The second Scarf Joint and The Process explained

I had two worries when it came to gluing up a scarf joint.  One was to keep the alignment of the two pieces of plywood parallel (within reason) and the second was to prevent one taper from 'climbing up' the other taper by being pushed too far (making the joint thicker than the plywood).  The "stepped-scarf" method would have easily dealt with both these issues, but the tapered scarf has both these possibilities.  

After some consideration I came up with this process.  The first piece is turned taper down and secured tightly to the table with screws.  This makes it such that pushing the second piece against it, the tapers cannot climb up (not without tearing the screws securing the first piece out of the table) and the two pieces align parallel simply by being pushed together until they can go no further.

During gluing up the second scarf (another 8-footer) I took some photos to document this alignment and gluing process.

Step one was to cover the area of the table with plastic.  I was concerned that when I push the scarf together that I may push the plastic also and have a fold of plastic pushed into the scarf joint.  To prevent this I taped the full edge of the plastic to the table top. 

Step two: With the two pieces scarf-taper up, I wet out the wood with straight epoxy.  The board in the picture acts like a paint roller tray.  I spoon some epoxy out of the mixing bowl onto the tray, wet the roller up well, and then roll it out on the tapers.

The wet-out is completed.

Step Three: The smaller top-piece of plywood is then flipped over, taper down, and screwed down to the table with the clamping blocks.  The clamp blocks have plastic tape on the bottom to prevent being permanently glued down.  The blocks are about 16 inches apart, and in fact use the same screw holes from when the scarf was cut.  The screw in question is the one about in the middle of the blocks.  It looks far from the edge, but is just beyond the taper edge underneath.  The blocks are extra long on the right side to provided leverage to hold the outer edge of the taper down better during the process.

Here is the thickened epoxy glue and the tools I'll use.

Step Four:  Gluing up the taper.  Using the putty-knife I put some beads of glue across the taper and then spread them with the notched trowel.  Okay... I didn't get enough down and not close enough together.

That's better!

Completed

 Step Five:  Before pushing the joint together, I first pulled the plywood back to clean the excess off the plastic.  Don't want a smear underneath.

Step Six:  I push the plywood to within an inch of closing up the joint.  Then I set up two ratchet straps to help with the final squeeze.

Step Seven:  Working the ratchet straps carefully, I close the joint up until I get the joint edges looking to be a proper distance.  I had previously dry fit the joint and knew what the distance should be without a glue layer.  I also knew from the taper angle that a 1mm glue layer would mean the distance would be 6mm wider than a dry fit.  I was also rewarded with seeing a nice amount of glue squeezed out of the joint.  Little to no glue squeezed out of yesterday's scarf joint.  I made the glue less thick than yesterdays and put more of it on the joint today.

 Step Eight:  I screw down the further end of the clamping blocks and remove the ratchet straps.  I also scraped away the excess glue so I will have less to sand down later.