Sunday, March 06, 2011

Peterson Fence Project

... or what I did with most of February.

Fence and reason why. / Full scale layout drawing. / Prototype Bracket

The customers have a board and batten fence around the front and down the driveway on their property. With a new (young and energetic!) dog, they are concerned that he will be able to jump the existing fence. There are posts set roughly every 8 feet, the fence boards are cut on a sweeping curve in a sideways D shape. The difference between the peaks in the middle and the level at the posts is about 12 inches.
As a an alternative to replacing all the fence boards, they asked me if I could work up a decorative metal extension in increase the effective 'blocking' height of the fence. My solution was to use a horizontal line of 1 inch diameter pipe, held above the existing fence top by a set of decorative brackets. The intent is to raise the line of the fence by 4 - 6 " at its highest point (so 16 - 18" above the post area.
To fill the gap around the posts will require placing a total of four brackets (using a roughly 6" square grid as the spacing guide). The pipe will consist of a number of 8 foot pieces, with a small gap just above the individual posts. This allows for any sway to the fence line. It will also make installation a lot easier, even allowing to raise the height of the pipe line should that prove necessary.
The individual brackets will be forged to individual organic curves. The top end tapers to a leaf shape, which wraps around the pipe to secure it. The leaves hang down below the top line, helping to block the gap above the posts. I also wanted to enhance the organic feel of the brackets. For that reason I forged a separate smaller 'tail' which will be welded to the main structural part of each bracket.
To ensure there would be enough physical strength to the support, I chose 1 1/2 wide by 1/4 inch thick flat stock. The tails are forged from 3/4 or 1 inch wide by 1/4 (roughly half of each width).

Creating the initial prototype took roughly two hours. You can see the ground areas over the MIG welds. To calculate how much stock would be required, I actually forged the main support from two pieces of known length, then cut and welded to proportion. The finished brackets will be roughly 30 - 32 inches tall.

Each starts with a strip of 40 inch long material. These are the individual forging steps to create *just* the profile - before the forging of the pipe wrap or any of the organic curves. Each of the steps below represents 'one heat' cycle.

- Cut length from 20 foot starting stock
1) Hand forge the corners of rectangular end to round, flatten 'ripple'
2) Air hammer the last 3 inches into a rough point

3) Hand forge this shape smooth and to a sharp point

4) Hand forge the start of the shoulder profile with wide shoulder tool
5) Hand forge to finish the shoulder profile with a spring shoulder tool

6) Air hammer to start taper to bottom of shoulder

7) Air hammer middle portion of taper

8) Air hammer starting portion of taper, start to work back for an even line
9) Hand hammer over completed taper to smooth lines as required
Showing completed group of three *. The bar has increased from 40 inches to roughly 46 inches long.

10) Hand forge the corners of rectangular end to round, flatten 'ripple' (other end of bar)
11) Air hammer end to tapered point (about 6 inches)

12) Air hammer middle segment to extend taper (about 6 inches +)

13) Air hammer top segment to finish taper, start working lines towards tip to even

14) Air hammer middle towards tip, evening taper lines

15) Air hammer to tip, finish evening taper lines, additional hand forging to sharpen point

The starting bar has increased from 40 to roughly 56 inches by the end of initial profiling.
* Now, I found that the ideal arrangement was to have three bars in the forge at any given time. By the time I had worked over three pieces as one step, the first bar I had worked had gotten back up to correct forging temperature. I did use my two burner propane forge for this part of the project:
1) Its winter time, and that's what I use to also heat the forge room
2) These are long straight shapes, ideal for fitting in the limited fire box of the propane forge
3) For production work like this, the gas forge will not overheat the other bars in a series
Normally I would place the next group of three to one side of the forge as I was drawing heat for the last step on the earlier bunch. This pretty much kept me from having too much waiting time before metal was to working temperatures. (In the image above, the door has been opened to take the photo. The door on this forge pivots on the right hand side, making it ideal for this kind of work. There is also a small pass through door on the rear left.)

I found that I could produce a total of NINE pieces as described in roughly THREE hours working time. And that's about all the effective forge time I can manage in a session.

Repeat for a total of 62 pieces!

The work (over the 62 elements) described here represents about 1/3 the total effort required to complete the overall project.

(Thanks to Karen for the image of Thoka at the Fence)

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February 15 - May 15, 2012 : Supported by a Crafts Projects - Creation and Development Grant

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