Best topic for cleaning, adjusting chucks?

[tmenyc]

I am swapping out my 6" 3-jaw for my 5", having learned that smaller chucks are better for accuracy than larger ones. The 6" isn't bad, but its .003-.005 runout is a bit much for the small work I'm finally getting around to doing. Both (and my 6" 4-jaw) came with my Logan 820, so I haven't purchased a chuck, pretty lucky in that regard. The 5" runout is > .025, so I'm assuming it's either got something stuck in one of the jaws or the jaws were installed in the wrong order, or something... and, of course, if there's something I can do to improve the 6" performance, that would be great, too.

Could someone please point me to the best post here or source for info on how to prepare and maintain a 3-jaw or 4-jaw chuck for use? Also, for setting the 4-jaw's jaws precisely? I haven't learned that method yet.

Many thanks!
Tim

 

[darkzero]

In what sense are smaller chucks better for "accuracy"? I have not heard this before. Like swapping to a 5" chuck from a 6" chuck is not going to improve runout if both chucks are of equal quality.

Here's a recent thread on using a 4-jaw that may help you.

Learning to dial in a 4-jaw

I got the 4-jaw mounted up on the new backplate today and so tried my hand at chucking up some round stock. It was a bit frustrating as I struggled to start from a place where the shock was even reasonably centered so my indicator was spinning round like a top. I was using the rings scribed on...

www.hobby-machinist.com

 

[DavidR8]

Depending on if the chucks in question have backplates the accuracy of the backplates will be a factor to consider.

A great chuck on a poorly fitted backplate is not going to indicate well.


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[darkzero]

The 5" runout is > .025,

I did not notice this the first time I read your post. Did you forget a 0 or is it really .025"? If the later, how did you install the new 5" chuck? I'm assuming you have a threaded spindle mount. Did you get a new backplate for it or did you reuse an existing one? How close does the chuck register fit on the backplate boss? What are you using to measure runout for the chuck & what is the runout measured on your spindle?

.025" is way too much runout, more likely a mounting issue than a chuck issue. .002"-.003" is typical for a plain back scroll chuck.

 

[mikey]

Tim, the size of the chuck has nothing to do with its accuracy. Make and quality, yes, but not size.

All 3 jaw chucks will have some run out and I am assuming you are measuring yours by chucking up something that is accurate, like a dowel pin or end mill, and measuring the run out with that thing locked in the chuck, right? Most 3 jaw chucks will run out 0.002-0.003" under these conditions BUT if you put a work piece in that same chuck and turned it, then measured the run out on that piece without removing it from the chuck, you will find that it has zero run out ... zero. It is zero because that first turning is called a first operation and that is what 3 jaw chucks are used for.

A second operation is when you chuck something that is already turned. If you do this with a 3 jaw chuck, it will run out; the amount it runs out will differ with the diameter of the work piece because the run out depends on where on the scroll the chuck happens to lock down. You can test this yourself. Try chucking up different drill bits and measure run out and you'll see that it changes with diameter. The point is that if you need accuracy, use the 3 jaw for first operations only and switch to a 4 jaw independent for second operations work that has already been turned or is accurately ground. I hope the difference is clear; if not, sing out.

As for 3 jaw chuck maintenance, I am attaching something to read. 4 jaw chuck maintenance is a no-brainer. Just back out each jaw until it disengages and pull it out. The screws that move the jaws can then be removed. Clean everything, lightly oil everything and then reassemble.

I am not going to discuss how to adjust a 4 jaw chuck in this thread. You can look that up yourself or watch videos on Youtube. If you have questions on it, though, we can all discuss it further.

 

[DavidR8]

Thanks for the great write-up @mikey!

 

[John TV]

I wonder if the op saw this YouTube vid on winkey's workshop? It talks about chuck weight and overhang. There are 3 short. Vids on the matter. This is a link to the first one.

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[Tom1948]

I too have a PM1020 lathe with an import 5 inch chuck. I have taken it apart and cleaned and lubed the scroll and can get the runout down to less than .001 when checking with a new 17 mm. wrist pin at about 1 1/2 inch away from the jaws. However, when I chuck a larger piece up the runout increases. I am just wondering if a guy was to tumble/ micro polish all parts if this would be beneficial or could lead to other problems or be a wasted procedure. I am not sure weather it would be worth time and effort. Tumbling could take quit a bit of time. Anyone have any thougts?

 

[Nogoingback]

I too have a PM1020 lathe with an import 5 inch chuck. I have taken it apart and cleaned and lubed the scroll and can get the runout down to less than .001 when checking with a new 17 mm. wrist pin at about 1 1/2 inch away from the jaws. However, when I chuck a larger piece up the runout increases. I am just wondering if a guy was to tumble/ micro polish all parts if this would be beneficial or could lead to other problems or be a wasted procedure. I am not sure weather it would be worth time and effort. Tumbling could take quit a bit of time. Anyone have any thougts?

If you're getting less than .001 runout with a 3 jaw chuck, you're doing pretty well. Is that an Adjust-true chuck by any chance? I can't imagine that polishing the parts would improve accuracy beyond what you've got. Just clean it and lube it.

 

[Tom1948]

No, its the cheap import chuck that came with the PM lathe. It takes careful manipulation of the 3 bolts on the backing plate as well as how you tighten and the order in witch you tighten the 3 jaws. Now I have a friend with a Harbor Freight 12 inch lathe that claims he can get his down to .0008. Now I dont know if thats at all openings, probably not. I dont have anything larger such as hydraulic tubing to check mine out. The reason for asking about polishing, the scroll in particular has some very sharp edges. I cant help but think that deburring would have some effect just as in any other piece of equipment. I think I might go for it. If It screws it up a new one is $100,00 or so plus the cost of the tumbling. Had some motorcycle transmission gears tumbled once. It was a 3 step process but they came out looking like chrome. You could actually feel the smoothness when rotating the two shafts during assembly.