memory in the belt, especially if it's a cheap belt.

"Lifetime" sealed bearings do translate to last forever. They just don't require maintenance during their lifespan. 8 years is not a long time, but hey...
Blades are usually the culprit. Don't ever cheap out on blades.
Bent arbors are not all that common, but eccentric blade washers are. They are usually just stamped steel. A good set of machined blade washers will often do the trick.
Even tooth count can have an effect on vibration. Anything high speed can and does develop harmonic noises. I've seen industrial machines that straightened right up by simply bolting a big chunk of raw steel under the table.
Most anything deeper begins to need specialty equipment like dial indicators to measure runout. However, if nothing above has an effect, a simple dial indicator and a magnetic stand can tell you many hidden tool secrets.

Good luck

 

[mikeswoods]

Excellent explanation Shop Rat--

 

[Hammer1]

Basically, you need to go through the saw. Just because bearings are sealed, doesn't mean they don't go bad, only that you can't grease them. They usually last a long time and I wouldn't suspect them as the cause. Very often, it's a drive belt or pulley that is loose. The Unisaw should have three drive belts. Before doing anything, unplug the saw. Remove the blade. Check that it was free to fit against the arbor collar. You know that you only tighten blades finger tight, you don't use a wrench or you can bend the blade. The blade can get caught in the threads of the arbor or there can be some debris on the collar, either one, inner or outer. It may just be tension on the belt/s. Also check the alignment from pulley to pulley with a straight edge. A bolt or two may have loosened, allowing the motor to shift, releasing tension and going out of alignment. There is an allen head set screw in the grooves of the pulleys that often align with a key, a small rectangular piece of steel or a flat in the shaft. These can come loose. If the belts are off, you can turn the arbor by hand, like trying to break into a safe, to feel any roughness in the arbor bearings.

This is always a good time to go completely through the saw, checking every bolt. Don't over tighten any since tapped holes can easily strip. Open the electrical switch, clean all the dust out, under the saw, lube the lifting and tilt mechanisms, check blade alignment, set the fence, miter bar, reset the angle indicators, etc. Every saw should be gone through from time to time.

 

[Shop_Rat]

Basically, you need to go through the saw. Just because bearings are sealed, doesn't mean they don't go bad, only that you can't grease them. They usually last a long time and I wouldn't suspect them as the cause. Very often, it's a drive belt or pulley that is loose. The Unisaw should have three drive belts. Before doing anything, unplug the saw. Remove the blade. Check that it was free to fit against the arbor collar. You know that you only tighten blades finger tight, you don't use a wrench or you can bend the blade. The blade can get caught in the threads of the arbor or there can be some debris on the collar, either one, inner or outer. It may just be tension on the belt/s. Also check the alignment from pulley to pulley with a straight edge. A bolt or two may have loosened, allowing the motor to shift, releasing tension and going out of alignment. There is an allen head set screw in the grooves of the pulleys that often align with a key, a small rectangular piece of steel or a flat in the shaft. These can come loose. If the belts are off, you can turn the arbor by hand, like trying to break into a safe, to feel any roughness in the arbor bearings.

This is always a good time to go completely through the saw, checking every bolt. Don't over tighten any since tapped holes can easily strip. Open the electrical switch, clean all the dust out, under the saw, lube the lifting and tilt mechanisms, check blade alignment, set the fence, miter bar, reset the angle indicators, etc. Every saw should be gone through from time to time.

Well, I may as well get this party started. The finger tight thing is, in general, probably not one of the better recommendations for Joe Public. It is also not the blade changing procedure by any saw manufacturer that I can find. Just a few offerings:

http://www.steelcitytoolworks.com/blog/how-to-change-tablesaw-blade/

http://www.highlandwoodworking.com/installingtablesawblades.aspx

http://woodworkingwithajo.com/2013/04/14/how-to-keep-from-overtightening-your-table-saw-arbor-nut/

From Delta's operators manual:

CHANGING THE SAW BLADE

USE ONLY 10" DIAMETER BLADES WITH
5/8" ARBOR HOLES, RATED AT 3450
RPM OR HIGHER.
DISCONNECT MACHINE FROM POWER
SOURCE.
1. NOTE: Two 7/8" wrenches are supplied with the
saw for changing the saw blade: a box end wrench (A)
Fig. 69, and open end wrench (B).
2. Remove table insert (C) Fig. 69, and raise saw blade
to its maximum height.
3. Place the open end wrench (B) Fig. 70, on the flats
of the saw arbor to keep the arbor from turning, and
using wrench (A), turn the arbor nut toward the front of
the saw. Remove arbor nut, blade flange, and saw
blade.
4. Assemble the new blade, making certain the teeth
point down at the front of the saw table, and assemble
outside blade flange and arbor nut. With wrench (B) Fig.
70, on the flats of the arbor to keep it from turning,
tighten arbor nut by turning wrench (A)
counterclockwise.
5. Replace table insert.

(All other manuals are similar)

I am not advocating that you do anything differently than you do. But the overwhelming consensus is to finger tighten, and then add 1/4 turn on the nut. Snug but not tight.

 

[notskot]

Has it vibrated for a while, or was it fine and just start vibrating out the blue?

 

[woodnthings]

I understand that the blade self tightens ....

The rotation of the blade under load tightens the blade, at least theoretically. I've only had one blade "free wheel" on the arbor after a jam even though it was tightened with 2 wrenches as suggested ... scared the crap out of me. I jammed a scrap in the spinning blade to stop it. WHEW.

I've always used 2 wrenches and will continue to so so, if I ever need to change a blade. :surprise2:

 

[Hammer1]

Glad you understand the problems with over tightening the blade. You cannot use two wrenches on cabinet saws, there are no flats for a second wrench. If you know about blade tightening, you may also know how to "tune" a table saw. We never know with most posters, some may have experience, others may not. You didn't give any pertinent info on your original post. Considering your question and what little you offered, it would be normal to assume you are a novice, most posters are. We all were at some point.

 

[michaelpugh]

Glad you understand the problems with over tightening the blade. You cannot use two wrenches on cabinet saws, there are no flats for a second wrench. If you know about blade tightening, you may also know how to "tune" a table saw. We never know with most posters, some may have experience, others may not. You didn't give any pertinent info on your original post. Considering your question and what little you offered, it would be normal to assume you are a novice, most posters are. We all were at some point.

I have a grizzly 1023 5hp cabinet table saw. It came with two wrenches. It does have "flats" for a second wrench.