Joining oak boards to plywood underlayment - Woodworking Talk - Woodworkers Forum
 
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post #1 of 16 Old 09-28-2012, 01:38 PM Thread Starter
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Joining oak boards to plywood underlayment

I am building a bar top with 1x6 oak boards onto 3/4 plywood. My original plan was to attach the plywood to the bar and then add the oak to the top by edge gluing the boards together as well as to the plywood. I was going to use biscuits and pipe clams to ensure tight edges and then using wood screws from under the plywood to keep the wood secured to the ply.

My concern is with the oak shifting from the ply. I am not very advanced with wood working and have been search all over the internet for how to do this correctly. Some say to just do as i said, but others say to only use screws and in only certain spots to allow the oak to move. Although I do not really understand where exactly to put the screws. I also read that I should also poly the underside of the oak since I will be finishing the top.

Any held is appreciated. I just need to fine the easiest and safest way to attach the oak boards to the plywood.
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post #2 of 16 Old 09-28-2012, 01:54 PM
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Picture and more information will help in the suggestions.

Wood moves with moisture changes over the year. So it will lose moisture during the winter (dry) and gain moisture during the summer (wet).

Wood move very little in the length. It moves most in the width (right angles to the grain).

The wider the assembly, the greater the overall movement.

Is the bar straight or does it have corner(s).

It is a good idea to apply any finish to all surfaces to try and have any moisture change be the same for top and bottom, otherwise the wood can cup.
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post #3 of 16 Old 09-28-2012, 05:21 PM
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"Wood move very little in the length. It moves most in the width (right angles to the grain). The wider the assembly, the greater the overall movement." Dave's right.
"apply any finish to all surfaces" that includes, especially includes, the ends.

A 2' wide oak top could shrink and swell as much as 1/4" in extreme relative humidity conditions, a bar might be extreme.
You do not want to fasten top to plywood in any way. U may even want a slip sheet between them. Or don't use plywood at all. Let top rest on horizontal stretchers like a table top. There are everal shop made top fasteners that allow top to move. And fasteners you can buy.

If top can not move it will split. If edges are fastened, top will bow upwards, if glued down it will split top or plywood. When it shrinks back, split off chunks will prevent it from laying flat. If top shrinks it will split, possibly even open glue joints.

Biscuits will help align boards, but at times, being glued in can cause splitting. That's kinda rare tho. But use smaller biscuits, even #0. I have glued up panels, trying to keep glue from biscuits, spritzing them with water , quickly inserting them B4 they swell and gluing up.

Shrinkage and expansion depends on moisture content of wood and humidity changes in room. There are online charts and calculators to figure that. here's one
http://www.woodworkerssource.com/movement.php
Here are some ways to fasten top http://benchnotes.com/Fastening%20Ta...table_tops.htm

You should allow oak to rest in room where it will be used for several days to acclimatize, B4 building and finishing top.

Can you put a raised frame around top rim of bar? or will bartop overhang bar? A 1x3 with 3/8 or 1/2 extending above bartop Cut 3/8 to 1/2 deep groove slightly thicker than bar top 3/8 down from top edge of 1x. finished size of top should allow all edges to be half way into grooves all around. If 3/8 deep groove top should be 3/4 less than outside to outside of frame. slide top into grooves, do not glue. This is similar to raised panel cabinet door. Thicker frame would allow deeper groove allowing more movement. You could also cut an El shape frame instead of groove making a lip that extends inward. When fastening frame to bar but spacer between lip and bar top. Business card thickness will do.

Let us know when bar is finished and open for business. You gonna have some single malt back there?

Plumb outta square and off on a tangent.
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post #4 of 16 Old 09-29-2012, 10:10 AM
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I would not build the bar top onto the plywood. You could attach the plywood to the cabinet as a sub-top but the solid wood top should be separate. What will happen is the solid wood top will shrink and being glued to the plywood on the edges top will split down the center to relieve the pressure. I would just attach the solid wood top to the cabinet with a minimal of screws.
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post #5 of 16 Old 09-30-2012, 12:34 PM
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The " minimal of screws." would be one in center of center board at each end. Perhaps a few down the center of that board.

I dunno why i didn't think of this idea B4, it may be in one of links I posted;
Do not glue top to plywood, and slip sheet is good idea. Even sprinkling of talcum powder on ply if it will not sift out, and your bar will smell like babies.
At ends and sides of ply drill over sized holes or even slots perpendicular to board length. Use large head pan head screws or pan heads with fender washers from under ply. Do not snug screws down, Use bizz card thickness spacer underneath head. You could even leave card in place, bit of slip sheet and/or wax or talc.

If as time passes top wants to bow or split loosen outer side screws a bit, add a few to center.

Plumb outta square and off on a tangent.
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post #6 of 16 Old 09-30-2012, 11:52 PM
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I think you could get away with more screws than a few down the center. I believe I would be more likely to put one on each corner. If the top shrinks the screws will give but if you put too many it won't. One thing I forgot to mention is I would put at least one coat of finish as a sealer on the underneath side of the top. This will help prevent warpage. If you finish just one side of a board moisture can get into the wood from the other side even if it is sitting on a sheet of plywood. If the moisture content gets higher on one side than the other the wood will swell causing the warp.
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post #7 of 16 Old 10-01-2012, 12:40 AM Thread Starter
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Great stuff guys, thank you. I have attached a picture of the bar at where it is right now. It is L shaped and will be wider where were the Keg box is in the front of the picture.

I think that I am going to go with screws on all corners and a few down the middle. I will use over sized holes through the ply to allow movement. I am not sure what pan head screws are, or what the advantage is.

Should I use a washer on the screws so they pull the ply tight to the oak? Also, how tight should I secure the oak and plywood? If it is too tight, will it negate the over sized holes in the play for movement?
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post #8 of 16 Old 10-01-2012, 07:21 AM
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Quote:
Originally Posted by bub7es View Post
Great stuff guys, thank you. I have attached a picture of the bar at where it is right now. It is L shaped and will be wider where were the Keg box is in the front of the picture.

I think that I am going to go with screws on all corners and a few down the middle. I will use over sized holes through the ply to allow movement. I am not sure what pan head screws are, or what the advantage is.

Should I use a washer on the screws so they pull the ply tight to the oak? Also, how tight should I secure the oak and plywood? If it is too tight, will it negate the over sized holes in the play for movement?
I would do the glue up for the top boards, and have rails on the bar top edges to mount the top to. Even with finishing both sides, screwing to plywood changes the airflow to one side.

If all the boards are edge glued, mounting that one piece top can be done allowing for cross grain movement by screwing the center board at both ends as it has been said. The edges or anywhere else that needs to be fastened can be done with slotted holes on the top rails , and using pan head screws. They are flat on the underside of the head, as in the image below. They can be drawn close, but not tight.
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post #9 of 16 Old 10-01-2012, 10:40 AM
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If you make a "washer" out of a business or index card, slide that on screw after a fender washer, then tighten screw just to barely compress card you'll be fine. Perhaps even better would be nylon fender washer under metal fender washer. You don't want the top to rattle and you don't want to be able to slide it by hand. The center screws can be tighter.

Is that already "topped" area on right the only place that is getting oak? That short you don't have to worry about length movement.

Or is bar top going to be L shape? If so keep oak running in same direction. Trying to join boards at right angles can certainly be done, but requires different techniques to allow end grain boards to move against side grain boards.

Bar is not as wide as I expected, you're not going to have a lot of movement, but better safe than sorry. Especially since it looks so great. Don't want bowed or split top on that fine base.

Have you got the brass rail yet? How about giant painting, "The Cowboy's Dream" is old faorite and modest by today's standards, for behind it.

Here is 'nother pic of pan head screw, cause I pulled it up from file afore I saw cab.s pic. And just in case, a fender washer is just a bigger diameter washer, same size screw hole, often thinner than regular, so you can drill good size over size hole. Hole should be just slightly smaller than diameter of regular washer. May need regular washer behind fender to keep over tight screw from dishing it into hole. In fact dishing may be clue to tightening screw, if washer dishes, its too tight.

Be sure to post pics when it is finished.
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Plumb outta square and off on a tangent.
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post #10 of 16 Old 10-01-2012, 11:09 AM Thread Starter
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The Oak will be going on the entire top in an L shape. What you see now is just 2x6 nailer that I will use to attach the plywood to. As car the the 45 degree corner, I was planning on glueing and biscuiting them together once the 2 sections were finished. Should I do anything special hear to allow for movement?
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post #11 of 16 Old 10-02-2012, 07:16 AM
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Quote:
Originally Posted by bub7es View Post
The Oak will be going on the entire top in an L shape. What you see now is just 2x6 nailer that I will use to attach the plywood to. As car the the 45 degree corner, I was planning on glueing and biscuiting them together once the 2 sections were finished. Should I do anything special hear to allow for movement?
I would just proceed as you are going. You have it all worked out and shouldn't worry about any movement of the cabinet. The cabinet with a subtop on it won't affect the top.
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post #12 of 16 Old 10-02-2012, 08:02 AM
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Quote:
Originally Posted by bub7es View Post
The Oak will be going on the entire top in an L shape. What you see now is just 2x6 nailer that I will use to attach the plywood to. As car the the 45 degree corner, I was planning on glueing and biscuiting them together once the 2 sections were finished. Should I do anything special hear to allow for movement?
If you do a glue up of the boards for each direction, and then make a miter joint, I wouldn't glue the joint. I would make a blind spline groove in each side of the miter, but stop it short of showing on the exits. Cut a snug fitting spline from either hardwood or plywood and dry fit. This will help maintain the boards' alignment at the joint.

If you glue that joint, that will stop the ends of the boards from moving cross grain. You can screw the two sections to the plywood in the same manner allowing for movement with the slotted holes as described earlier.

Just a tip on a visual note. Laying out the grain for the bar front, the end stiles can run full from top to bottom. Intermediate stiles ( IMO, in this case) can stop at the upper and lower rails. The grain on the panels can be vertical. It's likely a bit late at this stage, but, something to consider for the future, or anyone planning this type of project.





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post #13 of 16 Old 10-03-2012, 09:50 AM
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If your short bar piece is just going to butt into the side of longer, cabinetman's spline is still good idea, its basically just a long biscuit. The Miter would certainly look better and if you glued up top as one piece then mitered the planks will line up. You'll get a triangle of oak to get creative with too.

You could use biscuits here, If butt joint you can glue them in slots of side of long piece. Over long slots in end grain. If miter, over long slots in end grain, if biscuit is completely in width of just one board and small biscuit, you can glue one side. You could alternate glue from side to side. Remember movement will add up over width of top so make "dry" slots towards each side plenty wide. Or use biscuits in continuous slot. Since joint itself is unglued, the spitz of water on bisquit, long slot, and qwik assembly B4 they swell may be best connection.

If the edges of top are going to be hidden by a band or rim, you can make dove tail slots and spline with cross section like straight sided hour glass.

That bar looks great

Plumb outta square and off on a tangent.
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post #14 of 16 Old 10-03-2012, 11:38 AM Thread Starter
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The reason that the grain on the inside of the panels is horizontal is because that is a single sheet of oak ply. To be honest, this is my first project of this level, and I was going to build a simple bar, and wasn't to worried about grain pattern or anything like that. Although, once I noticed how good it was starting to look I slowed down and now am realizing I have something really nice here and want to make sure I do everything correctly.

As for as the corner, I am going to glue the sides up individually and then miter them before fastening. I agree with the spline joint, but I only have a biscuit joiner. So to do biscuits on the miter I'm not sure what is being mentioned by notmrjohn as far as dry slots and alternating gluing.

I will have 3 boards wide for the long side with a miter being joined to 3 boards wide for the short side also mitered both at 45s. Are you saying I should glue 2 of the 3 boards and dry slot the other onces with wet biscuits. Sorry for not understaning that part, bare with me I am a beginner.
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post #15 of 16 Old 10-04-2012, 12:46 PM
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I thot that looked like solid front. But panels look inset, did you cut them out? Is not way someone with fully equipped shop would do it, but hey it worked! You work with what you got. And is idea I have toyed with.
Dry slot-no glue. Alternating-- Long side has boards 1L, 2L, 3L. Short side 1S, 2S, 3S. 1L meets 1S, 2L-2S, 3L-3S. Glue bisquit in 1L , 3L, and 2S.
But forget about it. I thot you had more narrower boards, would have slots in almost every one. You'll have more movement in each board, would need two or more bisquits each board, could still alternate slots but...


No router? That would do long slot. Bisquit cutter could be used to make longer slot each board of dry splines. Be a chore to make one long slot of even depth.
Table saw? Cut dados on bottom of mitered ends, 3/8" deep, 1" wide, put 3/8X2 strip in with slots for short screws. Slot width close to screw diameter, length parallel with strip.

I am making this harder than it has to be. what tools do you have? How'd you make that bar using only jack knife?

Pro'lly easiest way is just screw through oversize holes in plywood into miter ends of top. Movement will be along line of miter, not much of one leg pushing against other causing open joint when they shrink back. One tight hole screw in center of each center board at each end would stop that opening and closing anyway.

Sorry for confusion, I just throw out ideas as they occur to me. Can be hard to communicate from what ever it is I have for brain to other people.

Figured out what your going to do with triangle of oak? Cutting board for on top of bar?

Plumb outta square and off on a tangent.
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post #16 of 16 Old 10-30-2012, 07:40 AM
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Use oak ply on the top. Find some flitch cut or slip ,attached oak and use that. Use your solid oak for a 1-2 inch border.
You can't fasten down 6 inch oak to anything.!
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""I am building a bar top with 1x6 oak boards onto 3/4 plywood. My original plan was to attach the plywood to the bar and then add the oak to the top by edge gluing the boards together as well as to the plywood. I was going to use biscuits and pipe clams to ensure tight edges and then using wood screws from under the plywood to keep the wood secured to the ply.""
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Look at hardwood flooring. Tongue and grove with nails in the tongue to allow the board to move with the seasons. The edges are given a slight chamfer to help camouflage the joint that opens a bit in the winter dry period and closes in summer when the humidity is up. You rarely see boards wider than 3 inches because the movement can be too much. Modern engineered wood flooring "floats" on the floorboards to allow for expansion and its glorified plywood.
You can't have a wide miter in solid wood. Again the seasonal movement will cause the miter to open a lot. The inside corner will open when the wood shrinks. NO finish can stop the movement for more than a day or two. Finishes help with looks and wear but only slightly slow the wood taking on moisture if it is there(humidity).
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It's a good looking cabinet. Why not just use the oak on top with a boarder of solid wood for wear to protect the fragile edge of the ply?? Any exposed edge gets an edge board. That's where biscuits help with alignment if you need them.
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