Building the Octagon Pt.15. Glued wedge brackets?

*

The CN building experts are suggesting I use construction adhesive to strengthen and stiffen my build. A trial, dry build is recommended before applying the construction adhesive. Once glued, there is no going back to adjust levels.

I can well understand the advantages of gluing the beam support blocks [brackets.] Even with the planned use of 12mm [1/2"] bolts and heavy, load spreading washers, the joints rely only on friction. Glue, these days, is usually stronger than the timber itself. I tried to get bulldog toothed washers while shopping for 7" bolts but none of the outlets had the right size in sufficient numbers.

I plan to wrap 2x6 timber around the posts in an L-shape as beam support brackets. The beams themselves are only 2" wide so increasing the support area only reduces crushing forces. With doubled beams the support area is also doubled provided one isn't mean with the supports.

Bolting the beams through the post will increase support.
Local flattening of the post's sharp corners will increase friction and reduce crushing forces.

A 22.5° mitered block [dotted line] cut from 4x4 might make more sense in place of the 2x6 brackets in the image. Such a wedge would provide far more support area. Without requiring an exceptionally long bolt to hold both beams to the post. Hot galvanized studding [all thread] could also be employed here instead of bolts.

I am not sure how long a wedge can be cut at 22.5° on my compound miter saw. The figure of 22.5° is actually 67.5° but that is thwe marking on the miter saw. Perhaps a suitable wedge can be assembled and glued for this purpose from two or more pieces of 2x8 timber? If the laminations were laid flat on the 22.5° angle of the post there would be no tendency for the laminations to shear along the glue line. Any limitations of the saw to cut 4x4 material on the diagonal could then be overcome.

Only local counter-boring or pocketing to provide a flat surface for the bolt heads, washers and nuts is required in the posts. It is not good good workmanship to use a bolt on a sloping surface. It will try to apply a lateral force to the materials being joined. Not to mention the local bending forces on the bolt. The bolt head and nut will be asymmetrically supported and unable to provide the pressure and resistance demanded. With consequent loosening or damage to the materials being joined over time.

The next image shows what happens when real timbers are mocked up to show the connection with reality. The beam at the top of the image passes right over the bracket and rests upon it. That's fine. The second beam is a problem. I cannot cut a true 22.5% to fit inside the small green angle since the saw can only leans over by about 45° maximum.

I can cut a 25° [true 65°] to butt against the upright support post. Though that means there is a gap to the second beam. So the two beams cannot be fixed directly to each other. I shall have to add a series of solid timber spacers along their length. This seems be acceptable practice when building support beams for decking. Provided, of course, the beams don't rely entirely on coach bolts for post support. The post could be notched [undesirable in my build as it would weaken the posts] or support brackets provided for both beams.

Each beam to post connection would have a separate "packing wedge" cut at 22.5° on the miter saw to fill the empty angle between the post and the beam. This would spread the compression load between the post and beam without needing to cut flats on the posts.  Long bolts [or studding] would pass right through the doubled beam and the post. With a small 22.5° wedge shaped packing piece on the opposite side of the post to provide a perpendicular bolting surface.

Then I thought I could use the inner beam as the packing piece. It just meant I had to saw the acute miters by hand saw rather than using the miter saw. Which couldn't even be lifted high enough for the saw blade to pass over the top of the 2x8 set on edge! I removed the large stop screw to allow a little more elevation but then it was difficult to balance the 2x8 on edge.

I then fitted the tall fences and stuffed a wedge of timber behind the 2x8 but it didn't really help much. The image shows the results of my labours with both beams clamped against the post. I only need to cut four of these acute miters so I shan't get much practice at miter sawing by hand.

It was suggested that I could raise the far end of the plank and then saw with the miter saw set right over at 45°. Sadly, that didn't work because the DeWalt's guard linkage got in the way.  The last image shows how deep the blade would go before it would go no further. I think I may be marginally better at sawing by hand. And was, after the first two trials.

I am still being advised to notch the posts for better location and support of the beams. I still have the crude router jig I made earlier.

Click on any image for an enlargement.

*