Had to trim the hedge the other day. Being a perfectionist, I spent hours trying to get it *exactly* straight, level and square. Ho hum.

That gave me plenty of time to think about better ways to do it. Like having rails and moving blades and a...no, wait - level, straight, square? It has to be a laser-level! High-powered (or high enough to singe off the sticky-up bits), on a levelled tripod - aim, fire it up, and sweep the beam across the top of the hedge - there, perfect!
-- Frankx, Aug 03 2006

I always thought hedges looked stupid (or fake) when they were perfect. I would think that a laser that could cut a hedge would do a number on everything around: you, the neighbors porch, the cat...

Why not use a couple of poles and a string?
-- MoreCowbell, Aug 03 2006


Ah, MoreCobewell, why do you always have to simplify the halfbakedness out of it? Poles and strings for topiary uses are already baked, and already a pain in the posterior.

Poerhaps a couple of poles and some monofilament razor wire at least... but that would not be laser topiary.

This idea has a lot of potential for simplifying my life. Granted, a bush trimmer might work just as well, but that is not so exciting.

Before Laser topiary can get off the ground, a few serious issues must be looked into though. Namely, avoiding ignition of the bushes, and preventing damage from stray shots.

A hacksaw shaped device with a mirror on one end to send the laser back into it's output, or to some other safe point might be wortwhile to prevent stray shots. Adding a water sprayer could prevent this from making burning bushes... if that turns out to be a problem.

Just for safety, you might also design the laser to specifically target cellulose, or some other plant material, so that when I'm working too close to a rough wall, or my arm, or the neighborhood pet... well, you get the idea.
-- ye_river_xiv, Aug 03 2006


An obvious idea, really. Cutting a straight line? Use a laser.

To make this anything but a wish, it needs to have some hint of how to make it work. For instance, vegetation looks brighter in infra-red photos, so we know an infra-red laser would reflect. Obviously, a green laser would reflect also, as plants reflect green light. Therefore, an ultraviolet laser would be best for this cutter. See?

That isn't right, by the way, but at least it makes an attempt at halfbaking an invention. Until this "idea" has something more than a wish, I'm fishboning.
-- baconbrain, Aug 03 2006


...maybe he meant *razor*?
-- xandram, Aug 03 2006


high powered laser on a tripod. Now, Bring me a shrubbery! And be careful with the laser!

So we can get the two level effect with a little path running down the middle.

Did I say laser? I, of course, meant A Herring!
-- Zimmy, Aug 04 2006


Yes [baconbrain], it does need a bit more detail, sorry.

As [ye_river_xiv] said (thanks), with cellulose peak absorption (at 680 and 700nm), a ruby laser (at 694nm) would be the closest, but I suspect not available at a suitable power. Possibly krypton ion (see link), Nd-YAG, but certanly CO2 lasers with sufficient power are available - but down in IR wavelengths

I'm not sure that wavelength would be critical, as you just need heating rather than excitation. A visual wavelength would be an advantage, so you could see where the beam was.

You're probably going to need something fairly high powered. Laser cutting machines for woods and plastics output typically 50W, focusing the beam down to around 0.2mm, which gives about 1.6kW/mm^2, but that can cut through tens of millimetres of wood. For a laser with a raw (unfocused) beam diameter of 1mm and divergence of 1mrad (which seems typical) that would mean a 3kW+ device to cut the hedge over a range of a metre. That's well within the range of industrial cutting lasers - but would need a seriously hefty power supply, and water cooling too.

As for setting up - a mirror placed at the back of the hedge, deflecting the 'unused' beam into the ground (oops, sorry worm!), and the laser head placed on a tripod, or something else, that allows you to set it level, and pan the beam across the top of the hedge.

Oh, and a hose to put out any fires - best to spray the hedge first, to damp it down a bit too.

Ofcourse, you could use a computer-controlled galvanometer mirror, to carve your hedge into pretty shapes, instead of boring old 'straight'.
-- Frankx, Aug 04 2006


YEAH! now you're halfbaking!

I don't know about sending the beam to the ground... Might vitrify it, or mess up the cement a little.

Better than hitting the stucco of my house I suppose, but you'd want to aim that end too if you did it like that.
-- ye_river_xiv, Aug 04 2006


I have a privet hedge on my property.. a big one. This sucker is about 70 feet (22.5 meters) long, about 7 feet (2.2 meters) high and 5 feet (1.5 meters) wide. It takes me 3 to 4 hours to cut it with a electric trimmer. Each time I cut this monster, I design and build the laser cutting system described above in my head. If you build one some day, I will buy it... really, I will… a bun for you
-- tossthedog, Oct 23 2007



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