View Full Version : joining plywood with puzzle joints???


Psuedomonas
11-03-2010, 05:54 PM
I will soon be making 1/4" plywood into 16' lengths. Previously I used a common scarf joint, but with only 1/4" to work with, these are not too strong. Can anyone suggest a method or router jig to make interlocking joints across a 48" surface?

rasorinc
11-03-2010, 06:24 PM
here is a link on a method I'm going to use. I only need to buy the bar pattern and use lots of epoxy.http://www.duckworksmagazine.com/06/howto/puzzle/index.htm If you break the joint between frames you could put a but block out of ply on the inside or use regular wood. That wiil insure greater strength then the regular ply offers.

PS Where did you buy your wet exhaust manifolds for the subi engines? Did you make them? Stan

Ike
11-03-2010, 08:16 PM
At the recent Wooden Boat festival I saw that Chesapeake Light Craft is using puzzle joints on their kit boats. It seems to be a good way to join them. I suppose the difficulty is cutting out the joint.

wardd
11-03-2010, 08:29 PM
you could take a 4' long piece of 1/4" thick steel as wide as 2 templates plus holding stock to a shop that has a cnc wire edm machine and they could cut it in half forming two interlocking templates perfectly matched

CatBuilder
11-03-2010, 09:03 PM
In case you still prefer scarfs:

A quick note to say that scarfing even 3mm (3/32nd of an inch) plywood is a breeze if you do the following:

Take every piece of plywood you want to scarf and stack them on a table, staggering them the appropriate (12:1) distance in a stair step pattern. (about 1.5" step for 3mm plywood)

Carefully clamp down the plywood to the table so it doesn't move.

Use a good low-rpm buffer/polisher with a sanding disc attached and sand that stair step into one smooth, uniform surface.

Follow up with a palm sander to get things perfect.

PRESTO! You can get perfect 12:1 scarf joints even on 3/32" plywood.

I did it this way and was able to put a perfect 12:1 scarf into 18 sheets of 3mm ply - taking about an hour for all 18 sheets. I did 144 sheets total, scarfs on all 4 sides, in about a week's time.

Was a hell of a good way to do scarf joints, just in case you still want to do them.

tom28571
11-03-2010, 09:09 PM
Why not just learn to make a scarf joint. Its not hard to do and is the best of all such methods. 1/4" scarf joints are routine. 1/8 is a bit harder but still not too difficult for any reasonable woodworker with opposable thumbs. Locking joints are easier in many instances for assembly of CNC kits but are more difficult to make with ordinary tools and generally weaker.

michael pierzga
11-04-2010, 04:30 AM
they use a finger joint in some kayak construction methods...dont know how practicle it is for full size sheets...have a look here

http://oneoceankayaks.com/stitchglue/plyshophtm/scarflock3b.htm

PAR
11-04-2010, 08:41 AM
Bingo Tom, the usual choices of finger joint aren't especially easy to make with hand tools, aren't very attractive and are generally weaker then a scarf. A 6:1 or 8:1 scarf ratio in 1/4" ply, with epoxy is well past stronger then the plywood itself, so I'm not sure why there's an issue,
I used a common scarf joint, but with only 1/4" to work with, these are not too strong.
If there's a strength concern, it's not the physical properties of a properly done scarf at these ratios.

As has been mentioned, a scarf isn't particularly difficult to make. You can eyeball one fairly well with epoxy or use a jig, of which there are many types.

Conversely, a Payson butt joint makes the scarf irrelevant. If the Payson joint is hollowed out and done under clamps, then it's about as simple as they get.

tom28571
11-04-2010, 08:52 AM
Paul, I consider a simple scarf easier to make than a Payson butt joint if the joint is to be well faired out on the surface. I sometimes use the butt joint with tape on both sides without the hollowing and fairing if the joint is in a non stressed area and fairing is not an issue.

PAR
11-04-2010, 12:26 PM
I too consider the scarf easier and considerably faster then the Payson butt joint. I do like the extra length you can get from the Payson joint and more importantly the nearly flawless faired result, with some setup on the hollowed version. Alignment issues are avoided with the Payson as well. This said I can hack out a good scarf in a few minutes and have it waiting for a cure in a few minutes more.

lumberjack_jeff
11-05-2010, 01:09 AM
A scarf joint is stronger, but one disadvantage is that a scarf creates a "hard spot" in the joined hull panel that will sometimes come out unfair.

Psuedomonas
11-06-2010, 09:27 AM
OK guys- you convinced me. I'll stick to the old scarf joint, but I'll try Catbuilder's method of stacking. Many thanks for the input

michael pierzga
11-06-2010, 10:57 AM
To make a conventional slash scarf you need a good work surface to cut the scarf on and to glue up. Spend some time building a work surface. Hand planes, powerplanes, grinders, circular saws all will accomplish the task if you have a good work surface. By the way all the scarf techniques...Payson , conventional, fingerjoint have value according to the need. Those finger joints look great when naturally finished.

tunnels
11-11-2010, 07:14 AM
they use a finger joint in some kayak construction methods...dont know how practicle it is for full size sheets...have a look here

http://oneoceankayaks.com/stitchglue/plyshophtm/scarflock3b.htm

I like it its neat and because the fingers are short and long and are staggered it will be much stronger than the ordinary finger joining in a straight line that would break along the dotted line so to speak , but with staggered fingers makes it much better !!!!:D:P:p

michael pierzga
11-11-2010, 08:43 AM
All the joint ..scarf techniques, have value. Its very difficult to pull off a scarph in plywood that will be bright finished. Very precise technique and skill is required if you expect to have a razor thin transition between sheets. That finger joint looks good. Id love to learn how to perform it.

PAR
11-11-2010, 11:38 AM
Finger joints long terrible under varnish and the only good ones are machine made. So, everyone pull out their personal 2 axis milling machine, plot out a finger joint and hope the stock doesn't move during the cut. Of course after this I'll have my robotic welder make up a new chair for me to sit in while this is going on . . .

michael pierzga
11-11-2010, 12:09 PM
Well, I looking straight at a finger joint in a varnished teak plywood interior trim piece. Fabricated by a cabinet maker in the Netherlands 17 years ago and it still looks perfect. Obviously not suitable for general marine carpentry or structural work, but it is beautiful !!! so finely fit that only the grain of the wood gives it away.

LP
11-17-2010, 09:04 AM
Here is another scarf to throw into the mix. Obviously, If you don't have the hobbyists CNC machine, it's a moot point. Interesting concept none the less.

http://clintchaseboatbuilder.blogspot.com/2010/03/cnc-boat-kits-and-prep-for-maine.html

Paul, do you hollow(taper) the edges of the Payson joint individually or do you butt your pieces together and grind out the hollow as a unit? Then glue it, cure it and flip it do the other side?

PAR
11-17-2010, 01:51 PM
Yep, I've seen Clint's joints, but they do present a fair bit of localized stress under load. Again, these CNC made joints don't do much for me, because for them to work, you have to have a 3 axis machine and the precision that comes with it. It's not practical for use in the field, nor in the average guy's work shop, so I don't pay much attention to these joints, other then the novel shapes employed.

The step or notched scarf can solve the feather edge issue with bright work, but does introduce some edge set stress along the joint, depending on how deep the steps or notches are.

You can taper the Payson joint edges separately if you want and I'll do this if I have a bunch to do. I'll stack them up and stagger them back. Then I just plow out with a power plane or big grinder. It doesn't have to be pretty, just deep enough to have a place for the fabric and goo to live. Shoot for a good, smooth taper, which eliminates the stress risers.

If doing one joint at a time, I'll butt the two pieces together and hit the seam with a 10" disk and some 24 grit. Once I'm through and fairly feathered on a couple veneers, it's time for goo. With practice, you can glue both sides at once. This helpful Greg?

LP
11-17-2010, 03:05 PM
Yes, very helpful, Paul. Thanks. I really like the fact that you don't loose any length to the scarf. I will plan to use it the next I get a chance to build something.

On thin material, have you tried a 1/2 Payson? (Single Payson?) Tapering only one side to bury the tape for the fair surface and then only taping the flat(nonfair) side.

PAR
11-17-2010, 08:38 PM
Yea, you can do it both ways, but the buried way can be made fair with a coated board, clamped over the joint during the cure. I generally bury both sides, unless I know the area will be out of sight, though recently I did a panel, which was hidden inside a locker, but I still buried both sides, just in case someone did a repair and cussed about my poor workmanship after opening up the locker.

LP
11-22-2010, 07:35 AM
One more question. What do you use on your boards as a parting agent? Does it leave behind a residue that needs to be removed?

I've used polyethylene bags taped over filled areas to promote a more fair surface to start working. A poor man's vacuum bag. This though has limits, but the bags peel away very nicely.

PAR
11-22-2010, 10:41 AM
I use several different things, depending on a few factors. If it has to bend, but in a simple curve, Mylar and plastic packaging tape are favorites, especially Mylar, which is heavy enough to prevent wrinkles if placed under pressure. Packaging tape is cheap, fast and conforms to compound surfaces, but you get a tape line seam (which easily sands out). Polyethylene sheeting works, but is prone to wrinkle unless quite heavy. It can also be affected by heat and does tend to squirm under clamping pressure, which makes wrinkles.

If I'm molding a part, I'll use plain old automotive wax and usually give the mold 3 coats, before I apply goo.

A good poor man's vacuum bag are those closet organizers that use a vacuum to suck the air out and compress the blankets into a little ball. The bags are exactly cheap, but I've been known to cut out the valve and reuse it on other stuff. Hook up a shop vac, suck out the air and it'll usually hold until the goo kicks off.

michael pierzga
11-22-2010, 11:37 AM
Wide Mylar tape does an excellent job. get some and practice on a few scraps. Very handy stuff to have around your shop.

DGreenwood
11-27-2010, 12:33 AM
With a few hours of practice, even a ten thumbs hack can master making a nice scarf. The hard part is clamping. Learn to do that well and you will make beautiful, nearly undetectable scarfs every time. There are a couple of ways to make an ordinary shop compressor develop enough vacuum to do a great job of this too.
Don't waste valuable time on complex and less reliable joints...spend it on the things that make a difference...like a fillet that doesn't look like it was done with a broom from five feet away.

DGreenwood
11-27-2010, 12:43 AM
Yea, you can do it both ways, but the buried way can be made fair with a coated board, clamped over the joint during the cure. I generally bury both sides, unless I know the area will be out of sight, though recently I did a panel, which was hidden inside a locker, but I still buried both sides, just in case someone did a repair and cussed about my poor workmanship after opening up the locker.

Every time I cut a cross section of some poor bastards work from many years ago and find myself cursing his sloppy technique, I try to imagine his discomfort in being forced to produce second rate work by whatever pressures he was suffering under at the time. Isn't it fun to be able to build something that will make that jerk that cuts through your work 50 years from now raise his eyebrows and say "wow, I never would have been so careful"!

sabahcat
11-27-2010, 02:59 AM
I have to ask
I always do scarfs on thick ply but ion thinner stuff what about just but and glass?

I have done several tests and they always break outside the glass joint and look at how the duflex z joint is done

http://www.duflex.com.au/files/products/z_joint.jpg

Only the thickness of the glass gets the 12:1 , not the whole material

PAR
11-27-2010, 06:13 AM
DGreenwood, as I've ripped open may boats over the years, I've seen both impressive and considerably less so workmanship. I've often cussed a former repair person, sight unseen, just to ask the same question in regard to the economic, personality or owner "restraints" placed on him, to force this type of repair or building decision. I too have had to hang upside down, through a hatch or freshly cut access, while applying a repair "as best as I can" given the situation or conditions. As I've gotten older, I've found I care more about what another might think 20 years later when he has to open up the area for what ever. I want them to be as impressed as I have been, when I've done the same to some another's previous work and not to just cuss my unknown name. I guess this is vanity.

dbierman
12-01-2010, 08:16 AM
I tried the method from Duckworks (http://www.duckworksmagazine.com/06/howto/puzzle/index.htm) and the fingers kept breaking off when I practiced with 3/8 BCX ply. Not sure if it was the cheap plywood or the fingers were too small and brittle.

Looking at trying the dogbone method now http://www.duckworksmagazine.com/04/s/articles/dogbone/index.cfm

PAR
12-01-2010, 10:43 AM
It's pretty easy to write an article and submit it with glowing remarks about the "latest joint", especially to an online magazine that doesn't read or vet their submissions. You're not going to be too impressed with the dog bone scarf either, especially after you spend all that time with setup and jigs. It's just another piece of wood added to the joint (more complication) and added to the joint cutting process. Adding more wood to the process is just introducing more potential for "slop" in the joint, not to mention several extra screw holes from the jig too. In the end, bend this joint across something, like a bulkhead and watch what happens. You'll hear the issues before they "present" themselves.

cutyourway
12-02-2010, 07:33 PM
If you laser cut your plywood, you can have any kind of splice you want. Fingerjointed, PuzzleJointed, horizontal joint, follow-the-woodgrain joint, whatever. If you find a 6-axis laser cutter, you could even do interlocking-puzzle-scarf joint! However, most laser cutting systems are only 3 axis, so it's easier/cheaper to only cut your splice at right angles.

www.cutyourway.com

PAR
12-03-2010, 12:33 AM
The next time I find a 6 axis laser cutting machine with a 50" x 98" bed, I'll have to run over and grab it up . . .

cutyourway
12-03-2010, 12:41 AM
Try Mazak, but remember they are the most expensive

PAR
12-03-2010, 05:31 AM
I'm not sure what you're attempting to push Peter, cut files, machines, new customers, but CNC machine cut anything for a back yard builder is just cost prohibitive. Developing a cut file or paying to have one done, paying to have the materials cut, transportation is a given. How can a typical back yard builder, who's project is an 18' or smaller, single chine, powerboat (80% of the market) with maybe a dozen scarfs at most, justify the cost of machine done joints? Their trying to get the whole boat in for less then a couple of grand and your joints cost how much of a percentage of the project? For what? Accuracy that isn't remotely necessary on a set of plans that only go down to an 1/8 inch? They're doing the project to work with their hands.

That West System scarfer attachment is junk except on rough work that will be heavily faired latter.

LP
12-03-2010, 10:28 AM
The next time I find a 6 axis laser cutting machine with a 50" x 98" bed, I'll have to run over and grab it up . . .

Paul, you're such a cut up! :D

michael pierzga
12-03-2010, 11:03 AM
Whats important to consider is that you can..at this moment....order marine ply by the sheet with the puzzle joint pre cut into the sheet of ply, ready for work. . In many applications the puzzle joint is the correct choice, so why not use it when called for. .

PAR
12-03-2010, 03:34 PM
Again,Michael you've offered nothing. How about substantiating your claim that;In many applications the puzzle joint is the correct choice
Also can you post a supplier of BS-1088 plywood panels with the joints you describe. Just one link will do. I'm just dieing to find out how much a finger joint costs on a full sheet. Should be a simple request and comparison, wouldn't you say, Michael?

DGreenwood
12-04-2010, 12:25 AM
I don't know what kind of luck you fellas were born with but if I ordered puzzle joined ply wood I'm betting the ends would be so banged around and buggered up by the time I got them from the shipper, that I would have to spend a day sanding just to get them to fit together again.

michael pierzga
12-04-2010, 12:55 AM
Again,Michael you've offered nothing. How about substantiating your claim that;
Also can you post a supplier of BS-1088 plywood panels with the joints you describe. Just one link will do. I'm just dieing to find out how much a finger joint costs on a full sheet. Should be a simple request and comparison, wouldn't you say, Michael?


PAR, normally I wouldn't waste my time responding to your thoughts, But for your benifit, I suggest you really should get out more and open your mind. .


I can walk to the local furniture, kitchen cabinet, component maker and ask him to cut puzzle joints with his milling machine in any grade of ply I purchase. I live in a small city. Many milling machines around.

In the US I can simply order ply ,pre cut, from http://www.clcboats.com/shop/products/new/new-supplies/puzzle-plywood.html

If you have situation i which the puzzle joint is the best joint for the job, order it pre cut . It with save you the time spent fabricating a template. .

PAR
12-04-2010, 02:09 AM
Well, looky here the reply. A finger joint for 50 dollars (CLC offering), on a piece of 1/4" Okoume plywood, well yes, that's an economical option. So glad you pointed this out. Lets see a single $50 joint on an $80 sheet of plywood, well you've discovered something here.

As usual, you can't justify any of your your comments, though on this one rare occasion you have offered up a link to a service, where a single joint jacks up the base product cost by 40%.

View Full Version : joining plywood with puzzle joints???