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What am I doing wrong?

I'm working my way through Rowleys "Fundamentals" trying to learn the art, and so far I've been having pretty good luck. Seems like every time I run into a problem, it goes away when I stop to sharpen my tools.... :-)

But this time I'm stumped. I'm trying to turn a goblet in madrona, and I'm getting an inordinate amount of chatter while hollowing the cup. I've got a

3" x 11" piece relatively free of cracks (still working off the firewood pile) in a homemade screw chuck, which is working fine for outside turning. Runs smooth, solidly seated, and no vibration at 1720 RPM. I drilled out a starting hole for the cup, but when I started hollowing with a 3/8" spindle gouge, I got a lot of chatter, especially towards the outer edge. Which would make sense due to higher speeds there, I suppose.

I tried switching to a roundnose scraper, and it actually cuts better than the gouge in the bottom of the cup, but there is just as much chatter on the sides. It's so bad, my tools aren't cutting at all. I'm steadying fairly hard with my off hand, but the only effect that's having is that my glove is getting buffed to a high sheen.

Does anyone know what may be going on, or what I'm doing wrong? All tips would help.

Thanks!

Snakewood

Reply to
snakewood
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A few things that might be...

  1. Maybe the screw chuck isn't holding it well enough and it's somewhat loose. Try turning a tenon and then using a scroll chuck.

  1. Perhaps the bevel is rubbing too much. try cutting with just the edge.

  2. Maybe the walls are too thick. Madrone moves FAST. You need to turn it quickly once started because it will go out of round almost immediatly. No need to pre-drill but turn down to finish thickness a little (inch of so) at a time so there as much supporting wood as possible. It the wood gets too thin it will vibrate like crazy and you'll never get a good cut.

Anyway...those are my thoughts.

rr

snakewood wrote:

Reply to
Randy Rhine

Good thoughts all. Reason I'm not using a scroll chuck is financial. Don't have one, can't get one. The screw chuck is holding well though, and I can cut just fine on the outside of the piece.

I haven't started to turn the stem of the goblet yet, so the cup has a full three inches of wood supporting it.

I've varied my angle of cut from scraper to full bevel, and it doesn't seem to make a difference.

Yes, the walls are too thick. Can't do anything about it until I fix the chatter though... :-)

Guess I'll keep trying.......

Snakewood

Reply to
snakewood

Just some additional thoughts.

Is the interior of your piece out of round? Occasionally a piece can go out of round for any number of reasons, especially if the "chuck" gives at all. Try holding your scraper flat against the tool rest and up against the inside edge of the workpiece as you hand turn the piece. This should show if it is out of round. Even the slightest bit can cause "chattering" and poor cutting.

How far over the tool rest are you reaching? A 3/8" gouge will begin to flex/chatter if extended too far, especially cutting into endgrain.

My experience is that scrappers really aren't for working the sides unless you use them in a more "shearing" motion. Typically you'd have the scrapper flat against the tool rest and angled slightly downward as you work the bottom. As you begin to bring it into the side, slowly lower the handle as you bring the scraper toward the outer edge.

Some things to try . . .

-Verne

Reply to
vrhorton

Hollowing can be very difficult to get the hang of. You say you drilled a starting hole. Are you hollowing from the bottom of the hole outwards, ie. with the grain? Start at the bottom of the hole, roll the gouge over on its left side until its almost vertical and cut on the way out. Maybe you are already doing this, but I didn't catch it from your post.

Barry

Reply to
Barry N. Turner

I would guess the screw chuck is the problem. If you don't have a scroll chuck mount a waste block on a faceplate and true up the face. Then turn a recess the diameter of the blank a 1/4" deep or a tad less. then glue it in with ca glue. A bead around the outside of the joint helps also. Use the tailstock to aid in centering. This is assuming you turned to a cylinder to start with between centers and trued up the foot end. When you start hollowing a light touch will reduce chatter. Let the wood come to the tool. Once your hollowed stuff a piece of styrofoam in the cup and bring up the tailstock for support.

Bob, Naugatuck Ct.

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Reply to
Bob Pritchard

This all sounds like good advice. I'll see if I can firm up the srew chuck at all, and take it from there. I hope I don't have to start messing with glue, but if that's what it takes......

Snakewood

Reply to
snakewood

You should epoxy the nut into a slightly oversize hole and skip the CA entirely. Epoxy the hole before putting the nut in and clamp to hold the nut down. I would guarantee this would work. Epoxy is not as brittle as CA. From your description, it sounds like you were relying on the CA, with a fillet of epoxy just for backup.

Reply to
Derek Hartzell

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