Monday, August 31, 2009

Building a Cold Frame for the Winter

Last winter I read a great book on winter gardens called Four Season Harvest. According to this book, one of the keys to having garden vegetables year round (or at least during an extended season) is the use of a cold frame.

The book describes how to build one of these mini greenhouses in detail, but the width was too great for our garden beds. So after measuring to be sure (3' 3" maximum) I sat down to draw out new plans in Sketchup on Sunday morning. Then I cataloged what I had on the wood rack and what I needed to buy. The whole list looked like this:

  • 2 sides 3' 3" x 11.25" x 1.5" to be tapered to 7.25" at one end
  • 1 back 7' 9" x 11.25" x 1.5"
  • 1 front 7' 9" x 7.25" x 1.5"
  • 2 long sacrificial bottoms 7' 9" x 1.5" x 1.5"
  • 2 short sacrificial bottoms 3'3" x 1.5" x 1.5"
  • 1 cross brace 3' 4" x 1.5" x 1.5"
Light (x4):
  • 2 light sides 3' 3" x 1.5" x 1.5"
  • 2 light ends 21" x 1.5" x 1.0"
  • 2 stops (to hold the glass in) 3" x .75" x .5"
  • 1 piece of tempered glass 1' 10.5" x 3' 1.5"
Notched prop sticks: (to hold the lights up and vent the frame during warmer days)
  • 4 prop sticks 2.0" x 1.5" x 16" (two inch notches with one inch of material in between)
  • 50 Kreg self-tapping 2.5" pocket screws (everything is screwed together)
  • 16 Kreg self-tapping 1" Pocket screws (or some other 1" screw for holding the stops on)
A trip to Home Depot and Lowe's later I had all the supplies, including the 1/4 router bit I needed for milling the grooves the glass will sit in. Sunday afternoon was dedicated to milling most of the parts for what will become two cold frames. Many of the parts were cut down from larger lumber. The 2 x 2 stock, for example all started as 2 x 4 or larger.

To cut the tapered ends, I marked the end points of each side (minus about 4" for clearance and support), screwed a piece of pine from one mark to the other, registered it against the front edge of my Radial Arm Saw table, and set the saw blade even with the longer end. I was ready to make the cut, but first I set two combination squares to the depths of those marks. On each of the other three ends I just marked the length from the combination squares and screwed down the same piece of pine as a straightedge. It worked perfectly.

The only hand work was cutting angled notches in the front and back. Here I learned that crosscut really can make a difference, and since the first notch was started with a rip saw and finished with a crosscut saw the fit of the cross brace was a little sloppy. The second one was nice and tight, just like I would have wanted. In the picture below, the blemish is a knot hole.

I nailed the sacrificial sections to the bottoms of all the sides (these can be removed and replaced when rot starts to become a problem), and took one set of parts out into the yard to screw it together with Anne's help. It came out well. With luck, I'll get the lights done next weekend.

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