4" 4 Jaw chuck

[mjarus]

I just got a new 4" 4 jaw chuck to put on my Cummins 7x12 Lathe. It is pretty big with the adapter, which leads to my question:

Is it normal for this chuck to cause a LOT more vibration than the stock 3" 3 jaw chuck? I realize it is a lot bigger, but anything over 400-500 rpms makes the lathe want to dance (with no load)! My lathe isn't bolted down yet, but it still seems pretty extreme. Is this normal or is the chuck "off"?

Another question: Has anyone had the red packing grease "stain" a product before? I tried everything to get it out, but it looks like there are a bunch of red blotches all over it. The grease is off... just the stain remains. Looks like crap.

Thanks in advance,
mjarus.

[WhiteTiger]

The chuck should be nominally in balance with all 4 jaws at the same radial position. One quick check is to just remove all 4 jaws (and the screws if they aren't captive) and see if you still get the vibration. Sometimes if it's an open back casting it can be irregular enough for the chuck body itself to need balancing.

Needless to say, if the jaws are scattered out to random positions then it's going to shake like a belly dancer no matter what


Tiger

[MarkT]

As tiger pointed out, most 4 jaw chucks are independent jaws. On a small lathe such as yours it will not take alot of an out of balance state to create a "hammering" effect. Wait until you get an out of balance part in there! Be careful, I would bolt down everything!
Keep us updated!
Good Luck.
MarkT.

[mjarus]

I realized early on in my testing that the jaws were probably throwing it off a little so I took them out. It made it better, but there was still VERY noticible vibration. Are there any easy tests that I can do that will help guide me to the problem point?

Thanks for all the help!

mjarus.

[pastera]

The adapter plate may have extra holes for the different spindles. Plug the holes you are not using and the vibration should go away


Aaron

[WhiteTiger]

Process of elimination is about the only low tech way to locate where the imbalance is. Try running with just the adapter plate mounted... if the vibration goes away then the body of the chuck is almost certainly out of balance, since you've already ruled out the jaws.

There are a few ways to go about balancing it, but if you can I'd suggest just exchanging it as defective. The balancing is a tedious pita


Tiger

[mjarus]

Thanks for all of the good replies.

Well, I tried it with just the adapter plate and that alone had significant wobble, way more than the stock chuck does, so that may be the issue.

I put a dial on the top of the adapter and it was off by .0015 through a whole rotation.

Pastera, you are right, there are 2 unused, off centered holes... but how do you go about plugging them and what with?! They have a smooth bore (non-threaded). Also, wouldn't it have to be something that weighs the exact same as what it displaces? I tried quickly putting some bolts that were the right size through them, but it did not seem to help much, if at all.

I will try to call the vendor in the morning and see what they say. In the meantime any other ideas would be appreciated.

mjarus.

[MarkT]

Instead of attempting to plug the alternate driver holes, why not machine the symetrical patern complete ( if it has two holes of a four holde pattern, drill the other two in)
As suggested, if sonething like this does not fix itm send back. Make sure that a t a mimum the machine is bolted down.
Good Luck!

MarkT

[pastera]

Originally Posted by mjarus Thanks for all of the good replies. Well, I tried it with just the adapter plate and that alone had significant wobble, way more than the stock chuck does, so that may be the issue. I put a dial on the top of the adapter and it was off by .0015 through a whole rotation. Pastera, you are right, there are 2 unused, off centered holes... but how do you go about plugging them and what with?! They have a smooth bore (non-threaded). Also, wouldn't it have to be something that weighs the exact same as what it displaces? I tried quickly putting some bolts that were the right size through them, but it did not seem to help much, if at all. I will try to call the vendor in the morning and see what they say. In the meantime any other ideas would be appreciated. mjarus.

use your 3" to turn up some tight fitting plugs from cold-rolled steel. Insert with locktight.The density difference between CI and CRS is small enough for this to work well.

To balance the chuck you could center drill a 6" length of 1/2" round. Mount the bar evenly centered axially in the 4" chuck and indicate center. Remove the chuck and adapter without disturbing the bar and mount the chuck/bar between centers. Once it is between centers the heavy point should rotate low and you can balance by drilling the adapter. Make sure you mark the adapter and chuck orientation in case they are ever separated.

Aaron

[mjarus]

Aaron is my hero (for today)!!! I finally got the 1018 CRS plugs done and it is even MORE balanced than my stock 3 jaw!

Now the problem with the fix: 1018 is a royal PITA to form on a 7x12. Cutting that stuff off is a nightmare! It heats up and sticks to your cutter if everthing isn't exactly right. I will avoid it like the plague if at all possible in the future

I finally got it though, no need for loctite the fit is so snug they will not come out unless popped out by hand. I have not actually tested the chuck yet as I am reveling in my glory. I may do that later tonight.

Anyways, thanks a million Aaron. You da' man!

mjarus.