Recycled HDPE Plastic Crosscut Sled Runners

I recently purchased a new beefier table saw for my shop and, while I made a crosscut sled for my old one, the spacing for the original runners were:

1) made of wood

2) the wrong width, and

3) spaced differently

Therefore, I needed to re-adjust, but instead of redoing everything with wood, I decided to make the runners out of recycled plastic, particularly HDPE.

Old milk, water, detergent, etc. bottles (cleaned and broken down into smaller pieces)

scale (optional but really helps minimize excess)

Toaster oven

wax or parchment paper

gloves

respirator

wood to make a mold

clamps

calculator

screws/screwdriver or a nail gun

wood glue

grinder (optional)

Melting your own plastic not only helps minimize waste but it is also, in my opinion, satisfying to take trash and make it useful. It is nice to know that some things can be repurposed and not take up space in a landfill. But, before you go jumping into melting your own plastic , you need to understand that these compounds can be harmful to your health! For my Instructable, I am using high density polyethylene, or HDPE. You can tell it is HDPE (in the USA) if you find the recycle symbol with a #2 inside. For more information you should look at David Hakkens YouTube page (which is where I got a lot of my information). There you can get a lot more detailed information but for the quick and dirty of it, HDPE will melt around 125 degrees Celsius which equates to around 257 degrees Fahrenheit. At this temperature melting your own HDPE in a well-ventilated area may not cause harmful effects to your body, but I always wear a respirator when melting (and I do so outside of my house) just for my own personal sake, so proceed at your own risk.

That being said, if you look at my photo in this section, I have a mathematical “road map” in order to know how much plastic I [should] need to melt to be the most efficient. Basically, I have the volume of my mold and multiply it times the density of HDPE. (for HDPE, it should be noted that the density is not set-in stone due to the manufacturing process. It may be slightly different based on whoever makes it, so I just roughly use something in the middle which is 0.93 grams per cubic centimeter)

I went metric for this because I am a chemist. Most of my lab work was done in metric and it just makes things so much easier!

First things first, you need to gather your material. I used jugs from water, but if you were to use milk, or detergent, or yogurt , etc. then please wash and dry your plastic before you stick it in the oven.

I cut my jugs down to size to make it easier to mold and melt. If you look at other videos on YouTube, you will see that some people will shred their plastic into tiny pieces, which will make the process go way more smoothly and it will decrease your time to melt. Take that for what it is worth. My time and equipment at the moment would have required me snipping them with scissors, and I would prefer not to go to that much level of effort. If I were to use HDPE for some specific component that I was to replace, then perhaps I would go to the detail of snipping it into a tiny confetti-like pieces. Now do you have all of the plastic that you need, it is time to weigh it out and set it aside.

Now you need something for the plastic to mold into. For this I used scrap pieces of wood that you can see in the photos above. Basically, what I did was I made a recess where the plastic would rest after melting. You can see that in photo #4, which is why the long pieces of wood rest up against a tiny (darker) slit of wood. That is for the clamping piece of wood that you see in photo #5 to rest on top of while being clamped down. Also, I added the riser piece on the center of the wood in photo #5 for the clamp to force the middle section down & outwards, minimizing bowing on the length of the piece.

I set my oven to temperature and give it ~30 minutes for the largely cut pieces of plastic to melt. For the record, I purchased a rinky dink toaster oven from a thrift shop for like 5 bucks. So, I used the aluminum tray that the oven came with, lined with parchment paper, and melted the plastic on top of that. I have learned from experience, that if you put the plastic directly on the aluminum tray or in a glass dish, it will stick and it will make it very difficult for you to get it out. I also wear gloves that have good thermal insulation because, for one, you are dealing with hot materials. And two, depending on how fine you get your plastic for melting, you may have to twist and mold it to get the air bubbles out before sticking it in your block. You know that it is ready to mold (and twist if necessary) when it is translucent (at least for this type of HDPE. If you use a non-transparent jug, the color change may vary). If you wait too long you will see the edges turn white again like a milk jug usually is in the market (in which case, you might have to re-melt it in order to make it moldable again). Once you are happy with the product you can stick it in the mold and clamp it down to force your shape. However, if you look at picture #2 above, you will see that there is a slight bow, width-wise, running the length of my plastic piece. That is because I cooled it down rapidly, as opposed to letting it cool naturally inside the mold. Keep that in mind, but for this project it's not the end of the world. You can see from photo #1 and #3, that I used way too much plastic and it seeped out the ends. However, that is also not the end of the world because I would rather have more than less. Another thing to keep in mind is that if you use more and you clamp with too much pressure, you will risk breaking your mold like I did in the video. Hence, this is why I said you could use screws and a screwdriver or a nail gun in order to make your mold more robust. In photo #4 above, you can see the product in the track and there is very little wiggle room, which is a plus for a crosscut sled. And in photo #5, I have the piece (and obviously a duplicate piece on the other side) screwed into my crosscut sled. I had to use a grinder to lob off the end tip of the fastener because my screws were too long and I didn’t feel like getting shorter screws just for this project.

And that is it! It goes without saying, that I could have gone to the big box store to buy specifically molded dimensional plastic and ripped it down on my table saw in order to create the runners quickly. But I like doing it myself and trying new things. HDPE is very strong once it cools down to room temperature so for this application, I felt it was a good choice.

I hope that you find this idea inspiring and that you try it out yourself for whatever plastic pieces that you may need.