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Picture of Hoop Bender
Low tunnels make great season extension tools. They are MUCH cheaper than a high tunnel and MUCH MUCH MUCH cheaper than a greenhouse. They can easily be made from stuff you can find at your local hardware store and nursery. Elliot Coleman (a pioneer in organic gardening) Explains how to make them out of 1/2" PVC conduit HERE .

There are advantages to making them out of galvanized EMT (electrical metallic tubing) durability being a chief one. Johnnie's sells a bender that looks like it's made out of the exact stuff that it is intended to bend and for the not-so-bargain price attached to it, I figured it was time to make one myself.

Having procrastinated on getting cool weather crop seeds in the ground to the point that the crops won't be ready by the time it freezes, this little project should keep me out of trouble with the wife: good-bye evil eye, hello broccoli!

After an exhaustive search, I found many temporary designs that utilize screws in plywood or stakes in the ground but I wanted something a little more like the one that Johnnies sells but made from the scrap wood that never seems to get any smaller...but that's a topic for me and a shrink. Any way, let's get started!
 
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Step 1: Measure and Cut

Picture of Measure and Cut
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Since I was going for 30" wide hoops, I assumed that there would be about 10% spring-back in the 1/2" EMT once it was bent. So I measured out for a 28" diameter semi-circle (14" radius). The actual diameter is closer to 27" once I routed the 1/2" groove (as you see in a later step). After using the bender, hand manipulation of the pipe in the bender seemed more important to the final shape than the radius of the bender.

Using some 3'4" plywood I rough cut a couple of squares or rectangles then stack them on top of each other and screw them together. Thais way you will get IDENTICAL shapes. Cut the semi-circle out with a jig saw. Mine was out on loan so I made due with a recip saw. Yes it was kinda like using a sledgehammer on a tack which is why I had to bust out the belt sander and clean up the edge.

If you notice, mine are not full semi-circles, but it doesn't really matter as long as the radius is right.

You can see my improvised workbench is a hand truck with the work c-clamped on the lifting plate. I wanted to keep the sawdust outside and the weather was FANTASTIC that day to boot!

Step 2: Route groove

Picture of Route groove

Unscrew the two halves of the plywood and mark the insides of the boards. This is important unless you managed to cut a perfectly symmetric semi-circle. Otherwise the groove will not line up when you reassemble the pieces.

Load a 1/2" cove bit with pilot into your router and set the depth so that the bottom of the cut just removes the edge of the board on a scrap piece. Once the router is set-up, route coves in both halves of the semi-circles.

Step 3: Assembly

Picture of Assembly
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Match the two halves together and secure with wood screws.

Step 4: Finishing touches

Picture of Finishing touches
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Add a strap of any kind (as long as it's strong enough to hold the pipe while it's being bent) to one side of the bender. I used the left side since I'm right-handed.

I also put a couple of boards on the back so I could place it on the top ledge of my deck rail to prevent it from turning. You could devise any convenient method like directly screwing it to a picnic table, use the stake hole in a pick-up truck bed rail, or drill holes though it and pound some re-bar into the ground.

Step 5: Operation

Picture of Operation
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I was looking for about 24" of straight tubing on either leg with a 30" diameter bend at the top. To get the right measurements to use as a template, I just put a little extra length in the strap bent the hoop and trimmed the ends.

You can see in the picture the orientation differs from the orientation in the video. After bending the first one changed it to be easier to work with.

The Johnny's high tunnel bender is an INVALUABLE tool for the homestead or small commercial farm. using 21' top rail at $0.61 per ft we are able to build 80' tunnels for less than $1,000 and they pay for temselves in ONE SEASON!

It's always good to have a cheaper option!