another wood cracking / mounting question

[Mike Minto]

wether i turn 'less than dry' wood with a faceplate screwed into a blank, or grab a tenon with a chuck, i obviously have a large thickness of wood at the bottom of my work, thicker than the rest of the rough-out. this will often crack as it dries - is there some way to avoid this? if i could glue a block on a 'green blank' to grab with a chuck, would this help? thanks, mike

[charlie knighton]

where are you located, east coast large place, i am sure if you could work with someone your cracked tenon problems would dimenish, also would be safer

[Steve Schlumpf]

Mike - I use a tenon and rough out everything to 10% or slightly less. A few times when I started turning I had the wood crack but not so much anymore. The only thing I did was pay attention to the wall thickness and make sure it's consistent. If anything - the bottom of your bowl should be slightly thinner than the 10% rule - and if possible - never thicker.

[Jeff Nicol]

Mike, If I use a face plate and leave some extra wood at the base mainly when turning eng grain pieces I will cut a goove with the parting tool to make sort of a stop gap for the part of the wood I will eventually remove. Then seal that good with anchor seal to slow the drying down on the tenon or waste. If I use the tenon and plan to use it as a foot then you have to account for that as part of the thickness of the base. Like Steve said make sure that your wall thickness is very consistent from rim to bottom and that will definitly help. Also each type of wood will react differently as it dries so take that into acount also. It is a game that we all must play!

Have fun,

Jeff

[Leo Van Der Loo]

wether i turn 'less than dry' wood with a faceplate screwed into a blank, or grab a tenon with a chuck, i obviously have a large thickness of wood at the bottom of my work, thicker than the rest of the rough-out. this will often crack as it dries - is there some way to avoid this? if i could glue a block on a 'green blank' to grab with a chuck, would this help? thanks, mike

Mike I came to that conclusion some years ago, and so I changed to a recess rather than the tenon, as I had used both and had very little splitting in the bottom when I had used that.
The other thing I do is use the 10% rule, but also use that same rule when lower down on the bowl, I mean on a 10" bowl I would leave a 1" thick rim, and on a 15" bowl a 1½" rim, so I said when turning farther down on that 15" bowl, where that bowl would be 10", why have a 1½" wall, I wouldn't do that on the 10" bowl, so why here :).
Thus I got into the habit to reduce the wall thickness as I am turning lower down gradually, and very often end up with about a ½" thick bottom where my recess is, it does work for me :D
Here's a picture I made last year or so, just check it, you'll see just one tenon, I used it because of the shape of the log and I wanted that bottom shape on the bowl, all the other have a recess, and that is my usual way of holding for hollowing, faceplate or Woodworm screw when roughing the outside

[Bernie Weishapl]

I use a tenon all the time. I use the 10% rule also. If the walls at the top are 1" then the bottom is 3/4" or so. Like Steve if you keep the bottom slightly thinner I have never had a problem.

[Mike Minto]

i'll have to try that gradual thinning from rim to bowl bottom; i just want to make sure i have enough material to 're-round' each bowl. i'll have to try more recesses and judcious use of the expanding mode on my scroll chuck, so i don't break a form (as i've done more than once or twice :o). thanks, mike

[Steve Kubien]

Mike, are you talking about roughing out green wood and then being able to set it aside to dry for re-turning later? If so, by all mean use a glue block.

Mount on a faceplate and make the outside the shape you want, making sure the bottom is dead flat. Remove from the faceplate ans set aside for a moment. Now, attach a glue block to you faceplate and true it up so the face angles in towards the centre. Spread thick CA on the bowl-to-be around where the glue block will meet. Spray accelerator on the glue block itself. Press the two together and allow to cure using tailstock pressure to keep things steady. Spray some more accelerator around the joint and let it soak in.

Now you know where the bottom of the bowl will be and you can thin it down some to avoid cracking. Remove the glue block before you set the rough-out aside to dry. When your blank is dry, true up the bottom and do all of this again.

Chuck? Who says you need a chuck?

Check out Lyle Jamieson's bowl dvd for more info.

Steve

[Mike Minto]

Mike, are you talking about roughing out green wood and then being able to set it aside to dry for re-turning later? If so, by all mean use a glue block.

Mount on a faceplate and make the outside the shape you want, making sure the bottom is dead flat. Remove from the faceplate ans set aside for a moment. Now, attach a glue block to you faceplate and true it up so the face angles in towards the centre. Spread thick CA on the bowl-to-be around where the glue block will meet. Spray accelerator on the glue block itself. Press the two together and allow to cure using tailstock pressure to keep things steady. Spray some more accelerator around the joint and let it soak in.

Now you know where the bottom of the bowl will be and you can thin it down some to avoid cracking. Remove the glue block before you set the rough-out aside to dry. When your blank is dry, true up the bottom and do all of this again.

Chuck? Who says you need a chuck?

Check out Lyle Jamieson's bowl dvd for more info.

Steve


Steve, how are you then remounting such a rough blank to true up the bottom again, with the glue block having been removed? since it has been hollowed and has no glue block on it, are you remounting it with a vacuum chuck or cole jaws, and then putting on the glue block again? interested, mike

[Steve Kubien]

Mike, I use a jam chuck and tailstock support. With that, you can start truing up the outside.

Honestly, get the Jamieson dvd. He explains it soooooo much better that I ever could.

[Rob Cunningham]

Leo,
How deep are the recesses on your bowls? Are there any "standards" for the size and depth of a recess, compared to the size of the bowl?

[Leo Van Der Loo]

Rob as usual I go by what looks to be right for the bowl, I tend to go a little deeper for a deep bowl and shallower for a smaller thinner lower bowl, most are anywhere from 1/8 to 3/8, most often around 1/4".
I also keep the type of wood in consideration, with softer wood/sapwood, again a bit deeper than if it's harder wood.

Oh yes,------ and I always use only one hand to tighten the chuck jaws, going around a few times on my stronghold so the jaws sit nice and snug, that's all it takes

[Leo Van Der Loo]

Mike I have used a glue-block once or twice, you got to watch the dry glue-block on a wet blank, the dry wood doesn't shrink and the wet one does while turning, mind you I haven't had one come apart while turning, but they did split a bit apart when turning thin, though I noticed before it did come apart and go flying, there are times you like to use all the wood you have, and a glue-block does give you that option when needed.