Live Center / Dead Center?

HBilly1022

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I am new to machining and recently bought my first lathe, a King Canada 10 x 22 (same as Grizzly G0602) and have spent the last month learning / playing and working out some of the bugs. My intro lists a bunch of bugs that I have fixed so far, based on information from this site. In the process of learning I have turned a few small pieces of steel rod 1" and less plus a 3" round that I tapered over a 10" length, for an anvil I am making. At first I used a dead center in the tail stock and the 3 jaw chuck in the spindle but found that the dead center would get hot and if I put oil on it it would smoke and stink up the shop. So I bought a live center thinking that would be better but with the heavy 3" round it would wobble and no matter what I tried, I could not get it to spin on center.

Based on my reading so far, it appears that the dead center is better to use but what is used for lubrication. Does there need to be some sort of drip system to lube it or just let it get hot?
 
A live center has issues with runout and less secure support for a heavy workpiece. As you have found out, a dead center has issues with friction. You need to use lubrication or risk damaging the center and/or the workpiece. I usually put some oil in the pilot hole prior to seating the center. Even then, you may have to back the center out and re-lubricate from time to time.

Dead centers are also very sensitive to the seating force. You need enough force to securely seat the center but not so much as to greatly increase the friction and subsequent heating. After extended turning the workpiece can expanding length, increasing the force so checking and readjust the tailstock as work progresses is a good practice. Turning at a lower speed is also beneficial.
 
Welcome HBilly,

How did you make the centre in order to receive the point of the live centre? Assuming a half decent live centre there is no way it should be wobbling around if it is seated properly in the tail stock and the point is in the machined centre hole.

David
 
Welcome HBilly,

How did you make the centre in order to receive the point of the live centre? Assuming a half decent live centre there is no way it should be wobbling around if it is seated properly in the tail stock and the point is in the machined centre hole.

David

I used what I think is called a centering or starter drill bit in a drill chuck set in the tail stock. The drill bit is one of the ones with a short section of 60 degree taper, to match the dead / live center.

The live center is not a good quality one. The box states it is a medium duty one and it only cost $70 CAD. It was ok on the smaller diameter rod but when I removed the 3" round to check for fit and put it back into the 3 jaw there was a very pronounced wobble in the tip of the live center. I mounted the stock by setting it loosely in the 3 jaw (lined up with the register marks I made before taking it out) and then moved the live center up to is and slowly moving it into the tapered hole until it was seated. Then I tightened the 3 jaw one adjuster at a time and each was tightened in several stages. Tried that a couple of times but no luck.

I can tell from this experience that I really need to get the lathe onto something solid. Right now I have it sitting on a mobile scaffold.

RJ, I may have to play around with the amount of force I use with the dead center. I'm pretty sure I ended up with it being more than what it should have been. I'm guessing the right amount is just enough to prevent wobble.
 
Have you checked the run out of your chuck with an indicator. It sounds to me that you did the centre drill, did some work, removed the work piece, and then re-chucked it and now it is wobbling. I think is what I am understanding.

I would be instructive to check the run out on a 3" piece, and then re-chuck and see how repeatable it is. Where ever possible it is best not to remove the work piece from the chuck and then try and put it back. Sometimes it is better to remove the chuck with the work piece still in it if you want to check it out.

David
 
Thanks David.

I recall when I first set up the lathe I used a piece of cold roll I had in the shop that looked to be straight (it's all I had) and chucked that in the 3 jaw and used that to check the run out. I checked it at the 3 jaw and 12" out and believe it was ok but my memory is not what it used to be. I will do another check when I get some time. Right now I'm stuck in the house with an all day chore but will have to stop soon to go and deal with the snow that fell last night and is still coming down. There's over a foot of fresh stuff. This will be at least a 4 hr job, if I don't have to use the snow blower. If I do that will turn into a 6 hr job. Hopefully I can get back out to the shop tomorrow and check.
 
I have heard of using white lead grease on dead centers. Don't know that you can even get that stuff anymore. I would try a white lithium grease or something along those lines. As far as your live center goes, it sounds like either the center on the part was moved or the tail stock needs to be adjusted laterally.


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WOW, I haven't heard the name, "White Lead' in eons. Yes it was the go to lubricant many years ago. Then came "Lubriplate" which is still available. Here is some reading on "White Lead".

https://en.wikipedia.org/wiki/White_lead

"Billy G"
 
If you just keep putting off dealing with the snow, it will eventually just melt on its own :)

You have had good suggestions so far.
Dead centers are more precise than live centers, but a good live center will give the same results as a dead center unless you are holding under 5 tenths tolerance. You can get live centers this good, but they are not worth it IMO unless you are doing a lot of work like that.
I use a lube meant for dead centers, and it works really well. Just search for "center lube" from who ever you buy supplies from. It has more in common with hypoid gear oil than cutting oil - it needs to both bear pressure and sliding action.
Make sure you use a center drill, not a spotting drill. The drill should have a small diameter tip coming back to a 60* shoulder and the larger diameter. The drill you described sounds like a center drill. The little tip on the drill serves two purposes: it prevents the center from bottoming out on it's tip, and is a reservoir for oil. Just get a good dab of oil into the hole and put some on the center and it will be fine. If you will be using the dead center a lot, it is worth investing in quality center drills, and possibly a center hone. The better the finish on the center hole, the better it will center and the longer the center will last. I sometimes just put the corner of a fine slip stone or 320 paper into hole and polish it a bit before using the dead center (make sure you clean the hole out afterwards). Don't make the hole too perfect, you need some scratches for the oil to go in, you just want to polish off the chatter and burs.
The center should be just tight enough to support the work, but not so tight it is oil starved. The work should ride on a film of oil. With a little practice, you will get the feel for it. The ram will have sort of a sticky feel to it when you withdraw it as you over come the surface tension of the oil.

I doubt the problem you had is with the live center. Even the cheapest live center should not wobble. One of my centers is a medium duty live center from Grizzly, it works just fine and I use it often. More likely the work just did not go back into the lathe the same as it came out. This is common, and even more common with 3jaw chucks. Generally speaking, people do not remove work from a 3jaw chuck if they need to put it back exactly where it was. A really good chuck will get you really close (you may have paid less for the lathe than a good chuck), a cheap chuck will get you in the same country. If you need to remove the work and put it back in, there are a few options. Use a 4jaw and put it back reliably. Get a good "set true" chuck. Turn between centers (this is the most reliable way).
You can get it back in pretty well by putting marks on the chuck and work like you did. Add to that running the center up into the work before tightening the chuck and you will be even closer. You said you cut a taper on the work. Did you cut the taper by moving the tail stock off-center? I am not sure it would ever be possible to put the work back in a chuck on center if this is so. You should also use a live center when possible do it this way. If you do have to use a dead center, you will have to drip lube on it very frequently.
I was once a proponent of tightening all the keys on my 3jaw. The fine folks here set me right on this subject, you should use just the same key every time. 3" x 10" is a bit much for a 5" 3jaw and is pushing the limits of your lathe a tad. I would suggest using the 4jaw for work this massive in general. I just don't see being able to reliably drill a center hole with a piece of stock that large hanging out in the wind on a chuck that small. The 4jaw will grip much tighter and allow you to get it properly centered for drilling.
 
I am new to machining and recently bought my first lathe, a King Canada 10 x 22 (same as Grizzly G0602) and have spent the last month learning / playing and working out some of the bugs. My intro lists a bunch of bugs that I have fixed so far, based on information from this site. In the process of learning I have turned a few small pieces of steel rod 1" and less plus a 3" round that I tapered over a 10" length, for an anvil I am making. At first I used a dead center in the tail stock and the 3 jaw chuck in the spindle but found that the dead center would get hot and if I put oil on it it would smoke and stink up the shop. So I bought a live center thinking that would be better but with the heavy 3" round it would wobble and no matter what I tried, I could not get it to spin on center.

Based on my reading so far, it appears that the dead center is better to use but what is used for lubrication. Does there need to be some sort of drip system to lube it or just let it get hot?
HBilly, you stated that you turned a taper on the 3" material over a 10" length. How much taper? Did you create the taper by moving the tailstock over? If so, you may be having several problems. First, you cannot really chuck your stock in the 3 jaw chuck while is is also offset at the tail stock. The chuck jaws are trying to make the work turn straight. Tightening the 3 jaw while the tail stock is moved over will cause a tremendous side load on the tailstock center. I assume that you would have needed to tighten the chuck jaws after the work was mounted and offset. Besides the tailstock being pushed sideways, the chuck would not be able to close completely and would be gripping the work with the base of some jaws and the tops of the other jaws. That would cause the jaws to loosen on the work and I also think that could explain your wobble. Apart from the side load on the dead center, you also have an angle with the work that is not 60 degrees if the tailstock is offset, so the work will only be resting on a single line contact that is not concentric with the dead center surface, but changing its contact in a rubbing motion from tip to base ends of the dead center contact, rubbing and making friction while doing so. The only real way to do tapers by offsetting the tailstock is to turn the work between centers, using plenty of lubrication on both centers and not pushing the centers into the work more than enough to keep it from having side play. No smoke allowed, which leads to galling of the centers. You can use your 3 jaw to make and to hold a center for the spindle end. You will need to buy or make a dog to turn the work, and the jaws of the chuck can drive the dog.
 
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