Let’s let the dreariness of winter pass for a moment with warm thoughts of Spring shall we?

Outdoor living areas are becoming more intricate and popular these days. What was once just a barbecue and some furniture is now a full living space, often with a complete outdoor kitchen and lounge, with a fire place and so forth. As outdoor spaces have grown, the plastics world has grown with them and we want to highlight two excellent plastics for outdoor living areas.

The first is HMW PE 500 where the letters stand for “high molecular weight polyethylene”. This food-safe white plastic provides an excellent cutting surface for your outdoor food preparation needs. Unlike UHMW PE, HMW PE 500 will not dull your knife blades. The product is available as standard in 4′ x 8′ sheets. If you don’t have a use for all of that plastic, why not cut some of the extra into cutting boards for friends or family?

The second plastic might even be more exciting. It is “wood grain” HDPE plastic. This UV-stable and wear-resistant plastic has a faux wood grain finish. Strong and long-lasting, it replaces wood with a low-maintenance alternative for a wide array of outdoor living projects. Example applications include counter tops, cupboards, table surfaces, tree houses, or virtually anything else you can put your mind to. The sheets are currently available in a standard 4′ x 8′ x 3/4″ (thick) sheet. Currently the only color is brown but tan and black are being developed.

For pricing on these products please contact Redwood Plastics and Rubber.

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For members of the public PTFE (polytetraflouroethylene) and UHMW (ultra-high molecular weight polyethylene) seem to be very similar materials. They’re both white, soft, food-safe, and widely available from plastic companies. But are they that different? Oh yes they are! The first thing you would notice is the price. PTFE is literally in another category of plastics called the “high performance” plastics. This means the cost is going to be much higher than UHMW. So when do you need PTFE?

It would be an application where slickness is important above all other factors. UHMW, while less expensive, will outwear, outbear, and outperform PTFE in tough mechanical applications like homemade bushings, cutting board, etc. PTFE is very soft, so soft in fact it suffers from something called “cold flow”. This means that PTFE slowly creeps like a semi-solid liquid almost just sitting at rest in room temperature doing nothing. What PTFE does have in addition to outstanding slickness (low coefficient of friction) is that it takes very high temperatures up to 500 degrees Fahrenheit. UHMW does poorly in high temperatures and cannot handle more than 180 degrees Fahrenheit.

To be honest, in most DIY applications that call for a white plastic with balanced properties UHMW is going to be your go to. It’s too available, too cheap, and too balanced to go with PTFE. But in certain situations where very low friction is required (telescope mounts for example) or high heat will be encountered – PTFE may be your only choice.

For more assistance with your application please contact Redwood Plastics and Rubber.

Many members of the “DIY” community are attracted to the concept of plastic lumber. Usually made from recycled materials it carries both benefits to the environment by using less new material. In addition, plastic lumber can be manufactured in grades that are much stronger than regular wood. Most grades of plastic lumber are UV stable and involve much less maintenance than wood. They will not require repainting, will hold their color, will not rot or splinter, and will not come under insect attack.

However, with everything there is a “catch”. In the case of plastic lumber it’s the price and delivery. The problem comes down to two factors 1.) customers assume that plastic lumber is widely stocked in the available colors, sizes, and profiles they see on the internet. 2.) Customers assume that plastic lumber is, well, “it’s just plastic”. What people do not often understand is that many plastics, including plastic lumber, are not considered the “commodity” grade of plastics that the public usually encounters in everyday life. Commodity plastics make up consumer items, what’s in your car, your toys, your kitchen. Plastics are actually available in not one but three higher quality grades above “commodity” (yes, the actual grade of plastics used in consumer items is called ‘commodity’). The other three grades are, from lower to top, engineering, high-performance, and imidized.

The DIY crowd will usually only encounter high-performance plastics in PTFE, which is used in items like telescope mounts. They will never encounter the ultra-expensive and hard to obtain imidized plastics. What you need to understand is plastic lumber falls into the engineering grade of plastic and the most commonly quoted grade, fiberglass reinforced, is at the upper end of engineering grade plastic cost.

What are we getting at here?

You need to understand that the cost of plastic lumber vs. equivalent wood will be approximately 8-10x the cost of wood! We’re just stating the facts here, folks. Plastic lumber is not “just plastic” in the way a milk jug is. These plastics are considered a premium, specialty building material, which is why you see them in so many cool applications! It needs to be a great application to be worth the cost! The reason we provided a range on cost is that the color of the lumber actually plays significantly into the cost. Black is the least expensive, followed by wood tones, and finally really off-wood colors such as yellow or white. the difference is about 30% across the spread.

So when do you go for plastic lumber?

First of all, you need to be realistic about the cost. In addition to the lumber’s cost it likely will need to be shipped in from the manufacturing plant and this can easily cost several hundred dollars. You need to be realistic that the lumber will not get to you within a day or two (getting it on site in a month is typical). Finally you need to be realistic about your project. Hey, we love plastic here, but it has it’s time and place. If you want a premium, low-maintenance building material for your project, great, splurge and make your dream project come true! The issue is you need to have the facts on hand and analyze whether or not plastic lumber actually fits your needs.

 

 

Acrylic can be more complicated than many people would think. There are some assumptions people make about acrylic which actually could be detrimental to their application or cost them more money than is necessary. First of all there is the topic of “Plexiglas”. That name has been around for so long that people think it’s a material – it isn’t. It is a trademark for a line of cast acrylic. But, the name might or might not be important to your application.

See, acrylic actually comes in two forms: extruded or cast. Cast acrylic is the version that comes in the sheets that are oversized by 1″ on their length and width: 49″ x 97″ denotes a cast acrylic sheet. Extruded acrylic comes in standard 48″ x 96″ sheets like many other plastics. There is a difference in quality between the two: cast acrylic is stronger and has better optical qualities such as clarity and finish. As always, there’s a catch: cast acrylic is more expensive (perhaps 40-50% more) than extruded and is somewhat less widely available. In many cases especially for members of the public, extruded acrylic is perfectly fine for their application. However, if you’re a professional manufacturing a product that requires a flawless look, or is for the government or military, then cast is probably the way to go.

We would urge you to remember that brand names exist for many plastics and in most cases don’t specify the plastic itself. Be reasonable when it comes to brand names, be realistic with your application, and you’re on track for the most success at the least cost.

When machining a bearing at home often “DIY” fabricators will not consider that plastics have different tolerances than metals. Even more importantly, consideration if an application requires a press fit or running clearance isn’t considered at all. But it really should be to have a properly functioning bearing! To provide complete assistance on this topic we need to first define “press fit” and “running clearance”. Press fit is most often on the outer diameter of the bearing and it is a small amount of extra material on top of the designed diameter of the bearing to allow it to be forced into its mating partner (perhaps a wheel) and “stick” there without rotating. Frankly, if that is the type of application your bearing is going into – you need to be concerned with a press fit.

Same goes for a running clearance. In most cases the shaft in the center of your bearing needs to spin freely right? Did you account of that in the design of your bearing or did you plan to push through a 2″ inner diameter bearing over a 2″ shaft? What you’re most likely going to have is a shaft with a quasi-press fit that sticks on the plastic. Instead you need to factor into your design some extra room on the inner diameter (ID) of the bushing.

At this point you’re probably wondering how much press fit or running clearance? Redwood Plastics offers a handy online machinist chart showing guidelines for just that. You can find the chart here: https://www.redwoodplastics.com/brochures/Machinist-Chart.pdf

Admittedly plastic welding is a fabrication technique that is going to be attempted by few “Do-it-yourselfers”. Plastic welding will require the purchase of special tools and filaments which are not always easy to come by.  In addition, since most plastic welding is done by specialists, it is difficult to get fabrication tips from plastics distributors or manufacturers. You’re likely going to have to search the internet for ideas and while we cannot vouch for the tips, YouTube seems to have several good videos to get you started off right.

In particular the company “Techspan” which manufacturers plastic welding equipment has, what looks to us, as a good 4-1/2 minute video on the basics of plastic welding. In particular we like that it talks about preparing the plastic for fabrication/welding (something often overlooked in these types of videos) and it goes into topics such as “tacking” which is welding two pieces on a 45 degree angle to each other. We’d prefer to let the video speak for itself and we’ve linked it below:

 

Quadrant Engineering Plastics is a major manufacturer of industrial plastics. While they do not sell directly to end-users, and instead sell through distribution, they still invest in many resources for end-users to help them reach their goal with their applications. One of the best is the “Machinists Toolkit” which is available by clicking here. This gives a variety of tips from what coolant to use, to tool tips and even troubleshooting specific issues that come up. It also gives feed rates and end milling/slotting guides for various plastics.

One handy section the toolkit has is a rating of the machinability of various plastics on a rating system. Acetal is usually the best where tight, critical tolerances are involved. But like with all plastics, there are situations where acetal is not ideal. In those cases when reviewing the various options you need to know what the “next best option” is. More useful still, is on the left side of the toolkit page is a link to the chemical resistance chart. This will allow you to look up alphabetically various plastics and their resistance to various chemicals. Please do not think that just because plastics in general are resistant to many chemicals, that a given plastic will be resistant to chemical exposure in your application! And do not assume that just because a chemical is “household” that it will not attack your plastic – it might, so do not assume!

Finally, Quadrant has also released a short video giving some machining tips. While the video says it is geared for a few high performance materials, much of the advice given is relevant to any home machinist working with plastics. That video can be seen here: