Forum:

alternative energy

Would a pedal-operated wood chipper/shredder work, or am I dreaming?

Posts: 257

Location: Nicoya, Costa Rica

posted 7 years ago

Hi, two years ago we looked around for a wood chipper, but they were way too expensive (here in Costa Rica).

This morning I woke up and thought that if I didn't have the engine the price could easily be half as much.

I am very much fascinated by... I don't even know what they are called in English, multipliers? You know, a toothed wheel that spins fairly slow that fits into a smaller wheel that spins much faster. Meaning that I would be pedal without killing myself, but further along the machine the spinning and the power would be multiplied.

So, I am too ignorant about this, but would it be possible to fit a bicycle and its gears to a small, garden chipper and not have the blades get stuck? I am not planning on chipping branches, but I might need it for sugar cane, and that can get up to 3 or 4 inches across.

I would appreciate any feedback, even just to a source that would teach me the ins and outs of the mechanism I explained (big wheel, small wheel).

Writing from Madhuvan, a yoga retreat/organic farm on the West Coast of Costa Rica.

Dale Hodgins

master pollinator

Posts: 8818

Location: Victoria British Columbia-Canada

730

posted 7 years ago

The smallest wood chipper that I've ever used was a 5 hp unit. It was inadequate for my purposes.

A competitive cyclist can maintain about 1/4 hp. So the human body is able to put out about 1/20 of the power requirement to run a small wood chipper.

Pigs and other critters enjoy chipping wood and they do it for free.

Ken Peavey

steward

Posts: 2482

Location: FL

105

posted 7 years ago

Yes it can be done.
Caveat: wood takes a tremendous amount of energy to break into small pieces. The guy doing the peddling will put out a great deal of work for what may appear as miniscule results.

What you are attempting is to break the cellular bonds within the wood: splitting and chipping
or
remove small amounts of wood between larger sections of wood: sawing

For bigger pieces, much work must go into the wood as there is much material to separate. A man can only work so hard. Mechanical advantage may make it possible to do the job, but the pieces will be tiny-sawdust or shavings. For sugar cane, if it is squeezing the juice that you want to accomplish, many tons of pressure are needed. The pressure can be built up, but it will require peddling for some time.

Consider a large heavy wheel with a chipping blade attached. For that blade to rip a chip off a branch, it will have to be spinning at a certain speed. You can surely use peddle power to get the wheel up to speed, but each chip ripped from the branch will decrease the speed of the wheel. You have to peddle to maintain the speed of the wheel. Putting too much branch into the rig may slow the wheel until it can not chip through the branch. There would be a balance between how much material can be chipped with the continuous energy of one man. This can be controlled by how fast the material is fed to the rig.

Chipping-Rig.jpg

Seed the Mind, Harvest Ideas.
http://farmwhisperer.com

Sergio Santoro

Posts: 257

Location: Nicoya, Costa Rica

posted 7 years ago

Thanks so far.

This is what I've found in the meantime. In this video both the machine and the two guys are lame. There should be some kind of casing and funnel, but I guess they were just showing the mechanism. What caught my eye is that the rotating blades would cut along the fibers. So my first idea would be some machine that at first shreds lengthwise like that, and the next set of blades below would be much like a garbage disposal device in a sink.

I will want to get juice out of the sugarcane, but not at this time; it was mainly to chop it for my cows. I don't intend to chop and branches over 1" across. It was mostly for leafy twigs, corn husks, banana leaves and stalks. I just need to make stuff smaller, whether it's for mulching or make a cow feed, without whacking for hours with one machete.

Here is another video. It's very simple and small, even week, but the fact that the pedals are directly attached to the motor, so to speak, seems to me stronger. I get the impression that a chain would disperse some of the energy used; is it true or it's rather that a chain would work like a pulley and diminish the effort by half?

Writing from Madhuvan, a yoga retreat/organic farm on the West Coast of Costa Rica.

Trond Hogstadt

Posts: 16

posted 7 years ago

How "woody" is sugar cane? I have never seen it up close so have no idea how difficult it would be to chop with a machine.

I have a wood chipper with a 15 hp engine. It does make short work of green or dry branches and tree trunks up to three inch in diameter. But it slows down when a length of 3" is fed.

Note in that second video that the cutting wheels are rotating at pedal speed. When you try to speed up the output shaft by a factor of 4 for example, the input force must go up by a factor of 4 as well. Bicycles with multiple speed gears gear the output down when more power is needed at the wheel, as in going up a hill. I doubt that gearing up would be feasible unless the sugar cane is soft like leafy green plants we eat (chard, mustard greens, and so on.)

A chain and sprocket or gear drive can be used to change speeds up or down. The more steps, or gear wheels involved, the greater the frictional loses. With a simple 2 sprocket and chain arrangement the power loss would be negligible for most purposes. Bicycles use chain and sprocket drive and work quite well.

Sergio Santoro

Posts: 257

Location: Nicoya, Costa Rica

posted 7 years ago

Of course, what was I thinking. I guessed I haven't biked in a while.

Sugarcane is very dense, but I wouldn't call it woody.

Writing from Madhuvan, a yoga retreat/organic farm on the West Coast of Costa Rica.

Ken Peavey

steward

Posts: 2482

Location: FL

105

posted 7 years ago

If all you want to do is chew up soft leaves, a shredder can be assembled quite easily from simple parts.

The video clip you linked to has a pair of shredders chewing up debris. I've been meaning to get to making a leaf shredder, but I'm so lazy I figured I'd just pile them up and let them rot instead of going to all the trouble. I added up a picture to give you some idea of what I'm talking about:

You'll need several circles all the same, in 2 sizes. Plywood can do the job, wide planks will work, and you will also need some thin stock such as 1/4" plywood or luaun. It would be best if you drill the centers of the circles to help everything line up. Cut them out any way you can, they need to be fairly accurate. Once lined up, the circles can be nailed/screwed/glued together

You'll put together 2 shafts as seen in the lower left. A 1/4" circle would be added to each of the small circles in order for the two shafts to fit together. Build them into a frame such that one shaft can be spun. The other will spin as soon as material is added and the rig gets cranking. A space will need to be allowed for material to be crunched through the space between the shafts. It would not have to be much, a 1/4 to 1/2" gap is all you would need.

I thought about ways to protect the wood and add a sharp edge to the cirlces. Cutting up some soda cans into strips then fastening the strips to the outer edges of the circles might work, but this thing never got off the drawing board.

This rig could be cranked by hand, pedal, squirrel or motor. Hand cranking leaves one hand free to feed the shredder. For lightweight material such as leaves or pine needles, this might just do the trick.
I've not gotten into the details. Circle diameters would be maybe an inch or two difference to get a good bite.

leaf-shredder.jpg

Seed the Mind, Harvest Ideas.
http://farmwhisperer.com

Sergio Santoro

Posts: 257

Location: Nicoya, Costa Rica

posted 7 years ago

This sounds great. I wonder if I could make it more heavy-duty by using metal disks with the same grove as a chainsaw shaft and mount segments of chainsaw chain to fit on each disk. That should be able to do some more damage. There is a machinist in town that would do anything I tell him to. Those disks shouldn't be to hard to shape.

Writing from Madhuvan, a yoga retreat/organic farm on the West Coast of Costa Rica.

Ken Peavey

steward

Posts: 2482

Location: FL

105

posted 7 years ago

Steel would offer durability. Getting the disks precision cut with sharp edges would cut thicker stock. How about adding a means of altering the distance between the 2 shafts to handle larger stock? With the added mass, you may need to add gears to drive both shafts. The bigger the design gets, the harder it will be to power with muscles. With chainsaw sections welded on, you may have trouble with drag or with material clogging the sections. If you motorized it with the chainsaw sections, the machine starts to turn into a chewing monster. How much material needs to be processed? How much heavy duty needs to be built in?
More Options
-instead of wood or steel disks, use saw blades
the particle size would be tiny
-instead of disks, give the outside edge an incline
this would sheer material rather than chop
kinda like a series of meat slicer blades, keeping the edge honed would be a chore
-instead of disks, flailing hammers secured to a central shaft
this is in line with a mechanical chipper/shredder and would need a motor to spin the hammers at high speed
this is reinventing the chipper rather than figuring out a peddle powered device.

Seed the Mind, Harvest Ideas.
http://farmwhisperer.com

Sergio Santoro

Posts: 257

Location: Nicoya, Costa Rica

posted 7 years ago

Saw blades! Of course! You mean a circular powersaw blade, right? Aren't they too big in diameter?

For the rest of what you said, English is not my first language, and I just realized how ignorant I am as far as these technical terms. I'll ask my buddy who is Canadian.

Writing from Madhuvan, a yoga retreat/organic farm on the West Coast of Costa Rica.

Ken Peavey

steward

Posts: 2482

Location: FL

105

posted 7 years ago

A stack of saw blades.
it would be difficult to spin them fast enough by hand or peddle to cut wood, but I think they would do a job on leaves and soft material.

Instead of the 2 shaft system, how about a single shaft with a bunch of blades. Old, worn out, dull, screwed up blades would do. A box or hopper would be needed to keep the leaves contained during processing. As the blades spin, there would be some shredding. I think the leaves would be squeezed or shoved over to one side where the saw blades would pinch them as they spin around. Too much material could bog it down. Different blade sizes could still be done, 7.5" skill saw blades, 10" table saw blades, add washers if spacing is needed. Tack weld to a 5/8" rod, cut a slot for a woodruff key, turn the shaft(s) with whatever power is available. Saw blades are usually 1/8" thick, needing 8 blades per inch of shaft. For a wide shredder, it would be heavy. Using washers or several between blades would reduce the weight. Some space between blades might get you by. What if the blades were allowed to wobble-help clear out stuff that gets stuck between them

2 counter-rotating shafts of stacked saw blades would chew through material, but it doubles the amount of work. Spin them with a motor and all you would have to do is hold a tree trunk upright, let gravity feed the blades. The product would be sawdust.

I have a dado head set for my table saw, maybe it offers some ideas.

Seed the Mind, Harvest Ideas.
http://farmwhisperer.com

Robert Ray

gardener

Posts: 1404

Location: Cascades of Oregon

posted 7 years ago

Ken's idea of the heavy wheel" a flywheel" just like a potters wheel would maintain speed. The pedals powering up the wheel and the momentum of the heavy wheel taking the load.

"There is enough in the world for everyones needs, but not enough for everyones greed"
(Buckman)

Sergio Santoro

Posts: 257

Location: Nicoya, Costa Rica

posted 7 years ago

I realize the benefit of a heavy wheel and the inertia, but I'm also thinking, why should I use my legs to spin a 8" cylinder made of saw blades, if the part I need is only 1/2" deep? Why don't I get a steel rod of 3 or 4" and carve groves along it and sharpen them, so the hub becomes the blades at the same time? It would be the same cutting power, but lighter for me to activate by pedal, no?

Writing from Madhuvan, a yoga retreat/organic farm on the West Coast of Costa Rica.

Robert Ray

gardener

Posts: 1404

Location: Cascades of Oregon

posted 7 years ago

For me the ability to replace or sharpen the blades seems to make sense. The mass of a flywheel for initial contact or when the material hhas a hard spot also sounds a bit advantageous. Let us know how your design works.

"There is enough in the world for everyones needs, but not enough for everyones greed"
(Buckman)

Ken Peavey

steward

Posts: 2482

Location: FL

105

posted 7 years ago

For shredding leaves I have tried soaking them in a bucket of water, then using a drill with makeshift chopper. The water was supposed to soften the leaves. The chopper is a drywall mixing paddle. I took it to the grinder to sharpen the edges with the notion that it would cut better. A lawn mower would have been faster and done a better job.

The next attempt had the leaves soaking, then into a BLENDER.
FAIL
I still need to clean up the blender.

My most recent experiment had the leaves soak for a couple days, then go into a pot which I put on top of a camp stove.
Q Does cooking or several hours of constant heat do anything to break down the lignins and cellulose in leaves?
A No. It is a total waste of time. Cooking then blending wastes even more time.

My objective was to turn leaves into a slurry, mix with greens, and pour onto a section of garden bed as well as an independent compost heap. I want to take a look at how small particles improve or alter the composting process. It's all about insatiable curiosity.

The process Sergio is looking at is dry. I've tried mashing up leaves in a wet process for greater motion within the batch.

Seed the Mind, Harvest Ideas.
http://farmwhisperer.com

Ken Peavey

steward

Posts: 2482

Location: FL

105

posted 7 years ago

Perhaps we can consider reciprocating motion as opposed to rotary motion.

Seed the Mind, Harvest Ideas.
http://farmwhisperer.com

Sergio Santoro

Posts: 257

Location: Nicoya, Costa Rica

posted 7 years ago

Oh, but the cylinder I have in mind could be sharpened, why not?

Writing from Madhuvan, a yoga retreat/organic farm on the West Coast of Costa Rica.

Sergio Santoro

Posts: 257

Location: Nicoya, Costa Rica

posted 7 years ago

Also, I know what reciprocating means, but when it becomes a technical term I'm a bit lost.

Writing from Madhuvan, a yoga retreat/organic farm on the West Coast of Costa Rica.

Ken Peavey

steward

Posts: 2482

Location: FL

105

posted 7 years ago

I'll try to keep it simple

Seed the Mind, Harvest Ideas.
http://farmwhisperer.com

Sergio Santoro

Posts: 257

Location: Nicoya, Costa Rica

posted 7 years ago

Yes, but what did you mean?

Writing from Madhuvan, a yoga retreat/organic farm on the West Coast of Costa Rica.

Ken Peavey

steward

Posts: 2482

Location: FL

105

posted 7 years ago

rotary: rotating the saw blades
reciprocating: back and forth, side to side or up and down
How about a device that continually pounds/hammers/punches/stomps the material, perhaps through a sharp grating.

Seed the Mind, Harvest Ideas.
http://farmwhisperer.com

Fred Morgan

steward

Posts: 979

Location: Northern Zone, Costa Rica - 200 to 300 meters Tropical Humid Rainforest

posted 7 years ago

Hi Sergio,

What is the purpose?

First of all, if you are trying to grind up, you can purchase electric hammer mills pretty cheaply in a ferteria (I live in Costa Rica too). Ask for a picador. They are usually painted green here. The work fine for grinding up grass and food for animals.

If for compost, well we just chop them a bit with machetes, and pile other material on top of them. They break down really fast.

I had a 14 HP chipper / shredder - and sold it because I was never using it. Just chop the stuff up a little, and make sure it touches the ground, it will break down really fast, ESPECIALLY sugar cane.

And if you are trying to make sugar - they used oxen to power the machinery in the past, remember horse or oxen power for the equipment, it doesn't have to be you.

Sustainable Plantations and Agroforestry in Costa Rica

Sergio Santoro

Posts: 257

Location: Nicoya, Costa Rica

posted 7 years ago

Hi Fred,

Never seen an electric hammer mill, how big is it? And how cheap?

Picador is what they call a chipper, too.

We do have an ox, but everybody says his horns are too small. Then again, they only know the Guanacaste ways here, everything is else is just a rumor and for sure it won't work...

We are dreaming with a trapiche (sugarcan mill), but for now we don't have enough cane, and I'd be fine to start with a dehydrator and a biodigestor.

Writing from Madhuvan, a yoga retreat/organic farm on the West Coast of Costa Rica.

Sergio Santoro

Posts: 257

Location: Nicoya, Costa Rica

posted 7 years ago

Oh OK, I've seen the images on Google. Well, that's what I call shredder/chipper and last year we didn't find anything for less than $500, and we didn't think it was the case.

Writing from Madhuvan, a yoga retreat/organic farm on the West Coast of Costa Rica.

Fred Morgan

steward

Posts: 979

Location: Northern Zone, Costa Rica - 200 to 300 meters Tropical Humid Rainforest

posted 7 years ago

What are you trying to accomplish? Are you trying to make sugar, or just compost? I think usually for sugar, they crush it more than chop it up. If I was you, I would find an old Tico, about 70 or 80 years old and ask him what to do. My caretaker is 62 years old, it is amazing how much he knows, when I stop and ask.

For example, he knows how to make wooden shingles with a machete from laurel. From what I can tell, a roof of wooden shingles out of laurel will last up to three times as long as zinc tin roofs.

Sustainable Plantations and Agroforestry in Costa Rica

Sergio Santoro

Posts: 257

Location: Nicoya, Costa Rica

posted 7 years ago

For now I just need to process organic material and make it into tiny bits, whether it's for animal feed, or faster compost, or mulch. I just know that in many an occasion I wished we had a chipper.

Writing from Madhuvan, a yoga retreat/organic farm on the West Coast of Costa Rica.

Ken Peavey

steward

Posts: 2482

Location: FL

105

posted 7 years ago

instead of human power, that ox could offer a little extra muscle.

Seed the Mind, Harvest Ideas.
http://farmwhisperer.com

Ken Peavey

steward

Posts: 2482

Location: FL

105

posted 7 years ago

I had more reasons why I was looking at shredding up leaves
-to see if leaf powder could serve as substitute for peat moss in keeping mildew growth from forming on the top of the soil mix in greentree plant pots
-with the slurry, to make it possible to press a blend of leaves/hay/other material into fuel briquettes

Seed the Mind, Harvest Ideas.
http://farmwhisperer.com

Sergio Santoro

Posts: 257

Location: Nicoya, Costa Rica

posted 7 years ago

How do you train an ox to pedal, though?

Writing from Madhuvan, a yoga retreat/organic farm on the West Coast of Costa Rica.

Kathleen Sanderson

pollinator

Posts: 1249

Location: Green County, Kentucky

posted 7 years ago

I was going to suggest an ox, too....

An ox can't pedal, but it can turn a crushing mill, and crushing the cane would probably accomplish what you want just as well as shredding or chipping it. I've seen pictures of an ox walking on some kind of treadmill that then turned a shaft for equipment, but I suspect that by the time you built the treadmill, you might just as well buy a wood chipper.

Kathleen

Fred Morgan

steward

Posts: 979

Location: Northern Zone, Costa Rica - 200 to 300 meters Tropical Humid Rainforest

posted 7 years ago

Sergio Santoro wrote:For now I just need to process organic material and make it into tiny bits, whether it's for animal feed, or faster compost, or mulch. I just know that in many an occasion I wished we had a chipper.

In all honesty, you could find a machete, with practice, works as well. And you can buy one hp hammer mills, not sure how much, but you can buy them without motor, and then attach whatever you want to them.

but with a hammer mill, speed is what is most important. But really, just use a machete. I know, we do.

Sustainable Plantations and Agroforestry in Costa Rica

Sergio Santoro

Posts: 257

Location: Nicoya, Costa Rica

posted 7 years ago

Sigh... well, at first I did think of making a contraption much like this table top paper cutter, because chopping with a machete is not precise at all.

I really wanted the outcome to be uniformly small, like out of a chipper, and VERY small, too. It would take me a whole morning to make just one sack of anything. Plus, I mentioned the sugarcane, but as the most extreme possibility. For the most part it would be corn stalks, corn husks, banana bunch stalk, banana trunk, banana leaves, kitchen scraps, leaves, twigs, straw, dry bean shells, etc., etc.

I also thought of combining 3 machetes and using them in some kind of spring-loaded chopping machine.

What if I bought a picador without engine and connected to a treadmill instead of a bike? Would the tape of the treadmill count as a huge wheel, or all that counts is the small wheels inside the treadmill?

Writing from Madhuvan, a yoga retreat/organic farm on the West Coast of Costa Rica.

Fred Morgan

steward

Posts: 979

Location: Northern Zone, Costa Rica - 200 to 300 meters Tropical Humid Rainforest

posted 7 years ago

Sergio, please take this the right way, you need someone to teach you how to use a machete. I have seen our workers peel a coconut, remove the husk, the shell and leaving the kernal, with the milk still in it, in under two minutes while holding it in their hands. A machete is incredibly precise, and fast, in the hands of a pro. Even I am not that bad. Our caretaker can walk in front of me going through jungle and clear a path nearly as fast as I can walk. It is really incredbile. And he is 62 years old. (tough as nails, too)

Besides, everything, even limbs, break down in very little time. When we are harvesting trees, we just chop up the tops with machetes enough that the limbs touch the soil, within a few months, they will be melted into the ground. Granted, you live on the dry side from what I see, but during the rainy season, you don't have to get complicated.

Just pile everything in a big pile, it will break down before you know it in the tropics.

Sustainable Plantations and Agroforestry in Costa Rica

Sergio Santoro

Posts: 257

Location: Nicoya, Costa Rica

posted 7 years ago

Sure, I've lived here for 3 years, I am familiar with the people, their skills, and the weather. It's just that sometimes you need stuff cut fine NOW. And what about the feed? Should I feed the cows decomposed guanacaste pods, corn cobs, mung bean shells...?

Writing from Madhuvan, a yoga retreat/organic farm on the West Coast of Costa Rica.

Sergio Santoro

Posts: 257

Location: Nicoya, Costa Rica

posted 7 years ago

Are you talking ripe coconut or green?

Writing from Madhuvan, a yoga retreat/organic farm on the West Coast of Costa Rica.

Fred Morgan

steward

Posts: 979

Location: Northern Zone, Costa Rica - 200 to 300 meters Tropical Humid Rainforest

posted 7 years ago

Ripe, peeled, to just have the kernel.

My point is, one person power is better applied to a machete, than a shredder. The shredder uses a lot more power than a human can generate. I can't imagine it working, from an engineering point of view.

Regarding cattle, they don't need things very fine, that is what their teeth are for.

But why would you be trying to feed decomposing stuff to cattle? Why not just let it finish discomposing. I am missing something here - to decompose stuff is simple, and just put some dirt over it, cow manure and plant if you are in a hurry.

Sustainable Plantations and Agroforestry in Costa Rica

Sergio Santoro

Posts: 257

Location: Nicoya, Costa Rica

posted 7 years ago

Hehe, no, I don't want to feed them decomposing stuff at all, but you kept saying that to have small bits of anything I just needed to let it rot, so I said how is that gonna work for the cows?

Ok then, machete practice it is. How many fingers can I lose after all?

Writing from Madhuvan, a yoga retreat/organic farm on the West Coast of Costa Rica.

Fred Morgan

steward

Posts: 979

Location: Northern Zone, Costa Rica - 200 to 300 meters Tropical Humid Rainforest

posted 7 years ago

When we prepare silage for cattle, we don't do anything more than chop it up a little with a machete, say 4 to 6 inch pieces. They have very good teeth for grinding, after all. To explain, cattle eat with the tongue, unlike sheep and horses, who can bite things off. That is why, if you let sheep overgraze, cattle will starve. It is also why, if you want to get rid of spiny weeds (like dormilona which is very common in Costa Rica) sheep work wonderfully. They also are great on recently cleared brush areas.

When I cut our lawn with a machete, the sheep line up to be fed.

I just rake it up and throw it to them, they happily eat all they like. No shredding necessary. This goes for just about everything, too.

I really don't want to shred things, that is how you poison your cattle without knowing it sometimes. Imagine accidently getting in your feed a toxic plant. If it is whole, the livestock will avoid it, but if it is ground up, well, now you got a problem, and some dead animals.

Just let it rot if you are using it for soil improvement, just chop it up a little with a machete if it is for feed. I do that with leftovers of bananas plants at times, just cut it up enough they can get it in their mouths, after that, let they chew for a while. There have been studies that suggest they need this to properly digest their food, and to grind up the food too much is counterproductive.

And with a machete, it isn't normally the fingers you have to worry about, but your shins. May I suggest you work with someone who really knows what they are doing for a while? Also, there are different machetes for different purposes. You want a longer, grass machete, which is much thinner that one used for clearing out brush. Find someone from Nicaragua who works as a peon who has never used a weed whacker. They are the best usually.

Sustainable Plantations and Agroforestry in Costa Rica

Fred Morgan

steward

Posts: 979

Location: Northern Zone, Costa Rica - 200 to 300 meters Tropical Humid Rainforest

posted 7 years ago

Oh, perhaps I should say my qualifications. We have had business in Costa Rica for more than 10 years now, lived here for 7.5+ years and at times, employed 100 people. We own nearly 900 acres, or roughly 350 hectares, with 150 sheep, 20+ cattle, 2 oxen, 10+ horses, and planted more than 150.000 trees, which we maintain.

I personally use a machete a few hours a week, just for trails and getting around. Nothing like our workers though. They wear out a machete every 6 to 8 weeks!

Sustainable Plantations and Agroforestry in Costa Rica

Sergio Santoro

Posts: 257

Location: Nicoya, Costa Rica

posted 7 years ago

You've gotta be pretty bad to hurt your shin by cleaning a coconut in your hand with a machete!

Just kidding, I know how you mean. I've lived here for 3 years and have used a machete quite a bit. People would clip their nails with it here.

Writing from Madhuvan, a yoga retreat/organic farm on the West Coast of Costa Rica.

I want my playground back. Here, I'll give you this tiny ad for it:

A rocket mass heater is the most sustainable way to heat a conventional home

http://woodheat.net