Scarfing, Splicing, join for Ply

[gary1]

Morning,
I'm just seeking opinions on which method of joining 2 pieces of ply together gives the strongest all round join.
(1) Scarfing
(2) Splicing with Biaxl Tape the tape to be say between 150mm(6inches) and 200mm(8inches) wide the tape will be applied both sides of the join The ply that I have to join is 6mmm to 6mm and 12mmm to 12mm. Any advice on this would be appreciated as I have never scarfed 2 pieces of ply together before and it doesn't look like the easiest thing to do getting the correct angle on the scarf to get the maxium strength on the join.
Thank's Gary

[jimslade]

Scarfing is strong but its alot of work to get it right.

[Wynand N]

Originally Posted by gary1

Any advice on this would be appreciated as I have never scarfed 2 pieces of ply together before and it doesn't look like the easiest thing to do getting the correct angle on the scarf to get the maxium strength on the join.

Check this site - pictures tells a thousand words

http://aboatbuildingjournal.com/interest.htm

[PAR]

For a flat panel both will serve fine. On pieces that will receive some bend, the scarf will be more forgiving then the taped seam. The scarf joint will be lighter, but will not be as stiff as the taped seam. The scarf will permit similar bending and flexing properties as if the piece was continuous (without a joint). The taped seam will harden the joint area considerably, resisting bending or fair curves. Joint selection is usually based on its location and expected loading. Scarfing isn't any more difficult then grinding, buttering, applying cloth and fairing out a taped seam. I find it much faster and easier then 'glass work, if for no other reason, then you only have to wait for glue to dry once in a scarf.

[gary1]

Thank's Everyone,
Some of the joins are situated on straight runs of the ply,and a couple on curves. Just a bit concerned about scarfing as it doesn't look like I will have much room for error acoording to the plans in relation to making the panels fit on the ply. But the plans specify scarfing the ply so thats the way I will have to go I suppose. I'll do a couple of practice runs on some cheap scrap first just to see how I go with them.
It's got me stuffed why they don't make ply in 22ftX4ft lenghts.
Thank's Again Everyone
Gary

[hansp77]

I don't know if it is the best way, but when replacing my deck I simply got the scarfing joins done by running a router along the edge with a 45 degree bit.
A clean up with sandpaper and away we went.

[waikikin]

Gary, its not that hard, just stack the two sheets to be joined with the top one staggered back from the edge of the bottom one by the length of the scarf & mark up the top one by the same, clamp or screw to a nice strait bench or stack of ply & plane down with electric plane then block plane or smoother plane, the glue lines give a terrific indication of progress & check the slope with a strait edge, then its ready for glue. Until maybe 15 years ago you could get 20' x 8' sheets of ply in Aus, but pretty hard to handle without overhead lifting gear. Saw a Kurt Hughes video years ago where they stacked multiple sheets of thin ply staggered down & layed into them with a disc sander to create the scarfs for large vacuum bagged cylinder molded catamaran hull skins, but a very dusty grubby process although apparently effective.Some body also used to sell a circ saw attachment to cut em, we did it with a beveled length of hardwood screwed to the saw base, it didn't seem to save much time on the electric planer method though & had greater potential for bugger ups. Regards from Jeff.

[gary1]

G/Day Hansp77, Jeff.
Hansp77 I think the scarf is supposed to work on a ratio of 8/1 not exactly sure what degree angle that would work out to. Jeff I made some phone calls and apparently ATL Composites over here sell a jig that just bolts onto a circular saw. Sounds like it is supposed to work fairly easily I will most likely give it a go,if no good then i'll just stagger the sheets the way everyone has suggested and just go for it with the electric planer and sander. Thank's again everyone for the advice.
All The Best
Gary

[Oyster]

http://boatdesign.net/forums/showthread.php?t=14604
another thread addressing this topic.

[Crag Cay]

Might be worth reiterating that hansp77's method of using a 45 degree router does not, (if I read him right), produce a scarf joint. More like a butt joint with a slightly inclined glue line. Without a backing butt block (or glass tabbing) this is not a structural joint.

[hansp77]

guess I was wrong about that being a scarf joint.
Sorry. I did not know that 'scarfing' only applied beyond a certain angle.
As I have learned everything I know about all this pretty recently, and largely through third parties, I was following advice from someone at the boat yards where I was working who recomended 'scarfing' my deck panels together. When I asked what angle, he said something along the lines of 'if its supported underneath, then 45 degrees will be fine.'
On my decks, of course, these joins were supported underneath by wooden beams, so as far as my use of them is concerned I am pretty confident in their structural integrity.
Sorry for the bad advice.

[gary1]

Hey Hansp77,
Mate all advice is good when it is given freely with the best intent of helping someone else out, appreciate you taking the time to reply same to everyone else.
Stay Safe,
Gary

[Crag Cay]

hansp77 - The advice you got was probably correct. The deck beam underneath is part of the joint, by acting as the butt block. I'm aure as they knew more about your specific use that it will prove satisfactory. However, as the deck beams are using not that wide, it would be unwise to assume that this method is okay in every circumstance.

A scarf joint in ply is the method of making two pieces (or more) into one uniform length with the same stength and stiffness through out. Only a well made scarf does this. Testing practice scarfs is easy. Make up a joint using two reasonably sized pieces of ply, stick them together and then slice the board up into strips perpendicular to the joint. Bend these and you should see the curve is continuous and doesn't have any 'hard spots' at the joint. Then bend them further till they snap. The break should happen in the wood and not by the joint coming apart.

[rturbett]

West makes or made a device called a scarffer- it is an attrachment for a cicular saw that cuts the scarf bevel. My friend uses it and his scarf joints turn out fabulous. I use the belt sander method and have ok results. The part that makes it work for me is watching the different layers of ply as they are sanded away- make all the stipes even and your end result will be pretty good.
Rob

[catmando2]

On my last cat I bought one of those West/ ATL scarffer/circ saw attachments, maybe I was doing something wrong, but sent it back for refund.

I think it was only suited to 6mm ply.
I use the powerplain and 2speed sander with flat pad and 36 grit to finish off,I have a delicate touch, and have had great results with it.

For panels wthout much if any shape I butt and glass the joints. This is how Farrier does his joins on his designs.

While on the subject of scarfes, has anyone seen the z scarf that ATL use for joining Duflex together.? Seems to only have a glass overlap the same as the thickness of the material.

Dave