I am new to turning, having taken a couple of day classes. I am trying my first independent project, making an assortment of pencil boxes in the 5″ 6″ range. I am using cherry, ash, and maple. I am using a Fisch mini-lathe and Oneway chucks.
First, I round the stock using the spindles and a roughing gouge. I then mount the stock on a Oneway chuck to bore out the inside. Here is where I have a problem. When mounted on the spindles, the stock appears to be completely round. When mounted in the chuck, it turns slightly off-center, such that one side of the stock will be thicker than the other side. Obviously, when in the chuck, the stock is not perfectly round. The bottom is completely flat and the bottom fits in the chuck flush.
What am I doing wrong? Have I mounted it on the spindles wrong? Wouldn’t the rounding process on the spindles produce a perfectly round piece even if not perfectly centered on both ends?
Replies
It sounds like the error is occurring when you transfer the workpiece from the two centers to the chuck, so my guess is that you're not securing it to the chuck perfectly centered, or it's getting knocked off center during the hollowing process.
Try this and let me know if it works. Mount the rough blank between two centers and turn it into a rough cylinder. Then cut a short, round tenon at one end. Remove the blank from the centers and mount the short tenon into the chuck and continue using the the live center at the other end. True up the turning one more time. When you feel like the outside shape is ready, remove the live center and hollow out the inside. This way you're cutting the outside and inside without removing the workpiece from the lathe.
If it's still off-center, I'd say it's a problem with the chuck holding the workpiece. One trick I use here is to cut the tenon with a little flare to it, so that the chuck jaws can really grab it.
Alternatively, you can work backwards. Mount the chuck between two centers just long enough to cut the short tenon, then mount that in your chuck and hollow out the center while the outside is still rough. Next, screw a scrap of wood to a faceplate, and turn it into a short cylinder with a radius that matches the inside radius of your turning. Mount the workpiece back on the lathe with the hollow end jammed against the faceplate and a live center at the other end. Finally, shape the outside.
Let me know if that doesn't make sense.
Matt
I solved the problem and it was my own fault. I had made the tenon too long for the jaws, thinking, for some reason, that the shoulder of the tenon had to be outside the jaw grip so the bottom would sit flat. I found it works much better if the tenon is shorter than the jaw grip so the shoulder will fit flat and flush with the ends of the jaws. Making this corrrection eliminated the problem completely. A lesson learned the hard way usually sticks. What I had been taught in the classes obviously didn't. Now that I have this problem solved, saschafer's advice makes sense to me.
Great. I know exactly the problem you described. Glad you figured out the solution!
Think of it this way: (For the sake of discussion, let's assume that the piece is 1" in diameter and 8" long.) After you've turned it to a perfect cylinder between centers, you mount it in the chuck. When you do so, you find that the end of the piece that's the furthest away from the chuck wobbles back and forth a total of, say, 1/8". Well, if you go through the math, you find that the supposedly flat bottom that's pressed up against the face of the chuck only has to be out of flat by 1/128" to see that much wobble.
So that's the basic problem: You will always have to do some realignment after you change the way a workpiece is mounted, because of the slight imperfections in the material or the tool(s). So mount the piece in the chuck and rotate it by hand. Watch how much the end of the piece wobbles. Rotate the piece so that the wobble is at its vertical high point. While holding the workpiece with one hand, slightly loosen the chuck and adjust the position of the workpiece by about half the amount of wobble. Re-check the wobble and repeat the realignment until the wobble is reduced to near zero. You will quickly reach a point where you don't even have to repeatedly loosen and tighten the chuck--just leave the chuck in a "half tight" position and lightly tap on the workpiece at the high spot to nudge it towards center. Once the alignment is perfect, fully retighten the chuck.
-Steve
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