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Thread: Problem Piece
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26th November 2006, 09:27 PM #1Member
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Problem Piece
I've had a bit of a problem with this piece and I'd appreciate any thoughts anyone may have to fix it. It's a natural edged vase and the timber is camphor laurel. The outside polished up fairly well and I turned a recess into the base to re-chuck it for holowing the inside. I intended to leave the recess there when finished. When I started to hollow the inside the piece came away from the chuck because a large chip ripped out from the side of the recess. I glued that back in and started again but then the other side of the recess gave way also. Both failures were essentially because of the pressure of the chuck jaws pressing along the grain and pushing a "fillet" out. If you look closely at photo 4 you can see a U shaped crack attached to the bottom of the recess. That's the first failure, the faint cracks opposite was the second.
The recess is probably now strong enough to hold but I need to recut the base because the cracks are quite obvious to the naked eye.
My problem is how to re chuck the piece so I can turn the base. I have a Nova which will not expand enough to grab any part of the inside of the piece. I also have a Bonham which is big enough. You can see in photos 1 and 5 that I've cut a recess around the inside to try and fit the Bonham using the outside jaws - however because of the shape of the piece and the shape of the chuck the Bonham can't grab it either.
Can anyone suggest a way of chucking this piece so that I can returen the base without a major job of constructing a specialist chuck? Wall thickness is now about 10mm and I intend to turn down to about 5-6mm, so I don't have a lot of wood to play with.
Any advice would be appreciated.
(...and any suggestion that the tear outs were caused by poor scraper technique resulting in a scraper catching might well be correct....)
CheersMark J
Cairns NQ
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26th November 2006, 09:43 PM #2
Mark, I use a glue chuck in preference to a scroll chuck for the very reason you have just experienced. THis is the same process as I use for natural edge bowls.
JimSometimes in the daily challenges that life gives us, we miss what is really important...
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26th November 2006, 10:08 PM #3Member
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Thanks Jim - What's your basic process for finishing. I assume you glue what will be the base to some scrap, part that off when you've finished then hand sand/polish?
Mark J
Cairns NQ
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26th November 2006, 11:28 PM #4Can anyone suggest a way of chucking this piece so that I can returen the base without a major job of constructing a specialist chuck? Wall thickness is now about 10mm and I intend to turn down to about 5-6mm, so I don't have a lot of wood to play with.
Gluing a sacrifiical piece on the bottom now is probably your best bet and then finish off the bottom with a donut chuck.
(...and any suggestion that the tear outs were caused by poor scraper technique resulting in a scraper catching might well be correct....)Inspiration exists, but it has to find you working. — Pablo Picasso
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26th November 2006, 11:35 PM #5
Mark, I turn the base first and give it a coat of sanding sealer for two reasons. First it is easier to do in the lathe and second, that prevents the glue spilling over into the recess, a pain to clean up. Turn the project, sand and seal as necessary. Cut the job loose with a hand saw. Natural edge projects are not fun to catch when cut off with a parting tool in the lathe. Clean up the saw cut face on a sander or whatever. I spray lacquer for a final coat.
JimSometimes in the daily challenges that life gives us, we miss what is really important...
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27th November 2006, 12:33 AM #6
Do you know how to make a jam chuck? (He asks hopefully)
That'd be the way to go for reverse chucking that piece, perhaps with a jacob's chuck holding a dowel (with a rounded tip) in the tailstock for that extra bit of security.
- Andy Mc
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27th November 2006, 09:19 AM #7
On real problem pieces, it's sometimes easier to just clean the recess up by hand than it is to work up a chuck for it. I recently tried to finish off a rough-turned piece of peach-bush that had an extremely fragile top and had warped so much during drying that there was just no easy way of holding it. I just hand sanded and finished it 'as is'. The recess was removed by hacking the step away with a carbide burr, then sanding with a 50mm rotary sander mounted in the bench drill. It wasn't perfect, but with with a natural edge..... let the theme flow (IMHO)
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27th November 2006, 09:42 AM #8
Make a large dowel to fit into the bottom of the bowl. Put some double sided tape or carpet tape on the end of the dowel to fill the gap, bring up your tailstock to give a bit more support and to keep it running true.
Change the recess to a spigot and get a better grip on the peice.
Put the spigot into the chuck finish turning as you would normally when hollowing then reverse again and clean up the spigot or redesign the bottom to follow the outside shape.
Spigots are easier to work with than recesses and you can have an even wall thickness on your peice, not a chunky base that you may go through because you forgot to allow the depth of the recess.Jim Carroll
One Good Turn Deserves Another. CWS, Vicmarc, Robert Sorby, Woodcut, Tormek, Woodfast
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28th November 2006, 04:32 PM #9Hewer of wood
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The slight inward curve of the top edge does limit your options.
As an alt to Jim's option you could look at turning up some replacement MDF jaws for your chuck, to go around the outside rim, and then redo the foot with tailstock support if poss. Access can be fiddly but should be poss with a fully extended quill.
btw, I've almost never had probs with expansion mode chucking. Could you have overtightened it?Cheers, Ern
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28th November 2006, 05:12 PM #10Member
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Ern.......mate....mate.....maaaaate...overtighten! What do you think I am? Some sort of amateur.....
...yeah...probably a bit tight!Mark J
Cairns NQ
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28th November 2006, 05:26 PM #11Hewer of wood
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Mark, hope I didn't insult you; that's why I made it a question, non-rhetorical ;-}
I've got a small bowl turned out of a gorgeous bit of local carob - cream and pink. But I did overtighten the chuck in the recess and managed to finish it but with walls far too thick cos I didn't want to push it.
So it's back in the shed after umpteen years and I've read this thread with interest cos the foot needs returning so I can get the walls thinner. So I'm glad you raised the question.
btw, since then I learned a bit tight is good, and you can always check by tugging the piece to see if it moves. And do that several times as you turn cos turning heats and dries and can shrink the timber.
Always something to learn and this forum is a gem for learning.
Good luck.Cheers, Ern
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28th November 2006, 08:22 PM #12Member
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No offence taken at all Ern. I was just trying be funny with the amateur comment. Thansk for the advice.
cheersMark J
Cairns NQ
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29th November 2006, 03:39 PM #13Senior Member
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simple solution
Turn a waste wood disc with a centering hole for your chuck jaws to expand into that fits inside the recess at the top of the bowl at the natural edge, glue it in and go from there.
I typed a long detailed answer but the system wouldn't wait long enough for the answer and kicked me off before I got it done.
So if you have more questions about this then fire away and I'll give you short replies."Always cutting corners...!"
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29th November 2006, 08:21 PM #14Member
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Jeff
Not sure how that would work. The top of the piece curves inward. Anything of diametre small enough to pass through the opening wouldn't reach the sides to glue to. I think I'm missing something...Mark J
Cairns NQ
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30th November 2006, 01:51 AM #15Senior Member
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short reply...
Well, from the pictures that was alittle hasrd to spot! Not to worry! Two other options:
1. Turn a disc with a small Centering Spigot that will align with the recess on the bottom of the bowl, Hot Glue the bowl onto the disc. When I use hot glue in this situation I've found it's essential to cut grooves (concentric circles) in the face of the disc to allow the excess glue to squeeze into, otherwise you can get lumps that keep your attachment from being squared up. Theese groves need only be 1 or 2 mm deep, as it will take a lot less glue than you might expect.
or
2. Turn the disc as mentioned in my first post, find a way to shim it into place in the top of the bowl, and add a small bead of expanding foam around the disc to secure it to the bowl. Let it set up for a good day or so. The downside of this method in your case is the potential cleanup problem at the natural edge.
If you have enough material left at the top of the bowl to work with, you could use method 1. to create a jam chuck situation at the top. To do this, you would cut on the outside of the bowl from the top down to just past the lowest point of the natural edge about 2 or 3 mm or so, just enough to leave a lip that will square up the bowl in a jam chuck. You can then put the bowl in the jam chuck, bring up the tailstock for extra support (gently!) and clean up the bottom, leaving a centering recess for later. It would mean a couple of extra steps, but it will work."Always cutting corners...!"
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