Help newbie with centers

[Dan Beckman]

I'm a new turner and I am turning bowls on a Delta 46-760. I'm having a problem with catches causing my workpiece to work loose in the centers. I've had problems with a Stebcenter coming loose and the threaded drive on a Nova chuck. When I say coming loose I mean the workpiece spins loose in the drive and will not rotate. Also, the tailstock drive is getting buried in the workpiece. What am I doing wrong?

[Ian James Webster]

Dan,

I'm fairly new to this myself - so you may want to view my 'advice' with a little caution and wait for the experts to chime in first!! but...... I think you may be trying to take to aggressive a cut and/or tools not sharp enough. I still have a hole in one of my workshop windows from one of my earlier bowls (I left it there as a reminder). With a lighter cut and sharp tools I get far fewer catches and the piece stays put. Also try using a tenon with the Nova chuck rather than the screw part.

Ian

[Marty Eargle]

If I am understanding you correctly, the center is ripping up the wood. Sometimes, this will happen when you have a catch on some wet wood or if the centers are not planted firmly.

If you can't get the hang of making lighter cuts, I would try doing as much roughing as possible with a faceplate attached to the piece.

[Kyle Iwamoto]

I have a PSI version of the Stebcenters. I find they do NOT work well in soft woods or green/wet wood. As you say, it rapidly becomes a boring bit. Use the 4-prong drive that came with the lathe. This is the same problem I had when I started. My 2 methods: 1) use a wood mallet and pound that 4-prong drive in deep. Take it off the lathe, don't pound the blank on the center. I keep my tailstock unlocked, and as I turn, I keep adding tension until the drive seats and doesn't move. 2) lock your spindle, apply pressure with the tailstock. Rock (rotate) the piece back and forth against the locked spindle. This will cause the center to drive in. Tighten the tailstock. Repeat several times.

The other thing I'll chime in about, is balance. On the lathe, lightly seat the blank on just the points between centers. Let go, the heavy part will, of course, fall to the bottom. Unseat the blank and move it about until the blank is fairly balanced, then either 1) drive the center in or option 2) above. Since the blank is [fairly] balanced, you'll have a much easier time with speed. As you rough out the balnk, you can always re-mount it again. This of course will not work on large blanks.

[Thom Sturgill]

Make sure that the wood under the center is sound. Punky wood or bark will not hold. Make sure that there is constant tailstock pressure when using a drive center. Re-tightening as you work is normal, especially with green wood which will compress under the pressure more easily than dried wood.

Also make sure the face that has the drive center is square. This is also VERY important when using a screw chuck, also do not oversize the hole drilled for the screw chuck.

A heavy piece will try to continue rotating when you stop the lathe (especially if you grab the handle to stop it more quickly) and cause the same problem.

A stebcenter is supposed to spin out when you have a catch, but it should allow you to stop a rotating spindle without the center releasing the work piece. It shoulds also not split the piece which can happen with a spur center, especially a two prong center that was aligned with the grain.

[Dan Beckman]

Thanks for the tips. I have been turning dry pieces. I'll go back to the 4 prong drive center. I didn't have this trouble when I was using it. Also, I'm having the workpiece come loose when I'm roughing out the piece as I'm trying to put the tenon on. I know when I was using the screw in the chuck the face was not square, so the piece was not bottoming out all the way around on the chuck face. That may have been a big contributor to the problem.

[Jim Underwood]

Another thing you can do is get one of those chuck mounted centers made particularly for driving bowl blanks. They normally have to large teeth and don't drill holes like the smaller four tooth centers.

Surprised your screw chuck let loose though. I've never had any problem with those...

[Thomas Canfield]

At SWAT year before last, one of the demonstrators used a speed bore bit to form a recess for his drive center to give it a flat bottom and also contain the drive should there be a slip or catch. You might try that on both ends. I often will use some thin CA on green tenons or bark areas to harden the wood fibers to have a better seat.

[Curt Fuller]

And, in addition to all the good advice you've already received, take lighter cuts and make sure your tools are sharp.