positioning pin
Welcome back to our "What the Heck" series, where we discuss some of the unique fasteners and electronic hardware that manufacturers use when designing and assembling their products. Today, we will introduce you to dowel pins.
What is a positioning pin?
If you've ever shopped at IKEA or assembled furniture yourself, you're familiar with the nail-shaped unthreaded wood dowels, also known as dowels, used to connect pieces together.
For manufacturing purposes, dowels are solid, headless, cylindrical straight metal pins with a centerless ground finish. Often hardened and manufactured to precise fractional diameters and lengths, dowel pins come in a variety of sizes, styles, designs and materials which can cause confusion among buyers, engineers and end users! Today, we'll try to simplify this confusing category of fasteners.
Who Uses Dowels?
Dowels are used as hinges, shafts or pivots to locate or hold parts together in precision assemblies or fixtures.
They are used in a wide variety of applications in many industries including: aerospace, electric motors, hydraulic equipment, instrumentation, tools and fixtures, machinery, military, and many more.
Dowels are popular in assemblies because they can withstand frequent insertion and removal without deformation. And production favors pins because they require no additional fastening hardware to insert, no secondary operations, and no mating components. It all adds up to speed up production and keep everyone in the food chain happy!
What do I need to consider when choosing a locating pin?
Although dowel pins are available in a variety of materials and styles, there are a few major issues to consider when it comes to major commercial and mil-spec products.
Standard, extra large or small size?
Standard series dowels are used for initial applications. Their base diameter is 0.0002 inches higher than the nominal diameter. For example, a ¼ gauge pin has a diameter between 0.2501-0.2503.
Oversized series dowels are often used to fit into worn holes and are often used in the aftermarket for repairs. Their base diameter is 0.001" higher than the nominal diameter. For example, a ¼ oversized dowel has a diameter between 0.2509-0.2511.
Undersized series dowels are used for inconsistent holes. Their base diameter is -0.0002 inches below the nominal diameter. For example, an undersized ¼ pin has a diameter between 0.2500-0.2498. Mil-P-21143/2- falls into the undersized category.
End chamfer or radius?
Generally, commercial pins are manufactured in accordance with standard ANSI ASME B18.8.2. Standard alloy pins have a radius on one end and a chamfer on the other. However, stainless steel dowels are usually manufactured with chamfers on both ends.
Commercial or Military?
If you or your customers require domestic DFAR pins to meet the most stringent standards, military pins may be the best choice for you!
Alloy or Stainless Steel? Which stainless steel?
Alloy steel is the strongest pin available and is hardened. It can be finished with black oxide to provide better rust resistance than common alloys.
Type 416 stainless steel is the strongest standard stainless steel product and is the material used in the MS16555 and MS16556 series. Magnetic.
Type 18-8/303 stainless steel is the most commonly used stainless steel and is the standard material for the Mil-P-21143 series.
Type 316 stainless steel is the most corrosion resistant stainless steel available and is not associated with mil-spec parts.
Are there other factors to consider?
Dowels are usually shown under their mil-spec number, which can be crossed with the commercial equivalent. Some common Mil-Spec series for dowel pins include Mil-P-21143 (303 stainless steel), MS16555 (alloy and 416 stainless steel available in the standard series), and MS16556 (alloy and 416 stainless steel available in the oversized series).
If you are not ordering by MS or NAS mil-spec part number, Inch alignment pins comply with ANSI/ASME B18.8.2. For commercial pins, please take care to specify the required material and dimensional tolerances. Unless otherwise stated, dowel pins are precision ground, hardened and heat treated to the appropriate Rockwell hardness.
Remember, don't use a hammer! When installing dowels, never force the pin into the hole, always press it in for best results.
