One of the most common questions we are asked is “How much draft do I need for the texture that I want?”

The general rule of thumb is that you allow for 1.5 degrees of draft for each .001″ of texture finish depth. However, there are other considerations that must be taken into account due to the many new resins and polymers, molding improvements, and various other factors that come into play in modern plastic molding. Examples of situations that require additional draft are thin wall part design and high pressure molding.

Some important considerations to keep in mind are:

  • Is the vertical wall in question an inside or outside wall? If it is an inside wall, the part will shrink onto it during molding, so you will need more draft in order to apply a texture, or apply the texture at a lighter depth.
  • Certain plastics have very little shrinkage and will therefore not shrink away from outside walls as easily as other plastics. Thermosets, Ryanite, Glass Filled Nylon, Glass Filled Polypropylene, ABS, Polycarbonate, etc. will usually require more draft in order to mold parts without scuff or drag marks.
  • If the core is very simple, and there is nothing on the core to hold the part in place during ejection, the part will tend to hang onto the cavity, creating scuff marks. The part may require more draft, or perhaps texture could be applied to the core side. This helps hold the part onto the core during ejection. This method has been used very successfully to solve this sort of problem.

I hope you find this information helpful. If you have any questions regarding this or any other injection molding information, please send us an email or give us a call at (770) 901-3200.


When it comes to rapidly manufacturing injection molded parts, there are several key factors to consider. Here are a few of the top considerations to start off on the right track:


All successful injection molding programs begin with proper design for the process, and in this case for rapid production. When designing your part for rapid injection molding, the most important factors that contribute to lead time are part size and complexity. Whenever a larger part can be broken down into smaller pieces and then assembled, you will potentially shorten lead time. This is because simple, shallow cavity designs are produced quicker via the CNC machining process. Designing parts that are moldable with a “Straight Pull Mold” is a great place to start. This requires that all the part’s features be designed so that when the two halves of the mold are pulled from each other and the part is ejected, there are no secondary processes required.  This is due to mold material’s tendency to pull through part plastic (this is referred to as an ‘undercut’.) Undercuts require mold pieces to pull out sideways, perpendicular to the direction of the pull. These ‘side actions’ as they are called can require ‘hand loads’ for lower volume projects or automatic/mechanical loads for higher runs.


Ideal quick turn projects should utilize standard, off the shelf materials and colors that are either already on hand or can be quickly sourced from a material distributor. Generally, lack of need for name brand material does not cause issues, but this is not the case for all projects.  When a precise brand and type of material is required, the material can be ordered and shipped while tool cutting occurs simultaneously. Should the material not arrive within the allotted window, a substitute material can sometimes be used in place of the production material to, at the very least, confirm basic design and function of the part. Once production material arrives, a second sample run can take place before proceeding with higher production runs.


Of course when there is a lead time requirement for parts quicker than the standard, there are cost considerations. These considerations are driven by additional man hours required by the project up front and often result in overtime and extended shop hours to achieve the desired ship date. Those items that can be sped up? Things such as tool design, steel or aluminum delivery to the shop, part material ordering, and scheduling sample production runs.

It is important to remember that in many cases, all the money in the world cannot speed up certain processes. Cutting of the core and cavity, for example, is at the mercy of the almighty CNC machine. So while there are things within a tooling shop’s control, other things will always have a fixed lead time. This is why those factors mentioned become even more important to reduce the number of days to the finish line.

Selecting an appropriate material is, perhaps, the most important factor when implementing a design for injection molding. With literally thousands of different resin grades to choose from, an erroneous choice can prove to be disastrous. Thorough research and consultation is strongly advised, especially for anyone new to plastic part design. A simple web search, along with sites such as and are invaluable tools for any novice or veteran of injection molding.

Resin Selection Guide

Material selection is often based on the application of the part. While every part is unique, there are some generalities to follow. Click here
for your complimentary Plastic Resin Chart, which includes material names, trade names, abbreviations, descriptions, and most importantly, the most common applications for each particular material.

It is important to note that shrink rates for different materials differ, some more significant than others. Changing a material after a mold has been constructed can lead to inconsistencies in geometry. It’s always a great idea to check with the selected molder before changing materials.


Injection Molding

Here at Quickparts, we are in constant contact with engineers, mold makers, machinists, and other self-proclaimed experts of the manufacturing industry. Over the years, our molding lexicon has grown tremendously – to a “molding urban dictionary” of sorts. Listed below are some of the most common terms that frequent our ears daily.

What did we miss? We challenge you to send us your most creative synonyms!

Cavity Refers to the upper half of the injection mold usually the show surface of the finished product but is mainly concave
Core Refers to the side of the tool where the plastic part is injected from; also known as the bottom half of the tool
Gate Refers to where the plastic enters into the cavity of the mold.
Hand Load Aluminum or steel feature in a mold used to create undercuts in molded parts.  They are manually removed from the mold during the part ejection process.
Heel Refers to the portion of an automatic custom injection mold that keeps the slide in the forward position when the molding machine is closed on the mold
Horn Pin Pin used to actuate the slide on an automatic injection mold
Runner A channel cut into custom injection molds, in which plastic travels from the injection molding machine, through the sprue, through the runner and then through the gate ultimately filling the part
Shear Refers to when plastic enters into the mold and the melt is maintained by friction produced by speed and pressure. Too much shear can cause the plastic material to burn, too little can cause the material to freeze off causing short shot
Side Action Term used for slides and/or hand pulls used in the injection mold build process
Vestige Material protruding from the gate area after gate runner has been removed from the injection molded part. This vestige is usually trimmed by the molding machine operator

Design engineers don’t have to be fluid dynamics experts to injection mold plastic parts without a hitch. Pitfalls associated with flow dynamics can still be averted through the use of simple designs and by following general guidelines. The following rules will help engineers avoid problems when designing injection-molded plastic parts:

Rule 1: Keep Wall Thickness Consistent
Plastic part walls must be uniform in thickness. This is the most basic design parameter, and strict adherence to it will eliminate many manufacturing problems. Parts with uniform walls will not warp, will fill properly and will fit together because variable shrinkage is minimized. Wall thickness variations should not exceed 10% in high mold shrinkage plastics. In fact, even this slight disparity can introduce processing and quality problems.

Rule 2: Provide for Proper Gate Location
If varying wall thickness cannot be avoided, then designers should provide for proper gate location. If this is not supplied, then attaining uniform pack of the molded part will be nearly impossible. The most effective gate location is when the melt enters at the thickest part of the cavity and then flows to the narrower areas.

Rule 3: Determine Optimal Wall Thickness
Theoretically, there is no maximum wall thickness for injection-molded parts. But designers are more concerned with determining the minimum wall thickness because thinner is almost always less expensive. Two factors contribute to this: first, thinner parts require less raw plastic material, and second, they cool faster. To determine the most suitable wall thickness, engineers should first consider product requirements. Generally, strength dictates the wall thickness. Engineers can also rely on a finite analysis to select the optimal wall thickness.

Rule 4: Radius Corners Generously
During injection molding, the molten plastic has to navigate turns or corners. Rounded corners will ease plastic flow, so engineers should generously radius the corners of all parts. In contrast, sharp inside corners result in molded-in stress—particularly during the cooling process when the top of the part tries to shrink and the material pulls against the corners.

If the inside and outside radii of a part are each equal to half of the nominal wall thickness, a uniform wall around the corner can be achieved. Both sides of the corner will display equal amounts of shrinkage, and sink marks will be avoided entirely. Moreover, the first rule of plastic design—uniform wall thickness—will be obeyed. As the plastic goes around a well-proportioned corner, it will not be subjected to area increases and abrupt changes in direction. Cavity packing pressure stays consistent. This leads to a strong, dimensionally stable corner that will resist post-mold warpage.
Rule 5: Select Suitable Draft Angles
From a cost and manufacturability viewpoint, the ideal draft angle is the largest angle that will not lessen the customer’s satisfaction with the product. The minimum allowable draft angle is harder to quantify. Plastic material suppliers and molders are the authority on what is the lowest acceptable draft. In most instances, 1° per side will be sufficient, but between 2° and 5° per side would be preferable. If the design is not compatible with 1°, then allow for 0.5° on each side. Even a small draft angle, such as 0.25°, is preferable to none at all.

I hope you find this information helpful. If you have any questions regarding this or any other injection molding information, please send us an email or give us a call at (770) 901-3200.

We got a great response to last month’s money saving tips post. For this month, we wanted to provide you with 3 easy steps to ensure the success of your next tooling project.

Step 1: Get a Design for Manufacturability (DFM) Analysis

Most tool shops have the ability to provide some form of Design for Manufacturability (DFM) analysis, which can range from very basic to very detailed. No matter the level of detail, giving your mold maker the opportunity to review your designs ahead of time can go a long way in strengthening the customer-supplier relationship. Knowing everyone’s expectations in advance will streamline the tool build and lead to better molded parts.

>> Get a Complimentary DFM Analysis 

Step 2: Send Your Mold Maker a Rapid Prototype of Your Design

Any engineer knows that getting it right the first time is a rare phenomenon. Even after thorough DFM feedback and countless hours of CAD review, you never really know what you’re going to get until you hold the part in your hand. Do some research on which rapid prototype process suits your application the best, make sure the design is right, and then send a few sample parts to the mold making facility of your choice. Although they have surely seen thousands of parts, each design is unique, and seeing a rapid prototype part could change their perspective on the best way to mold the part. 

Step 3: Take Time to Thoroughly Review T1 Samples

After the DFM and rapid prototype phase, you can finally rest easy once the tooling is on order. The next challenge will arise when your molded T1 samples arrive. Although the race to get your product to market weighs heavily, it is extremely important to spend some time evaluating the initial parts off of the mold. Hastily signing off on your samples in order to produce thousands can be a disaster if the samples have not been properly evaluated. Along with fit and function testing, it’s a great idea to request hard data from your mold maker in the form of a first article inspection report.

I hope you find this information helpful. If you have any questions regarding this or any other injection molding information, please send us an email or give us a call at (770) 901-3200

We have some great ways to help you save money on your next injection molding project.

:: Top 5 Money Saving Tips

1. When selecting a material for your injection molded part, do not just assume that you need a material that has the best properties. A lot of people overcompensate by selecting materialsthat they don’t really need. Since material is sold by the pound, this drives the piece part price up. Figure out what your needs are, and discuss them with a material representative. These guys will help you select a material that best meets your criteria, and will save you money.

2. Try to minimize secondary processes such as pad printing, custom inserts, painting, etc. All of these processes require extensive setup times and costs which will need to be spread out over the piece part price.

3. Select the right molder. There are many different types of molders out there, some are very large, and some are very small. Keeping in mind the requirements for your parts, select a molder that is capable and has the right size machines for your parts. If your requirements are low, stay away from the big flashy injection molders with lots of machines. Their overhead is too high.

4. Try to order as many parts as you can at one time. This spreads out the setup cost over more parts, thus leaving you with a lower piece part price.

5. Design your part so it is as moldable as possible. Make sure there is plenty of draft to facilitate ejection, and eliminate any thin steel conditions that will cause more mold maintenance down the road.

I hope you find this information helpful. If you have any questions regarding this or any other injection molding information, please send us an email or give us a call at (770) 901-3200.

Injection Molding Design Guide

Download Our Free Design Guide!

If you’ve ever wondered if draft angles were a must, we’ve got the answer for you!

The justification for draft angles comes from the nature of the injection molding process, and the ever present issue of mold shrinkage. Injection molding is a high-pressure process. These high pressures force the plastic into intimate contact with all surfaces of a mold’s cores and cavities. This high-pressure packing of the cavities makes it difficult to get the part out of the mold, or “eject” the part.

Draft facilitates the removal of the part from the mold and is very important in injection molding where the molds are straight pull only (no side actions).

The guidelines associated with the number of degrees of draft required will vary with geometry and other part characteristics (e.g. surface texture requirements), but in general the more the better. Draft is your friend when building molds.

Here are some rough guidelines to follow:

  • We ask for at least 0.5 degrees on all “vertical” faces
  • 2 degrees works very well in most situations
  • 3 degrees is minimum for a shutoff (metal sliding on metal). Without this, the
    mold would lock up and be unable to open
  • 5 or more degrees is required for heavy texture

Remember, draft is your friend when designing molds.

To discuss draft for your next project or any other injection molding information, please send us an email or give us a call at (770) 901-3200.

Have you ever wondered how these items were made??

Injection Molding Design Tips - Overmolding - Screwdrivers
The answer is overmolding. The overmolding process involves the use of two separate materials to form one cohesive component. The most common type of overmolding is insert molding. Insert overmolding is an injection molding process where one material (usually elastomeric) is molded “over” a secondary “substrate” material (usually a rigid plastic or object).

Overmolding can add immeasurable value to product design by enhancing the end users experience in terms of comfort, ergonomics, and ease of use. In order to achieve this level of manufacturing there are two important concepts that must be understood for success to take place:

1) Know your materials

The materials used need to be compatible so that your designs attain a high level of molecular adhesion. Know what the melt temperature is of your substrate and overmold. If the melt temperature is lower on your substrate than your overmold material, then you are in for a big problem! Also, if you are using color, make sure your color concentrate is compatible with your other materials and won’t degrade their properties. Using the right materials could make or break your designs.

2) Understand your designs

When designing, you need to consider how much or how little you want your substrate and overmold to stick. Don’t count on the material alone to create the adhesion that you want. To ensure that the components “mesh” well with one another, use mechanical interlocks such as these:

Injection Molding Design Tips - Overmolding

Knowing the proper rules for overmolding can yield a very successful and aesthetically pleasing product. To discuss overmolding options for your next project or any other injection molding information, please send us an email or give us a call at (770) 901-3200.

How do you select the right injection molding material? This is a very difficult question. Making the decision even harder is the fact that there are over 300,000 different types of material available, and that number grows by 750 more every year.

Injection Molding SampleSome people think the best thing to do is just select the latest and greatest material that has the best properties and can take super high heats. They might think that their requirements will never exceed these properties and their part will be fantastic. This is almost never the case. When selecting resins, it is a good idea to contact your local representative whether it is for Sabic, Bayer, or DuPont. Let them know what your product is for, the conditions that it will be exposed to, and the colors that you would like it in, and they will certainly point you in the right direction. Most of the time, simple resins like: PP, ABS, PC, or PC/ABS will be more than sufficient for your needs. If you have an out of the norm requirement, resin makers can blend additives into the resins to meet your requirements. 

So how do you select the right material? Ask for help first or go to the resin manufacturer’s website, you will be amazed. Remember, it does not have to be the most expensive resin to be a quality material.

I hope you find this information helpful. If you have any questions regarding this or any other injection molding information, please send us an email or give us a call at (770) 901-3200.