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| The breadaway arm after treatment with citrus degreaser. The broken off part (upper right) has been lined up with the rest of the piece. |
The other week while using my New Holland 451 sickle bar mower I inadvertently hit a post with the mower bar and broke a part in the mower called the "breakaway arm." Based upon the way the breakaway arm is physically positioned in the mower it appears that it is not actually supposed to break. Rather, the arm is designed to pop out of a spring loaded clamp and rotate in such a manor that sickle bar will swing backwards without being damaged. Once the tractor is safely stopped, the bar can be swung back into place and the breakaway arm loaded back into the the clamp.
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| A close up of the broken portion. The red-orange color is from rust. When it was originally broken, the break appeared much more silvery or white, which could mean the part was made from white cast iron. Based upon what I've read, white cast iron is not repairable, but I'm not an expert on identifying cast irons, so I thought I'd give it a try anyway. |
Aside from the fact that the material may have been white cast iron, I also faced potential complications from grease absorption. Cast iron has the ability to actually absorb oils and grease and, because this part functioned as a sort of emergency extension hinge, it had been heavily greased since the mower was assembled 30 or more years ago. I've read that professionals have special ovens for burning clean oil saturated metals, but that an oxy acetylene torch can work in a pinch, so I gave it a try. I did notice grease burning out of the metal, but I don't know if I heated the metal long enough.
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| A closeup view of the bronze brazed area. |
After burning the grease out of the metal, I then brazed the broken pieces back together using a flux coated bronze brazing rod. Ultimately the repair attempt was not strong enough and the part broke again after 20 minutes of use. It was a long shot anyway, so I wasn't too concerned about it.
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| The raw materials ordered from McMaster-Carr. |
Rather that try to find a used part that was worn and over-priced, I decided to fabricate the part myself. Using a calipers, I made precise measurements and ordered the raw materials from McMaster-Carr. Whenever I need to order something that is reliable, accurate, and high-quality I will always try to order from McMaster-Carr. I've used them for years and never been disappointed.
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| Most of the parts ready for assembly. The two steel rods on the left side of the photo had short threaded pieces welded to their ends. These rods will be inserted into the sections of pipe shown in the center of the photo. While I could have simply welded the threaded pieces to the ends of solid steel bars, I felt that this method tended to be a little neater and more closely resembled the original item which had the threaded section machined out of the larger cast iron bar. The two pieces on the right of the photo were cut from scrap metal I had left over from older projects. Interestingly, when New Holland originally designed the part, they used both metric and US customary measuring systems. For instance, the large plate on the right side of the photo is exactly two cm thick and five inches long. |
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| The last two parts: Two large washers I cut from 1/8 inch thick steel. I used the torch to cut them, which isn't my strongest skill. |
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| The completed part. I used 0.035" mig wire with carbon dioxide for shielding. All the measurements match the original part, so I don't anticipate any problems, but if I do encounter issues I'll update this post. |
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