Thanks: 0
Likes: 0
Needs Pictures: 0
Picture(s) thanks: 0
Results 1 to 8 of 8
Thread: help please woodbending
-
25th April 2012, 03:53 PM #1Intermediate Member
- Join Date
- Mar 2011
- Location
- Australia
- Age
- 29
- Posts
- 43
help please woodbending
So for my major project i am making a hall table with bent legs and braces in the middle. I have made it tapered from 50mm down to 30mm and cut laminations to create the taper, it is then bent using a jig that i made. I have come across a problem but, for the crossed brace in the middle every section of it has a twist or a bow not to sure to be honest but when one end is flat on the bench the other end will be in the air about 10-20mm of the table.
Any suggestions on how to fix this problem would be greatly appreciated.
P.s. the timber is New guinea Rosewood, rough saw about 25-30mm thick, finished size needs to be approx. 19mm, all timber was from the same plank of timber.
could it be the stresses in the timber? once it was taken out of the jig it was straight but after awhile it bounced up.
-
25th April 2012 03:53 PM # ADSGoogle Adsense Advertisement
- Join Date
- Always
- Location
- Advertising world
- Age
- 2010
- Posts
- Many
-
25th April 2012, 04:57 PM #2
How long was it in the jig, and what sort of glue did you use? It does sound like internal stresses in the timber, and if the glue hasn't gone off completely there may have been some creep.
I'd try to plane the convex side flat, which may mean clamping the ends to the bench and working out from the middle to the ends. Then flatten the other sides. This will only work if you have enough thickness to work with.
Others may experienced the problem and found better solutions.
-
25th April 2012, 05:28 PM #3Intermediate Member
- Join Date
- Mar 2011
- Location
- Australia
- Age
- 29
- Posts
- 43
It was in the jig for about 24hours some where in for about 2 or more days. The glue was a pva glue. Pretty sure titrebond. Thank you for your suggestion I might try it out based off other suggestions. I'm just hoping have enough timber to work with
-
25th April 2012, 09:52 PM #4
-
26th April 2012, 11:54 AM #5
As Alexs said the glue has some creep in it. Epoxy is best where there is any stress. First check that the faces of the form are square as you may be building in the error. Another cause could be uneven squareness of the laminations. I have come across this making archery bows. Each laminatiom needs to be even across it's width or the stress finds somewhere to move. I overcame this by passing the laminations through a thickness sander to get then square. Mine was a sanding drum and fence on a drillpress.
Regards
John
-
26th April 2012, 11:55 AM #6GOLD MEMBER
- Join Date
- Aug 2011
- Location
- bilpin
- Posts
- 3,559
Dry bending is always going to produce stress in the timber. The type of glue will determin how much resistance can be placed on these stresses. The elasticity of PVA wouldallow the timber to creep after clamp removal. Epoxy would be a better choice.
-
26th April 2012, 01:13 PM #7GOLD MEMBER
- Join Date
- Apr 2011
- Location
- McBride BC Canada
- Posts
- 3,543
Might try steam bending like a boat keel.
Make up a jig with about 20% overshot.
Dad used galvanized rain gutter tube, electric kettle at the bottom, rag in the top
to control the steam flow.
Give it 6-8 hr with NO PEEKING.
Here's the deal = air dried wood runs about 12-14% moisture content. When you steam it, the steam transfers heat to that MC in the wood, heating it up. The noncellulosic fraction of the wood is quite plastic when heated. Lignins, hemicelluloses and so on.
In effect, you're going to slowly melt some plastic.
Into the jig, have a beer and go to bed. You should be there (shape) when it's cold.
We put the keels on hot (oven mitts). I was a kid, filled the kettle, never got a beer.
-
27th April 2012, 12:52 AM #8Intermediate Member
- Join Date
- Mar 2011
- Location
- Australia
- Age
- 29
- Posts
- 43
Thankyou everyone for your suggestions, I will try them out if i have to re make the brace. I'm just trying to see if i can plane and thickness it out fingers crossed i have enough room to do so