Archive for the ‘Nylon’ Category

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.



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 in  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.

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.


A quick search of  many “hobbyist” websites’ plastic forums will display for you a number of sheave projects amateur machinists are working on. The appeal is obvious, a sheave is a simple stock shape used in a variety of home applications including furniture, boats, trailers, etc. When small quantities are involved it can make more sense to fabricate these on your own rather than get a fabricator to do so.

Two materials are primarily used: cast nylon and acetal. We wanted to share a little information about both choices:


A robust material that can handle heavy loads and is both abrasion and wear resistant. Nylon is fairly easy to find and cost-effective for most sheaves. Nylon-Virgin


An easily machined and very hard plastic, acetal is known as a nylon replacement – especially in “wet” or marine applications. Sheaves for boating are a fairly common application – and in that situation acetal should be your choice.

If you require nylon or acetal in rod form Redwood Plastics can assist:

CDN: 1 800 667 0999
USA: 1 866 733 2684

3D printing is an emerging technology that is moving into the workshops of an increasing number of ordinary consumers – that means you! There are multiple 3D printing stations available now but one thing they share in common is the use of commodity-plastic such as ABS or sometimes PLA. While these plastics melt at a low temperature and can form colorful toys and trinkets, it’s difficult to fabricate any sort of useful part out of them because of their poor properties compared to engineering and high-performance plastics.

Recently; however, some 3D printing enthusiasts have started experimenting with engineering plastics such as nylon 6, acetal or polycarbonate. While these plastics are more difficult to “print” with at the moment, the potential of these materials will soon allow for functional and robust parts to be manufactured at home. After all – was that not the initial dream of 3D printing? To create objects that are both attractive and functional. To view the full blog post click here.


CDN: 1 800 667 0999
USA: 1 866 733 2684