Scarf Joint

I'm not going to get into a discussion about epoxy chemistry with you Frosty, as it's a bit more complex then you're understanding, but a mixture doesn't begin to thicken as soon as you mix it. In fact, the opposite occurs, before the gel stage, but you do what you want, as usual.

 

thank.I'll explain more precisely
i want to build laminate tee joint whit epoxy 5052 resin and carbon woven roving,the steps are: 1-i make two flat laminate whit hand lay up and deltoid region-2- i cure the two flat piece and deltoid, my parts is build-3-in this step i make laminate joint In other words,i assembly two pieces and deloid whit epoxy resin in form of tee.my question is this
what day after step two or making laminates,i must start step 3 or assembly pieces.
all condition is room condition

 

In an ideal situation, you would work the laminates while still chemically active, which in most cases is less then 12 hours at normal room temperature, preferably much sooner than this.

If you want to wait for a full cure, then you'll need to "tooth" the faying surfaces and mechanically bond them with epoxy. Most boats are built with these mechanical bonds, though small craft or highly organized production facilities can employ chemical bonds, which eliminates the need for scratching (tooth) the faying surfaces.

Simply put, if you want to insure the bonds are the strongest, you need to do them in sequence as soon as practical (within hours of each other). If you want to wait for a full cure, then 24 hours will do and you'll have to prep the faying surfaces for the next bond.

 

hi.what is the base material for dacron peel ply? it is polyester or nylon or another material?

 

Dacron is made from polyester

 

Speaking of Scarfs. Ive got to do 6 or 8 traditional scarfs on a bright finished teak cap rail.

Any tricks for cutting the scarf with a router ? I had a quick internet search and only see router formed " S " scarf.

These are shouldered scarfs, not slash scarfs.

http:// photo sharing sites

 

The slope on that "nibbed" scarf (above) is pretty steep and wouldn't be useful for much. There's lots of scarf types and each has "issues" to contend with.



This is a locked and nibbed scarf.

On big timbers I do simple (slash) scarfs, but lock (key) them with a dowel or square peg. It makes cutting them easy and the locking pin looks cool too, as well as being functional.

A hooked scarf is an option too, which can also be locked. The simple scarf is the easiest and cutting one doesn't require an engineering degree.

 

Michael,

How big is the cap rail?
I made router scarfs that were fairly wide (~12"). Two "tools" were required.
The first was to hold the board to be scarfed. It was an open topped U shape with the base "13" wide, with short vertical sides. These sides were the guide for the router and were sloped at the scarf angle, about 8/1. The total height was about 2x the two boards I wanted to scarf together.
The second tool was another open topped U, to mount the router in. The base board was wide enough to bolt down the router, the sides were high enough to give this tool enough stiffness to bridge across the base guide. The width of the router tool was a little more than 2x the 8/1 guide.

Clamp your two boards together at roughly a 8/1 spacing. Clamp them to the base guide.
Rest the router support on the base and start cutting. At first you will be cutting the tips of the boards to be scarfed so the router support will not evenly set on the base.

If the router support does not deflect and everything is clamped well you should be able to make a very nice and well controlled scarf with matching angles on each piece.

Personally though I will use a table saw with a much simpler guide if the cap rail is less than 3" wide.

Sorry for no pictures, I have not used this method for some years, not recently needing to make a wide scarf.

 

Michael, that's not really a true scarf IMHO since it does not cary the stiffness of the beam across the joint. Functionally, it's more of a tapered halved joint but more attractive and stronger. It would be just as strong done with a router - if you have one that's big enough - and probably easier with a suitable jig. Rounded shoulders would be slightly stronger than square ones. I presume it's pegged into the upright so there's no need for a locking pin.

 

Ive been playing with plywood templates and am going with a router cut scarf.

The teak stock is 3 quarters. The rail will be slightly crowned with a table edge bit..

I guess I use epoxy ?

http:// picture sharing

 

Epozy is strongest but teak can be oily and difficult to glue. Check your epoxy is formulated for such woods.

 

I'd set up the jig to cut it sideways. Most jigs cut the face of the scarf with the bottom of the bit (sloped jig), but I'd use a straight bit and cut 3/4" stock side ways (pattern jig). You only need a single shape for the router to follow, so each would be quite precise. I'd also probably use a laminate trimmer, rather than a router, so I could get tighter details, like your rounded shoulders.

For teak, mix up a combination of 1/3 toluene, 1/3 denatured alcohol and 1/3 acetone. Lightly scrub this into the surface, that gets bonded, permit it to flash off, wipe clean, then immediately apply epoxy. The solvents will de-oil the surface and open the pores of the teak, so epoxy can get a good grip.