Re: Large bowl staying oblong ...

beware of "as much as the job will tolerate" --- I've had thick walled bowls shatter due to the inertial forces, and it's not pleasant when the pieces bounce off the fluorescent lights and you get showered with glass while dodging the flying bowl fragments

"Leif Thorvaldson" wrote: (clip) counter-revolutionary old farts! *G* ^^^^^^^^^^^^^ Counter-revolutionary old fart = someone my age who likes to run lathe in reverse. *BG*

The end grain pick-up you've noticed is likely the initial cause of squirm, and a factor in the continuing problem. On the outside of a piece, where normal spindle rules apply, it's fairly easy to get the tool's point of tangency near the perpendicular to the grain to make a clean cut. The contour of the piece and the gouge both help you.

On the inside, where the piece does not curve away, but matches the gouge, the best you can do is minimize pickup by taking narrow thin shavings. As I and others have indicated, this means not referencing to the piece, but to the rest, and cutting at or a bit below center with the nose of the gouge. I've been lucky in my choice of lathe, because I never had to learn to cope with toolrests which moved or rattled, nor with rests which would not allow me to cut below center. I also find that the forged pattern gouges which came with the lathe are ideal for such narrow thin cuts, and with my curved cast iron rest, allow a continuous cut from rim to bottom, with the broader nose section guiding on the cut portion of the piece, minimizing the gouge instability you mentioned.

If you speed up, you merely discover a new resonance, increase the kinetic energy available for a catch, and may contribute to greater centrifugal expansion along the grain.

Wooden bowls are difficult to get round. Wooden bowls do not have even hardness all the way around, end grain cuts much differently than side grain and you have two different kinds of wood there etc, etc. Even on a modern CNC lathe the piece would not be round (it would be rounder but still not perfectly round) after you cut it and it will go more out of round when you sand it. It will warp and move as the humidity in the air changes with the seasons. If it is not noticeable don't worry about it. I guarantee that all your smaller bowls did the same thing just less.

I think you are right about bumping up the speed a bit to decrease the time there is a void under the tool, but I have one other idea. When I encounter a problem like this, I sometimes resort to a somewhat heretical solution. Instead of a traditional roughing gouge, I find the heaviest tool I have with a sharp point, like a 1" skew or the corner of a square ended scraper.(I also have a tool with a diamond-shaped carbide removable point, but I have no idea where to get these anymore).....The idea is to have as little tool surface touching the bowl as possible, and thus, as little bounce or catch. You of course get a 'rough' surface as you bring it to round, but you also control the tendency to follow the 'oblong' shape you are trying to eliminate. I also will sometimes follow this with a wide, square-nosed scraper for a bit until I get 'roundness' achieved and the surface relatively smooth. THEN I can go back to a gouge for cleaning up.

I have no idea how far down you are now, or whether you have done the inside of the bowl at all, but if you have sufficient wall thickness to play a bit more, you might try my 'cheat'. (I turn a lot of natural edged stuff and pieces with holes where I MUST increase speed to jump gaps, but your glue up sounds like it would absorb one or two speed increases ok...).

I have the solution, and it ain't LDD so you can relax fellows. Why not accentuate the negative in this case, since the bowl seems to want to be an oval. Call it an artistic feature. Of course you may have to turn your shop into an atelier or studio! *G*

"william_b_noble" wrote: beware of "as much as the job will tolerate" --- I've had thick walled bowls shatter due to the inertial forces, (clip) ^^^^^^^^^^^ Bill, I guess you exceeded "what the job will tolerate." But, your point is well taken. I should have said, "At higher speeds the tool is less likely to follow the contour of an out-of-round bowl." Having a bowl shatter is not so much related to the slight eccentricity, as it is to internal defects and other weaknesses in the wood. This hazard is always present. So when people say, "Turn the speed up until it starts to vibrate, and then back off a little," maybe they should be thinking of what Bill just described.

MSC, McMaster-Carr, Enco, or any other metalworking supplier. Look for "carbide insert tooling" - there are diamond shaped, triangular, round, square, etc...

Hey Bill, For about $2 apiece an electrical supply store will sell you a plastic tube that fits over the fluorescent bulb and helps keep the pieces from flying around.

Just make sure it is "ballistic" plastic! *G*

not pleasant when the pieces

Ok - here is an update... a lot of people are correct here on what is happening.

Basically to summarize:

1) It never really is getting round which is expected as noted by many 2) The outside wasn't as difficult because it is like a typical spindle turn and it seems it is more "forgiving". It is on a face plate only and not between the spindles. 3) I actually had to rotate the head stock so the bowl was not directly over the bed. This meant I needed to use the tool rest extension. This brought the tool rest a good 6 - 8 inches away from the bed. It caused it to bounce a bit more. I had a "catch" and it popped the tool rest so hard that it sheered the post off. Jet says they have seen this a few times and were sending me a free replacement. To get over this, I actually got my old lathe (haven't sold it yet) and use that as a "free standing" tool rest. That was a bit more solid and more successful. 4) It turns out that a 1" skew was my best tool of choice especially for the outside - too bad I didn't read Bill's post before I did it or it would have saved me a bit of time. 5) The stable free standing tool rest made the inner bowl easier but it still was a bear. I tried it with varying height of tool rest and I found it best if I put the bowl gouge at a 45 degree angle to the rest. So the handle was way down by the base of the tool rest and the gouge end was a good inch or two above the tool rest. It just seemed to be smoother there. The transition from the side of the bowl to the bottom was where it caught the most and so it will take some extra sanding there. 6) Overall I went from "this will be cool" to "I quit" to "ok it might work" to "all right this will turn out" 7) I kept the speed at 450 RPMs the whole time. I didn't want to catch it when moving at higher speeds. 8) When sanding I have bumped up the speed to 800 RPMs but I too have had bowls "explode" so I am a bit leary of it. The walls of the bowl are about 1/2" or so ... 9) So far so good ... just sanding away now.

Thanks to all that have helped.

Darren

wow...quite an adventure! I'm glad you saved it and are looking forward to a complete bowl. regarding this: "this brought the tool rest a good 6 - 8 inches away from the bed. It caused it to bounce a bit more. I had a "catch" and it popped the tool rest so hard that it sheered the post off. Jet says they have seen this a few times and were sending me a free replacement. "....I went thru this with Grizzly a few years back, so I got rid of it. NEVER again a cast-iron tool rest. For future projects, do you have one of those curved tool rests that allow positioning right close to the inner bowl wall? I did without for a long time, but after a year of using one, I am sold!

Got any way to post a picture when it's done?

"Darren" wrote:.(clip) This meant I needed to use the tool rest extension. This brought the tool rest a good 6 - 8 inches away from the bed. It caused it to bounce a bit more. I had a "catch" and it popped the tool rest so hard that it sheered the post off. Jet says they have seen this a few times and were sending me a free replacement. (clip) ^^^^^^^^^^^^ Darren, are we talking about the Jet 1236 here? I used to have that lathe, and I refused to use the toolrest extension, because it just looks like it is MEANT to break. Others in this group have reported injury accidents with this. If you need to do this again, I suggest putting a prop under it that reaches to the floor. That should reduce vibration, and migh save a toe or two.

It is the Jet 1442 but I think it is the same extension. You are right - it actually hit me square on top of the foot. I was wearing boots and it did but not bad. Using my old lathe as a stand alone tool rest made it better. However, when I sale my lathe, I will put a prop under it (if I need to use it again).

Fortunately, I am done with the "tool work" on this one. Now my biggest worry is that the thing will break up while sanding ... even though I only have it at 800 RPMs, I (and others here) have seen bowls shatter before. The bowl wall width is 1/2" but it is always a bit scary that it might get thin in an area or just not be enough.

Darren