HDPE Plastic Press // Made From Scrap

I was inspired to recycle HDPE and Polypropylene by folks like Precious Plastic and Brothers Make. I recently made a press to get larger stock products because (honestly) I am not fast enough to use hand clamps (the blob of plastic re-solidifies quicker than you may think)! In this Instructable, I will be using a 6-ton bottle jack, a discarded bed frame, some scrap wood, and garage door springs to make my own heavy-duty plastic press.

A bottle jack (my 6-ton may be overkill but it was second hand & cheap)

Scrap wood to reinforce the frame and make the platform (as well as a mold for the plastic)

Bed frame (or real cold rolled steel) angle iron

Garage door springs (cut in half x2, to get a total of 4 springs)

Threaded rod, nuts, eyebolts, & washers

Screws

Hand tools to cut/work the angle iron bed frame, I used: Wrenches, cold chisels, punch, hammer, angle grinder

Tools to frame the "angle iron," such as: Drill & bits, nut drivers, square, wrenches

To re-use the garage door spring and to stretch it for cutting: wrenches, cold chisels, propane torch, tiny anvil, hammer, pliers, vice, clamps

To make the base & frame: drill & bits, square, wrenches, nut drivers, angle grinder, clamps

Glue and Parchment paper help minimize sticking in your HDPE mold

My plan was simple: Use a discarded twin bed frame to act as the "angle iron" necessary to support my bottle jack press. The base/frame needed to be reinforced to take the force of the hydraulic jack and be high enough to span the jack's capability. Also, buy as little materials as necessary (That is kind of my thing).

Buying less was the easy part. The frame and garage springs were trash that I acquired. The 2x3's were left over from previous projects. Plywood was left over from my built-in bookshelf build. Hardware...you get it by now: leftovers. The only thing I really bought was the bottle jack. A local second-hand auction let me acquire that for $5.

The bed frame needed to be cut / modified to fit the build. This was a twin bed frame from what I could imagine. It wasn't very big. I will essentially make a big square with the iron to act as a guide for the pressing surface, which is attached to the base.

I had the idea, the mental model, and the materials. I just needed to get to work.

First step was to remove all of the lugs and associated supports from the bed frame, i.e. the legs and end caps that keep the bed from sliding off.

I started by removing the legs from the swinging parts that support the mattress. I did this by removing the heads of the lugs (the press fit metal thingies that held stuff in place) that connect the legs with an angle grinder (pic 1). I used pliers since the friction made the heads physically hot (pic 2). I then used my cold chisel (pic 3) to remove the leg (pic 4). To remove the swinging supports, I removed the lug head, used a punch to loosen it (pic 5), jammed a wedge (aka large flathead screwdriver) into the gap (pic 6) and beat the devil out of it until it released (pic 7). This would give me 4 pieces that measure 28-inches in length and had some holes that saved me the trouble of drilling later on.

Next came the 60-inch side supports. I needed to remove the end caps that kept the mattress from sliding off. Again, the angle grinder makes quick-ish work of the lug heads (pic 8) but I couldn't get all the way through. The shape and my small cutting wheel made that difficult. I had to use my cold chisel to knock the heads off (pic 9). The punch came back to loosen the remaining lug (pic 10) and then the ends fell off (pic 11). I removed the remaining lug and cut the 60-inch support to get 4 more 28-inch pieces, making it 8 total (pic 12).

I was going to attach everything with threaded rod, nuts, and washers so I had to get drilling. The 2x3 top came first since it was easy to access with my drill press (pic 13). Using a square, I got the corners clamped (pic 14) and drilled with a hand drill (pic 15). With the metal box frame prepped (pic 16), I moved on to the springs.

If you buy springs or have no need to modify a garage door spring, by all means, skip this step :D

The former owners replaced the house's garage door springs when we bought the place. Me being the pack rat I am, I never threw them away. They were just taking up space...until now!

I need springs to put a reverse tension on the bottle jack. This also will provide a force to release it from my molds when the knob is released.

Having two giant springs and needing 4, I simply bent the spring in half, marked the "center," and cut it in half with an angle grinder. So now I essentially have one end already bent at a 90-degree to attach to the pressing surface that will be attached to the bottle jack. The problem was bending the other end to 90-degrees. This is quite difficult and I will try my best to explain my process.

Knowing heat can cause springs to "remember" a shape, I pressed my cold chisel on the end to force it away from itself (pic 1). Then I heated it up with a propane torch (pic 2). The memory of heating it (so to speak) is shown in pic 3. I did this over and over until I got a large enough gap to get my hammer (pic 4) and some wrenches to help do some work. When I got a large enough angle, I used a vise to squish the ring opening (pic 5). This will help lock it into the threaded rod later. The hammer got the angle at more of a 90-degree (pic 6 & 7). With the first one done (pic 8) and proving this was a viable option, I repeated the process 3 more times (pic 9).

Obviously buying springs will save you some muscle but I had these and it was neat to get the process down. The first spring took me about an hour to bend to my whim and by the time I was at #4, it took me all of 10-15 minutes.

This step shows how I wanted to put the pieces together to reflect my hand written plans in step 1. The 8 angle iron pieces were all cut to 28-inches (pic 1).

The threaded rod will attach the bed frame angle iron together with associated washers and nuts (pic 2). It was cut to various length with an angle grinder.

The two 2x3s pieces were cut to 28-inches (pic 3) and drilled in the same spot as the top angle iron to thread together. The drilling pic 13 of step #2 shows where this was drilled to guide into and reinforce the tops and bottoms. I cut strips of plywood of equal length to screw into the bottom 2x3 support to make the sides(as shown in pics 4 & 5). Afterwards, I drilled and screwed the remaining two sides to the ply as well as other inside supports to reinforce the base (pic 6).

The top of the base was cut (pic 7). There were sections that I removed with the bandsaw in order for it to fit in the vertical guide rails. Pic 4 will show where/what I am referring to.

(Pic 8) shows some other aspects of the press that may vary based on your build but I will explain the finishing touches:

1) The pressing surface the bottle jack is positioned on is two layers of 3/4-inch ply with eyebolts recessed. This is recessed so as not to interfere with the flattening surface / process. The bottle jack sits in another piece of ply, I will call the skirt, to hold it in place, however the jack can be removed freely, when necessary.

2) The garage springs are added to the top of the frame and locked in place using two nuts and held with a 1-inch washer.

If you have another question about this, leave me a comment and I will do my best to leave a timely response.

I made a shallow mold to use for my initial press. It is 2 layers thick with 3/4-inch ply. Experience shows that using wood glue, brad nails, or screws alone can, and likely will, deform your mold. This was true for me using hand clamps so imagine what a bottle jack could do. Double up your methods or make it several layers thick. Also, do yourself a favor and don't use MDF nor OSB. . .

I proceeded to measure how much HDPE I would need. Measure your mold's L x W x H in centimeters and multiply them together. This will give you cubic centimeters that you can then multiply by the average density of HDPE. I use 0.93 grams/cubic cm. Understand that that number is to completely fill your mold. You probably don't want to do that since you will have nothing for your top piece to "bite" onto, aka the sides of the mold itself. Here I use less than 500 grams since my mold maxes out at ~800 grams (pic 1). That weight is sufficient enough to make a large enough piece without maxing out my mold space.

I have a shredder that I modified for this purpose (pic 2). I generally put shreds in a deep tray in the toaster oven (I set all my equipment for melting at 325F so as not to burn my plastic. That would not be a good thing). The shreds can melt together and I will roll it with heat resistant gloves to try and get out as many air bubbles as I can. If you have bottle tops, place them top side down, again, to minimize air bubbles. The griddle is a new addition for me and it works better than expected, IMO (pic 3). I started placing cut pieces (that are not processed through the shredder) on here coupled with the oven to minimize my melting time. The griddle has flat surfaces but I place a non-stick BBQ mat that I cut to shape to prevent sticking. When the plastic pieces are melted (they go clear), I twist the HDPE, add it to the oven (pic 4), and keep going until I have gone through my entire supply bin.

I take the entire ~450g piece of melted blob and stick that whole thing back on the griddle. I then place a heavy object on the lid to place some pressure on it to get the blob as flat as possible (pic 5). I try and "knead" the edges of the blob since they are generally rounded off (pic 6). This way, I can try and reach more of the corners of the mold when the press is in action. Be timely about it, however, since the HDPE will start to solidify rather quickly. Another handy tip is to glue on pieces of parchment paper to the inside of your mold. This will minimize the HDPE from sticking to the wood itself.

Once the edges of the mold are lined up (pic 7), I stick it under the press, center it as much as I feel is necessary, and start pumping the bottle jack (pic 8). With this being made from a bed frame, ply, and 2x3s, I would be lying to say I wasn't a little worried about the initial pressing. To my surprise, once I started seeing the plastic seep out of the edges of the mold (basically showing me that the air pockets were minimizing) and the frame keeping it's shape, I sighed with relief. The top of the frame did bow a little bit but it didn't stress the 2x3 into something of a full blown rainbow.

I let the plastic cool in the mold overnight and the next morning I released it. The top of the frame returned to it's normal shape, again, making me see that this could be a viable option for a (super) low tech press. The plastic did take the shape of the mold but the edges do need to be cleaned up (pic 9). I lobbed off any bubbled up edges that seeped out of the mold with my bandsaw. One edge was actually more square than I anticipated so I used that as the guide against my table saw fence. I cleaned up the other edges to get a nice piece of HDPE stock!

I have since done a handful of other presses with the same mold, the same weight of HDPE scrap (give or take a few 10's of grams), and I am happy to say that the mold & press are still going strong. I believe that this has the capability to produce more stock pieces if I make different (deeper or broader) molds.

What is the point?

I have used recycled HDPE to make runners for my table saw sled (yeah I could go to "Big Wood" and buy their stock ultra high molecular weight pieces but they are >30 USD and that was pre-Covid prices), replaced the broken crank on my drill press, and even fabricated parts to hold my camera for filming. Oh yeah and I made a jig to create box joints. You can even tap the HDPE like you could metal, granted metal is the superior choice in many instances but hey, it works for me when I need to drive screws to fasten parts. I also plan on lathing a piece of round stock (i.e. HDPE I squished in a tin can) to replace my zero clearance plate on my bandsaw. Imagination is key for whatever possibilities there are.

What would I do differently?

The biggest thing is I would have made the vertical rails of the frame shorter, perhaps 18-inch as opposed to the 28-inch it currently stands. I will likely make these mods later on to that I can get rid of needing my impromptu riser block but the jack cannot span that whole distance and I feel that could alleviate some of my bowing issues.

Attach a supplemental piece of steel that spans the length of the top rail for added support when pressing. Or use an actual piece of cold rolled steel as the top rail.

If I do lower the vertical guide rails, I would want to draw teeth on the pressing surface and base because I think that'd be hilarious. That is part of the reason I didn't paint it yet.

I think this will be a fine, cheap, fairly efficient addition to my personal HDPE recycling center! Of course you don't have to go the full scale like I did. Make it taller, wider, smaller, whatever. Use it to press prints, stamps, walnuts, books for binding, or recycle thermoplastics.

Hopefully you find this useful / inspirational and I'll see you on the next one!