Thread: do i start again

It depends of the procedures and wood working skills you employed as to the success you'll enjoy.

If the joints were tight and well fitting and the surfaces were wetted out, let stand then wetted out again, you're joint will likely be okay. If you didn't have tight a fitting joint and you didn't pre-wet out the surfaces, it's possible you've got a glue starved scarf, especially if you used a fair bit of pressure to hold them as the glue cured.

Describe the process you used and we'll have a look see.

If in doubt, just re-do it - it wont take long and will give you piece of mind.

If you don't have the timber length left to cut a new scarf, you can take the scarf apart easily by using a heat gun to warm the joint and a putty knife to help prise apart. Stick one end in a vise and apply heat. Wood is a good insulator so it will take a couple of minutes to transfer the heat through, moving the heat gun around so you don't scorch the timber.

Once apart, give the surfaces a good sand with 80grit sandpaper paper to ensure you have a good bonding surface. Wet out the glue surfaces with unthickened resin first then apply thickened resin to one or both surfaces and clamp up. You only need enough clamping pressure to hold the pieces together until the epoxy sets - about as much as you can apply by squeezing with your fingers. As PAR said, if you clamp too hard you will squeeze out all the glue and starve the joint.

The trick is not to thicken the resin too much. If it is too thick the scarf pieces will not come together nicely.

Hope this helps,

AD

thanks par and a d . the more i twist and bend the join the more i think it will be ok. hopefully there are some pics here to let people that know what a good scarf looks like to make the call.
Attachment 193966

Attachment 193967

Attachment 193968
hopefully there are some photos here.
thanks once again.

Your joint looks as if you did not get the 2 pieces quiet together, , in saying that, by what I can see in the Pic's, the joint will be fine if you are glassing the ply.

I think you should be ok, depending on what is the ply being used for ???, generally the plywood will fail before the epoxy , and you appear to have enough in the join.

Jeff

The scarf angle appears to be pretty steep. My estimation is it's only 2 or 3 to 1 which isn't very much, even for plywood. The smallest scarfs I employ are 6:1, meaning a 1/2" (12 mm) plywood scarf should be a minimum of 3" (76 mm) long. A 3/8" (9 mm) scarf would be 2.25" (56 mm) long and a scarf in 1/4 (6 mm) stock would be 1.5" (38 mm) long. These would be the minimums I would use on plywood. I'd use a "taller" ratio if the plywood was bending during installation or highly loaded (like a bulkhead or powerboat transom). In these cases I'd use 8:1 or higher. The drawing attached is part of the instructions I send with all plan sets and shows an 8:1 scarf and how to arrange it. The point to using a long scarf ratio is to provide sufficient gluing surface and as an added benefit, make the resulting joint act as if it's just one longer piece of wood.

What is the "slope" ratio of the scarf pictured?

Wot PAR said.
That scarf isn't long enough to be a stand-alone scarf.

Rather than rip it apart & re-do it, and subject to location & stresses, you could
perhaps treat it as an extended glassed butt joint & glass each side of it.
see a.b.b. - amateur boat building - howto joining ply
Scroll down to light fibreglass butt joins & Payson heavy glass joint.

cheers
Alan J

as always your advice is invaluable, and your quite right about the short scarf. the plans only call for a 3:1 joint. ive made this one 4:1 - due to the length of the ply longer was not really an option without loads of extra thinking. im assuming the joint ends up in a fairly lightly loaded area - i can already see it will be in a fairly flat spot. i was thinking about adding glass to each side - payson joint? - but have read that these can be a bit stiff and require more fairing. can i do this once the panels are glued to shape ? also i read somewhere that the scarfs should lie in a certain direction but now i cant find the reference.

Take a 7" disk grinder/sander with a very coarse grit disk and plow out a shallow groove (7" wide of course) across the joint on both sides. Go down about 1 and a half veneers into the plywood. Wetout with epoxy, then apply a couple layers of cloth or better biax tape. When this kicks off, apply a filler coat of thickened epoxy to bring it up flush. I do this all at once and place it under a protected board so I end up with a perfect joint that requires little fairing afterward. This will be a Payson joint over your scarf and will do two things. First it'll insure it stays where you want and second it'll compensate for any mixing error that may have been there.