Bowl rims, rounding over

I am new to turning and have just made my first small bowl (well, nearly!). I did quite well until I tried to change the flat top (rim) into a rounded over shape. I wasn't sure how to tackle it so I used a bowl gouge more or less on its side as I had done successfully for hollowing the inside, and I approached the inside edge very carefully, but I got a catch and the bowl came out of the dovetail chuck, damaging the base. I was able to glue it and try again but the same thing happened. Can anyone help, please?

Reply to
Bill
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Bill wrote: ...snip...."so I used a bowl gouge more or less on its side as I had done successfully for hollowing the inside, and I approached the inside edge very carefully, but I got a catch"....snip....

********************************** Bill,

Without seeing what you're actually doing, it's quite difficult to correct your approach. I'm not going to go through a long description of proper tool handling (I'm sure others will do that better).

Here's what I do when I *think* I'm using a tool right and it goes wrong: hold the tool as you were but with the lathe OFF. Hand turn the bowl and watch how the tool edge is reacting. You could have not turned it at enough of an angle, you want the edge to be more scraping than cutting as it would when hollowing the inside.

Hope this helps. Ruth

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Reply to
Ruth

Bill:

The time to get the right shape on the rim is early in the process, not after the bowl has been hollowed -- especially if it is thin. The rim will change shape and when you go back to it -- well, you know the result.

Generally, work from top to bottom and try not to go back up when working on the inside of a bowl.

Also, why do you want the rim rounded? A rounded and sanded-over rim is the mark of a machine-made production bowl. I'd suggest you give the rim some character -- it should have two edges (not sharp, though) and slant either inward or outward -- not straight across. It can be slightly rounded rather than flat. That way it looks to be a well- thought-out design element.

Bill

Reply to
Bill Rubenstein

Bill,

Ruth's advice is good. It is an easy way to diagnose what is happening.

If you were scraping the rim, then I doubt if you would get a giant catch. If scraping, do it lightly.

If you were cutting across the rim, which I suspect, the dynamics of a catch are very subtle. To explain what might have happened, try this experiment. With the lathe OFF, hold a skew point straight into the rim (just touching) with the handle parallel with the spindle's axis. Orient the cutting edge vertically, with the long point down. Now raise the handle slightly so that more of the skew's cutting edge contacts the bowl rim. Now, turn the bowl by hand. The sharp edge of the skew will make a line all the way around the rim if it is EXACTLY vertical. If it is even the tiniest bit tipped toward you, the skew edge will spiral out. If it is tipped away from you, the skew will spiral in.

When starting a gouge on a spinning surface, the gouge's cutting edge acts exactly like this until the bevel is rubbing. When the tool is laying on its side with the flute pointed to the left or right, there is a tiny piece of the cutting edge that is vertical and will track correctly around the bowl's rim. Even the slightly misalignment forward or backward will cause the tool to rapidly spiral in or out and possibly cause a catch. The trick here is to be firm with the tool when introducing it into the rim. For that brief amount of time that there is no bevel rubbing, the only support the tool has is your hand on the tool rest. Make the flute dead flat as you can, then be firm on the start of the cut. Assuming that you are cutting away from yourself, if the tool is tipped back a bit, the tool will tend to kick away safely from the work. If the tool is tipped away from you, the tool will tend to dig into the work and cause a catch. As you learn where that exact spot is, err on the side of a kick out rather than a dig in. Then you can make tiny adjustments on your hand positions until you hit it just right.

Hard to explain without showing you, but I hope it makes sense.

Joe Fleming - San Diego ==============================

Reply to
Joe Fleming

I used to have the exact same thing happen to me except my bowls usually exploded. Like Bill Rubenstein suggests, do your rim shaping early on in your hollowing process before you start hollowing below the rim very much at all. That's made the most difference in my bowl rims. And, as others have already mentioned, a light scraping action works quite well here.

- Andrew

Reply to
AHilton

The real answer already given - make edge detail early early while the bowl is still close to circular - I'll explain a bit of why the bowl blows up or runs off. As you look at a wooden bowl cut "normally" with the heart toward the bottom, it's not circular, but oval. The longer grain portions are less distance apart then the short grain. Nothing wrong with this, except it's the worst condition to have to try and work the rim. Your tool, unless carefully presented, will be going from a void into the uphill side of the long grain. This is a recipe for a catch or, at the least, an ugly spot of torn grain even when inside the bowl, so it's best to avoid having to do this on thin rims which might shatter.

But, if you are working the rim, start your cut into the face, not the slope, where your tool will have full support as it makes entry, and the difference in diameter will become merely a difference in shaving width, rather than an uphill tear, squirm and dismount. It also makes sense to make it a cut at minimum radial pressure, to avoid distorting what you have further, and possibly breaking it. I use the same entry cut when doing the semi final cuts even below the rim, as it allows the gouge to sever the fibers under inward compression rather than ripping them and creating sanding problems.

If I were going to scrape, it'd have to be a _really_ light contact on a _very_ narrow area, and I'd still start in full contact at the face and roll to the inside.

Reply to
George

Many thanks to everyone who responded to my question, especially Ruth, I particularly like her idea of turning the work by hand to see what's happening at the tool (and I like her web site). I managed to sort the problem by using a scraper but it's quite worrying how quickly a catch can happen. I did the inside of the bowl easily (much to my surprise!) but just coming on to the rim nearly wrecked it. Thanks again Bill

Reply to
Bill

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