lathe vibration

E

eddief

Eddie Fosnaugh
The lathe is a Eisen 14x40 w/VFD and weighs 2400lbs w/ a cast iron base.

I am getting vibration that I can feel at about 1000 rpm and above (max 2500rpm)

The lathe is level according to my machinist level .0002"/10in.

I did not feel this vibration until I put on my 8" set tru chuck that weighs 50lbs. I figured I better check face of the chuck mounting plate with my indicator. When I did, I discovered about .005" run out.

I faced off the mounting plate and re-checked the run out, it wouldn't budge the needle on my .0005" interapid. Re-mounted the chuck and checked it at speed and still am getting some vibration, although it seemed to only be half as bad.

The lathe is on my garage floor, I have steel plates and one hockey puck under each of the six steel adjustable feet to raise the height of the lathe a couple of inches.

I know some don't like any kind of rubber under the machine but thought I would try it.

My thought is the chuck is too heavy for the lathe (short headstock). The chuck is a BTC, so i checked the weight of other 8" inch chucks (bison, PBA and buck) and noticed that most other 8" chucks are only about 25 - 35 lbs vs. my 50 lb BTC.

What do you guys suggest? Do you thinks it's the weight of the chuck? Thanks!
 
By blocking a machine up as you have can compound vibration problems, even though, I have a lathe that sets on 4" square tubing. A 50# chuck needs very little imbalance to shake a small lathe, even a large one. If your lathe is OK with a different chuck, then your adjust tru is the problem. That is one of the negatives to an adjustable chuck. A chuck does not need to be as precise when it's adjustable, and if it's out very much then it will vibrate.
 
eddief said:
The lathe is a Eisen 14x40 w/VFD and weighs 2400lbs w/ a cast iron base.

I am getting vibration that I can feel at about 1000 rpm and above (max 2500rpm)

The lathe is level according to my machinist level .0002"/10in.

I did not feel this vibration until I put on my 8" set tru chuck that weighs 50lbs. I figured I better check face of the chuck mounting plate with my indicator. When I did, I discovered about .005" run out.

I faced off the mounting plate and re-checked the run out, it wouldn't budge the needle on my .0005" interapid. Re-mounted the chuck and checked it at speed and still am getting some vibration, although it seemed to only be half as bad.

The lathe is on my garage floor, I have steel plates and one hockey puck under each of the six steel adjustable feet to raise the height of the lathe a couple of inches.

I know some don't like any kind of rubber under the machine but thought I would try it.

My thought is the chuck is too heavy for the lathe (short headstock). The chuck is a BTC, so i checked the weight of other 8" inch chucks (bison, PBA and buck) and noticed that most other 8" chucks are only about 25 - 35 lbs vs. my 50 lb BTC.

What do you guys suggest? Do you thinks it's the weight of the chuck? Thanks!
Click to expand...
Don't get mad, but you didn't really level the machine! You reached a starting point. I'd remove the hockey pucks! Your pads should be somewhere between 3/8th" and 3/4" thick. Remove the chuck and tail stock, along with all the tooling on the compound. Get some modeling clay and create a seat for the level to set on (be nice if you had two levels). Crank the slid to where it's centered in the bed, and as close to the spindle nose as you can get it. Adjust the level so that it reads zero. Now go to the extreme end of the headstock and put pressure on the leveling screw so the the bubble just barely moves on the level (nice to have a friend to help you). Crank the apron over each set of leveling screws and adjust them to read level. Return to the starting going and rotate the level 90 degrees, and do the samething. Now start all over with the level following the cross slide. Eachtime you return to the spindle nose check the rear headstock screws for pressure! Once the lathe is within .0005" (really .001" is good enough) go around and check each screw for pressure on it. Just tweak them till the bubble just barely moves. Let it all set over night and check it again (probably will change). You do this till it quits changing on you. If the lathe was setting crooked (like somebody put a 2x4 under one end) you may have to do this for several days unless you have the lathe lagged down as well (best setup). Once it's all leveled, and the jam nuts tight; leave it alone! Now check the motor and spindle pulles to see if they're tight on the shaft. (this is common). Now run the machine with the chuck off it to see if it smooth. Check the mounting face for the check to see if there is a hickey or raised burr on it.

Now look at the check carefully. Remove the master jaws, and inspect for chips and crud inside the chuck body. Some chucks have a built in counter weight system for each jaw. Make sure each jaw is the right one for the slot it's in (they will be marked). Same goes for the counter weights if it has them. Do all the jaws look identical? Take a strong flashlight and look over the slots closely for signs of a wreck or a crack. Has the adapter plate on the backside been changed? Are there any holes drilled in the body that are not factory? If there are fill them! Look at the rear balancing holes to see if they are filled. You might have to have the chuck rebalanced.

Now for one last check. Get a 2x4 about three or four feet long. Set the indicator up to read on a bar chucked up. Take the 2x4 and pry up under the chuck. If it moves much more than .001" you ought to tighten the spindle bearing to where you have about .0003" to .0005". While in there look for something that might have come loose in the spindle group.

gary
 
I believe the vast majority of chucks require balancing... I have a 6 inch 3 jaw Pratt chuck which is considered quite high quality and I can feel vibration at 1000 rpm... and none with the chuck off.... and I have no idea how one would balance a chuck.
 
Do what squeakie wrote after you buy and install some real machine mount feet. You need to do this anyway whether it fixes your vibration or not.

Also keep in mind that your set-tru isn't going to run perfectly balanced if you have it offset from dead concentric with the spindle. If you have it set over it'll run lumpy. Grip something light and small in the jaws and true the chuck to zero run out. How does it run like that?

Did you run the machine with only the trued up backing plate? Did it vibrate less?
 
eddief said:
I did not feel this vibration until I put on my 8" set tru chuck that weighs 50lbs. I figured I better check face of the chuck mounting plate with my indicator. When I did, I discovered about .005" run out.

I
My thought is the chuck is too heavy for the lathe (short headstock). The chuck is a BTC, so i checked the weight of other 8" inch chucks (bison, PBA and buck) and noticed that most other 8" chucks are only about 25 - 35 lbs vs. my 50 lb BTC.

What do you guys suggest? Do you thinks it's the weight of the chuck? Thanks!
Click to expand...

No, the chuck is not too heavy for that size lathe but you are not going to be able to spin that much mass vary fast without some vibration. An adjust tru chuck is going to be out of balance any time you have to shift it to true a workpiece that is not true and in balance to start with.

Leveling a lathe will not effect vibrations within the rotating mechanisms. It might make the lathe cut with a taper or a swalth over a long workpiece but it will not induce or reduce rotational-sourced vibrations. Having a 4-footed lathe tweaked until it has only 3 feet on the floor might cause some odd movements but it will not effect rotational sourced vibrations.

Never run a lathe of any size with enough rotational vibration to cause it to "walk" in the first place.
 
JerrySharrett said:
No, the chuck is not too heavy for that size lathe but you are not going to be able to spin that much mass vary fast without some vibration. An adjust tru chuck is going to be out of balance any time you have to shift it to true a workpiece that is not true and in balance to start with.

Leveling a lathe will not effect vibrations within the rotating mechanisms. It might make the lathe cut with a taper or a swalth over a long workpiece but it will not induce or reduce rotational-sourced vibrations. Having a 4-footed lathe tweaked until it has only 3 feet on the floor might cause some odd movements but it will not effect rotational sourced vibrations.

Never run a lathe of any size with enough rotational vibration to cause it to "walk" in the first place.
Click to expand...

Jerry, I've ran into the vibration issue with lathes that appeared to be level, but were barely touching the leveling pads in the headstock area. It's a simple check to do, and if the feet are not right then it's time to relevel the lathe. Myself, I'd be more concerned about the chuck right now. But then again I do not really like giving advice on repairing chucks as it can be life and death if it fails.
gary
 
Dennis Sorensen said:
I believe the vast majority of chucks require balancing... I have a 6 inch 3 jaw Pratt chuck which is considered quite high quality and I can feel vibration at 1000 rpm... and none with the chuck off.... and I have no idea how one would balance a chuck.
Click to expand...

all chucks made over here are factory balanced, but it's also easy to violate the factory balance. There is equipment made to check the balance of a chuck, but also expensive. But I'd imagine an automotive balancing shop could do the job
gary
 
Part of your problem is your machine base. Mounting the lathe on the garage floor does not offer proper dampening of vibrations. The rule of thumb for rotating machinery is that the base should weigh at least 3 times the machine wieght. In your case, that would be 7200 lbs. Since your garage floor is most likely 4 inches thick (50 lb/sq ft), that would require 144 sq ft of floor, but the 4 inch slab is too flexible for dampening to work well.

For maximum dampening, your lathe should be mounted on an independant pad bigger than the lathe by 1 foot on all sides and containing about 2 cubic yards of concrete. The pad should have two layers of #4 bars at 12 inches on center each way, one at 3 inches clear of the dirt and the other at 1.5 to 2 inches clear of the top. The pad would be isolated from your floor slab with 3/8 inch premolded expansion joint filler all around.

I cannot really recommend installing a machine pad for a home workshop installation, but the lack of a pad is one reason that you are experiencing vibration.
 
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Something you could look at is , has the chuck ever been apart? Chucks need to be taken completely apart, periodically and thoroughly cleaned. Chips are attracted to the inside of a chuck like flies on........ I would take that chuck apart and really clean it, re-grease it and see if it is still on center.
Even if that's not your problem your chucks need a cleaning if they have any use at all. That reminds me that mine need it too. It's a thankless job but chips in a chuck can cause a lot of problems.

When a adjustable chuck gets chips in it, it is easy for someone to think it needs adjusted, which can cause them to vibrate. It could even have a glob of hard grease on one side if it has never been cleaned.

After you clean it and remount it, if it has a grease fitting, fill it full of grease. Just do not stand in front of it, the first time you spin it up to speed. Then keep it greased. We grease our chucks and especially our power chucks every time we use them.
 
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