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post #1 of 8 Old 03-03-2012, 05:51 PM Thread Starter
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doing big bowl/ frustrated

well decided to push the limits of this lathe and went with the biggest blank I could possibly get on inboard. All told it is about 15 inches in diameter 8 inches tall after losing a bit while rounding out. Turned it wet the form is done now all that is left is the finishing and it is impossible to get it finished because of the size and the fact that every time I glue up cracks sand take a break then come back to it the next day it has warped a little more, few more hairline cracks and Ive gotta go resand again and again. When it warps it means It's not sanding right and Ive got to take a little more material off so it will spin true and then sand from there. Probably wouldnt be such a bear if it werent natural edge which makes sanding a pain in the butt anyway. If I could get like a process you big turners use for doing your bowls Id greatly appreciate it. Im all in the dark on the big stuff. thanks in advance, happy turnin,
Bond
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post #2 of 8 Old 03-03-2012, 06:03 PM
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I'm assuming green wood? You've got to turn it 90% , let it dry, return to finished. Or turn to uniform finished thickness and finish and let it warp. If you're leaving it overnight you've got to wrap it in plastic bag to prevent drying.

That bowl was perfect right up until that last cut...
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post #3 of 8 Old 03-03-2012, 07:20 PM
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I've decided that the difficulty grows exponentially with size. I don't (can't) do anything that large but if I were you I'd bag it until I had time to turn past the checks, sand and get'r hollowed in the same day if you are going to finish it green. The overnight deal rarely works out very well for me.
I hope you can make yourself turn off enough wood to get well past those checks so they won't keep hounding you. (just the opinion of a novice.)
Good luck with it! What's the wood?
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post #4 of 8 Old 03-03-2012, 07:56 PM
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Another comment: if you are power sanding with foam backed paper nothing says you have to run the lathe while sanding. David Ellsworth does it that way. That being said you could consider skipping the whole sanding step, saving time and heat build up, until after you've completed the inside. It might help with those checks.
In other words, return the outside back to round and past the cracks, go straight to the inside, then sand in and out even though it will already be out of round again. Just a thought.
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post #5 of 8 Old 03-03-2012, 08:01 PM
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Bond,
ditto on what Sawdust said. If you're turning green, you cannot start and stop and start and stop. It is going to warp and crack if you do. Even if you are just roughing it out, you don't want to get it halfway through and stop for lunch. And if you plan on turning it start to finish, you have to turn it uniformily thin. I would be kinda leary of trying that on such a large bowl. I have done it on smaller bowls, usually around 6" and had no problem. If the wood is so green that you can see the moisture coming to the surface as you're turning, you will have a tough time sanding. You can go ahead and turn it to finish, set it aside to dry, and then sand by hand off the lathe.
Mike Hawkins
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post #6 of 8 Old 03-03-2012, 09:20 PM
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i had a wet cherry blank that i turned to completion it was about 11" so quite a bit smaller than yours but i started and finished it as these guys said.put it in a paper bag and let it dry then remounted it just to sand it smooth
it warped on me but i re turned the bottom to make it flat and it was one of my favorite bowls to give away
good luck with it
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post #7 of 8 Old 03-04-2012, 08:50 AM Thread Starter
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great information fellas. I suppose it's just some stubbornness on my part. Knew about the 10 percent rule but had some reservations about it. I just hate waiting around for things to be finished I suppose but seems like taking it off the lathe is really my only option. I just recently purchased a supernova 2 chuck but am wary about using it for the first time on such a large piece. The wood is maple and sadly even if I wanted to take it off let it dry and the like Im not sure that it would work because the waste block is still attached which is what is causing most of the cracks farther down the piece, and Ive left no room for a tennon even if I wanted to put one on the bottom im not sure there is room for one because the bowls depth added to a parting cut would bring the width of the bottom to about 1/2 inch at best. I suppose Ill just try to turn past the checks if there is room. finish as best I can and chalk this one up to experience. On the need to learn list would be- making proper tennons for large pieces and pieces in general lol and PATIENCE!!! and powersanding stuff, oh and calipers couldnt hurt either I suppose hahah thanks for all the help as usual. seems like there's always something to add to the wish list will let yall know how my crackmeister turns out, happy turnin all,
Bond
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post #8 of 8 Old 03-06-2012, 07:22 AM
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I rough turn most all of my larger bowls mostly because sanding green wood just isn't fun.
You can reduce the warping problem by keeping the outside of the bowl wet (I use an old windex spray bottle) while your turning, then cover it a plastic bag if you have to leave it for any reason. I cover it even when I stop to go to the bathroom. That keeps it wet, drying is what makes it warp. However some wood will warp simply because you've removed wood and relieved the stresses in the wood.
When I do need to sand the bowl while green, I flash dry the surface with a hair dryer. On some woods this is bad and can cause cracks so stop if you notice this and spray the wood again with water. If the bowl is thin you may be able to blow a lot of the water out with an air compressor, then the hair dryer doesn't seem to cause cracks.
Most of the time I put the bowl in a box to reduce air movement and let it dry on it's own for a few days or a week. Then I can put it back on the lathe for sanding. I power sand with the lathe off on these because the bowl is usually too warped to sand with the bowl running.
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