Eastern Plastics: Frequently Asked Questions

Eastern Plastics is the world's plastic machining specialist. We'll be pleased to answer your questions or help you understand the unique issues related to plastic machining, finishing, stress relieving, materials, assembly or other processing methods.

Q: When does machining make more sense than molding?

A: Your application, product development, and marketing requirements will determine the best plastic manufacturing method. There are twelve main considerations when determining whether to machine or mold your part.

• Low volume requirements are most cost-effectively machined.
• Closer tolerances are possible with machined parts.
• There is more design flexibility when parts are machined.
• Faster delivery is often possible when parts are machined.
• Some parts are impractical or impossible to mold due to undercuts, heavy walls, long straight holes, etc.
• Machining leaves no gate scars.
• Machined parts have lower residual stress.
• Machined parts have consistent properties.
• Machined parts require no draft angles.
• Machined parts have no weld lines.
• Molded parts develop “skin” effects.
• Molded parts may be less expensive to produce in greater volumes.
  

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Q: What types of bonding/gluing does Eastern Plastics do?

A: Eastern Plastics performs adhesive, diffusion (thermal), solvent, and ultrasonic bonding and welding.

Your application requirements, environment, materials, and bond strength demands will guide us in determining the best bonding method.

Eastern Plastics can use a variety of bonding methods in your application such as adhesives, solvents, thermal methods, and ultrasonic welding. We may also advise that simple mechanical fasteners be used in place of gluing.

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Q: How do you eliminate stress cracks?

A: Through correct tool geometry, machine feeds and speeds, and annealing.

Eastern Plastics spends a considerable amount of time developing tools, fixtures and machining methods that create the least amount of thermal and mechanical stresses. And finally, Eastern Plastics has twelve programmable annealing ovens that we use for intermediate and final stress relieving.

Many of the part failures that we see from other machining houses stem from improper or non-existent material stress management.

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Q: What types of plastic polishing methods are available?

A: Eastern Plastics utilizes vapor/chemical, flame, and mechanical methods to achieve desired surface finishes. We also use a variety of polishing/finishing methods to achieve the aesthetic and/or functional requirements for your part.

Usually, we'll make every effort to get the best finish using our CNC machines. When surface finishes or optical/aesthetic requirements demand better than what our machines can provide, then we implement vapor and chemical polishing, flame polishing, or mechanical buffing. The method used is determined by the material type and the desired outcome.

As you'll see from our website part photos, Eastern Plastics regularly achieves superior finishes and clarity, important requirements for many of our customers.

It is important to note that we perform these operations on parts that we have manufactured, not on parts manufactured by others. That's because control of residual stress, machining methods, etc. are critical to the success of any polishing method. If we have not manufactured the parts, we will not be confident that they have been manufactured correctly and can successfully be polished.

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Q: What are the smallest features you can machine?

A: As a general rule, Eastern Plastics can machine 0.006" drilled holes with 50:1 aspect ratios, 0.010" wide milled tracks, and hold tolerances down to +/- 0.0002".

Material type, part features, wall thicknesses, and other factors influence the low limits of machining possibilities. For some parts Eastern Plastics can even achieve +/- 0.000020" tolerances.

In some applications, we can achieve 100:1 aspect ratios in drilled holes.

The best way to determine the smallest features that we can machine is to let us analyze your drawings and application requirements. We will then give you an educated answer as to what we can achieve for you.

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Q: What plastics can be diffusion bonded?

A: Most thermoplastics including acrylic, PVC, Ultem^® polyetherimide, polycarbonate.

Diffusion bonding is a thermal process that fuses layers of material together, forming a permanent bond. Depending on your application requirements, Eastern Plastics can bond many clear and colored materials like acrylic, clear PVC, GE Plastics' Ultem^® polyetherimide, ABS and polycarbonate. Eastern Plastics may be currently bonding material you are using or may have diffusion bonded prototypes on hand (or in stock).

Eastern Plastics also employs other bonding methods that may be more appropriate for your application, like adhesive bonding, solvent bonding, and ultrasonic welding.

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Q: Is it all right to specify screw thread inserts, sometimes called Helicoils, in my part?

A: Screw thread inserts may be a life-long source of stress in your part.

Screw thread inserts (STI) can cause continual radial stress in plastic because of the nature of how they are held in the material, but STIs can still be used in many applications. We recommend that ultrasonically installed inserts be considered as an alternative. The part will need to be annealed.

Eastern Plastics would need to make a recommendation whether or not to use STIs after reviewing your application and material.

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