Monday, December 20, 2010

Plastic Extruder - Continued

I was a bit surprised to received so many questions about my plastic extruder. Hopefully this info will answer some of these questions:

There are 3 sections: bearing chamber, hopper, and heating chamber. These are made with a section of ¾” black pipe (gas pipe) and ¾” wood auger bit fits nicely into the pipe. There is a little bit of gap between the auger and pipe. I was concerned the molten plastic would ooze back out of the chamber, but it was never a problem. This unit can consume virgin HDPE pellets or cut up milk bottles.

The bearing chamber is about 3.5” long and is mostly dead space. The shaft of the auger bit is long and I didn’t feel like turning it down shorter. At the end where the shaft comes out, there is a thrust bearing placed on it to minimize the friction.

The hopper has half of the black pipe cut away to expose the auger. This is 4.5” long and has a metal hopper which holds around 1 cup of pellets. As the auger turns, some pellets get forced into the heating chamber while some just sort of move to the front of the hopper. Between the hopper and heating chamber is ¼” of plywood…to act as a heat insulator to minimize the heat loss through the metal.

The heating chamber has two heating zones. The main reason was to attempt to heat the plastic evenly since I wasn’t sure how it would heat as it moved through the chamber. This chamber is 5 inches long. The first temperature sensor is placed about half way through and the auger bit ends just before it (so it won’t hit against the probe). The second reason was I didn’t want to run a high voltage through the Nickel Chromium wire…too dangerous and I had a couple of PC power supplies I could run 12 volts at 8 amps. The pipe is wrapped in Kapton tape which is heat resistant….but you can see in the photo it did eventually burn through. Each zone is independently controlled by a microprocessor to maintain a consistent temp.

The heating chamber has a flange on the end which allows different die plates to be bolted on to the end. Depending on the size of the “hole” in the die, the plastic will extrude at different speeds. For the 1/4” slot, the auger turns at about 18rpm and can produce a ribbon of material at roughly 200 feet/hour.

Friday, December 10, 2010

Plastic Extruder for Growing Media

For several months, I’ve been developing a plastic extrusion system that has been able to take virgin HDPE resin pellets, or shredded milk jugs, and properly melt and extrude them into a shape that could be used as a low cost growing media for my Aquaponics system.

There was a lot of trial and error to get to this point. The biggest problem is that the plastic retains little moisture. If the seeds aren’t directly placed in the flood/drain cycle, they won’t get any moisture to germinate. I typically grow in stone and some of the stone above the water line is able to wick and retain enough moisture to provide water to new seeds.

Another issue with HDPE is that it’s extremely smooth (again, works well to repel water). Even adding texture to the media during the cooling process, the media still is smooth, which makes it difficult for bacteria to stick to it. I was also a bit surprised to see that the roots didn’t really care to grow in it and they would grow around the edge of the net pot instead.

On the plus side, the plastic is light, fairly inexpensive, clean, and easy to work with.

I hope some of the info in the video is useful to some of my fellow aquaponic/hydroponic growers in their quest to find a better, more cost effective growing media.

EDIT:  There is now a second blog entry with some more details about this.... Click on the "Newer Posts" link near the bottom.

Below is the transcript for the video…no need to read it if you’re going to watch the video… I just included it so some of the search engines could pick up on the keywords. ;-)

Hello Everyone. Today I’m going to show a plastic extruder system that I built. The end result was to produce a synthetic, cost effect growing medium for my Aquaponics system.

The extruder consists of a hopper for high density polyethylene pellets. An auger then forces the pellets through a dual zone heating chamber. The heated material is forced through a small die at the end of the chamber.

The temperature in each zone of the heating chamber is controlled by a Teensy AVR microcontroller which is monitored and adjusted through its USB port connected to a laptop.

The auger is driven by a windshield wiper motor and it is geared-down using an old bicycle sprocket and chain.

The hopper is filled with HDPE pellets where they are slowly forced into the heating chamber. It can also be filled with shredded milk bottles or shredded milk bottle caps to add color.

The heating chamber is covered in some fiberglass insulation to conserve heat. There are two thermal probes mounted near the middle and end which provides accurate readings to the controller as the material is heated. The heating elements draw around 16 amps at 12 volts.

The molten plastic that is extruded from the die is squeezed through a set of rollers which embed a texture into the material. A small tube blows air onto the pressed material to cool it, and to keep the rollers cool.

This is one of the rollers after I turned it on my lathe with a close-up view of the texturing.

And this is a close-up video of the material being extruded and pressed through the rollers.

Here is a close-up view of the finished material once it has been cut to length. There is a waffle pattern embedded into the plastic which provides plenty of surface area for bacterial growth. The media lies flat which helps to retain moisture during a drain cycle. The pieces have plenty of spaces between each other for water and root growth.

Most HDPE plastic is classified as food-grade. However, one problem is that nothing likes to stick to it. Even though a texture has been embossed into the plastic, a small amount of movement can disrupt anything that was clinging on it.

This is a time-lapsed video taken with my PlantCam over a 30 day period. There are 3 bean plants growing. I also planted lettuce seed which didn’t germinate, probably because the top inch of the media doesn’t retain moisture like stone or expanded clay.

After 30 days, I removed the beans from the aquaponic system. I had the net basket wrapped in foil to prevent the roots from wandering into the surrounding stone. The roots seem to have an aversion to growing in the plastic and mainly grew between the basket and foil.

Thanks for watching. If you have any questions or comments, please leave them in the comments section below. Also please subscribe to my YouTube channel to see future videos!

Tuesday, December 7, 2010

Winter season - DONE

In a tragic turn of events, my winter season is over. The circuit breaker for the greenhouse tripped and it went through the night with no heat.

The outside temps went down to 21F (-6.1C) last night while the inside temps went to 27F (-2.8C). Everything got frosted except a few lettuce plants. Tank water is at 38F (3.3C)...goldfish are conserving energy by sitting at the bottom of the tank. They'll be perfectly fine this way until spring.

Sunday, November 28, 2010

The end of the normal growing season

Today marks the end of the season for the “sustainable” greenhouse. Last night was the first night the heaters needed to run to keep the plants from freezing. (The heaters are programmed to turn on at 36F). My outdoor growing season ended just shy of 2 months ago so I’m still quite pleased with the extended growing season!

My definition of “sustainable” for this project is not having to add extra heat or lighting for the plants to grow, The other electricity for the pumps and automation is an integrated part of the greenhouse Aquaponics system and I classify that as part of the normal functions. ;-)

I still have peppers, tomatoes, and lettuce growing which should survive for the winter. Of course the cost to keep these plants alive will now skyrocket in electricity costs, but it’s still a nice treat to get a few fresh veggies during the winter.

Already looking forward for spring!

Sunday, November 7, 2010

The last of the great cucumbers

I picked my last cucumbers today. The official stats are:

  • 3 plants yielded 330 fruits for a total of 116.3 pounds (52.8kg)
  • First fruit was picked on May 31st, last on Nov 7th. Even though peak production was during the summer, this averages to around 2 fruits per day.

As a comparison, my regular dirt garden had 6 plants. I didn’t keep official results, I got no more than 20 fruits before the plants died off.

Overall, I was overwhelmed by this year’s results. Looking forward to next year already!

Saturday, October 2, 2010

Aquaponic Greenhouse Fall Update

I finally had some time to make another video update of my greenhouse. As you can see, I’m still suffering from a white fly problem and the strawberries just aren’t strong enough to survive. They’re starting to succumb to the flies and are getting mildew on them. I’m probably going to rip them all out, and this winter drop the temp below freezing to kill off the bugs. Bring back DDT! ;-)

There are some stats near the end, so you may want to watch it in full-screen hi-def so you can see the info!

Friday, September 24, 2010

Leopard Frog

This large leopard frog has been hanging out in the greenhouse for a couple of months. At first he would jump into the sump pump area whenever I would go in, but now I can walk right up to him and he doesn’t even care. Luckily, he’s too large to get sucked into the impellers of the pump!

Wednesday, September 15, 2010

Problem Solved

I was able to build a new wireless bridge. I was given a Linksys WRT54G2 router that "didn't work". These don't have a setting to run in bridged mode, but the firmware can be replaced with the open source firmware from (This firmware has far more features than the one that Cisco provides!)

Next I removed it from its shell and placed it in a surplus NEMA box. The antennas were simply hot-glued on to the circuit board. Working great!

Friday, September 3, 2010

Problems in the greenhouse

Anyone that has watched my greenhouse videos (Click for video) has seen I have it fully automated - I LOVE automation! The best part is I can spend very little time in there dealing with the vents, checking water levels, or even feeding the fish. I can easily disappear for several days and not worry about the system. Well, not really, I always worry about it. I just have to trust it keeps working!

The other day, my web site that collects the data stopped receiving information. I use a Wi-Fi access point (AKA Wi-Fi bridge) that transmits the data to our house - then to the Internet site. Upon closer inspection, the bridge wasn't powered up. I checked the power supply and it was good, then decided to pull apart the bridge. This bridge is designed to be used in the comfort of your home, not the harsh conditions of a greenhouse. It's easy to understand why industrial controllers can get quite expensive. Next time around, I'll probably get the same cheap bridge, then throw it in a NEMA (waterproof) box and try to figure out how to get the antenna through the case....

Friday, August 6, 2010


Picked these 3 bad boys out of the greenhouse today. They weigh a pound each! These are the Brandywine heirloom variety.

Wednesday, June 9, 2010

Building a hobby room

Something a bit different from my aquaponics systems. I built a custom hobby/craft for my wife. She will put it to good use!

(It may be best to click on the video to open YouTube in a new window. Blogspot like to cut the edges off!)

Friday, June 4, 2010

Official strawberry count of the season:

65 plants
679 berries
85.78 ounces (2.4 kilos)
~ 19 cups

Many of the berries were small because the majority of plants were everbearing. I have a few other plants that had some huge sweet berries and will take the runners from them and get rid of the everbearing.

Overall a good experiment. The funny part is I'm done with the season and I just got a message from the local orchard that their pick-your-own field is now open. ;-)

Wednesday, May 26, 2010


Enjoying the first cukes of the season out of the greenhouse. They're growing like crazy! I haven't even planted seeds in the outdoor garden yet!

Also found this baby giant walking stick in there.

Sunday, May 16, 2010

Strawberry Towers update

It's been slightly over a year since I installed the strawberry towers in the greenhouse. The plants have been producing like crazy. Each time I walk into the GH, I am greeted by the wonderful aroma of fresh fruit.

There isn't a huge amount to pick since there are only about 50 plants, but we are picking berries long before any of the local farms are producing. However, there is a cost to being the early bird. Because the plants are kept in a greenhouse there is a constant battle with aphids, white flies, and powdery mildew. Plus the added cost of keeping the GH slightly heated during the winter so the plants and fish can overwinter properly.

I'm loosing about 25% of my berries to the mildew. It's heartbreaking to see a perfectly good berry one day, and the next it's covered in mildew. The high humidity caused by the aquaponics setup is a factor, along with trying to push the growing season by keeping the vents closed to conserve heat.

I'm carefully logging thy quantity, weight, and volume! After coring, and discarding the bad ones, I was left with about 50 berries (2 cups & 8.55oz). I'm picking roughly every 3 days and am at around the peak right now and expect it to taper off soon.

Is it a viable solution for a commercial grower inside a greenhouse?....probably not. There is a tremendous amount of labor dealing with the insect and disease control. Every day, I go out and examine all the plants for diseased leaves and berries. Plus since it is so early in the season, there are no bees to pollinate the flowers - I go out each morning and "buzz" the flowers with an electric toothbrush. Works great!

NOTE: You can click on the images for a larger view!

Sunday, May 2, 2010

Indoors Aquaponic System

This is my new indoor system. I built it to replace the charcoal filter for my 45 gallon fish tank. I was spending about $5/week on these filters and would take about an hour to replace the filters and change out the water. This new system has been running for around 3 months and I haven't had to change the water. As an added bonus, we get some tasty lettuce!

Friday, February 19, 2010

NY Times Article

I'm quite excited to say that my Aquaponics greenhouse was featured in an article in the NY Times!

Click here to view article

Sunday, January 31, 2010

Things we do to pass the time in winter

There isn't a lot of gardening to do in this time of year when the highs are in the low 20's....

In the backyard, we like to set up a 45x80' skating rink each year. I made up this Zamboni ice resurfacing machine to keep the rink nice and smooth.

I've also included a link to a video of it in action!

Click here to view

Wednesday, January 6, 2010