Problems with a Royal live center

Overland · Nov 27, 2021

When I bought my "new to me" lathe it came with a Royal "Super Tri-Bearing" live center. Quite a nice piece of kit, I thought.
Well I was using it today. A piece of 1-1/2" steel bar about 36" long. I center drilled it while held with minimum stick out; then pulled it out about 30". I used the center to support it, and tightened up the chuck.
There was about a 10 thou run-out on the center. There's no apparent play in the bearings. When I pulled the center back, the bar was running out maybe 1/16th.
So the center was not able to overcome the natural run-out in the bar, but reduced it from 1/16th down to 10 thou.
This is on a Colchester 21x80 lathe in pretty good shape.
Is this an acceptable performance for the center, or should it have held the bar true ? (remember i supported the bar on the center before tightening the chuck).
There's no apparent play in the bearings with no load on the center.
Is this center re-buildable ? Seems like the taper and body are one piece with the center pressed in. Not obvious how to get it apart.
Thanks
Bob

Milland · Nov 27, 2021

Check the actual runout of the taper on the center by using a test indicator and spinning the point by hand. I suspect you'll find it's much better than the error you're seeing on the bar, which is most likely due to drilling off center at the chuck.

Overland · Nov 27, 2021

Milland,
Maybe I wasn't clear.
I drilled the center when bar was close in to chuck, so I feel pretty confident I was on center.
Putting a clock on the parallel part of live center shows no appreciable run-out, with no load on center.
When I pulled the bar out 30", it was running out about 1/16th".
My point is that this run-out on the bar "pushed" the center to about 10 thou run out.
It seems the center wasn't able to resist this and center the bar.
So am I asking too much of the center ?
Should I rebuild it ?
How do I get the darned thing apart ?
Thanks,
Bob

gbent · Nov 27, 2021

Be glad the center didn't pull the bar into perfect alignment. If it would have, when you removed the turned piece it would have been bent. If you want to turn good work using a tailstock center you have to dial the bar in so the center is serving as a work support, not distorting the work. There are a couple of ways to accomplish the task. You can put a center in the chuck and turn it in place so it is true. Then run your part between centers. You can also grab the bar short in the chuck so the axis isn't influenced by an off center chuck. You can also put a wrap of wire around the part in the chuck which makes the chuck act as if it is only locating on a point. Be aware that any setup where the part isn't set solid against the chuck somehow is liable to slip into the chuck, which will make the tailstock center loose.

Gordon Heaton · Nov 27, 2021

Royal centers are very good. I'll be surprised if your 'flex' isn't in your tailstock ram, etc.
An extended ram will move a great deal more than a Royal center, or any other decent center.

Milland · Nov 27, 2021

Overland said:
Milland,
Maybe I wasn't clear.
I drilled the center when bar was close in to chuck, so I feel pretty confident I was on center.
Putting a clock on the parallel part of live center shows no appreciable run-out, with no load on center.
When I pulled the bar out 30", it was running out about 1/16th".
My point is that this run-out on the bar "pushed" the center to about 10 thou run out.
It seems the center wasn't able to resist this and center the bar.
So am I asking too much of the center ?
Should I rebuild it ?
How do I get the darned thing apart ?
Thanks,
Bob

Your live center is almost without doubt just fine. Do not try repairing it, you will only ruin it.

When you stated that you drilled the bar with minimal stickout in the chuck, what you were really doing was trying to clamp a 36" lever weighing 18lbs by just the end. Without a support inside the headstock of the lathe, you had a tilted bar in the chuck, and so didn't drill a "true" center hole.

When you pulled the bar out, now holding the other end in the chuck, you had an eccentric (relative to the bar OD) AND off-axis cone that you were asking the live center to, well, center. Not happening...

Your chuck may not be running true either, that could contribute to the errors you're seeing. If in doubt, set up the part again as you originally had it for drilling the center hole, and check if the hole runs true. Now rotate the bar 180 degrees in the chuck and check the hole again. You will likely see an error at the rotation, if not the first chucking.

If still in doubt, set it up again and take pics of the setup and post them here for review.

moonlight machine · Nov 28, 2021

Put a dial indicator on the tailstock quill and the center body and watch them wobble all over hells half acre. Your center is off as in post #6. the slop in your quill and quill taper does the rest. The center is fine.

Overland · Nov 28, 2021

Thanks guys,
I got to thinking about it last night. What I should have done perhaps is index the bar in the chuck to find a place where it was running true, then use the center to support it.
I'll try it again and see if "the forces from trying to straighten the bar" are also causing deflection in the tailstock quill, etc.
The chuck is a 12" dia, 6-jaw Bison, or Burnard, can't remember which.
Always good to learn.
Thanks
Bob.

henrya · Nov 28, 2021

Don’t know what you are trying to make, but I’d start by chucking the bar with about 4 - 5 inches out and turning a journal about 3” long. Next, use a boring bar to cut the start of a center hole, followed by a center drill. Swap ends an do it again. This will get you a lot closer to turning the bar on its axis. The slight journal will stop any slippage into the chuck. It will also allow you to chuck and rechuck the bar in pretty close to the same location.

As mentioned above, a ring of wire in the jaws might help with mis-alignment. But now you have a chance to turn the bar to desired diameter or do what work you have in mind. You are also going to need a steady rest, but thats a different story.

Or turning this between centers is the best way. You can make a center to do this. Turn a piece of stock with a shoulder then flip it and turn the center point. Its as dead true as your machine can be. Figuring out a dog to drive it is no big deal.

MCritchley · Nov 28, 2021

A few things.
Rough and finish the center drill, center drill as normal, then go in with a drill bit to open up the straight portion of the center drill. Then go back with a center drill at a low rpm and just touch the taper. The tip of the center drill is fighting the the taper. You will have a good tru center this way rotating with the axis of the spindle. Check the taper with a tenths indicator, you will be surprised.

Don’t be afraid of a steady rest, they are there for a reason. Drill the center with the shaft In its turning position with the end supported in the steady rest. The steady is a whole conversation about setting that up. It is very necessary for large work and to get a good center.

Gbents advice about the wire is very important- think of the physics of the bar griped straight in the Chuck, it will steer the workpiece to where it wants. When using wire the stock will be driven off a single plane much like a center.

4GSR · Nov 28, 2021

Take your ball peen hammer and hit the OD at the end of the bar until it runs true. May want to back off the dial indicator while you do this. :skep:

I've seen this done so many times over the years, I catch myself doing it! Most of the time I grab the bar on the end pull it toward me a little, on the low indicator number, and usually get it running within a couple of thousandths. The center usually picks it up and both will run fairly true. Just my nickels worth. Ken

Overland · Nov 28, 2021

All good advice thanks.
I guess I was being lazy, expecting the center to true everything up for me.
Thanks for not flaming me for being a dumb-ass.
Bob

michiganbuck · Nov 28, 2021

Royals are very good, perhaps someone reground the point with the center locked and so put/ground some run-out in it from that grinding.

As many said the part likey had more error that the tail center could bend the part straight.

One way to chick a center is to bring it to a faced part ane with just enough push on the face part to just be able to turn it, check it with an indicator...and then give it a push-pull to see if it has side movement.

To grind a live center you put some pressure on the point and then turn the point in its own bearing against a running grinding wheel...60 grit is the normal wheel for finish quality.

Even between centers with the tail on a live with the headstock run out .005, you will see some run out at the tail on a live or dead center. The part has wobble from the headstock and so some error will show on a part held on a perfect perfect tail center.

Servicar rider · Nov 29, 2021

You don't know how straight the lathe bed is either? Lots of ways to be off that amount over that distance?

michiganbuck · Nov 29, 2021

One can wrap a wire around the chuck held end, and put the out end on the tail to make a bent part run better at the ends.

But the bend will still be in the part's center area.
Ok for a slow-running device where balance doesn't matter.

Flipping the part to tickle the wire held on the tail makes the two bearing fits very good/OK, with the part still having the bend in its center area.

a bent part can't even be made good/OK in a 4 jaw with not having a wire wrap.

Overland · Nov 30, 2021

I did some checking yesterday.
With no axial load on the center and a clock on the cross slide, by pulling and pushing on the point of the center I got the following readings:
- at the tailstock barrel, less than 1 thou overall movement.
- at the body of the center about 5 thou.
- at the tip of the center, about 10 thou.
Seems there are some problems with the center.

Milland · Nov 30, 2021

If you're certain that the center is indeed faulty, I'm pretty sure that Royal offers a rebuilding service. I'd send it to them before I'd try to fix it myself.

Royal High Performance Live Centers – Royal Products

If you really want to DIY, there may be useful videos online.

Royal Live Center Disassembled | Lathe Live Center - YouTube

Gordon Heaton · Nov 30, 2021

Overland said:
I did some checking yesterday.
With no axial load on the center and a clock on the cross slide, by pulling and pushing on the point of the center I got the following readings:
- at the tailstock barrel, less than 1 thou overall movement.
- at the body of the center about 5 thou.
- at the tip of the center, about 10 thou.
Seems there are some problems with the center.

Those measurements, and the way they increase, are consistent with a less than perfect taper mount. I would not expect a problem with the center to be progressive like that. Have you put a drill chuck or morse mount reamer, drill etc. in the tailstock and tried the same test? Even if another tool checks out, you could have an issue with the center's shank.

edit: I've used the Royal refurb service mentioned by Milland. The turnaround is quick. You'll get back a tool at new specs but at a much lower cost than new.

gbent · Nov 30, 2021

You have the center in a sleeve. You need to get a center that fits your tailstock without a sleeve, the sleeve is just one more place for error and movement.

Overland · Nov 30, 2021

More follow-up after reading the advise.
The body of the center is one-piece with the taper; so the 5 thou deflection I was getting on the body is clearly in the tapers somewhere.
So, the 10 thou I'm finding on the tip is largely from the tapers.
I called Royal, thanks for link. The tech said once there is an axial load on the center the movement will go away,(probably not from the tapers though !).
I need to pull all the tapers out and clean them up thoroughly.
By the way, the tech said they will regrind the tips for free.
Thanks for all the help !

Bob

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