I need to make a simple “L” shaped top [80″ and 37″ legs] for a stub wall in a condo. Since it will be painted, I plan to use 1×12 poplar mitered at the intersection and glue a rim of 1×1 poplar under the edges for a thicker profile. There is an existing plywood sub-top in place upon which the new top will be fastened.
I can use a biscuit joiner to help with surface alignment, but I’m not sure how to clamp the glued miter joint without slippage. I suspect that pipe clamps would be difficult to align and to balance pressure. I’d thought of screwing cleats parallel to the miter joint and bar-clamping, but that would require a repair step afterward that would be unacceptable in stain grade materials.
What’s the secret?
BruceT
Replies
You can use pipe clamps successfully as long as you balance the pressure from both directions. Alternatively, there are fasteners made for this purpose that you can use in blocks from underneath the countertop.
David Ring
http://www.touchwood.co.il/?id=1&lang=e
Pocket screws on the underside would work great with this.
"Pocket screws on the underside would work great with this."With, or without biscuits?
BruceT
I would just use the screws and glue. Leave a little room around for expansion.
Edited 7/8/2007 8:21 pm ET by USAnigel
I believe it was Frid who suggests using pieces brown paper from shopping bags to be glued with hide glue on both sides to attach the cleats. Then clamping the joint as you suggest. When the joint is dry the cleats came be easily removed and the glue comes off easily and wont ruin any staining.
Several other ways to do the same thing , you could rout a 1/4" X 1/2" slot and glue a spline in one side then glue the joint together and use 5/8" pins from the under side . If you make a good fitting cut and joint it will take little pressure to bring the pieces tight together . Clamp the long leg down and press the other leg into it the glue should do it's thang .
Your bar clamps only have to span the 37" direction . Also you could use what we call tie bolts the same as laminate counter tops get in the corners to pull them together .
Lastly imo the edge build up should go flush with the top and then down an 1" not under the top , from the edge no seam will show .
good luck dusty
Bruce,
Seasonal movement will make it difficult to keep a miter closed that's that long. Even a relatively stable wood like poplar will shrink enough to open up a significant crack in a 17" long miter joint. At the very least, you'll want a really good spline along that thing. Better to use plywood, you are planning to cover the edge anyway. As for the clamping problem, triangular glue blocks with paper between the block and the top, as another poster suggested, would be how I'd get pressure where it's needed. It needn't be hide glue, tho there's nothing wrong with that, Titebond works as well. Just scrape the remainder off after splitting away the block.
Ray
Can you clarify the seasonal movement problem? I've not done a miter this size before, but it seemed to me that if I glued a miter joint with both pieces cut from the same piece of wood, that they should expand/contract the same amount. What is going to cause that miter joint to open?BruceT
As the piece absorbs moisture it will expand across the width of the boards, but not along the length. Consider the pieces to be fixed at the inner corner. As the boards expand in width, they will no longer meet at the outer corner.
Well duhhh. I should have thought of that. As the boards become wider, but not longer, the cut angles must become smaller.Thank you for explaining it to me.What happens if the legs of the "L" are glued together end-to-side instead of mitered? Would the end-cut leg separate from the longitudinal surface of the other leg? Maybe I should cut my "L" out of a piece of plywood, then glue on border pieces to get thicker-looking edges, but I'm not confident of being able to make such a clean cut with my circ saw and home-made zero-clearance cutting guide. I guess that's what wood putty is for.
BruceT
A right-angle butt joint is the classic cross-grain joint and will fail. If the new surface is to be painted, and there's support underneath provided by the existing structure, I'd recommend using MDF for the new surface. If you go this route, you'll want to use oil-based paint (or at least primer) on the exposed edges.
Trick for cutting wide miters. First rough-cut the mating ends as closely as possible. Then temporarily join them fastened to a scrap piece underneath. Clamp a straight edge parallel to the joint offset one eighth of an inch plus half the width of your router then using a 1/4" diameter straight bit cut through the joint making multiple passes
I don't agree with the thought of using MDF for the mitered wall cap. On the surface it sounds good, and it will look great while it is new. But the problem is that the MDF will quickly and easily get dinged up around the edges and show that it is MDF. I think that the end user will be happier with a plywood cap that has been edged with poplar. Personally I am a fan of the Burgess System for applying a wood edging to ply. Pocket hole screws would be my first choice for aligning/clamping along the miter, but here everyone has their own prefs.
Hello Bruce,The mitre joint will open when the timber shrinks width wise, I have made bench tops like that out of stable timber but after 2 years in a hot summer the joint just burst open with a big bang.
The timber was 1/2" smaller width wise.
The shrinking causes the angle to go to 44 degree or something like that.
You can set this out on a board by drawing the 45 deg angle over the width you want, now make the top say 1/2"smaler and see where the front corner end up, because this corner is sliding back from the same position it starts to its new place under 90 deg from the front edge.
Hope this helps.
Bernhard.
Bruce,
As the boards swell, they get wider. But they don't get correspondingly longer, too. That means that the angled end of each board is no longer a true 45*, but something more obtuse. The result is that the joint wants to open on the outside of the corner. The opposite thing happens when they shrink- the board gets narrower, making the angle on its end more acute, which opens up the inside of the miter.
This can be ignored on narrower stock, especially if splined, but anything wider than 3" or so becomes problematic, where humidity % varies very much.
Regards,
Ray
<<As the boards swell, they get wider. But they don't get correspondingly longer, too. That means that the angled end of each board is no longer a true 45*, but something more obtuse.>>Ray,That's odd -- I find that as I age, I'm also getting wider and more obtuse.Mike
Mike,
You're just a sample of one--but add me, and we're a group!
Wider, and more obtuser, too,
Ray
Not certain I understand the whole issue, but here are a couple of options:
1. Use Miter connectors like for a laminate countertop. Route a pocket in the sub-top for these.
2. Make a few clamping strips from plywood or 2x's and draw them together with clamps.
3. Assemble the cap on a sheet of plywood. Attach blocks around the perimeter of the top. Draw the glue joint together with wedges and hold it with screws through the back side of the sacrificial plywood to assure flatness.
Greg
•••••••
Exo 35:30-35
Oops. Missed the part where it is 1x12. Missed the part where it is a wall cap instead of a countertop too.
It's not as clean a design, but can you use a corner block and allow for movement at the 90 joint? Maybe design the block with a nicely designed shape and profile-ie notched or angled corners, cove radius, etc?
Edited 7/10/2007 6:53 am by Cincinnati
Have you considered making the L out of 3/4" say Maple or other smooth plywood with the added wood edge ?
Since it will be painted , this would remove all the movement of the long joint that has caused so much concern .
may the wood Gods smile on you
dusty
Thanks,I think that is the best solution.
BruceT
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