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October 29, 2010
The corner posts


Gail drills holes in the corner deck posts with a hand drill

Over the past several weeks, we have been trying to figure out the best way to engineer the deck railing posts for our mountain home. We are using a cable railing system instead of traditional wooden rails to preserve as much of our panoramic view as possible.

Normally, this is a straightforward process of drilling holes straight through the 4x4 composite posts so the 3/8” wire cabling can pass through. Our inspector/friend Dennis told us that as long as the posts do not bear any actual tension, composite posts (a combination of wood and plastic) should be fine.

A particular challenge, however, are the posts on the corners. According to the plans provided by Topsider, the corner deck railing posts do not have the cable pass straight through. Instead, the cable is supposed to turn a 90-degree corner through the post. Topsider does not advise exactly how this is supposed to happen.

    
Topsider’s deck plan.
In the inset, Topsider specifies corner posts (circled in red), but doesn’t specify how to construct them.

After some consultation with Dennis, we decided that if we used composite for these corner posts, they would either bend or break over time due to the cable tension. Instead, we decided to use 4x4 pressure treated wood. Fortunately, Gail had several boards of this available at our Bay Area house.

On Saturday, October 9, Russell and Gail decided to take the morning to get these boards cut and drilled. Once again, we used the drill press that had belonged to Steve, the late husband of Gail’s sister Debbie.

Our original idea was to drill holes halfway into two adjacent sides of a post. This would provide us with the maximum strength against cable tension. After we drilled one set of test holes, we decided that we had better confirm that we could actually get a cable through these holes.

    
Our first plan was to drill holes halfway into two adjacent sides of a post

This provided the exact kind of engineering problem that Russell loves and Gail hates. How do you get a 3/8” cable wire to enter a hole, turn 90 degrees and exit through another hole? We tried sticking some wire into the hole. It bumped up against the 90-degree bend and wouldn’t move. We tried bending the cable. It wouldn’t go into the hole.

Gail claims that in another life, Russell would have been an engineer. At the very least. Russell is a borderline obsessive-compulsive disorder candidate. Russell had an idea to pull a lead string through the hole, then use the lead string to pull the cable through. Unfortunately for Gail, we ended up spending several hours Saturday morning driving to various hardware stores to find the pieces for this solution.

In the back of our van, Russell demonstrated the apparatus. First, we would insert a tube containing a wire loop through the horizontal hole. Second, we would drop another wire containing a small weight through the vertical hole. The horizontal wire loop would snare the vertical weight. When we pulled the loop out of the hole, it would pull the vertical string as well.

         
Russell’s over-engineered solution:
1. A wire loop would be inserted horizontally;
2. A weighted wire would be inserted vertically;
3. When the horizontal loop was pulled out, it would snare and pull the weighted wire with it

On the positive side, the demonstration worked beautifully. Russell was able to pull a sample cable wire through the hole. On the negative side, Gail counted the total number of corner holes we would need: eight holes each in six posts, or a total of 48 corner holes. She was reluctant to repeat this exercise 48 times. Furthermore, this method would only work when the posts were laid down on their sides. How were we going to do this when the posts were set in place vertically?

    
Russell's apparatus (weighted wire on top; loop wire on bottom);
While successful as an experiment, it would not be feasible in practice

It was back to the drawing board, and our Saturday was already half gone. Reluctantly, Russell agreed that the better solution was simply to drill a hole diagonally through two adjacent post sides. This would not be as strong against the tension, but at least we could physically feed a cable through. To increase the strength of the post, we drilled the holes off-center.

The rest of the day went much more smoothly. Russell fashioned a jig to hold each post at a 45-degree angle under the drill press. As usual, the drill press was only able to drill partway through each post; Gail had to finish each hole with a hand drill.

    
Our final solution was to drill a single hole diagonally through two adjacent sides of a post.
Russell created a jig so each post could lay at a 45-degree angle under the drill press.

Over the next few weeks, Gail sanded each post to reduce splinters from the pressure-treated wood. She also painted the posts to match the grey of the original composite posts.

On Friday, October 22, Russell transported the six corner posts up to our mountain home. After they are cut to length and tapered, the next step will be to install them.


The composite posts (top) and the pressure-treated corner posts (bottom), color matched

 

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