Precision Metal Cutting for 2-Axis Cutoff: How to Achieve the Best Results for Your Close Tolerance Small Metal Parts

August 15, 2018 Joshua Jablons

Table of Contents

Introduction
What are your options for 2-axis cutoff of metal parts?
How do you choose among the precision metal cutting options?
How can you get a more accurate quote?
How do you choose a precision metal cutting partner?
What should you do to ensure quality before production starts?
Conclusion

 



Precision Metal Cutting for 2-Axis Cutoff : How to Achieve the Best Results for Your Close Tolerance Small Metal Parts

Introduction

When you’re a manufacturer in need of small metal parts, especially in large quantities,  precision metal cutting offers multiple highly effective options for 2-axis cutoff. Where the simple goal is tight tolerance rods, tubes, or extrusions cut to the correct length and free of burrs, there are many different machines that are capable of delivering great results.
 
But how do you choose a cutting method and ensure that it gives you the results you need for your specific application? In a perfect world, determining the right precision metal cutting method for your close tolerance components would be a snap — a relatively easy choice among the many decisions you must make before production begins.

The reality is the different precision metal cutting options vary in characteristics and appropriate applications, making the choice not quite so easy. And the wrong decision can result in production delays, material waste, or other quality issues that can cost you time and money.

Let’s take take a broad look at some of the factors that go into choosing a precision metal cutting method and how to gets the best results. We’ll discuss:

  • Some common options for 2-axis precision metal cutting
  • How to compare methods and choose the best one for your metal cutoff job
  • Ways to create a quote request that reflects what you really need — which will help you get a more accurate quote
  • How to choose a vendor for your precision metal cutting job
  • Ways to help ensure quality in the production process

What are your options for 2-axis cutoff of metal parts? 

For burr-free, 2-axis cutoff of parts, we’ll take a quick look at eight precision metal cutting methods. Ranging from fast and simple to slow and specialized, they are:

  • Shearing
  • Cold sawing
  • Abrasive cutting
  • Electrochemical cutting
  • Automatic lathe cutting
  • Waterjet cutting
  • Wire EDM cutting
  • Laser cutting

Of course, there are other ways of cutting metal. However, none are ideal for simple 2-axis cutoff, which is essentially taking something long and making it short. Even among the eight methods of precision metal cutting we will look at below, there are respective benefits and drawbacks depending on the job.

Shearing

Also known as die cutting or multi-slides, the metal shearing process is often used to cut simply shaped parts, such as rods and tubes, quickly and inexpensively. While there are many different types of shears, the basic process for precision metal cutting is the same: It is the application of extreme pressure by a moving blade (the shear or punch) pushing the workpiece against a fixed blade (the die or anvil). The cutoff of the workpiece is made from one end to the other, not all at once; this reduces the amount of force required to cut the metal.

With improvements in technology, high-volume shearing has extended beyond its CAM-driven roots. As with the other precision metal cutting methods we’ll look at, shearing has benefited from advances in CNC, which allows cutting processes to be automated.

Shearing at a Glance

Pros

Cons

Fast and cheap

Most metals

No kerfs

Any diameter

High volume/speed

Deformations/Burrs

Crushed and closed tubing

No very short cuts under 0.125” (3.175 mm)

Less cost-effective for short runs

Diameter/Thickness impacts volume/speed

For more details see our blog on the pros and cons of shearing

Cold Sawing

Cold sawing is a method of precision metal cutting that uses a circular blade to remove material in a process that “captures” the heat generated by cutting and transfers it to the chips created by the saw blade. This is what keeps the workpiece, as well as the saw blade, cold — hence, the name “cold sawing.” This heat transference is what enables cold saws to perform cutoff without damaging any protective coating on the workpiece.

During cold sawing, the metal is removed in a shearing action by the saw teeth as the blade turns and a feed mechanism moves the blade forward. To achieve the best results with this precision metal cutting method, the appropriate number of saw teeth, blade type, cutting speed, and feed rate must all be carefully selected based on the type and size of material being cut.

Cold Sawing at a Glance

Pros

Cons

Fast and high volume

Tight tolerances

Long blade life

No sparks, discoloration, or dust

Large kerfs

Heavy burrs on rods and small tube IDs

Potential saw teeth damage

No very short lengths or small diameters

For more details see our blog on the pros and cons of cold sawing

Abrasive Cutting

Abrasive cutting uses a very thin, non-reinforced abrasive wheel to remove material through grinding and erosion by tiny cutting particles, rather than by cutting with saw teeth. Modern technology has advanced this abrasive method of precision metal cutting to where it produces high material removal rates and tight tolerances.

That means thin-wheel abrasive cutting lends itself to applications requiring clean cutoff at high volume and at a moderate price. The abrasive cutting method is also much faster than other precise but slow methods such as wire EDM and laser cutting.

Together, the characteristics of abrasive cutting make it the ideal precision metal cutting method for 2-axis cutoff of rods, tubes, extrusions, and other small metal components.

Abrasive Cutting at a Glance

Pros

Cons

All metals

All small diameters under 1” (25.4 mm) for solids and 3” (76.2 mm) for tubes

Self-dressing wheels

Small kerf

Burr-free

Tight tolerance

Smooth end finish

Cannot cut large diameters over 1” (25.4 mm) for solids and over 3” (76.2 mm) for tubes

Raw material must be in straight lengths (cannot be cut from a spool)

Non-diamond wheels cannot cut carbide

For more details see our blog on the pros and cons of abrasive cutting

Electrochemical Cutting

Similar to thin-wheel abrasive cutting, electrochemical cutting (also called ECC) doesn’t cut with saw teeth. Instead, the ECC precision cutting method combines electrochemical grinding and erosion to produce a burr-free, shiny cut surface on electrically conductive materials. 

This precision metal cutting process involves a positively charged workpiece in a conductive fluid. The cutoff occurs as the workpiece material is eroded by a negatively charged conductive grinding wheel, which never comes in actual contact with the workpiece. So, material removal is the result of the chemistry and conductivity of the process itself and of the workpiece material.

ECC at a Glance

Pros

Cons

Burr-free, shiny surface finish

Ferrous metals and stainless steel

Very long lengths

Tight tolerance

Special chemicals needed for each metal

ID burr contamination risk

Wide kerf

For more details see our blog on the pros and cons of ECC

Automatic Lathe Cutting

The automatic lathe is a precision metal cutting method designed for shaping pieces of metal, usually from cylindrical bars. The workpiece is held and rotated by the lathe while a tool moves into the workpiece to perform the cutting action. Automatic lathes are often used to produce screw threads, tapers, drilled holes, knurled surfaces, and chamfers.

An automating lathe is also use for parting off — the process of using a blade-like tool to cut off a workpiece while it is held in the lathe. Parting off can be used for 2-axis cutoff of lengths of rod or tubing. However, it is most often used to cut off finished workpieces after other machining processes have been completed.

Automatic Lathe Cutting at a Glance

Pros

Cons

Cutoff of rods and tubes
Non-hard metals

Utilize existing equipment

Designed for complex shapes

No extrusions

No bundling

Burrs and pips

For more details see our blog on the pros and cons of automatic lathe cutting

Waterjet Cutting

Waterjet cutting of metal uses a high-pressure stream of water in combination with an abrasive. This precision metal cutting method works by directing the stream onto a narrow line on the workpiece and removing material by eroding it. The addition of abrasive at the nozzle allows the waterjet to be switched between water-only and water with abrasive as needed.

The classic precision metal cutting applications for the waterjet method are complex shapes cut out of large-scale, flat metal or composite material sheets, including very thick ones.

Waterjet Cutting at a Glance

Pros

Cons

Complex shapes

Metals and composites

Water-only or water with abrasive

No heat affected zone

Tolerances as close as ± 0.005" (0.127 mm)

Difficulty cutting voids and bundles

End cut defects

Tapered kerfs

Surface finish hazing

Abrasive issues

For more details see our blog on the pros and cons of waterjet cutting

Wire EDM Cutting

Wire EDM cutting uses controlled sparks along a single strand of metal wire to remove material from electrically conductive materials. Repeating rapidly — up to 250,000 times per second — the electrical charges erode the workpiece along a cut line. The wire diameter and material varies with the application; for instance, zinc-coated brass wires cut more quickly, while stronger wires (such as molybdenum) cut more accurately.

For precision metal cutting, wire EDM works especially well for cutoff of small solid parts with tight tolerances at high volumes. It can cut conductive materials in a range of hardnesses, but not composite or dielectric coated materials.

Wire EDM Cutting at a Glance

Pros

Cons

Precise and versatile

Small, solid diameters

Any conductive metal

No burrs

Small kerf

High Ppk/Cpk

Very slow

No length cuts under 0.125” (3.175 mm)

No cutting of tubes

No non-conductive composites

No dielectric coatings

Rough surface finish

For more details see our blog on the pros and cons of wire EDM

Laser Cutting

While laser cutting is versatile and precise, it is also the slowest and most expensive of the precision metal cutting methods we’re comparing. 

Laser cutting uses a focused laser beam directed at a material, which then melts, burns, vaporizes, or is blown away by a jet of gas. There are a growing number of laser cutting machines that vary in laser beam delivery, speed of cutting, and capacity. For 2-axis precision metal cutting, lasers can produce a small kerf and can cut to a tight tolerance. However, both kerf and tolerance are dependent on the material thickness.

Laser Cutting at a Glance

Pros

Cons

Versatile and precise

Small kerf

Tight tolerances

Very slow and expensive

Rough finish on thicker parts

Cannot cut multiple parts at one time

Max 0.5” (12.7 mm) thickness

Damage from heat stress

For more details see our blog on the pros and cons of laser cutting.

As you can see, across the spectrum of precision metal cutting methods for 2-axis cutoff of parts, no one method is suited to all dimensions, materials, tolerances, or capacity, speed, and cost needs. So, how do you make the right choice for your requirements?

In the next section, we’ll  look at some factors that go into narrowing down the choices.

How do you choose among the precision metal cutting options?

As you saw in the previous section, there are different benefits and drawbacks to each precision metal cutting method for 2-axis cutoff. The choice ultimately comes down to the requirements of the specific job you want to do.

Your challenge is to balance the trade-offs with how well suited a precision metal cutting method is to your metal cutoff needs. You can get closer to the right solution for you by considering some key parameters.

What kind of part do you need to cut?

It may seem obvious, but it bears repeating: Consider what type of part you will be working with — rods, tubes, or extrusions — before you choose a 2-axis precision metal cutting method. Not all methods excel at all part types. For example, while wire EDM is precise, it is only good for solids and can’t be used to cut tubing. Finding that out after you have already specified a particular process could cost you valuable time and money.

What type of metal do you want to cut?

The physical properties of metals have a tremendous impact on the effectiveness of the different precision metal cutting methods. For example, you may need to consider factors such as the hardness or softness of the metal you will be cutting. Each cutoff method will produce very different results depending on whether you are cutting stainless steel, titanium, high nickel-content ferrous alloys, nickel-titanium alloys (such as nitinol, or NiTi), or tungsten.

Other general physical properties of metals that may have an effect on how well a precision metal cutting method performs include heat conductivity, electrical conductivity, ductility, malleability, strength, and melting point.

What are your part dimensions?

At Metal Cutting Corporation, where we specialize in small precision metal parts, we typically talk about 2-axis metal cutoff capabilities terms of lengths, as follows:

  • Very short = under 0.125” (3.175 mm)
  • Short = 0.125” (3.175 mm) to 1” (25.4 mm)
  • Long = 1” (25.4 mm) to 1’ (304.8 mm)
  • Very long = 1’ to 6’ (304.8 mm to 1828.8 mm)

Some precision metal cutting methods have real limitations when it comes to part length. Just imagine the consequences of factoring in a particular method that excels at one aspect of your spec but can’t produce the length you need.

Depending on the part you need to produce, you may also need to consider dimensions such as the ID and OD, or inside diameter and outside diameter, as well as wall thickness. For solid parts, only the OD is relevant; here at Metal Cutting, we typically are looking at ODs from 1” (25 mm) maximum to 0.001” (0.025 mm) minimum. For parts such as capillary tubes, which require exceptionally clean, thin walls, some 2-axis precision metal cutting methods won’t work for such small IDs and delicate wall thicknesses.

What part tolerance do you have to achieve?

Determining the tolerance you need and the amount of variation that is acceptable is an important step in choosing a production method. For 2-axis cutoff, all of the processes we talked about above are good for difficult-to-achieve tolerances. However, some precision metal cutting methods are more effective in certain tolerance ranges.

In addition, there is a relationship between tolerances and cost. Extending a tolerance out by just a single decimal point can increase the cost by a factor of two or three. Unless a tight tolerance is within the nominal capabilities of the particular precision metal cutting process you want to use, asking for that tight a tolerance will increase the cost of production. 

For more on how to get an accurate quote, check out our guide to fine tuning your quote request to your maximum advantage

What other cutoff considerations do you have?

Similarly, characteristics such as the kerf — the width of material a process removes — must be considered. In general, the minimum amount of kerf is the goal. The more precise the cutting method is, the smaller the kerf.

Since it can drive up the cost of materials, it is important to keep in mind that kerf width varies from one precision metal cutting method to the next. In addition, factors such as material hardness or thickness can affect the kerf for each method.

What are your production/capacity requirements?

One of the most overlooked considerations when choosing a precision metal cutting method is the relationship between volume, speed, and cost. By prioritizing and clearly stating your requirements in these areas, you can determine which method is best for your part volume and timeline/deadlines.

So, basically, you need to determine whether a precision metal cutting method is cost-effective for the volume you need and how quickly you need it.

How do the parameters and cutting methods come together?

The efficiency of any precision metal cutting method depends on the how well the method is matched to the work at hand. For example, if your task is to produce short lengths of corrugated shaped extrusions for chemical applications or even HVAC systems, you would not want to use shearing, which would damage the extruded profile. However, since a jagged end finish and some burrs can be acceptable for this application, you could use cold sawing for fast cutoff. 

On the other hand, you would not want to use cold sawing for thin stainless steel tubing with a 0.002” (0.050 mm) thick wall, due to the risk of a torn wall and burrs on the ID and OD. Instead, you could choose thin-wheel abrasive cutting. Its abrasive embedded wheels will remove, within the width of the kerf, only the metal from the wall without creating a burr, albeit wearing away the wheel itself at a rate faster than a saw blade.

The table below provides a quick and easy overview of the pros and cons for comparing each of the eight cutting methods we’ve discussed.

Table 1: Comparison of 8 Precision Metal Cutting Methods

Cutting Method

Advantages

Disadvantages

Metal Shearing Process

  • Fast and cheap
  • Most metals
  • No kerfs
  • Any diameter
  • High volume/speed
  • Deformations/Burrs
  • Crushed/Closed tubing
  • No very short cuts under 0.125” (3.175 mm)
  • Less cost-effective for short runs
  • Diameter/Thickness impacts volume/speed

Cold Sawing

  • Fast and high volume
  • Tight tolerances
  • Long blade life
  • No sparks, discoloration, or dust
  • Large kerfs
  • Heavy burrs on rods and small tube IDs
  • Potential saw teeth damage
  • No very short lengths or small diameters

Abrasive Cutting

  • All metals
  • All small diameters under 1” (25.4 mm) for solids and 3” (76.2 mm) for tubes
  • Self-dressing wheels
  • Small kerf
  • Burr-free
  • Tight tolerance
  • Smooth end finish
  • Bad for large diameters over 1” (25.4 mm) for solids and 3” (76.2 mm) for tubes
  • Raw material must be in straight lengths (cannot cut from spool)
  • Non-diamond wheels cannot cut carbon

Electrochemical Cutting

  • Burr-free, shiny surface finish
  • Ferrous metals and stainless steel
  • Tight tolerance
  • Special chemicals needed for each metal
  • ID burr contamination risk
  • Wide kerf

Automatic Lathe

  • Cutoff of rods and tubes
  • All/Most metals
  • Repurposes existing equipment/capability
  • Designed for complex shapes
  • No extrusions
  • No bundling
  • Burrs and pips

Waterjet Cutting

  • Complex shapes
  • Metals or composites
  • Water-only or water with abrasive
  • No heat affected zone
  • Tolerances as close as ± 0.005" (0.127 mm)
  • Difficulty cutting voids and bundles
  • End cut defects
  • Tapered kerfs
  • Surface finish hazing
  • Abrasive issues

Wire EDM Cutting

  • Precise and versatile
  • Small, solid diameters
  • Any conductive metal
  • No burrs
  • Small kerf
  • High Ppk/Cpk
  • Very slow
  • Subject to conductivity and correct settings
  • No very short cuts under 0.125” (3.175 mm)
  • Bad for tubes
  • No non-conductive composites
  • No dielectric coatings
  • Surface finish

Laser Metal Cutting

  • Precise and versatile
  • Small kerf
  • Tight tolerances
  • Very slow and expensive
  • Rough finish on thicker parts
  • Cannot cut multiple parts at one time
  • Max 0.5” (12.7 mm) thickness
  • Damage from heat stress

Once you’ve chosen the precision metal cutting method you think best matches your job requirements, it’s time to put what you want and need into an RFQ. So next, we’ll look at ways to use your requirements to get a more accurate quote.

How can you get a more accurate quote?

The fundamentals of parts sourcing — tolerances, dimensional accuracy, and materials — can be very complex, especially when we are talking about parts that are small. Creating a quote request that reflects what you really and truly need will go a long way in helping you get a more accurate quote for your precision metal cutting job.

Specifying your requirements as thoroughly as possible in the areas of tolerances, dimensions, and materials will ultimately help you get a quality product. And since the quote you receive will also form the basis of your vendor partnership, you want to make sure you’re starting the process with an accurate statement of what you need.

Below are some quick tips to help you prepare your quote requests for precision metal cutting — and not only for 2-axis cutoff, but also for any metal machining, finishing, or fabrication project.

Don’t over-engineer.

It an ideal world, a tighter tolerance is always best. However, it is important to be realistic about the tolerances you specify for precision metal cutting. Depending on the how the part will be used, you may not need to hold the very tightest tolerance possible on a given machine, driving up the cost of the part unnecessarily.

Decide which dimension is most critical.

By looking at where a part will go, how it will interact with other parts, and what it needs to do, you can distinguish between critical and non-critical tolerances. When you have one part with different attributes that require tolerances — such as both a diameter and a radius — you need to decide which dimension is more critical.

Save your tight tolerance for your most critical dimension.

It’s probably the one that will ultimately determine how well the part will function in its end application. And the tighter tolerance is the one that determines what type of machine and tools will be used — and therefore, drives the cost of your part. 

Sometime a single part has an easily met, loose tolerance on one dimension and a tight tolerance in another dimension, making the part more difficult to produce. Often these conflicting tolerances require a compromise. For example, you might need to ask for a tighter length tolerance in order to hold a tight diameter. The good news is that adjusting the one tolerance slightly can help you achieve your most critical dimension.

Include your dimensions and tolerances on an engineering drawing.

An engineering drawing, with callouts for GD&T tolerances and all of the part dimensions, is a vitally important part of your request for a precision metal cutting quote. This is equally true whether you are working with a new vendor, creating a new part, or looking to make improvements to an existing part.

Related blog: Geometric Tolerancing in Parts Manufacturing

Describe your part characteristics in detail.

For instance, if some burr is acceptable, don’t just say “Some burr allowed.” Provide a measurement for the maximum burr allowed. If you have a profiled part with diameter steps, provide the minimum and maximum inside corner breaks allowed. If some surface defects are permitted, specify how deep any allowable lines may be. 

Specify the calibrated instrument used to measure your parts.

Calibration of measuring instruments helps to ensure that devices are accurate and reliable, and that their measurements are traceable to accepted standards. It is important to make sure you and your precision metal cutting vendor not only use the same type of measuring devices, but also that the devices that are correctly cross-calibrated.

Tell your vendor how the part will be used.

Understanding the end application for your metal part can help your vendor make recommendations regarding which precision metal cutting method to use or what metal might be required — such as a medical-grade stainless steel for a part will be used in a medical device.

Specify your raw material and its source.

Be aware that if your precision metal cutting vendor has to provide the raw material for your parts, that increases their costs and, in turn, your quoted price. But if you can provide the raw material, that puts you in control of the sourcing and exactly how much you want to spend. But in either scenario, include the size, grade, and quantity of the material you need to cut, as well as the source.

Be specific about quantity, too.

Part quantity has an impact on pricing, delivery time, minimum charges, and other aspects of building a quote for precision metal cutting. Being as thorough as possible in your request will help your vendor provide a realistic quote. Is it a one-time job or ongoing? How many pieces will you need to cut on an hourly, daily, weekly, or monthly basis? Will they be long production runs, short runs, or individual cuts? Will your quantity start small and increase in the future?

Include your targeted deadline and pricing.

Of course, everyone wants their parts as soon as possible and as affordable as can be. And sometimes, fast and cheap are necessities. But since a rush order means added cost, providing a realistic deadline will help your vendor work with you to come up with a production proposal that meets your needs without busting your budget. Likewise, knowing your target price (or a ballpark figure) will help your vendor recommend a method and timeframe that are practical for your budget and your metal cutting needs.

Learn more! Check out our complete guide to RFQ success.

By putting time and effort into creating a complete and accurate RFQ for precision metal cutting, you can help to ensure that you and your vendor will be working together toward a shared goal: the very best quality precision metal parts for your application. Speaking of which — up next are some tips for choosing the best partner for your metal cutting project.

How do you choose a precision metal cutting partner?

Picking the right partner for your 2-axis cutoff will help you get the quality results you want plus great customer service for your precision metal cutting needs. Being quoted a great price is not enough: You want to be sure your vendor can deliver the best product, on time and on budget. So, how do you begin to choose? 

Ask if the vendor is ISO 9000 certified.

ISO 9000 certification establishes quality management standards for customer focus, leadership, engagement, process approach, improvement, decision-making, and relationship management. When a precision metal cutting company is ISO 9000 certified, it shows you that the organization has invested in their quality management system (QMS) and in having those QMS practices verified by an independent, accredited auditor.

Ask about their metal cutoff expertise.

Look for a precision metal cutting partner that has expertise in the material you want to use. Different vendors may be more experienced in cutting certain materials, such as non-ferrous metals like tungsten and molybdenum, stainless steel, nickel- and titanium-based alloys, or other specialty metals.

Depending on your parts and your application, ask a prospective partner about their track record in:

  • Producing parts that are free of burrs and have minimal kerf
  • Cutting different diameters to meet the need for a range of part sizes
  • Cutting thin tube walls, such as 0.001” (0.025 mm), without deformation
  • Cutting composites or coated metals without any deformation or damage

For small diameter metal cutoff, naturally you want to ask about the ability to deliver burr-free results and tight tolerances on the part lengths that you need. You want a precision metal cutting vendor that can handle complex metrologies and meet demanding dimensional requirements. And you want a partner that produces results that are not just accurate, but also repeatable.

Ask about their metal cutting equipment.

It’s a good idea to work with a precision metal cutting company that offers a choice of cutting options, equipment, and tools available in house. This provides greater flexibility in the type of metal you can use and even the size (or sizes) you need. Having everything in house can also save you startup time and cost.

Ask potential partners if their precision metal cutting equipment has advanced features designed to enhance precision and provide the ability to customize the process. For instance, programmable operation controls provide flexibility for production setup and increased changeover speed. Features such as computerized cutting speeds and feeds, as well as linear in-feed encoding, can help to maintain process accuracy and hold tight tolerances.

For small diameters and a large number of cutoff metal parts, ask about the ability to bundle materials for greater process efficiency and cost effectiveness. For tubing, ask if the vendor uses mandrels for supported tube cutting, to prevent burr and end deformation.

Ask about the vendor’s capacity.

Of course, you want a partner that has the capacity to handle your order volume and deliver the number of cutoff metal parts you need, on schedule and on budget. Also ask how much lead time the vendor needs, to get a sense of how quickly a job can be set up.

Choosing the best vendor for your precision metal cutting requirements may be the most important decision you’ll make. The right partner will work with you and go the extra mile to make sure to make your project is a success. That’s why we encourage you to ask all the questions you need to in order to make sure you're picking the best possible partner for you — one that will deliver quality metal parts and responsive, personalized service.

Once you’ve picked a precision cutting method, gotten a quote, and selected a partner, you’re ready to launch into production, right? Well, not quite . . . There is still one more important step we recommend and will discuss below  — and that is, putting in place some agreed-upon quality control measures before the job starts.

What should you do to ensure quality before production starts?

In addition to making sure your precision metal cutting partner is ISO 9000 certified and follows stringent quality practices, you can and should establish some other vital QC practices before your metal parts cutoff begins. After all, if you have gone to the trouble of determining the correct dimensions and tolerances for your precision metal cutting project, it makes sense to also specify how you will verify the results.

Agree on your inspection method up front.

Ensuring a quality end result requires thinking about how you and your precision metal cutting vendor will determine whether the finished part meets your specifications. Not only that, but the inspection method you decide to use should be included in both your RFQ and your part specifications.

With small metal parts often produced in quantities of thousands or millions, sampling plans are a common method of inspection in precision metal cutting. At Metal Cutting Corporation, every project usually begins with a sampling plan that spells out exactly how we will inspect a customer’s metal parts. Our sampling plans include an associated Acceptable Quality Level (AQL) and Index Value; they determine how many randomly selected parts in each lot will be inspected.

We almost uniformly recommend using AQL 1.0 c=0, which is a zero acceptance sampling plan. Basically, that means that if one defect is found among the sample size, the entire lot is rejected or subject to 100% inspection. In our experience, AQL 1.0 c=0 enables us to deliver acceptable quality levels while allowing us to inspect fewer parts and reduce the cost of inspection.

Agree on the inspection tools you’ll use, too.

It is critical to make sure you and your precision metal cutting vendor agree not only what will be measured, but also how. This is especially true with very small precision metal parts, where it may not be possible or practical to measure a part for its actual value. In these cases, the tiny part is usually inspected using a pass-fail tool such as pin gages.

For example, you don’t want to be in a situation where you are measuring the ID of finished parts using a pin gage, but your precision metal cutting vendor is using optical measurement to inspect the part IDs.

Don’t just agree — put it in writing.

Whatever inspection method you choose, your RFQ and specs should also include any calibrated measuring devices that will be used. For instance, there are different classes of small pin gages with different tolerances attached to them, based on the tolerance allowed in the manufacturing process of each pin.

The smaller the part, the more the tolerance of the pin gage matters. A tighter tolerance pin gage such as Class XXX will give you a straighter gage that is more uniform throughout its length. This make the XXX gage more accurate for checking critical dimensions such as the ID of a small diameter, tight tolerance tube.

Make sure you are calibrating to the same standards.

Customers, suppliers, and manufacturers across the precision metal cutting industry all calibrate the devices they use to take measurements. A device is typically calibrated to NIST-traceable standards in order to ensure consistency, accuracy, and reliability.

Here at Metal Cutting, we routinely calibrate the pin gages and other tools we use to inspect the precision parts we produce. In addition, the tools that we use to calibrate other tools are themselves sent out to be calibrated. In that way, we can be sure our inspections use tools that are traceable to NIST standards.

Working with your vendor to spell out and agree on exactly how your parts should be inspected, including the calibrated tools and procedure to be used for measurement, you can smooth the precision metal cutting process and help to ensure a quality final product.

Conclusion

As you can see, many, many different variables go into choosing a precision metal cutting method and partner — so many, in fact, that we could not possibly cover all of the possibilities in an overview such as this! However, it is our goal that the information presented here provides a basis for comparison as you begin to look at your precision metal cutting options.

In conclusion, we’d like to leave you with our best advice for achieving a successful and satisfying outcome in precision metal cutting — and that is, to always take the time to:

  • Carefully consider all of your project’s distinctive variables and special challenges
  • Include every detail you can think of in your RFQ and specifications
  • Ask your potential vendor some questions — then ask some more
  • Partner with a precision metal cutting company that has the flexibility and willingness to work with you to find the best solution for your 2-axis part cutoff and other precision metal cutting needs

 

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