Replies

1. 
   Pascanale | Nov 19, 2004 04:08am | #1

   Wood expansion will possibly be and issue depending upon how deep the rabbet is for the panel and the panel's overall width. Veritas has a table you can purchase for looking up such info. Meanwhile, such cabinets are/were built using a ship-lap joint between the boards when the panel was over a large length such as a china cabinet (4-6 feet wide). The panels were about 6" each. A shiplap, is two rabbets mated like interlocking "L's". If you really want solid poplar, this would be the authentic way to go. Otherwise, use baltic birch veneer plywood, especially since you're painting it.  Baltic birch is very stable, flat and available in smaller sizes, too, both thickness and surface area (1/8 x 30 x 30 for instance).

   Scrappy

1. 
   BG | Nov 19, 2004 02:38pm | #3

   Scrappy,

   I glued up the panel yesterday and the overall dimensions will be about 20wx30L. I want to use the solid wood back to learn how to do it and because this is really just using up some scrap poplar. 

   I could rip the panel and include the ship-lap....maybe four 'L's with an 1/8" expansion/shrinkage room?...maybe run a bead on the face side of the boards?  What do you think?    

1. 
   Pascanale | Nov 19, 2004 05:00pm | #6

   BG,

   OK, 20" is borderline. It's just a large conventional panel door when its all said and done. By this I mean, a normal raised panel door would have a dado in the rails and stiles of maybe 5/16-1/2", allowing at least 1/4" for the panel and 1/8" for expansion. That's at least 1/4" of total movement (1/8" on each side). Your estimation of expansion is generous, too.

   So, Feel free to dado the cabinet's sides and let in the panel as you have it, in one solid piece. But, be sure to not glue it on its sides or ends near the sides. There is some clever products that are soft pellets that rest in the dado to keep the panel centered yet allow for seasonal movement. Alternatively, a single point of glue at the top and bottom center edges of the panel presuming you've oriented the grain vertically (along the longer axis), will keep the panel still. And even that's not necessary since this isn't a door that will be moving.

   If you do decide to rip and ship-lap, the beading idea is a very nice touch--I like that. And, if you do, each board will need to be fastened at the center of its ends. Either glue of brad will do.

   Sounds Great!

   Scrappy 

1. 
   BG | Nov 19, 2004 05:26pm | #8

   Scrappy,

   Actually, the front will be a large raised panel with rails and stiles.  I have a slab of 5/4 poplar about 14" wide that I've been sitting on for the last year or so..and my plan is to use this for the raised panel portion.

   The sides of the case will be through dovetailed and the shelves will have half dovetails.  If I did rip the back panel into four pieces and ship-lap. bead, etc. do you see any problem glueing the end pieces to the sides (long grain to long grain only) and just tacking the other two pieces with brads?  This would give me a bit more strength...perhaps it's overkill...  

1. 
   Pascanale | Nov 19, 2004 07:12pm | #9

   BG,

   You'd get no additional strength other than to strengthen the sides against laterall deflection which you won't have any. What would be the forces on the sides other than that when the doors were opened and that's marginal since the hinges would be located near the top and bottom ends causing the least amount of potential deflection. Secondly, you said you'd be dovetailing the shelving into the sides. That along with the dovetailed corners, this 4-sided box is way strong without considering any additional actions.

   That back panel is considered to be of no structural, load-bearing value. If you do glue those two outside-most panels to the vertical sides, all you'd accomplish is a loss of movement of the panel into the dado groove--that's counterproductive to your original issue of wood movement.

   Sorry I don't have the moisture-movement tables to set this issue to bed for you once and for all, from a hard-data approach. This is not a significantly large width requiring great accommodation. I read another reply to your posting that mentioned the bathroom being a higher range of moisture. I'd hazard to guess that the swings aren't that higher, just peak moisture moments during shower/baths. The period would not exist long enough for the wood to reach any equilibrium approaching the increased moisture level for that breif timeframe.

   Lastly, consider more the relative moisture in your shop or wherever these boards are stored versus their final home. This is the only change that you may experience above normal seasonal movement for your home in your locale. Northern homes experience a wider swing due to our climates versus southern locales.

   Later,

   Scrappy

2. 
   PlaneWood | Nov 19, 2004 05:54am | #2

   A 12" wide (across grain) piece of Poplar will shrink 0.27" as it's moisture content decreases from 14% to 6%.  Conversely, it will expand the same amount as the moisture content increases from 6% to 14%.

   Ct = 0.00289 in that moisture range.

   R = 12 * 0.00289 * (14 - 6)

   PlaneWood by Mike_in_Katy (maker of fine sawdust!)
   PlaneWood

   
   

   ---

   Edited 11/18/2004 9:56 pm ET by PlaneWood

   
1. 
   BG | Nov 19, 2004 02:42pm | #4

   Mike,

   Thanks. I'll have to guess at the mositure content but I'm figuring on a 20" wide poplar board if I give it a max of 1/2" expansion, shrinkage I should be safe... 

1. 
   PlaneWood | Nov 19, 2004 04:56pm | #5

   BG -

   If you can somehow pin it in the middle, then each side will only move 1/4".

   Did you notice the difference in Cr & Ct in the table?  That means that boards with wild grain can warp.  One part of a board can exp/con at different rates than another part.  

   Lota people use 1/4" plywood for the back of a cabinet and avoid the issue.  With 2 panel doors in front and by pinning the panels in the middle, then edge movement is kept to under 1/8". 

   Oh Yeah, in a bathroom, the swings in moisture content may far exceed 8%.  The coefficients are larger at moisture contents above 14%.  You should seal the back well on both sides.

   PlaneWood by Mike_in_Katy (maker of fine sawdust!)PlaneWood

   Edited 11/19/2004 9:01 am ET by PlaneWood

1. 
   BG | Nov 19, 2004 05:16pm | #7

   Mike,

   I'm going to schellac it and paint it with at least two coats so I think it can't get much better than that...   The sides of the case will be 3/4" thick so I could easily dado that adequately to accomodate the expansion if I leave the board solid...centering it on the opening and tacking in the center at the top and bottom.  The wood I selected is relatively straight grained poplar...just different colors.  If I rip up the back and ship- lap and bead the edge...that could be more fun...hmmm!!