Friday, January 16, 2015

Snow barrier

I have worked through the stack of logs and that has left me free to tackle a project that has been looming. A fence designed to stop snow slipping off of a steep roof into a neighbours property. The juiciest bit for me was a curvy top rail for the fence, which is about 8m long. I noticed these two logs had a similar curve in them and sawed them to about 18cm thick along the axis closest to the shared curve. Then I used a little jig for the chainsaw to make a perpendicular cut along a curved line for the top and bottom of one beam and then traced that curve onto the matching piece. The beams taper from 18cm at the far end to about 12cm at the near end. The curve having been cut I marked out level lines onto one side of each beam. I decided that the bottom surface at the tip would be the lowest point and the underside of the beam at the center would be 240mm above that. You can see a stick tacked on to the far end of the right hand beam, I marked that at a few points and used those to snap in the level lines with an ink line. The level lines obviously allow me to measure the height of the curved beam where the pillars intersect, but they are also important to measure along and find the 2m centres for those pillars.

This is the chainsaw jig, I was worried that a normal drill would have trouble with going through the tool steel on the bar, but it worked fine, perhaps just the area around the rim of the bar is heat treated. Anyway, the bar is bolted onto the jig using two threaded inserts in the plywood.

Having drawn in the morticed for the pillars I needed to make them properly perpendicular. With the beam in the workshop underside facing up I wedged up the thin end on a block to orient the beam correctly, then with a spirit level on the morticer I was able to orient that to cut into the timber at the correct angle. I had already put in a little profile on the beam at this stage using a curved blade in a groove cutting tool that I made several years ago.

I needed a kind of fancy lap joint to mate up the two halves of the beam in the middle. I have written about a self tightening version of this joint before, but this time I used a little hardwood slat to push the joint halves tight together.
Here is the finished joint.

This shows how the little spline acts on the two halves to drive those little nose portions snugly into place.

This shows the beam and pillars erected on site from the neighbours car park. I have to go back and nail planks top and bottom to finish the fence and also fit some braces that will tie the structure to the house. Last year's heavy snow came straight off the roof and onto the wimpy metal fence knocking it off its socks, hopefully this addition will keep the snow in bounds.