Manufacturers have many decisions to make, from concept and design to marketing and production, and finally, sales and distribution. Every step involves weighing choices for your company’s success. One of the most critical decisions a manufacturer makes includes deciding which machining vendor to choose to fabricate precision parts. This page will help identify and understand the different aspects of CNC machining to look for when selecting a machining vendor.

Choosing the CNC Machine Shop that will Best Serve Your Needs

There are many different machine shops worldwide with varying capabilities to choose from, making the decision-making process appear overwhelming. Some of those choices include smaller local shops, domestic, regional manufacturers, and international facilities. The local machine shops have a limited range of customers they serve, while the larger international plants service the orders from the corporate giants. That leaves most precision part fabrication work to the domestic, regional machine shops, leaving companies with many choices.

At Plethora, we understand that dilemma. Here, we hope to aid companies in asking the right questions about the shops they evaluate by exploring the different areas of machine shop operations. This information will facilitate an informed decision when selecting a machining vendor.

We will look first at the essential capabilities of a machine shop, followed by explaining the different aspects of quality to seek. Finally, we will inventory the services a machine shop can offer and what to expect from that potential partnership.

Capabilities of a Machining Vendor

When choosing between CNC machine shops, engineers and OEMs should first consider whether or not a candidate can complete a project successfully. The machining vendor must produce cost-effective, quality parts that meet a project’s specifications, making equipment the first point of inquiry. From there, explore the minimum and maximum part sizes that the shop can work with and their tolerance and precision capabilities. Additionally, examine their options for surface finishes and how much capacity they can handle if future plans include scaling up production. A chosen machining partner should also provide quick-turn delivery and the ability to immediately source any necessary materials that they don’t keep in stock.

Equipment and processes

Machine shops rely on two primary pieces of equipment to fabricate precision parts: CNC mills and CNC lathes. Over the years, milling machines have grown from simple hand-operated tools to complex computer-controlled instruments for working in multiple axes. Simultaneously, lathes have progressed from their hand-operated origins to computer-controlled precision instruments. And in addition to turning cylindrical parts, the CNC lathe can perform milling operations with live tooling capabilities.

Many types and formats exist for both CNC mills and lathes, and to find a machine shop that can best fabricate a part, companies should understand what machines they have and how they use them. For instance, at Plethora, we support continuous 5-axis, 5-axis-indexed, and 3-axis milling using the latest technology in CNC machines. These machines allow us to use approach vectors with the milling tools from any angle to fabricate complex geometries. We support turning inside and outside features, threading, and turning with live tooling with our CNC lathes.

A part being milled at a machining vendor

A part being milled at a machining vendor

Part sizes and tolerances

Along with finding out what equipment a machine shop has available, companies must determine if their minimum and maximum part sizes align with a project’s needs. Additionally, ensure that the machine shop can hold the tolerances a project requires for its precision. Machine shops will vary in these values, and this is a critical consideration to make before committing. At Plethora, we support the following part sizes and tolerances:

Part Sizes

CNC Milling 3 Axis

CNC Milling 5 Axis

CNC Turning


26” x 18” x 5”

660.4mm x 457.2mm x 127mm

16” x 16” x 5”

406.4mm x 406.4mm x 127mm

Ø 10” x 12”

Ø 254mm x 304.8mm


0.15″ x 0.15″ x 0.15″

3.81mm x 3.81mm x 3.81mm

0.15″ x 0.15″ x 0.15″

3.81mm x 3.81mm x 3.81mm

Ø 0.125” x 0.625”

Ø 3.175mm x 15.875mm

Standard Tolerances

CNC Milling

CNC Turning


± 0.003″ [± 0.08mm] (1)

± 0.003″ [± 0.08mm] (2)


± 0.005″ [± 0.13mm] (1)

± 0.005″ [± 0.13mm] (2)

Hole Diameters

0.020″ [0.51mm]

0.020″ [0.51mm]

Features with Radii

0.032″ [0.81mm]


  • Tighter tolerances to ± 0.001″ [± 0.03mm] available, depending on part geometry.
  • Tighter tolerances to ± 0.0005″ [± 0.01mm] available, depending on part geometry.

Surface finishes

A part machined on a mill or lathe will evidence machine marks due to the mechanics of the process. A rough or “as machined” surface may suffice for some parts, but most will require some sort of finishing for protection, strength, and aesthetics. Before making a final decision on which machine shop to use, confirm that they can apply the surface finish a project needs. At Plethora, we offer many surface finishes to our customers, including the following:

  • Anodizing
  • Alodine Coating
  • Powder coating
  • Passivation
  • Electro Polish
  • Blasting
  • Plating

Scalable production

Part production usually starts with prototype development and limited runs to introduce the product. As long as a machine shop has the proper equipment and processes in place, they shouldn’t have any problems producing an order. However, as stated above, if the needs of a project include scaling up production, ensure that a chosen machining vendor can handle the increased quantities.

A machining vendor will use various manufacturing methods to scale with a company’s needs, including tombstone fixtures and automatic pallet changers to increase productivity. The number of machines that the shop employs can also impact a project, as part quantities in the thousands will require multiple mills and lathes. At Plethora, we can service manufacturing needs from single prototypes up to large production orders.

Capacity and on-time delivery

For a long time, companies outsourced part manufacturing to overseas machine shops. Now, with offshore labor costs rising, trade wars, shipping difficulties, and other problems, many companies seek to reshore part production back home. Most OEMs turn to domestic, regional machine shops to supply their critical components due to the cost and complexity of running an internal machine shop.

When looking for a machining vendor, ensure that they can build a part to specifications and complete work according to a strict schedule. Look for CNC machine shops with an On-Time Delivery (OTD) rate above 90%. At Plethora, we have manufacturing facilities in California and Georgia, allowing us to serve customers in the U.S. very quickly. We have a 57,000 square foot production facility to handle large capacity orders while maintaining capacity for quick-turn, lower volume orders.

Production materials

Depending on the needs of a project, some materials might work better for a part based on factors such as price, machinability, strength, durability, and finishes. Additionally, the material chosen for a prototype may differ if it means accelerating product development. It is essential to select a machining vendor that stocks the necessary materials, collaborates on material choices, and can quickly source unique materials not readily available.

At Plethora, we stock an assortment of standard materials for most of the work that we do, including:

  • Aluminum
  • Stainless Steel
  • Steel
  • Copper
  • Brass
  • Bronze
  • Plastics including ABS, ACETAL, HDPE, and Nylon

Stock materials used by a machining vendor

Stock materials used by a machining vendor

Quality in Machining

Once a company has narrowed the field of available machining vendors down to those with the capabilities necessary for a project, the next focus involves quality. An adequately equipped machine shop won’t work out if its overall quality doesn’t match expectations. To find out more about a machine shop’s commitment to quality will require some in-depth conversations with them. Ask about their quality control procedures and processes, their adherence to industry standards, what certifications they carry, and the training programs they provide for their staff.

Quality management processes

The first step in assessing a machine shop’s commitment to quality involves learning about their quality management. The following includes three areas to ask about when screening a potential machining vendor:

Written quality policy

Machine shops that place a high value on their commitment to quality will typically document their quality processes in writing. This document will detail the shop’s equipment, manufacturing processes, material and testing reports, and inspection schedules for testing equipment. At Plethora, we highlight our commitment to quality on our website.

Designated quality team

Quality-driven machine shops will establish a designated quality team responsible for preventing production errors throughout every step of the manufacturing process. This prevention includes First Article Inspections (FAI) and incremental inspections throughout production. At Plethora, we embed our quality team members within our manufacturing process to guarantee the highest quality from design analysis to final finishing operations.

Quality management system (QMS)

A QMS documents the processes, procedures, and responsibilities necessary for achieving the quality objectives set by the machine shop. Shops set up these systems according to the structures outlined in the ISO 9001:2015 international QMS standard. At Plethora, we use our QMS to foster continual improvement in our manufacturing processes. As an ISO 9001 certified manufacturer, our quality teams ensure that our manufacturing yields the highest quality possible.


Industry standards and certifications

The next step in evaluating a machine shop’s commitment to quality includes discovering their industry standards and certifications. Most machine shops have ISO 9001 certification—the international standard for quality management and processes. Beyond that, machine shops may hold certifications in other standards to demonstrate they have the training, processes, and procedures for doing work for that industry. One example is registration with the International Traffic in Arms Regulations (ITAR) to secure data and products when manufacturing parts for military and defense purposes.

At Plethora, we hold both ISO 9001:2015 certification and ITAR registration. We staff our manufacturing and quality teams with professionals experienced in the aerospace, medical equipment, defense, and automotive industries. We understand each of these industries’ different quality and security requirements and work towards exceeding our customers’ expectations.

Continual professional training

Don’t forget to ask about the continual training programs a machine shop uses to keep their staff knowledgeable in the latest industrial processes, technologies, and certification requirements. At Plethora, we place a high value on the capabilities of our staff and provide continual team training in all areas of our manufacturing and production.

A machinist’s tools


Service from the Machine Shop

At this point, a company has hopefully discovered what a prospective machine shop can do and how effectively. The next area of inquiry involves how they evaluate a new project. The “how” begins with the service received when first contacting the shop about a new project. It’s valuable to know what processes they have in place for evaluating a part and how they will quote the job.

Companies should also determine how a design’s complexity or unique requests might affect the final cost and whether or not any price breaks exist. Establish a direct line of communication with the machine shop and how much engineering help to expect when submitting a part for manufacturing. Finally, it’s expedient to research evaluations of this machine shop from their list of references.

Part analysis and quoting

Before building a part, the machine shop will review it to verify its manufacturability. When done manually, the process of submitting a paper request and waiting for engineering review from the machine shop can take a lot of time. As an alternative, many machine shops today use automated online analysis and quoting tools that speed up this process.

Benefits of online part analysis and quoting

  • Uploading data: Users simply upload part data online and transfer all the required information into the machine shop’s systems. Once the system finishes the quote, the same data is used for manufacturing, saving days on production schedules.
  • Automated part analysis: The advanced AI of the online part analysis tools will report the part’s manufacturability back to the user within seconds. Not only does this speed up part quoting, but it helps engineers find and correct errors resulting in better-designed parts.
  • Manufacturability report and quote: The customer can quickly correct any errors reported back with either design changes or changing the parameters of the part request, such as which materials to use. The system will prompt the user to contact the machine shop directly for additional help for more complex problems.
  • Payment: Once the shop accepts the part request, customers can pay online, and manufacturing begins.

At Plethora, our online part analysis and quoting system provides immediate feedback on the manufacturability of a part and prompts users to complete the quote to begin production. Additionally, we have staff ready to take any call regarding a quote, request, or another concern.

Project costs

The quote for a part request involves more than just the bottom-line price. The cost of building a part may comprise several factors to understand before comparing the cost value between different machining vendors. Some of the cost factors to consider include:

  • Machine operations
  • Labor
  • Materials
  • Part complexity
  • Finishes
  • Shipping

When evaluating the costs between vendors, ask about price breaks for quantity builds, added costs for prototyping or quick-turn, and potential hidden costs. Additionally, ask about payment terms and the machining vendor’s cancellation policy. At Plethora, we included our costs in the online quote, and customers can contact us directly for additional information.

Communication and engineering support

One of the most essential components of a successful partnership with a manufacturer includes open communications. Ideally, a machine shop collaborates early on in the design process to provide immediate feedback on the manufacturability of a design. The machine shop’s engineering personnel should make recommendations on the needs of your project by analyzing the design and its related components.

At Plethora, our representatives have years of engineering experience, and they will work closely with customers as needed. They always take the time to fully understand the requirements of a project to help with material choices and design recommendations. We make it our goal to optimize designs, cutting down production time, increasing yields, and lowering costs.

Customer references

Lastly, get a second opinion of a chosen machining vendor by checking their references. Look for online reviews and find out what other customers felt about the level of service they received. For instance, did the shop meet or exceed the reviewer’s expectations? Were there any quality issues or missed delivery schedules? If so, how were these problems resolved?

At Plethora, we welcome inquiries into our services and capabilities. Our work is a point of pride, and we stand behind the products we build for our customers.