Fence Line String Trimmer Modification

At Farm Life Farm, we strive to coast more and flap less. The farm life is hard and expensive. We are constantly trying to recreate the wheel and make a better mouse trap. I have seen some really neat mowers made for trimming around field fence. They are expensive and not anywhere near our budget.

Thinking about our options, I thought, maybe, we can just rotate the guard 180° and run the guard along the fence, under the electric. Oh yeah, I should mention the reason this is a thing: Pigs and sheep and goats are escape artists. The grass is always greener on the other side. As such, they will all try to get out. In an effort to keep them in, we have an electric wire running about 6 inches off the ground to keep the critters inside. We also run a wire along the top to keep predators out. Though we do have the Parmak Fieldmaster3 powering the line, field grass does cause an issue.

On dry days, the grass and weeds touching the fence causes a negligible drop in power; maybe .2 or .5 volts. This is completely acceptable. However, in the morning with dew or during rainy weather, the moisture makes the grass a true conductor. One or two sprigs touching is not a problem, but when a thousand feet of fencing is overgrown, you are gonna lose your voltage. Not only will this cause the fence to not shock your animals, it also means tons of power is being sent to the ground and wasted. For that reason, clearing the fence line becomes one of the myriad tasks that must be performed.

We have several trimmers. A Shindaiwa for Nana, and two Stihl Commercial style trimmers. We keep either a saw blade or a dual-chain-head on one of them and string on the other. The brush trimmer does not have a guard, so the string trimmer was the one. As I approached, I realized that the shaft was straight, not curved like the Shindaiwa. My simple idea of loosening the clamp and rotating the guard was not an option. The guard on this thing is screwed onto a flat plate that is cast as part of the shaft. I had to get much more creative. In the picture

to the right, you can see the cast mounting plate.

Another detail I had overlooked was the line cutter on the guard...little black thing on the right side of the guard under the string. Being flipped around, the cutter would not cut. I grabbed the angle grinder and sharpened the "other" side of the cutter.

Next step was to figure out how to get the guard to stay in place. I grabbed a hole saw smaller than the base of the shaft and cut out a circle. Then, with the Dremel tool, I carved the plastic until it snapped on.

The square plate on top was under the plastic that I cut out when the guard was in its original position. The two metal arms are actually two of the male prongs from an old 240volt dryer plug. They were thick and strong and the bends were a perfect match.

In the picture below, you can see the head lock hole has the plastic locked onto it. You can also see that the bolts up top in the picture to the left are not individual bolts, but a U-bolt from a satellite antenna pole. The u-bolt strap is in place, then an extra thick washer (spacer) on each side, then the arms, and finally that square metal plate. As I tightened the clamp nuts, the u-bolt strap bent to conform to the shaft.

Drilling through the shaft was clearly not an option. I would have needed to tap the metal and then grind down screws so the tips would not hit the spinning head. I was not willing to invest that much time, however the angle of the tube made it impossible to clamp anything to the shaft. I began tinkering with a few different brackets and other ideas, I tried the u-bolt with a pretty good fit. As I tightened the nuts, it pulled everything together. After taking it all apart, I put the hold down arms on the drill press and made bolt holes, The top already had holes in it. The left lower bolt would not fit any other way than from the bottom. The right side is a self tapping screw. The one failure I have with this mod is the string length. The old mounting location added about two more inches distance from the head to the cutter. Now the string is 4 inches instead of 6. Not the biggest deal and with how thick the grass is, a shorter string should cut better. Not having to carefully gauge our distance from the fence saves a great deal of time. Not having the string catch on the field fence will save us money on string and save the time we used to spend on bending fence wire back into normal position. No longer having the fence grab your string and jerk you back: Priceless.

close up view of the u-bolt holding our front guard together.

I cannot stress that last point enough...If you have never trimmed field fence, you cannot fathom the frustration and physical pain one feels every time that string grabs on the fence. It just might be one of the truly miserable experiences a farmer can have.