Posts Tagged ‘Redwood Plastics’

BRAXX Anti-Slip Sheeting

Posted: December 20, 2018 in Uncategorized
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Ever worked on a home project where you need a rugged anti-slip surface? Could be stair treads, maybe the side of a pool, a deck or anywhere slippery. One option is BRAXX anti-slip sheeting for an application that does not require load bearing material, IE. you are going to simply screw, nail, or bolt the anti-slip surface into a substrate. BRAXX comes in a standard 3′ x 9′ sheet that is 0.30″ thick and this is the only size available. There are two options, a blue UHMW plastic with sand surface anti-slip buttons or the more popular safety yellow UHMW with LUNS (clean coal slag) anti-slip buttons. See picture below for detail of each. This product is very strong as UHMW cannot break and it was originally developed for military applications such as the floor surface of naval tank carriers.

The product cannot be ‘glued’ using a liquid adhesive. Mechanical fixation is required but there is no special hardware for this…Nails, bolts, screws, whatever you have lying around will work. UHMW is easily fabricated with power tools found at home. This is a premium product, you can expect a cost of approximately $600.00/sheet US funds before freight is factored in. However, for a premium anti-slip surface from the demanding DIY individual, it’s the best there is.

This product is available from Redwood Plastics and Rubber: http://www.redwoodplastics.com

Often members of the DIY community are unsure how to machine engineering plastics. It’s one of the main questions that comes up. Redwood Plastics and Rubber has a handy sheet that gives both tooling and run speeds for various common industrial plastics. You can see those below:

 

 

 

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.

Sheave Design: Advanced

Posted: August 9, 2017 in Education
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On our previous post we taught you the bare minimum that is required to design a simple sheave. Now, we’re going to discuss some ways to add advanced features to your sheave. Firstly, is how to calculate webbing. “Webbing” in regards to a sheave is removing material outside of the hub and outer diameter to lower the overall weight of the sheave. A webbed sheave would look like this:

 

 

 

 

But how do you know how much material you can machine off? The math is actually quite simple: W = 1.2r where W is the “minimum web thickness” and “r” is the radius of the rope or cable. So for example, based off a 1″ diameter rope the minimum web thickness is 1.2″. This naturally segways us into a discussion about the hub. As you can see in the picture of the webbed sheave, the hub has to be wider than the webbing. But by how much? Again, the math is simple: H = 1.5b where H is the “hub width” and b is the bore size. Lets assume the bore is 1″ again, you would then require a hub no thinner than 1.5″. Typically the hub is at the very least as wide or wider than the rim, so always run off that rule of thumb.

Finally, the last calculation is to figure out a press fit if you’re going to push a bearing into your sheave bore. You need to know how to precisely bore but leave just enough room that the bearing won’t slide around. That is done as follows:

 

This will give you the bore diameter you require to fit your bearing. You now have all the tools to make not only a sheave but a fairly complex one if you’re so inclined. If you want to download the whole Redwood Plastics sheave design manual, where this information was taken, you may do so here.

If you need a quotation on some sheaves or sheave materials please contact Redwood Plastics.

 

 

 

 

 

Have you ever heard of “HMW PE 500“? If you have we’d be surprised. Even though the material has been around for years, we at Redwood Plastics, the patron of this blog, have only recently started advertising it. It’s cutting board material. Professional-quality cutting board material, not something for your ordinary kitchen, but something to use in a premium DIY kitchen or outdoor cooking area that you want to show off. UHMW polyethylene gets a lot of love in cutting board applications but as resilient as it is to cutting and wear there’s one problem: it dulls knives. HMW PE 500 is a grade of HDPE plastic which will not dull the blades. In addition, it is FDA and EC compliant. In fact, in addition to being food-safe it actually comes in a variety that is anti-microbial!

It was designed for this purpose.

If you’re wondering why you haven’t heard of this stuff before, well, times have changed in what people expect out of their kitchens. People with the means to do so are building bigger and better kitchen areas indoors and out and expectations are increasing. HMW PE 500 would have previously been kept to the realm of the restaurant and professional chefs only – but nowadays has a role to play in the modern custom kitchen. If you’re just looking for a small cutting board this isn’t your thing: it will be more expensive and it comes in 48″ x 96″ sheets! To utilize this plastic you really do need to have a large cooking area and have space in the budget for this sheet which can be upwards of $250.00 USD, depending on quantity, once freight costs are factored in. But for a DIY application for the cook who wants the optimum material, HMW PE 500 is for you.

If you’re interested in the product please contact Redwood Plastics. 

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First things first, we here at Redwood Plastics (the administrators of the Plastichowto blog) are happy to answer your application related questions. That said, we might be able to save some time with your future DIY projects by helping you narrow down what plastics you might need for your application. If you’re still hesitant or have additional questions just ask us. Without further adieu, a list of plastics and where they might fit in to various applications:

UHMW polyethylene:

An incredibly versatile plastic, UHMWPE is the “Swiss army knife” of plastics. It’s good at a lot of things, great at a few things and substandard for a few applications. If you need an impact-zone UHMW works as it’s virtually unbreakable and it also works as synthetic ice (though unlike HDPE, it will dull skate blades). It functions well as light-load bushings (under 500 PSI) but cannot hold tight tolerances (+-) 0.05″ is about the best you’re reasonably going to get. We’ve seen UHMW used as sheaths for bladed objects and cutting boards as well. UHMW has benefits of being inexpensive compared to other industrial grade plastics and is also widely stocked.

Nylon:

Nylon’s main application in DIY applications is as sheaves and bushings. Nylon machines well and can handle 4000PSI in operation, which is why it works so well under load. You do need to be aware if your application is exposed to the sun (and therefore need UV-stabilizer) and if your application is marine. For “wet” applications acetal is recommended as a substitute because nylon will swell. In addition, nylon gets brittle below -10 degrees C.

Acetal:

An excellent all-around plastic, acetal can be substituted for nylon in most applications as it handles a similar load for applications like bushings and sheaves. In addition, acetal is the best engineering plastic to machine. It holds tight tolerances and is excellent for small, complex parts. A popular DIY application for acetal is replacing metal parts in paintball guns.

Tuffkast:

A premium nylon-like material, Tuffkast was designed to overcome the drawbacks of nylon. Tuffkast is better in the cold and absorbs much less moisture than nylon. It can be substituted in most applications the only potential issue is that it is softer than nylon, which may mean reduced wear properties in some applications. Otherwise, it is extremely versatile and would delight most DIY’ers if they only knew it better.

Acrylic/Polycarbonate:

Acrylic and polycarbonate are used where you need a clear plastic. Acrylic is not as strong as polycarbonate but it has better scratch resistance. Both plastics are much stronger than glass. In addition, acrylic resin is naturally UV-stabilized where only special grades for polycarbonate are. Safety glass, windows, canopies and tabletops are DIY applications for these plastics.

Phenolic/Industrial Laminates:

Industrial laminates are a very large family of plastics where different resin systems, substrates, and additives mean there isn’t a “one size fits all” phenolic. For the DIY community phenolics are fairly expensive and difficult to work with as you require dust exhausting systems and masks. Some are glass-filled which means special tooling to work with them. Phenolics can handle a large amount of load, often in excess of 20,000PSI and are primarily used in mechanical applications by the DIY community. So anywhere the plastic’s job is to provide strength, rigidity and form. It’s hard to narrow down specific applications for this – we’ve seen almost everything! But what comes to mind is, for example, replacing the metal collars on a sailboat (which hold the sail masts firm and steady) with phenolic. Remember, unlike metal, phenolics won’t corrode due to salt and water.

There are several other plastics we could talk about but their use by the DIY community would be limited. If you’re interested in discussing your application feel free to contact us.

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UHMW polyethylene has countless applications for the DIY community but as we head into winter there is one simple application that we have to highlight on this blog. That is the UHMW plow blade for snow plows. Let’s not over-complicate things: this is just a UHMW strip with some holes drilled in. But in order to get what you need, you need to know what to ask for! First of all know that the material you likely want is the reprocessed-black UHMW grade. While being less expensive than the natural grade, the cross-linking in its production actually improves wear properties. A nice bonus when you’re also saving some money.

You also need to know what thickness of blade you want. In general, the blades are almost always 1″, 1.5″ or 2″ thick with 1.5″ being the most common. If you don’t know what you need, pick 1.5″. Many plastic companies will pre-drill holes for you if you need them for a fee (usually about $80.00) but we would recommend you do not. Firstly to save money, secondly you need to remember that UHMW is not a dimensionally stable plastic. Changes in temperature may expand the blade from when the holes were drilled meaning by the time you get it – the holes don’t line up! To avoid disappointment we recommend you do the drilling if at all possible.

If you have questions about UHMW snow plow blades please contact us.

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SAMSUNG