http://wowjoke.com/gif/white/1332.gif How critical is this? If you have a blank that is rough cut with a chain saw and trimmed up with a band saw or your table saw...you of course are unable to find exact center points. What do you do in this case? I would assume chuck it up ,run low speed and with a roughing gouge turn it down to a cylinder.
Ain't no such thing, Dick.
It's the old machinist's lament: "Nothings round."
You'll have to knaw it round with your chisels. Start at low speed. For me that's 500 RPM, slow as mine goes.
Gently begin cutting away the high spots. It takes time, and it's kind of a controled catch and release. Pretty soon the spinning blank will get the high spots gnawed off and take a rounded shape.
As you continue to turn it the cutting will get smoother and smoother and you'll find a "sweet spot" where the tool is drawing a curl of wood shooting away from the edge of the chisel.
I watch the wood coming over the top of the blank and gently try and make it uniform.
Once you have it fairly round, try a scraper tool. That's the chisel that's flat on both sides with a rounded beveled cutting edge.
I advance the speed when I feel the blank is getting round. the step up makes the tools cut more uniform, and things get smoother still.
I usually jump from 500 to 1250 RPM, but I've been turning >6 " blanks at the start (making +/- 4" turnings)
I started small and am working up to bigger (and Better) things.
Your gonna get some catches, your gonna wreck some stock, and you may loose a few and have to chase them around your shop. :o
But your started.... you'll do fine! Just take your time.
And don't go in the house till you shake off the cuttings that will be head to foot.
That's why I want to put a urinal in my shop someday. At night I can pith in the backyard. But broad daylight is a different matter. ;)
In regards to centering, what Sonny said. Center it as best you can, start slow, turn it to the round and square the ends. It helps to have some extra weight on your lathe stand. I have about 400 lbs of sand bags on mine. If your stand is too light and your blank too far off balance your lathe will start to dance across the floor.
If you are turning a blank where the grain is NOT parallel to the lathe bed, such as a bowl blank, use a round nose scraper to get the blank to the round. If you use a roughing gouge you can get some really nasty catches and possibly split the wood. If your scraper is sharp and has a nice smooth burr you'll get some really nice shavings and leave a pretty good finish.
Once you've trued up the blank you can turn up the speed to whatever is comfortable for you relative to the size of the blank.
http://wowjoke.com/gif/white/1332.gif Steve I tried that round nose scraper on the vase and it wouln't cut sh!t.It may be technique but it looked and felt like it's name implied "scraper".I'll have to read something to get the directions on that motorscooter cause it sure wasn't friendly to me.I thought at the time something must be wrong here, they wouldn't sell a POS like this,its got to be me but I'll get there.
The round nose scraper is used in bowl turning. I works very well on end grain and the inside bottom radius of a bowl. There are varying agruments about using it with the bevel up or down. My father has turned 100's of bowls and dishes and uses his long side down. I prefer to use mine long point up.
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I do it a little differently, I use the bowl gouge for roughing. It seems faster and I have less cleanup of torn grain to fix when it is round. But everyone does it their own way and there is no "correct" way.
I think the problem you are having is most likely due to the scraper not being sharp. Try to get a nice smooth edge with a nice smooth flowing curved end and it should work surprisingly well. My scraper is ground at 79 degrees, a steeper ended tool will be more aggressive, a more sloped angle more controllable. You will eventually find you comfort zone angle. But as you get more practice, it may change to a more steep angle, since you will have more control of the less controllable tool. (if that makes any sense)
As others mentioned, you probably just need to give your scraper a good sharpening. I usually begin sharpening a scraper by grinding the bevel. I grind the tool "upside down" so that the handle points up rather than the normal way of grinding a bevel with the handle pointing down. Either way works fine but because I grind the sides on my round nose scraper I find this method gives me slightly more control. After grinding, I remove the burr by honing the topside of the tool with a wetstone. This is important because the burr left by grinding is not that great. I also lightly hone the bevel. After honing there is no longer any burr. If I need to take really light cuts on a workpiece that is jam-chucked, I will stop here and use the tool. Otherwise, I will put a nice smooth burr on the edge with a Vertias Scraper Burnisher. At this point the tool will act more like a cutting tool than a scraper. You should be able to get nice curly shavings. Remember that when you are using the scraper to keep the handle pointing slightly upwards. As you start to lose the burr, touch up the tool by rehoning and reburnishing.
Note: the first two pictures, top to bottom, show the sample woods I bought to match: mahogany, walnut, oak, the bottom is the side of the table. The remaining 3 pictures are of the wood in question...