Beware of knots

by Mike
(Ottawa, Canada)

This is not so much a question as just something to watch out for.

I prepared a number of posts with my hole saw and started pounding in the post anchors. They all went smoothly except for one which stopped dead 1/2" from bottoming out. A bigger sledge did not help.

I pried it out with a crowbar and discovered the problem. The edge of the pipe can cut into end grain easily but the cross grain of a knot is much tougher. All I managed to do with the bigger sledge was to bend the rim of the pipe!

I was able to fix the problem by grinding the pipe back into shape and flipping the post around and drilling the other end.

But I recommend anyone using the anchors to cut their posts in such a way as to avoid large knots in the critical bottom 3.5".

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Editor's Note:

This is correct and why it is mentioned on the first step in the instruction sheet included with every post anchor as well on in bold text at the online store.

Knots are extremenly dense relative to the fiber in the rest of the post and are oriented perpendicular to the length of the post and direction of the tube. The tube of the post anchor is designed to cut easily in a parallel direction to the layers of the grain. It is not designed to cut across the grain and this applies for knots as well.

All you need is about 6"-8" of clear wood and small tiny knots are not usually a problem unless they extend deep into the center of the post.

If you try to pound the post anchor through a knot you can bulge the part of the tube not yet in the post and break it off or apart.