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Identifying the Right Material for Machining

The raw metal or plastic used for parts is just as important as how the parts are machined; selecting the wrong one could unnecessarily balloon part costs. For instance, superalloy and darling of the aerospace world, titanium, is hard to machine, and parts made of it will almost certainly cost more than ones made of aluminum or stainless steel. The point? If it’s not truly needed, opt for a more inexpensive metal. Polyether ether ketone (PEEK), the Superman of polymers, is strong enough to replace metal in certain applications but prepare yourself for some sticker shock, as PEEK is typically around five times the price of other high-performance thermoplastics. Other technical considerations that will help you choose a suitable material for your part’s application include specific measurements such as tensile strength, heat deflection, and overall hardness.

2023

05/31

Designing for Accurate Threads

Adding threaded features to machined parts can also be a challenge. Internal threads can be created with a tap, a cutting tool that closely resembles the bolt or fastener that will at some point be screwed into the workpiece, or a special cutter known as a thread mill. Either way, deep threads are difficult for the same reason that deep holes are difficult, namely chip evacuation, and in the case of thread milling, radial cutting pressures. In most cases, a thread depth of twice the diameter provides plenty of strength, and costs less to produce. If this is insufficient, consider using inserts such as Heli-Coils or key inserts to bolster thread integrity, especially on plastic CNC parts. Finally, thread tolerances are specified with an “H” limit, the most common being H2 or H3. The latter has a tighter tolerance, however, and is therefore a bit costlier to produce, so the best bet is to call out an H2 for all but critical applications.

2023

05/31

Navigating Sharp Corners

In machining, corners can be tricky, too. Say you’re designing an electronics housing for a product. On one side of the part, you need a pocket, inside of which will sit a 2-inch square circuit board. Someone unfamiliar with machining practices might design a square-cornered pocket, one just slightly larger than the board itself so as to provide clearance. Not a good idea. Those square corners will cost you dearly, as the only way to generate them is to burn them out with EDM, a machining process common in the injection molding and tool and die industries. Space permitting, consider oversizing the pocket so that an end mill can be used instead—in this example, a 1/2-inch tool might be appropriate, which means adding half its diameter (1/4-inch) on all sides of the circuit board, plus whatever additional clearance is needed to fit the circuit board. Another option is to cut reliefs or “dog ears” at all four corners. This might give the pocket a cloverleaf or T-shaped appearance but will make machining much easier. There’s plenty more to think about. Just as deep pockets are a no-no with milled parts, overly deep grooves can be challenging to turn, and long, slender shafts can be tricky, too. Breaking the edges on turned parts with a radius or chamfer is no big deal, but requires an extra machining step on ones that are milled. Each has its own advantages and may affect the appearance of the finished product, as well as its cost.

2023

05/31

Drilling Deep Can Be Tricky

Holemaking is the most commonly performed of all machining operations. It’s most often done with drill bits that are a little different than the ones you find in any hardware store. As holes get deeper (say five to six times the drill diameter) evacuating the metal “chips” formed during any machining operation becomes increasingly challenging. If your product design requires deep holes, so be it, just know that the deeper they are in relation to their diameter, the more expensive the part or parts will be.

2023

05/31

Use Caution with Thin-Walled Parts, Too

2023

05/31

Use Caution with Tall Walls and Narrow Pockets

Cutting tools are made of hard, rigid materials such as tungsten carbide and high-speed steel (HSS). Despite this, they do deflect ever so slightly when subjected to machining forces, a phenomenon that becomes increasingly troublesome the farther out the tool protrudes from the toolholder—depending on the operation, carbide cutters are good to a “stickout” of roughly four times the tool diameter, maybe a bit more on soft materials, while HSS tools become problematic at about half that distance. This leads to chatter (an ugly rippled surface), difficulty meeting part tolerances, and poor tool life. The lesson for a designer? Watch out for deep, narrow pockets, or part features situated alongside tall walls, lest cutter deflection create problems for those doing the machining.

2023

05/31

Texting or LOGO going ahead

Machined text looks really cool. It’s great for permanently marking parts with numbers, descriptions, and company logos. The problem is, it’s fairly expensive to produce. Each character must be traced with a tiny cutter, consuming valuable machine time. And don’t even think about raised text, as this means milling away everything that doesn’t look like a letter or number. Better options do exist, including laser marking, silk printing, and etching.

2023

05/31

Consider Part Tolerances—When Necessary

Making parts more accurate than is absolutely necessary is another common mistake. When tolerances are tighter than needed, the machinist may be forced to modify the part program, use a special cutter, or even perform a secondary operation to meet that tolerance. Whenever possible, it’s better to stick with the default “block tolerances” called out on any part drawing, or ask your machining partner for advice as to what’s reasonable.

2023

05/31

Keep it Simple to Make the Actual Production Easy

One of the most common mistakes even experienced design engineers and product developers make is to overly complicate their part designs. Consider breaking up single-piece, multi-faceted “super parts” into simpler components that can be bolted, glued, or screwed together. Unless required for functionality, avoid swept surfaces, as these generally require lengthy, more costly machining with a ball-nose milling cutter. Design parts with features that can be cut from one side wherever possible. This avoids multiple operations and possibly special fixturing, as well as having to use a more expensive five-axis machining center or 6-Axis capabilities.

2023

05/31

Optimizing Part Design for Machining

If you’re someone who designs parts for a living, you might be wondering: Who cares? As long as I get my parts on time, and at a reasonable price, it doesn’t matter to me how they’re made, right? Well, not necessarily. Just as you need to have a basic understanding of how a motor vehicle works to arrive safely at your destination, a reasonable grasp of machine tool technology is necessary for any parts designer. This knowledge is especially important when working with a digital parts supplier such as PFT, which can drastically accelerate the machining process—and often reduce costs—if certain design guidelines are followed.

2023

05/31

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Shenzhen Perfect Precision Product Co., Ltd.

products

CNC Turning Parts

CNC Milling Parts

CNC Turning Milling Parts

CNC Machined Aluminum Parts

CNC Stainless Steel Parts

Machining Plastic Parts

CNC Brass Parts

lyn@7-swords.com 86-189-26459278

Building 49, Fumin Industrial Park, Pinghu village, Pinghu town, Longgang District, Shenzhen City, Guangdong Province, China

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