HL Parts | Ultra-high Precision Mechanical Machining Parts Manufacturer

Maximize part quality, reduce costs, and optimize designs using standardized tolerances on machined parts.

The concepts of part interchangeability and dimensional tolerances have become fundamental in manufacturing. However, improper application can lead to significant issues. For example, overly tight tolerances may require additional processes, such as grinding or EDM, which unnecessarily increase costs and lead times. On the other hand, tolerances that are too loose or incompatible with the mating parts can result in assembly issues, rework, or even make the final product unusable.

To avoid misuse of tolerances, this guide provides tips on how to correctly apply part tolerances in HL Parts and defines some of the commonly used annotations.

Standardized Tolerances for CNC Machining

Our production services at HL Parts can help you achieve the tightest tolerances required for custom CNC machined parts, even when they are non-standard.

* Please clearly indicate tolerances for nominal sizes below 0.5mm on your technical drawing.

Depending on the part geometry and material, we can usually achieve higher accuracy as long as you let us know your requirements. For these and other exceptions, please be sure to note this in the part design when uploading the file for a quote.

Also, please note that these are bilateral tolerances. If expressed in one-sided terms, standard tolerances will appear as +0.000/- 0.010 mm (or +0.010/- 0.000 mm).

All of these are acceptable, just like metric values, as long as you specify them in your design. To avoid confusion, stick to the “three-digit” dimensions and tolerances shown and avoid extra zeros in 1.0000 or 0.2500 inches unless there is a significant reason to do so.

Geometric dimensions and tolerances
This is another consideration. As mentioned before, we can accept GD&T tolerances. This provides a deeper level of quality control, including relationships between various part features as well as shape and fit qualifiers. Here are some of the more common ones:

• True Location: In the bracket example cited earlier, we plotted the hole location by specifying the X and Y distances and their allowable deviation from a pair of vertical part edges. In GD&T, the location of the hole will be determined from its true location in a set of reference datums, with the qualifier MMC (Maximum Material Condition) or LMC (Minimum Material Condition).

• Flatness: Milled surfaces are generally very flat, but some warping may occur once the part is removed from the machine due to internal material stresses or clamping forces during machining, especially on thin-walled parts and plastic parts. The GD&T flatness tolerance controls this by defining two parallel planes in which the milled surface must lie.

• Cylindricity: For the same reason that most milled surfaces are very flat and most holes are very round, the same goes for turned surfaces. Manufacturers use cylindricity, defined as two concentric cylinders within which the machined hole must lie, to eliminate this unlikely scenario.

• Concentricity: The rings on the bullseye are concentric, just like the wheels on a car are concentric with the axle. If a drilled or reamed hole must exactly fit a coaxial counterbore or circular boss, concentricity callouts are the best way to ensure this.

• Verticality: As the name suggests, verticality determines the maximum deviation of a horizontal machined surface from a nearby vertical surface. It can also be used to control the perpendicularity of the turning shoulder to the adjacent diameter or center axis of the part.

There are other considerations for GD&T including parallelism, straightness, contours, and angles; however, as with any other non-standard tolerances, they must be noted in the design at the time of upload.

Design highly complex machined parts faster and more efficiently with these tips.

The capabilities of CNC machine tools are increasing year by year. Power tool lathes can mill a variety of shapes and drill off-axis or radial holes—operations that once required separate trips to the milling department. The machining center is equipped with an indexing head and supports 3+2 processing, which can complete multiple sides of the part at one time. This is great news for designers and engineers. Not only can extremely complex parts be produced now, but they can be produced with higher quality, lower costs, and shorter lead times.

But that doesn’t mean everything will happen automatically—certain machining rules still apply. Failure to adhere to them can lead to costly rework and project delays. This design tip explores some key considerations that any part designer should know, including hole locations, mill depth features, threads and inserts, text, and part radius.

HL Parts features 5-axis milling or 3+2 milling, enabling the machine to clamp the bottom of a workpiece and machine its top and sides in one go. This type of milling can produce more complex parts, such as brackets with undercuts on the sides or deep irregular holes.

Like HL Parts’ milling centers, CNC turn-milling on high-speed lathes is capable of completing many complex parts in a single operation. Power tools and Y-axis capabilities allow us to turn the bolt, mill wrench flats, and drill a cross-hole for a safety wire. More complex examples might include a hydraulic piston with an alignment groove on one end, a fitting with an adjustable wrench hole in the surface, or a shaft with an external keyway. In some cases, it’s even possible to "turn" parts that are more orthogonal than circular.

Here are five elements to consider when designing complex parts:

1. Hole Location

   On-axis and axial holes on HL Parts’ CNC lathes have a minimum size of 1 mm and a maximum depth of 6 times the diameter. Radial holes should be at least 2 mm in diameter. Holes that go all the way through turned or milled parts are usually OK, but depending on part size, hole diameter, and material, the cutting tool may not have adequate reach. HL Parts will machine from each side if possible, but be sure to check your design analysis for potential limitations.

2. Deep Features

   External grooves on turned parts cannot be deeper than 24.1 mm or narrower than 1.2 mm. All other slotted milled features are generally the same size as drilled holes, but a good rule of thumb is to keep the depth less than 6 times the width of the feature. Leave at least 0.5 mm of wall thickness on adjacent material. Large flat and other milled surfaces depend entirely on part geometry in relation to available tool size. Deep ribs and grooves can be challenging, regardless of where they are made. Check your DFM analysis and send us a drawing if needed.

3. Thread Machining

   There is a lot of overlap in threading capabilities between HL Parts’ turning centers and milling centers. Generally, HL Parts can use threads from M3 x 0.5 to M10 x 1.25, depending on machine type and functional layout. Always check the thread guide for exact measurements and details, and ensure proper modeling of internal vs. external and milled vs. turned features. Coil and key inserts may be a better option in softer materials like aluminum or plastic.

4. Permanent Marking

   Complex aerospace and medical parts often require permanent marking. Recessed text can be time-consuming, so it’s better to use electrochemical etching or laser marking. If you must engrave text, keep it short and simple with a clean font. We recommend Arial Rounded MT font 14 points, 0.3 mm deep for soft metals and plastics, and Arial Rounded MT 22 points, 0.3 mm deep for hard metals.

5. Radius

   A common mistake on machined parts is sharp internal corners. HL Parts' turning tools typically have a nose radius of 0.032 mm, so any mating parts should consider this. The diameter of the milling cutter is reduced to 1 mm, which means the inside corner radius of any cavity will be slightly larger than half that. Milling with such small tools takes time and is limited to cavities no deeper than 9.52 mm. The best approach is to eliminate inside corners or allow the largest possible inside radii in the mating part design.

Final Note:

Failure to apply good design-for-manufacturing practices can make challenging machining operations more difficult and costly. While this may not matter much for prototypes, when the part goes into production, even small design flaws can cause significant cost waste. If you have questions about complex parts or part functionality, don’t hesitate to contact HL Parts at sales@hlparts.cn.

Higher-Volume Machining makes it easier to get lower costs, fast lead times, and finishing options.

HL Parts’ CNC machining is different from traditional manufacturing. Our process is fully automated – from CAD analysis to automated toolpaths and digital inspection – and we’re incredibly fast. This automation allows us to increase speed. Machining is also suitable for jigs, tools, fixtures, and other low-volume parts, allowing for flexibility and economy in part production. This tip covers the details of our high-volume machining capabilities, including pricing, lead times, finishing options, and more.

Machining to Meet Large Volume Requirements

At HL Parts, we’ve found a way to fill the production volume gap and address upfront costs and warehousing costs. With our vast machining capabilities of nearly 100 CNC machines, we can mill or turn parts at a day’s speed for high-volume part processing or for low-volume end-use part production, which reduces machining costs without increasing turnover or delivery time.

The nominal “break point,” the price break between part processing and production processing, is approximately 100 parts. Production machining can also help ensure part quality through FAI reporting, Certificate of Compliance (CoC) documentation, and certifications such as ISO 9001 and ISO14001.

Production machining does not offer the same economies of scale as molding or casting processes, especially at high volume levels (tens of thousands or millions). However, as machining throughput increases, the cost per part also decreases (low-volume production of tens to thousands). Production machining also solves warehousing and inventory issues, providing supply chain flexibility by producing parts on demand. In fact, in many cases, our customers are finding that our machining services now allow them to use a single-source supplier for everything from proof of concept to low-volume production to high-volume production.

High-Volume Processing Provides Supply Chain Flexibility

We have several key advantages, especially when you need to produce a large number of parts relatively quickly, or even in varying quantities. With our capabilities, we can produce more parts faster than other manufacturers. Our end-to-end process starts with design analysis and quotation. Upload your CAD model and get a free analysis and quote within hours. If you need a prototype, request a quick quote and get finished parts as fast as a day. When you’re ready to produce more parts, request a production quote and get parts in as little as fifteen days. Our production capacity and extensive material inventory ensure this quick turnaround. The entire production process from toolpath development to machining to finishing is handled in-house for maximum speed, quality, and process control.

Associated with flexible quantities, utilizing machining eliminates the high initial costs of mold or die production. Once you develop the toolpath, you can order machined parts in quantities as small as 100 pieces. On the other hand, if your end volume is high enough to justify molding or casting, you could use machining for bridge production and push your product out while you wait for the production mold, die, cast, or forge to be made.

Production Machining of Plastics

When production volumes are 1,000 or less, processing plastic may be cheaper than injection molding. Additionally, machining can produce parts that are difficult to form. These may include parts with uneven wall thickness or with wall thicknesses exceeding 0.150 in. (3.81 mm), often required as fixtures or wear plates.

As part size increases, the overall speed advantage of machining over injection molding increases at moderate volumes. Additionally, machining plastic eliminates the risk of dents, warps, and weld lines that can occur in molded parts, and machined parts don’t require draft angles like injection-molded parts.

In some cases, engineers might consider using 3D printing to achieve these yields, but the fact that machined parts are cut from solid blanks gives them several advantages over 3D printed parts. Because machined parts are not layered, they may have higher physical integrity than printed parts. They can be cut from materials that 3D printers cannot use and can be machined to a smoother surface than printed parts.

Plastic production materials used by HL Parts for processing include ABS, acetal, acetal copolymer, PEEK, and PEI.

For low to medium volumes, machining end-use metal parts offers significant advantages over die casting. Like with plastics, machining can be faster and more cost-effective than casting at the right volumes.

Machining can start immediately, while die casting requires the production of hardened steel molds, a slow and costly process. Additionally, there is more metal available for machining compared to die casting. Die casting leaves a rough surface, similar to that of cast iron cookware, which can be smoothed through machining, but this adds time and cost.

Moreover, the finished product from die casting is often not as strong as machined blanks. Die-cast metal can be porous, brittle, and prone to elongation, making machining a preferable choice even if casting might seem like a more cost-effective option.

HL Parts works with materials like Aluminum 6061, Aluminum 7075, Steel 1018, and Steel 4140 for metal production.

Once the part is machined, HL Parts can complete the production process with a variety of finishing options, depending on the metal. These include:

• Type II, ROHS Compliant, Class 1 (clear) and Class 2 (black) anodizing

• Type I, Type II, Class 1A, and Class 3 Chromate Plating

Anodizing and chromate plating are effective methods of protecting machined metal parts from corrosion, as well as enhancing their overall appearance. Our anodizing process is RoHS compliant, using environmentally friendly materials that contain virtually no hazardous substances such as mercury, lead, cadmium, hexavalent chromium, PBB, or PBDE.

Chromate plating differs from anodizing in that it doesn't add metal to the surface. Instead, it's a conversion coating that alters the properties of the metal surface itself, providing excellent corrosion protection.

HL Parts also offers CNC machining services with various threading options. These include UNC, UNF, NPT, MC, UNC STI, and UNF STI, available in standard, tapered, metric, and standard helical threads.

For additional support with design or custom requests, HL Parts' engineers are available for consultation via email at sales@hlparts.cn.