Best way to edge join plywood? - Woodworking Talk - Woodworkers Forum
 
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post #1 of 14 Old 05-15-2013, 04:29 PM Thread Starter
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Best way to edge join plywood?

Hi,

I am building an octagon poker table that will be 60" wide. To create the base of the table top I need to edge to edge join plywood. This base will have a racetrack and a smaller octagon covered in felt sitting on top of it so it will not be seen. On a previous table I used biscuits and haven't had any problems yet, but after researching a bit more for this table it seems like maybe biscuits aren't the best way to go? If it doesn't matter how well they line up, what is the strongest way to join the two pieces of plywood?
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post #2 of 14 Old 05-15-2013, 04:43 PM
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Full length hardwood spline.

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post #3 of 14 Old 05-15-2013, 05:30 PM
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I have a tongue and groove two bit set. One cuts a tongue on the wood edging, and the other cuts a groove in the plywood. Same principal as a spline, just easier for the glue-up. I am trying to recall where I purchased my set.

My set is similar to this, but the tongue and groove are slightly angled to help alignment.

http://www.eagleamerica.com/product/..._-_glue_joints
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post #4 of 14 Old 05-15-2013, 06:00 PM
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Quote:
Originally Posted by Dave Paine View Post
I have a tongue and groove two bit set. One cuts a tongue on the wood edging, and the other cuts a groove in the plywood. Same principal as a spline, just easier for the glue-up. I am trying to recall where I purchased my set.

My set is similar to this, but the tongue and groove are slightly angled to help alignment.

http://www.eagleamerica.com/product/..._-_glue_joints
Are you referring to a beveled tongue and groove? Check option "E" on your link

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post #5 of 14 Old 05-15-2013, 06:32 PM
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Quote:
Originally Posted by hoover40 View Post
Hi,

I am building an octagon poker table that will be 60" wide. To create the base of the table top I need to edge to edge join plywood. This base will have a racetrack and a smaller octagon covered in felt sitting on top of it so it will not be seen. On a previous table I used biscuits and haven't had any problems yet, but after researching a bit more for this table it seems like maybe biscuits aren't the best way to go? If it doesn't matter how well they line up, what is the strongest way to join the two pieces of plywood?
I use a half lap joint. The laps can be whatever you make them. You aren't limited to profiles afforded by router bits.






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post #6 of 14 Old 05-18-2013, 11:13 PM
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The problem is to glue long grain to long grain. A plywood surface is about 1/2 of each but getting the correct parts together may take some checking of the geometry. Splines or biscuits if they are in the right levels might work.
Plywood glues well to solid wood as you get a 1/2 bond which is usually enough. If you put a narrow piece of solid wood between the two plywood panels you would brobably get an OK connection. Glueing a strip on the bottom of the joint would strengthen it if the bottom was hidden.
Try a test piece.
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post #7 of 14 Old 05-18-2013, 11:23 PM
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Be it biscuits or splines, on ply it is aways a long grain to long grain glue-up - the only variation is orientation but still long grain.

Ply is the only time biscuits are ok. That or splines are easier in terms of layout than half laps but any of those will work fine.

I am wholly opposed to biscuits and pocket screws with only one exception - plywood.
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post #8 of 14 Old 05-19-2013, 08:29 AM
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In boatbuilding, the most accepted plywood joint is a scarf joint made by creating a long bevel on both pieces.


http://www.ncboatbuilder.com/scarfing-plywood.html


The place I get plywood sells 5' widths.
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post #9 of 14 Old 05-21-2013, 12:35 AM Thread Starter
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Thanks for all the responses! I still haven't quite decided what I'm going to do yet, but thanks for all the answers.
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post #10 of 14 Old 06-02-2013, 02:57 PM
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Rout a path along the underside of mating edges and glue a strip of plastic or aluminum to each side after pushing them together. This makes a lap joint that is strong if the strip has as much tensile strength as the plywood (after routing it).
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post #11 of 14 Old 06-14-2013, 11:07 PM
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The best way to join 2 pieces of plywood edge to edge is to use a scarf joint. In aviation its the only acceptable joint.

For me this was one of the hardest joints I have ever done. The proper way calls for a 1:12 joint. Which means getting both edges angled to 12 times the thickness of the 2 pieces. The thinner the wood the harder it is to get right.
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post #12 of 14 Old 06-14-2013, 11:58 PM
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Quote:
Originally Posted by michialt
The best way to join 2 pieces of plywood edge to edge is to use a scarf joint. In aviation its the only acceptable joint.

For me this was one of the hardest joints I have ever done. The proper way calls for a 1:12 joint. Which means getting both edges angled to 12 times the thickness of the 2 pieces. The thinner the wood the harder it is to get right.
I don't doubt what you're saying, but I have to ask: how do you go about cutting a perfectly straight 4" long taper in a piece of 3/4" plywood?

Edit: 9" wide, I mean.

Last edited by BZawat; 06-15-2013 at 12:29 AM.
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post #13 of 14 Old 06-15-2013, 06:31 AM
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Quote:
Originally Posted by BZawat View Post
I don't doubt what you're saying, but I have to ask: how do you go about cutting a perfectly straight 4" long taper in a piece of 3/4" plywood?

Edit: 9" wide, I mean.
Good catch.






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post #14 of 14 Old 06-15-2013, 06:41 AM
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Choosing a method would depend on why the plywood needs edge joining and its thickness. From experience I'll say a scarf joint would be very weak and difficult to keep in alignment when gluing.

For ¼" plywood, a lap joint would be my choice. I've had to do that on many occasions because as my luck has it I'll need a cabinet back that's just an inch or two wider than the plywood. Since I use mostly plain slice veneer plywood, I can get a joint that is closely flitch matched.

For thicknesses of ½" or more, half laps work very well, if they are fitted properly. Structurally, a spline might be used, but I would not use biscuits.






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