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Thread: turning burls
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9th June 2014, 09:48 AM #1GOLD MEMBER
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turning burls
Straight up no photos so this didn't happen.
I've now blown up 2 burls first one was a small piece 5cm across and 12 cm long looked to have an egg hiding in it so screw mounted with live centre other end, used a roughing gouge to get near shape then spindle gouge to finish, end polished up nicely, reversed the piece put into matching cup bring up live centre begin turning with roughing gouge and kaboom snapped I think into 3-4 pieces flying throughout the shed shattered into lots of tiny pieces.
Second one was 20cm across and about 12cm deep I decided on a natural edge bowl. I mounted it the same way, first heavy bit of gouging and the thread tore in the burl, remounted slightly off centre and gingerly cut out a foot mount, it cut and then polished up ok. Then I mounted into step jaws and was able to get a nice shape and finish on the outside. Started gouging out centre got wall thickness to 8 mm started using scraper got to about 5-6mm and kaboom left with foot in jaws and pieces no larger than 2cm spread throughout shed.
Each time the tools were sharpened first.
Question am I unlucky to have had 2 unstable burls? or is there some special technique to mounting and working aussie burls ? I have watched utube with no enlightenment.
thanks DennisSome people are like slinkies - not really good for anything, but they
bring a smile to your face when pushed down the stairs .
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9th June 2014, 12:00 PM #2Novice
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Hey ya,
I recently got back to doing some turning after too long. Sounds to me like what I did the other day; tools became blunt as you are working and gradually you apply more force to get them to cut, and then the impending catch on an imperfection makes the whole thing go bang. Tools will get dull really quick on burls, in my limited experience.
Hope this helps.
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9th June 2014, 12:48 PM #3GOLD MEMBER
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Could just be the burl I have scored some dodgey ones, Big sap pockets and the one I turned a bowl out of had a dead branch in it! Looked sound, but hollowed out real quick fist size and smaller! In the blink of an eye!
I personally prefer a spigot or tennon on burls rather than a recess.and keep walls a bit thicker but I play it safe if unsure!
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9th June 2014, 12:58 PM #4
Roughing gouge a bit to rough. Use a bowl gouge (with a kind of swept back grind. ) and go easy. And kinda go from the middle outwards like its a cross grained bowl. (So from the tail stock outwards. ) (Do you need pictures? I'll see if I can take some today if you like. )You can't always tell which way the grain is going. Well, it goes every which way. So you need to take it easy.
If the amount of tool you are cutting with is bigger than the amount of wood you are holding in your chuck you will probably break the wood off.
Sometimes a small scraper will work the best. Cos, like, the grain goes every which way.
And go easy.anne-maria.
Tea Lady
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Follow my little workshop/gallery on facebook. things of clay and wood.
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9th June 2014, 02:07 PM #5
As they said, a light touch and lots of trips to the grinder.
A close inspection of the grain patterns before mounting can also show up not so obvious weaknesses (small cracks, voids or just grain running in an undesirable direction) which make you 'second-think' the way you were about to mount it.
Even after mounting, it's a good idea to stop the lathe frequently and eye-ball your progress, to inspect for any such freshly revealed potential problems.
For any really irregular burls I also tend to slow the lathe more and more as the walls become thinner and thinner. It makes the turning slower, but increases survival factor.
To me, it sounds like a significant amount of bad luck was involved with yours. You have my sympathy; it always sucks to lose a piece.
- Andy Mc
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9th June 2014, 07:12 PM #6
Also noticed tht you have used expansion mode holding the bowl. Puts extra pressure on a burl as it gets thin. Probably using a spigot would be better.
anne-maria.
Tea Lady
(White with none)
Follow my little workshop/gallery on facebook. things of clay and wood.
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10th June 2014, 08:26 AM #7GOLD MEMBER
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Thanks for all the replies
gets down to practice practice practiceSome people are like slinkies - not really good for anything, but they
bring a smile to your face when pushed down the stairs .
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10th June 2014, 12:09 PM #8GOLD MEMBER
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Fubar,
Think of a burl as jello fruit salad, lots of hard chunks barely held together. I agree with making a spigot to grab rather than a recess that forces the base apart.
On any suspicious bowls I make the spigot, grab with chuck and turn the outside, then wrap several turns of tape up close to the rim and hollow the inside leaving about twice the final thickness. I take it out of the lathe and let it adjust itself for a week or two.
Then I re-chuck and do as much of the outside as I can reach, coming from the bottom slightly into the tape, then clean up the rim slightly into the tape, then I do the inside, sand, and apply oil finish.
Then I remove the tape and run the lathe one speed slower than normal, I clean up the part that was under the tape, using a 3/8 inch bowl gouge and a rounded scraper in the trailing position, taking off just the slightest sliver with either tool. Sharpen frequently.
Then sand and finish. Burls can be a real pain, but I think they are worth the trouble.So much timber, so little time.
Paul
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