Wood expansion and contraction desk - Woodworking Talk - Woodworkers Forum
 
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post #1 of 19 Old 09-08-2015, 08:25 PM Thread Starter
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Wood expansion and contraction desk

Hi, i'm building a computer desk and was wondering about expansion and contraction. I previously built a dresser with a top that had a maple inside framed with walnut with mitered corners. Now the corners are no longer tight and the glue joints are broke. Is there any way to do this where the joints won't separate and I can leave room for expansion and contraction? I heard for the ends you can do a tongue and groove and put in dowels that have over sized holes in the tongue. Also, is it ok to glue panels together for sides? The drawers would be flush with the sides of the panels so do I have to worry about expansion and contraction there. And what is the best way to attach the top? It is just a simple case and then the top.
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post #2 of 19 Old 09-08-2015, 09:15 PM
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Originally Posted by cck View Post
Hi, i'm building a computer desk and was wondering about expansion and contraction. I previously built a dresser with a top that had a maple inside framed with walnut with mitered corners. Now the corners are no longer tight and the glue joints are broke. Is there any way to do this where the joints won't separate and I can leave room for expansion and contraction? I heard for the ends you can do a tongue and groove and put in dowels that have over sized holes in the tongue. Also, is it ok to glue panels together for sides? The drawers would be flush with the sides of the panels so do I have to worry about expansion and contraction there. And what is the best way to attach the top? It is just a simple case and then the top.
It's not the method of joinery that caused your mitered joints to separate, its the fact you can't put a piece of wood across the grain of another piece of solid wood in a perpendicular direction. If this is the design you wish the thing to do is band a piece of plywood instead of solid wood. What you are describing about the tongue and groove joint for such an application is like a breadboard end on a table top. On a breadboard end the board attached to a top by gluing it in the center only and fastening it on the ends with dowels or screws. It won't save you if you miter a piece of wood to go down the side. The joint would still break open on the miter when the top shrinks. On some antique tables with breadboard ends it's very common for the breadboard end to be 1/8" to 1/4" longer than the table is wide. Over decades the top of the table has just shrank that much.

You can glue solid wood together for your desk sides. Just don't fasten wood very solid in perpendicular direction to the width of the side. The side would need to be allowed to shrink in width.

As far as attaching the top you might use the table top fasteners that Rockler sells. You would just have to cut some grooves in the cabinet by running dados or use a biscuit cutter. http://www.rockler.com/table-top-fasteners
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post #3 of 19 Old 09-08-2015, 09:33 PM Thread Starter
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Originally Posted by Steve Neul View Post
It's not the method of joinery that caused your mitered joints to separate, its the fact you can't put a piece of wood across the grain of another piece of solid wood in a perpendicular direction. If this is the design you wish the thing to do is band a piece of plywood instead of solid wood. What you are describing about the tongue and groove joint for such an application is like a breadboard end on a table top. On a breadboard end the board attached to a top by gluing it in the center only and fastening it on the ends with dowels or screws. It won't save you if you miter a piece of wood to go down the side. The joint would still break open on the miter when the top shrinks. On some antique tables with breadboard ends it's very common for the breadboard end to be 1/8" to 1/4" longer than the table is wide. Over decades the top of the table has just shrank that much.

You can glue solid wood together for your desk sides. Just don't fasten wood very solid in perpendicular direction to the width of the side. The side would need to be allowed to shrink in width.

As far as attaching the top you might use the table top fasteners that Rockler sells. You would just have to cut some grooves in the cabinet by running dados or use a biscuit cutter. http://www.rockler.com/table-top-fasteners
Ok thanks a lot that helps a lot when it comes to the rest of my designing. Is there any way to completely frame a top? I don't need to do the mitered corners.
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post #4 of 19 Old 09-08-2015, 09:39 PM Thread Starter
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Would it be ok to run strips parallel the length of the panel and run a bread board across the end grains?
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post #5 of 19 Old 09-08-2015, 09:44 PM
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Ok thanks a lot that helps a lot when it comes to the rest of my designing. Is there any way to completely frame a top? I don't need to do the mitered corners.
About the only way you can get away with banding a solid wood top is route a groove around the parameter of the top and insert a veneer inlay. In the event the top had any major shrinkage it would bust the veneer instead of the top. This is much easier to fix.

Yes you can run strips parallel with the length and a properly done breadboard end across the end grain would be fine.
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post #6 of 19 Old 09-08-2015, 11:02 PM
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Just a thought, you could also glue the face side of the bread board to the panel to fix it in place so it will always look good. This will allow the expansion/contraction of the panel to take place to the back/rear side of the desk, out of sight out of mind yeah!

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post #7 of 19 Old 09-09-2015, 02:36 AM
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Just a thought, you could also glue the face side of the bread board to the panel to fix it in place so it will always look good. This will allow the expansion/contraction of the panel to take place to the back/rear side of the desk, out of sight out of mind yeah!
Just put the tight dowel on the outside end of the breadboard, if you glue the end and have a tight dowel in the middle there is no room for movement in that half.

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post #8 of 19 Old 09-09-2015, 12:43 PM
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I didn't look closely enough at the diagram and missed the non slotted dowel. I'd still glue and peg the front ends, slot the middle and rear holes both ends for expansion. I'd also ensure the panel was at the lowest MC possible for your shop before applying the cover coat and applying equal coats of whatever cover you use all the way around the panel. This'll help minimize and or eliminate expansion due to MC absorption. Heat expansion occurs but isn't as extreme.

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post #9 of 19 Old 09-10-2015, 10:38 PM Thread Starter
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Would it be possible to do this to the sides? I would biscuit the maple and center walnut piece together and attach the top walnut pieces like you would a breadboard. Then could I just run a huge tenon down it and then run a mortise down the leg? Or am I making this way to complicated. I wish I could do it like a floating panel, but I don't have maple that thin.
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post #10 of 19 Old 09-11-2015, 12:59 PM
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I think the side panels should be restriction free, use space balls to the panels within the frame

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post #11 of 19 Old 09-11-2015, 11:14 PM Thread Starter
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I think the side panels should be restriction free, use space balls to the panels within the frame
I think I figured out what i'm going to do. I'm going to bevel the maple pieces and let it float in between all the walnut. That should allow for proper expansion and contraction. To do this I think i'm going to use the table saw and just angle the blade. Does anyone have experience doing this on the table saw?
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post #12 of 19 Old 09-12-2015, 02:00 PM
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Not since I built my 1st router table, it can be done, but I think you'll come to see the limitations of the TS in this regard. Now I use the TS to square up the panels only. I did use the TS to build some utility cabs in the mid 80s. If I recall right, it did take me some considerable time to set the TS up along with jigs for the different cuts, I wasn't happy with the limitations. If you're going for simple flat panels no sweat but if your intentions are for something as simple as a traditional cut you're in for some work and compromise.

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post #13 of 19 Old 09-12-2015, 02:35 PM
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I think I figured out what i'm going to do. I'm going to bevel the maple pieces and let it float in between all the walnut. That should allow for proper expansion and contraction. To do this I think i'm going to use the table saw and just angle the blade. Does anyone have experience doing this on the table saw?
Do a search for "raised panels on a table saw", lots of info out there.

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post #14 of 19 Old 09-12-2015, 10:32 PM Thread Starter
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Thanks for everyone's help! I'm going to do it on the table saw cause thats all I have at the moment. I have a 3 1/4hp router and a router plate ready for a router table, but I haven't got around to building that yet so next time i'll be able to do them on the router table.
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post #15 of 19 Old 09-13-2015, 12:03 PM
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To state the obvious a flat platform and a couple sawhorses make an RT. I still have the original plywood lam'd table top that sat on the fancy cab and I use it at job sites, no fancy fence, just a 34" long squared piece of wood and a couple clamps.

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post #16 of 19 Old 11-11-2015, 09:30 PM Thread Starter
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Here is what I ended up doing. These are panels with a rabbit all the way around the outside in grooves in the walnut. There is a little under 1/8" of room in between the grooves in the walnut and the panel so it has room to expand.
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post #17 of 19 Old 02-27-2016, 11:21 PM Thread Starter
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I have not updated this thread in awhile. Looking at what I said here makes me laugh. I have learned so much building this project. I did the breadboard ends like the picture that Steve attached. I went a further step and drawbored breadboard on. It didn't turn out perfect, but it was a learning experience.

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post #18 of 19 Old 03-01-2016, 12:03 PM
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Looks very nice. Can you post the address of your earlier thread or threads. I'd like to see more info on how you attached the breadboard ends.

Thanks.

Howie..........
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post #19 of 19 Old 03-03-2016, 06:51 PM Thread Starter
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Looks very nice. Can you post the address of your earlier thread or threads. I'd like to see more info on how you attached the breadboard ends.

Thanks.
This is the only thread I have, what I did was I created a tenon all they way across the top and then I cut out parts of the tenon to make "distinct tenons", what I mean by that is the entire tenon was initially 1 1/2" long and then I cut out sections so there were tenons that were 1 1/2" and then a tenon across the entire length that was 1/2". Then I just mortised the breadboard piece and then I drilled holes through the breadboard piece where the longer tenons were, after that I put the breadboard on and marked where the holes were and then made a mark 1/16" in and drilled the hole there. That way when you put the dowels through it will draw the breadboard into the top. I used a file and elongated all of the holes in the tenons besides the center one. When I glued I only put glue on the center tenon. This is done so that the top can freely expand and contract. Here is a picture similar to what my ends looked like http://i0.wp.com/www.chrisfinke.com/...9/IMG_2290.jpg
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