How to Choose a Machining Subcontractor | Key Points to Check Before Placing an Order and How to Identify a Reliable Vendor

What criteria do you use when selecting a subcontractor for machining?

“When I hired the previous contractor, they didn't meet the deadline,” “I'm having trouble with inconsistent quality,” “I asked for a quote, but their response was slow and things aren't moving forward.”

We frequently hear these concerns about outsourcing machining work from procurement and purchasing managers in the manufacturing industry. While there are many suppliers to choose from, selecting one based solely on “low price” or “they said they could handle it” can lead to problems that affect subsequent production stages.

We’ve compiled a list of common mistakes we’ve observed in the field, along with key points to consider when selecting a contractor.

3 Common Mistakes When Choosing a Vendor

Before we get to the checkpoints, let’s take a look at some common mistakes we often hear about in the field.

Scenario 1: They said they could do it, but the quality was inconsistent

It is not uncommon for a company to respond that it can handle an order at the initial stage, only for the actual product to arrive with inconsistent dimensional accuracy or a surface finish that does not match the drawings.

Even if the answer to “Can we handle this?” is “YES,” whether we can consistently maintain the required precision and quality is another matter entirely. Stable quality can only be achieved when all the following factors align: the precision of the equipment, the condition of the tools, the inspection system, and the technical skills of the operators. If even one of these elements is missing, quality will vary from batch to batch.

When you consider the impact a single defective product can have on subsequent processes, the resulting costs can far exceed the difference in unit price.

Scenario 2: Prioritizing “low cost” led to higher expenses later on

There have been cases where choosing the lowest-priced contractor based solely on the quoted price resulted in defects that required rework or corrections, as well as delays in subsequent processes, ultimately driving up the total cost.

In some cases, low unit prices for machining services result from cutting corners on investments in equipment, inspection processes, and quality control systems. There is always a reason behind a low price. It is important to determine whether that reason is acceptable before placing an order.

Scenario 3: Production halted while waiting for materials

When a manufacturer sources its own materials, the availability of those materials and the procurement lead time directly affect the production schedule.

It is not uncommon in the non-ferrous metals industry to encounter materials that are listed in JIS standards but cannot actually be sourced. If you place an order with a supplier that lacks a strong network of material distributors, processing may come to a halt while waiting for the materials to arrive. Since this directly impacts development schedules and mass production plans, material procurement capabilities are an important point to verify, even though they are often overlooked.

5 Key Points for Evaluating Outsourcing Partners

① Do you have experience machining that material to that level of precision?

The first thing to check is whether the manufacturer has a proven track record of processing materials, shapes, and tolerances similar to those in your order.

Machining characteristics vary significantly depending on the material. Non-ferrous metals such as copper, aluminum, and brass present challenges—such as welding, burrs, and thermal deformation—that differ from those of ferrous metals. Having equipment capable of machining metal is entirely different from being able to consistently handle the precision machining of non-ferrous metals.

We also recommend asking specifically about the supplier’s actual track record in meeting requirements for machining diameter, tolerances, and surface roughness. Suppliers who provide concrete answers—such as “We have a track record of mass-producing parts made from this material with this level of precision”—are more trustworthy than those who simply say, “We can handle it.”

At Tatsumiya Metal, we specialize in precision machining using NC automatic lathes for parts ranging from 2 to 51 mm in diameter, and we have a proven track record in mass-producing parts made from difficult-to-machine materials, including SUS304. Since 1985, we have been providing machining services for non-ferrous metals, with a focus on copper, brass, and bronze, for over 40 years. We have been ranked 4th out of 486 companies in the Metrie machining category, and our track record within the industry is reflected in these objective figures.

② Speed of response

You can gauge a provider’s responsiveness as early as the inquiry stage, before the transaction begins.

The time it takes to receive a response after submitting a quote request, and the speed at which they reply to specification inquiries. This promptness in initial communication often carries over once the actual business relationship begins. Especially during the prototyping and development phases, inquiries regarding specification confirmation, changes, and additions arise frequently. If a day or two is spent waiting for a response each time, the entire development schedule will fall behind.

Tatsumiya Metal boasts a 100% response rate and an average response time of 9.6 hours on “Metry,” a comparison platform for industrial products. Users who have requested quotes have left reviews such as, “It was helpful to receive a response regarding whether they could handle my request immediately after I inquired,” and “They responded quickly and provided courteous service.” Even when we are unable to perform the requested processing, we make it a priority to communicate this promptly and politely.

③ Ability to source materials and expertise in materials

Whether a machining contractor has a system in place to procure materials has a direct impact on delivery times and quality.

With non-ferrous metals in particular, the selection of the material itself directly affects the quality of the finished product. Even within the category of “copper,” there are many types—such as pure copper, brass, phosphor bronze, and Eco-Brass—and the appropriate grade varies depending on the application. If you entrust the work to a contractor lacking knowledge of materials, they may be able to perform the machining, but they won’t offer suggestions such as, “This material would be more cost-effective for this application,” or “This material is prone to thermal deformation, so you should reconsider your tolerance settings.”

A contractor with a network as a materials trading company can confirm material availability, propose alternative materials, and shorten procurement lead times. If you are currently “ordering materials and processing separately,” consolidating these with a single company can help reduce management costs, transportation costs, and lead times.

Tatsumiya Metal, founded in 1935, is a specialized non-ferrous metals trading company that deals directly with major domestic manufacturers such as Sumitomo Metal Mining Copper, Mitsubishi Materials, JX Metal, Daido Steel, and the UACJ Group. Our 90 years of accumulated expertise in materials and our procurement network provide the foundation that underpins the quality and delivery times of our machining services.

④ Quality Management System and Third-Party Certification

It is also important to verify what equipment and methods are used for post-machining inspections.

A simple report stating “machining is complete” does not confirm whether the parts actually fall within the tolerances specified in the drawings. The standard for quality assurance is whether the company has a system in place that allows for numerical verification after machining, utilizing precision measurement equipment such as coordinate measuring machines, image measuring instruments, and surface roughness meters.

Furthermore, obtaining certification for a quality management system such as ISO 9001 serves as proof that a third party has evaluated the company’s commitment to quality control. While certification alone does not determine quality, it serves as one criterion for assessing the level of sophistication of the management system.

Tatsumiya Metal obtained ISO 9001 certification in 2005 and handles everything from machining to inspection entirely in-house. Furthermore, we have continuously maintained KES Environmental Management System (Step 2) certification since 2003, demonstrating our ongoing commitment not only to quality but also to environmental stewardship. We also issue inspection reports that provide numerical proof of the quality of our machined products.

⑤ Are you capable of making VE/VA proposals?

There is a significant difference in the long-term value of a business partnership between a contractor who simply “machines parts according to the drawings” and one who “reviews the drawings and proposes ways to reduce costs and improve quality.”

For example, improvements such as “significantly reducing material costs and machining time by proposing the use of pipe stock for parts that were previously machined entirely from solid stock” or “reducing the number of parts and assembly labor by changing multiple parts to a single machined piece” can be achieved when the machining contractor is involved from the design stage.

This ability to make such proposals does not arise from technical expertise alone. It emerges only when deep knowledge of materials, machining experience, and an understanding of the customer’s product come together.

As a “trading company × manufacturer” hybrid, Tatsumiya Metal specializes in value engineering (VE) proposals from a materials selection perspective. We can offer practical, on-the-ground suggestions—such as “Is this material really necessary?” or “Using pipe stock could reduce costs by this much”—right from the design stage. This is a unique strength of Tatsumiya Metal, distinct from trading companies that merely sell materials or manufacturers that only perform machining.

Choose “We have a proven track record” over “We can handle it”

Finally, when selecting a subcontractor, I want to emphasize that you should place more trust in the phrase “we have a proven track record” than in the phrase “we can handle it.”

In the world of machining, any company can say “we can handle it” as long as they have the necessary equipment. However, whether they can consistently deliver stable quality, meet deadlines, and provide valuable proposals depends on their accumulated experience and organizational structure.

I believe a reliable subcontractor is one that can provide concrete examples, such as, “We have a track record of machining this material to this precision in these batch sizes,” or “We have solved this kind of challenge in this way.”

If you’re having trouble selecting a subcontractor for machining, please consult Tatsumiya Metal. From material selection to machining and inspection, we’ll work with you from a hands-on, on-site perspective.

Masamichi Okude, President and CEO, Tsumogiya Metal Co., Ltd.

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Tatsumiya Metal Co., Ltd.
[Headquarters] 570-0046
1-8-20 Nishitsutsumi-Hondori Nishi, Higashiosaka City, Osaka Prefecture
TEL: 06-6789-5831 FAX: 06-6789-5838
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