Thanks: 0
Likes: 0
Needs Pictures: 0
Picture(s) thanks: 0
Results 1 to 6 of 6
-
12th February 2012, 06:40 PM #1SENIOR MEMBER
- Join Date
- Jan 2004
- Location
- St George area, Sydney
- Age
- 65
- Posts
- 640
Effects of expansion in the construction of a box lid
When constructing a lid which is basically a flat feature panel surrounded by 4 sides/edges how important is it to cater for expansion.
I understand that I can make the panel float within the frame I want the lids to look solid.
I am concerned that if I glue it together and give the box away then 12 months down the track the joints will separate.
Is there a good refernce that I should read?
-
12th February 2012 06:40 PM # ADSGoogle Adsense Advertisement
- Join Date
- Always
- Location
- Advertising world
- Age
- 2010
- Posts
- Many
-
12th February 2012, 07:04 PM #2
Hi Clint,
I actually use loose tenons (dominoes) to join the centre panel to the borders and have no problems with movement. I have done this with several different timbers, including Huon Pine and Red Gum.
Regards
Rob
-
13th February 2012, 11:34 AM #3
I have never "joined" the panel in the frame of the box lid. I have always left it floating to allow for expansion. It is essential to allow a little room across the width of the timber but not so important for the length of the timber.The gap only needs to be a mm or so to provide enough room for the expansion and contraction of the floating panel.
The floating panel can be quite thick and solid.
You can see in the sketch I have made the profile of the frame and the floating panel how this can be achieved.
Diagram A shows the profiles and Diagram B shows the floating panel fitted in the frame.
C. shows the top of the floating panel, which can be shaped to suit the box, rounded over for instance.
Attachment 198333Reality is no background music.
Cheers John
-
3rd March 2012, 02:12 PM #4SENIOR MEMBER
- Join Date
- Jan 2004
- Location
- St George area, Sydney
- Age
- 65
- Posts
- 640
I was just looking at some pics of dovetails which are done with 2 different timbers for the front and sides.
Is expansion in this arrangement not such an issue because any expansion is across the grain and therefore less than lengthwise expansion?
-
3rd March 2012, 09:50 PM #5
John has the way to build a floating panel but hide the expansion gap
expansion across the grain is always greater than expansion along the grain
the box/drawer sides in different timbers to some extent hold themselves together because of the dovetails, because the width of the sides is not too great and because although the timbers are different its the relative difference that matters.
say the box sides are 100mm high, say the dark timber has a 6% expansion, and the light timber is 8%.
The relative difference is only 2% or 2mm over the width of the sides, and half of this might be taken up in the clearances needed to assemble the DT joint, and the rest in a moix of compression in the 8% (expansion) piece and tension in the 6% piece.regards from Alberta, Canada
ian
-
4th March 2012, 09:24 AM #6
Not sure how I missed this before.
You do need to make allowance for panels to expand, and if you don't want it to be obvious, John's method is the one.
Ian's explanation is correct, but the examples quoted are way greater than experienced in practice. A timber that is subject to a lot of change, like casuarina, will move about 6% tangentially for a 10% change in moisture content, but if the timber has been properly dried, the moisture content won't vary by more than a couple of percent, and relative movement will be tiny indeed.
However, for panels, even though the movement will be small, it will occur, and if you don't allow sufficiently for it, it will destroy the box.
The attached table, from AWR #51, may be of assistance.
Similar Threads
-
Timber Allergies and Effects
By Burnsy in forum TIMBERReplies: 28Last Post: 3rd August 2009, 01:47 PM -
Wood grain and effects
By patelSP in forum WOODWORK - GENERALReplies: 4Last Post: 24th March 2009, 07:37 PM -
Timber expansion in Frame and Panel construction
By Knight_of_Ni in forum WOODWORK - GENERALReplies: 2Last Post: 10th June 2008, 11:15 PM -
Oh dear, the after effects....
By Gumby in forum NOTHING AT ALL TO DO WITH WOODWORKReplies: 23Last Post: 4th December 2006, 02:12 PM