Archive for the ‘Acetal’ Category

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.

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There are a lot of flashy “do it yourself” projects that hobbyists get in to with plastic but one application that keeps coming up that you might not think of is the simple gear. The general reasoning to use a plastic gear as a replacement for a metal gear make intuitive sense: the plastic gear will often be mated to a metal component and the fact that you have a plastic on metal connection now should greatly increase the life of the mating components. The problem is hobbyists do not really know what to use: we’ve heard of HDPE, UHMW, nylon and even polyurethane be requested by the DIY community for a home made gear application. But how suitable are these plastics for the application?

Actually – not very. Most plastics cannot be machined to tolerances as tight as metal be but many plastics, especially the polyolefins such as HDPE and UHMW, are very soft and could have the gear teeth quickly lose their shape once that gear starts working. Nylon is better, but it cannot take much impact at all – especially in the cold – meaning it is considered to be fragile. The best material for the application is actually acetal. Acetal is a very hard plastic that machines very well and holds excellent tolerances. It is widely available in rod stock from plastics distributors across North America. The gear in the picture below is made of white, homopolymer acetal. Black copolymer acetal is also widely available and would work well too – its properties are slightly worse than homopolymer in some respects but it is also less expensive.

Acetal

 

 

Acetal Ball Maze

Posted: December 15, 2014 in Acetal, Cool Projects
Tags: , , ,

You know what they say about simple ideas – sometimes they’re the best!

We found a video of a DIY project where a CNC machine is used to etch a ball maze into a piece of acetal plastic (of which the name of the homopolymer variety is ‘Delrin’). Apparently the project was for students who designed the game from an initial paper sketch all the way through the CAD program. This project is simple enough for students yet creates a functional and fun piece of work. In short, it seems like genius. Acetal is a great plastic for machining, probably the best thermoplastic in holding tight tolerances.

Acetal has numerous other “Do-It-Yourselfer” applications. Most common is probably aftermarket paintball equipment, which we have blogged about previously here. Acetal replaces small, precise metal parts and often replaces polyamide (nylon) in applications where moisture is a concern.

The video is a little blurry but you will still get the gist of the project and the final design:

 

One everyday application that uses performance industrial plastic is guitar picks. The rigors of many thousands of abrasive strokes against guitar strings means quality plastic is ideally suited to this application. ULTEM (semi-transparent amber or black color) is sometimes used but acetal (opaque white or black) is more common. Black nylon is also a good plastic for this application but is less well known. We recently found a website all about a do-it-yourself product called the “Pick Punch” this lets you take acetal and punch your own picks at home – you might never run out again! This is much more economical (and fun) than simply buying picks, wouldn’t you say?

The website gives lots of tips on how to finish your picks as well as which types of plastic or items to NOT punch with the machine. You can check it out here: http://www.pickpunch.com

redacetal

 

Home machinists are often bewildered by the wide variety of plastics available. Each plastic has its own advantages and disadvantages. Two that seem similar to the uninformed are acetal and UHMW. However, as the YouTube video we found shows – machining the two materials is very different. Acetal is extremely hard and machines to close tolerances without “gumming” up lathes. UHMW on the other is soft and is difficult to machine and suffers from thermal expansion. Both materials are impervious to moisture and come in FDA compliant forms. Price is a major factor between the two as UHMW is much more economical and this means for projects that do not require maximum precision, UHMW will usually perform very well. An example “diy” UHMW application would be sled tracks, popular in Arctic locations.

Acetal, as you might expect, performs better in precise – typically small – parts. Acetal is also extremely hard and can replace metals (and is often marketed for that reason), such as in the case of the paintball marker bolts highlighted in one of our recent blog postings. For more information check out these acetal and UHMW website sub-pages and watch this video that shows some of the machining differences:

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:

Nylon:

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

Acetal:

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:

E-MAIL: sales@redwoodplastics.com
CDN: 1 800 667 0999
USA: 1 866 733 2684

In the world of engineering plastics there are many niche uses for materials, applications where one material is prized by a select group of engineers or machinists. One of those areas is the sport of paintball.

For those that still have not heard of the sport, paintball is popular throughout North America. Players use devices called “paintball markers” to fire round balls containing a water-soluble paint. These markers are all gas-powered by either CO2, nitrogen or compressed air. With the sport’s increasing popularity in the mid-1990’s a culture of customization of markers started as small manufacturers and individuals with machining ability attempted to gain any sort of edge. An early discovery was acetal for use as the bolt of the marker:

checkitbolt

Acetal has a number of useful properties including zero permeability to moisture and little to no permeability to gas. It is also quite hard. However, most importantly was that acetal machines to excellent tolerances and can be used to create a precision part. Over the years a number of larger paintball equipment manufacturers started to carry lines of acetal bolts, to capitalize on the excellent properties acetal offers to the component. The popularity of this material remains to this day, with acetal being a sought-after material for aftermarket bolts both by manufacturers and those same talented machinists working at home who are still looking for that extra edge in performance, that acetal can provide. For an example of the acetal “Check It Full Force Bolt” bolt click here.

E-MAIL: sales@redwoodplastics.com
CDN: 1 800 667 0999
USA: 1 866 733 2684