Posts Tagged ‘nylon’

So you’re a “DIY’er” at heart. You want to make your own plastic sheaves but don’t know where to start. You’re not sure what material or grade is best for your application and you don’t know what is the minimum amount of “engineering” needed to make or procure a plastic sheave? This write-up will help you through that process.

First of all, material. Assuming your sheave is not going to take a lot of impact and is not used in a wet environment go with moly-filled nylon. This is the same nylon used on crane sheaves and is optimized for low-RPM, high load applications. If your sheave will take impact or be used in a wet environment we would recommend Redco Tuffkast. This is a co-polymer material which overcomes many deficiencies in nylon: Tuffkast can take impact and is better in wet or cold environments. It is more expensive than nylon, however.

After material selection you need to know these basics for the simplest design (a non-webbed, bearing-less sheave):

  • Bore diameter of the center hole.
  • diameter of the rope or cable to be used on the sheave.
  • Overall diameter of the sheave

Next you’ll have to do some very simple math. Firstly, to figure out how deep the groove in the sheave should be: (rope/cable diameter) x 1.75. This will give you the minimum groove depth you need, but in most cases just round to make it a little deeper and give yourself a safety margin. For example, if your sheave is 15″ in total diameter and you have a 1″ diameter cable. That is 1″ x 1.75 = for a required depth of 1.75″. But for the sake of safety margin you can make this an even 2″. The inner diameter of the sheave is now 11″. Please note that for the inner diameter you are taking that required groove depth x 2.

The last thing you need to consider is the thickness of the sheave. For most smaller sheaves just go with a 1/4″ wall thickness, these are the “shoulders” of the sheave on either side of the rope groove. So, for example, if your rope groove is 1″ wide, then you add another 1/2″ for the walls (wall thickness x 2) so you would have an overall thickness of 1.5″. The last thing to touch on here is the radius of the rope groove (the curve of the groove the rope sits in). this is almost always 30 degree and in rare cases, 45 degrees. Run with 30 degrees as a standard.

There are some guidelines for figuring out parameters for more advanced sheaves such as webbing or thickening the hub and we’ll discuss those next time in “Sheave Design: Advanced”.

For help with your sheave applications and to purchase sheave materials please contact Redwood Plastics.

 

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Nylon is a fairly popular plastic used by the DIY community: and it should be! Versatile, strong, and available in small quantities it offers many properties valuable to the public’s plastic applications. In most cases, nylon will be an ideal material for mechanical parts such as sheaves or bushings. But it isn’t perfect and it like anything it has its drawbacks in certain applications. Here are some tips on using nylon that will serve you well.

1.) Don’t use it in the cold

Ok, well you can but you just need to be aware of impact. Nylon gets brittle in the cold, at about 5 degrees Fahrenheit and if it’s taking any sort of impact it could break. In fact inĀ  any application where you expect impact, use Redco Tuffkast instead (it has been developed to replace nylon in applications with impact.)

2.) Don’t use it in water

Unlike most plastics, nylon absorbs a significant amount of water – up to 4% of its volume in 24 hour saturation. For marine applications or those involving tight tolerances you probably want to go with an alternative material. Acetal is commonly specified in this case but Tuffkast may be an option as well, it depends on the application, so ask your distributor.

3.) Do use it under load

Nylon can handle 4000 PSI in application and this is one of the highest loads of readily available thermoplastics. This makes nylon excellent as a bearing, sheave, or other load bearing part.

4.) Pick the optimal grade

Nylon isn’t just “nylon”. It’s available with a variety of fillers: glass for dimensional stability, moly for high load low RPM applications, oil filled for reduced friction, UV stabilizers for outdoor use, and PVM (pressure velocity maximum) for the highest load applications. These fillers add only a minor cost, or in some cases cost the same as the natural grade, and are well worth it for certain applications. Unsure if you need a filler? Discuss your application with your distributor.

Even though three of these four tips are “don’ts” knowing when to avoid a material is just as important as knowing when to use it! Don’t get us wrong – nylon is a versatile, excellent, affordable plastic for a wide range of applications. Just keep in mind that it has advantages and drawbacks: just like every other material out there.

Are you a “DIYer” who makes plastic bearings at home or perhaps looking into doing some? Not sure how to calculate a press fit or a running clearance for your bearings? Fortunately there is a useful tool available from Redwood Plastics availableĀ  on their website: the machinist chart for plastic bearings found here.

This chart provides valuable information for bearing manufacturing using Redco 750 or Redco nylon bearing materials. While many in the DIY crowd like to use UHMW polyethylene for everything, including bearings, this is not a good bearing material and has large and variable tolerances. The bearing chart is not intended to be used for UHMW bearings. Acetal is similar to nylon and therefore nylon’s values can be substituted directly.

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.

Rover1

Choosing Your Plastic

Posted: March 8, 2016 in Education
Tags: , , , , , ,

The question comes up a lot in the DIY community: “I am planning to make _______ so what plastic do I need?” The good news is selecting a plastic for your application is very similar to how heavy industry would select a plastic for their projects. You need to select a plastic based on certain properties it gives you, not some sort of bias to what you “heard” worked – and especially not based on color!

So when thinking about your what you need for your application consider the properties of these plastics:

 

UHMW Polyethylene:

-Slick, low-coefficient of friction

-Good wear properties

-Good abrasion properties

-Thermoformable (at home)

 

Polyurethane:

-Elastomer: will regain its shape after depression (excellent as mallet heads)

-Excellent cut & tear resistance

 

Nylon:

-Bearings (takes up to 4000PSI)

-Wear plates

 

Tuffkast:

-Replaces nylon in cold operating environments or where impact is a concern

 

Acetal:

-Small parts, replacing metal

-Where machinability is key, can hold tight tolerances

-Replacing nylon in “wet” applications

 

PVC:

-Anywhere a “frame” is needed.

 

Industrial laminates/Phenolic/Micarta:

-Mechanical or electrical applications

-High load bearing

 

Sometimes a little inspiration doesn’t hurt, especially when you’re a member of the DIY (“Do It Yourself”) community who searches out new projects. On this blog we like to highlight particular applications people are doing but sometimes you just wonder in what type of projects should I use certain plastics? Well, when you search out content like we do for so long – you can bet we see some patterns!

UHMW Polyethylene

Readily available and extremely versatile, with DIY projects UHMW is often used to provide slickness or wear resistance.

  • Toboggans
  • Snowmobile skids
  • Axe or blade sheaths
  • Jet boat bottoms or wear pads
  • Boat trailer support pads
  • Custom cutting board for outdoor kitchens

Acrylic

Scratch and weather resistant it is easy to get a hold of in clear, much more difficult to find in colors or frosted. Good for artistic projects.

  • Art covers or flower presses
  • Table tops
  • glass substitution

Polycarbonate (twin or multi-wall)

Polycarbonate is not scratch resistant but it is very impact resistant. Any reputable distributor will sell UV-stable twin/multi wall polycarbonate sheet as UV-stability in the product is mostly standard. Also, if stocked, multi-wall polycarbonate is quite inexpensive compared to other plastic sheets.

  • Awnings
  • Solariums
  • Greenhouses
  • Safety glass

Nylon

Nylon is a strong, engineering plastic with excellent load bearing capabilities.

  • Homemade bushings
  • Sheaves
  • Pulleys

Acetal

Acetal is a very hard plastic and often replaces metal parts. It machines very well and can replace nylon in “wet” applications since it doesn’t absorb water.

  • Bushings
  • Marine components
  • Guitar picks
  • Paintball gun bolts

Fiberglass wall panel

FRP wall panel is a CFIA/FDA approved sheet for lining the walls of food processing applications. It’s also used in gas stations.

  • Mud room lining
  • Workshop lining
  • Pet area lining

PVC (Pipe & Joiners)

PVC is one of the most affordable, easy to procure, and versatile plastics people can use for DIY projects. The creativity we see with it is endless!

  • Water sprinkler play zones
  • Go-Karts
  • Bolus games
  • Outdoor movie screens
  • Pet bird perches

There are countless other applications that could be done with those applications! And if you have questions, we’ll try to help if we can. Just email us here.

 

 

Believe it or not one of the most popular “DIY” plastic projects is making bushings. It makes sense as bushings are a part of so many applications and plastics are an excellent bushing material, outperforming metals such as bronze and babbit in many situations. Plastics are easy to machine and usually last much longer than metal in a bushing application. Cast nylon is probably the most popular material for bushings, as it can take loads up to 4,000PSI and is readily available in filled grades to increase wear resistance and low RPM performance (moly-filled nylons) and reduced coefficient of friction or reduced lubrication requirements (oil-filled nylons). Nylon does have three weaknesses: shock/impact, cold, and water. If impact may occur to the bushing, if it’s in an environment -10 degrees Celsius or below, or in a wet (or marine) operational environment then Redco Tuffkast by Redwood Plastics may be an ideal solution for all three problems. It is a bit softer and can handle a little less load but in many DIY applications this will not matter.

Redwood Plastics offers a handy bearing machining guide that not only supplies typical running clearances but gives an honest comparison between nylon and other bearing materials. You can find the PDF Bearing Machining Guide here.

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