Wednesday, June 5, 2013

Buying Custom Mechanical Parts on the Internet

Prior to the widespread use of the Internet in mid 90s, getting a custom mechanical part manufactured was a time consuming task. For example, if you were an inventor with a brilliant idea living in a small town, you had to travel to the nearest city that had the appropriate manufacturing facility. Once you got there, it might take you days to meet the manufacturing expert and find out how many and what kind of changes were needed to make your concept work from the manufacturing point of view.

Today, if you have an Internet connection, you have access to companies who will be happy to make your custom part. Once your CAD model is ready, you can order the part with a few clicks of your mouse. The Internet has enabled new e-commerce models in the manufacturing space and you have many options. You can directly order parts from manufacturers, let a broker find you a manufacturer, or work with a manufacturing service provider. Basically, you don’t need to leave your home to get your parts manufactured. 
So a natural question is – what option should you choose? Let us quickly review what you might need to think about before answering that question. Here are the four basic issues that you need to consider: 
  • Can the process under consideration make your part? Every manufacturing process imposes restrictions on shape, material, and achievable accuracy. So it is important to ensure that the process can produce the part.
  • How much will it cost? For some people, cost is the main driver. Other issues are less important. In many situations, other considerations are more important and hence cost minimization is not the right approach.
  • How long will it take before the part is delivered to you after you place the order? Sometimes, people are under tremendous time pressure and getting the part as soon as possible is the most important criterion. Some customers are willing to pay a premium price to get the part shipped quickly.
  • What is the probability that the part that is delivered to you actually conforms to your specifications? Unfortunately, many things can go wrong when placing a part order on the Internet. Moreover, an outfit with a good looking website and a promise of the lowest possible price may not actually have the right capability or expertise. If you receive a defective part, then it may cause a major problem for your project schedule.
Depending upon your requirements and situation, you may need to consider the following four other issues:
  • There might be a few different ways to make a given part. For example, a part can be laser cut or can be made using a water-jet cutter. So it might be useful if the manufacturer can provide multiple process options to you.
  • If you are new to designing mechanical parts, then you might need help in performing manufacturability analysis and improving your part design. Different companies offer different levels of help in this area.
  • If you are working on a sensitive project, then you may worry about protecting your intellectual property. How do you know that the manufacturer will not inadvertently share your CAD models with others? If this is your concern, then you may need to carefully review the data protection policy of the manufacturer. You may need to sign a non-disclosure agreement (NDA) with the manufacturer. Please keep in mind that enforcing NDA with an international company might be quite hard.
  • Different manufactures require different CAD model formats. So you will need to find someone who can accept files produced by your CAD system.
There are three different types of models to buy custom mechanical parts. I will use representative companies in each model to explain the basic idea:
  • Direct Purchase from Manufacturers: There are many job shops with websites. You can upload your CAD model and they will make it and ship it to you. A well-known example is Protomold ( for ordering injection molded parts. Usually, directly working with a well-known manufacturer gets you a good price and the fastest delivery. However, the process options might be limited. This appears to be the best option when you have experience with the process under consideration and do not need significant help in ensuring manufacturability.
  • Purchasing from Manufacturing Service Providers: Quickparts ( uses a number of manufacturers to fulfill its orders. They take care of all the backend details of working with the manufacturer after you order the part. This appears to be the model of choice if you want process flexibility and do not want to directly deal with the manufacturer yourself. This model also provides good support to new designers. However, you might not necessarily get the lowest possible price or the fastest delivery time.
  • Finding a Supplier Using a Brokering Service: There are brokering services that will allow you to find a manufacturer to make your part. For example, MFG.COM ( can help you get quotes from different suppliers. You can then select the supplier who meets your needs. This appears to be a good model if you have experience in dealing with job shops and want to minimize the cost.
In summary, this post gives you a list of questions to ask as you attempt to buy custom mechanical parts on the Internet. I look forward to hearing your experiences. Did I miss anything important?


  1. Interesting post.

    What is the most common practice nowadays among the three different types of models to buy custom mechanical parts ?

    Also, it seems to me that the third type (Finding a Supplier Using a Brokering Service) is a search engine-like Website that generates results enclosing the first two models, is this the case?

  2. This blog is certainly related to the direct digital manufacturing for custom parts: a concept for the factories of the future. There is great role for software agents and AI, for brokering, coordination and control.

    As mentioned manufacturability of the part without compromising the functionality, cost and time constraints are key issues to be considered, when ordering custom parts.

    You may find the additive manufacturing bureau services for custom parts to be interesting as well:

  3. You've touched on this throughout the article, but this might be one of the most important aspects of any of these options: process selection. This is an iterative and potentially decomposable problem that is intimately tied to the requirements of the part, as well as the system in which it is situated.

    For example, a designer who isn't familiar with all of their options might try to have a part milled, when in fact a molding process would be more appropriate. The manufacturer would have to put in the extra effort to communicate with the designer, and confirm that milling is what they really want.

    There may be other situations where the part could easily be redesigned to take advantage of a cheaper manufacturing process, or where a complex part could be broken down into an assembly of easy-to-manufacture parts. Sometimes, the system in which the part is situated might be modified for the purposes of manufacturing.

    All of these situations require iterative feedback and extensive communication between the designer and manufacturer. I'm sure that brokerage services provide this service to some extent, but there may be a need for independent manufacturability consultation services. These services could work with designers to ensure that what they want is the same as what they need.

  4. me also doing this type of work so I appreciate it. thanks as I find some of other about me.

    MRO Supply com.