Dowel pins are industrial fasteners that are used to join two or more items together. They are short, cylindrical rods made of various materials including wood, metal and plastic. Dowel pins can be tapered, slotted, grooved, or otherwise altered to change its mechanical properties. They are commonly available in imperial or metric units.

Dowel Pin Operation

Dowel pins do not possess moving or actuated components. Dowel pins' mechanical capabilities stem from their high coefficient of friction, and any adhesive that may be applied when they are inserted into press-fit predrilled holes. They must be rigid while in use so they are capable of keeping the assembled parts aligned without further hardware fastening. For a firm fit, the hole should be exactly the same size or slightly smaller than the dowel's diameter. Dowel pins typically have working loads identified, with a breaking strength measured as when a double shear occurs.

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For aesthetic applications where the hardware must be accessible or seen, a dowel pin can appear uniform to its assembly--a distinct advantage over other fasteners. For this reason, dowels are commonly used in furniture. They can also be applied as hinges and simple axles.

Dowel Production

Wooden dowel rods are produced on the same mill machinery that produces other finished cylindrical wood products, like fence poles and furniture pieces. Dowel pins are shortened lengths of full-sized dowels. These dowel pins are usually of hard wood, like birch or maple. Dowel pins may undergo a secondary operation, such as planing or grooving, if desired.

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Metal dowel pins undergo a melt and cast process, as indicated by the infographic below:

Image credit: Timken Co.

Common metal materials for dowel pin manufacture include:

• Aluminum, which is light, ductile, conductive, and very resistance to oxidation.
• Brass is strong, ductile, conductive, corrosion resistant, and demonstrates low magnetic permeability.
• Stainless steel has a high pressure rating, and is chemical and corrosion resistant.
• Steel that is hardened and ground is compacted to produce a very hard, though brittle, metal. It has gone through a hardening process such as quenching or induction. Unhardened steel is more malleable, but is still suitable for many applications.
• Titanium is strong, with good temperature and corrosion resistance. It is 44% lighter than steels.

Plastic dowels are formed via plastic injection molding.

Dowel Pin Sizing

After material, dowel pin sizing is the other major specification manufacturers need to consider.

• Outer diameter is the measurement across the edges that form the dowel pin's width.
• Length is the measurement of the dowel's longest cross section.

Most dowels produced are of the straight dowel variety. A dowel may have diameter tolerances of ± .010 inches compared to the dowel pin's nominal size. This tolerance ensures that the dowel mates in either a loose-fit or press-fit fashion with its corresponding hole. If the pin has two separate tolerances on each end, it is considered a 'parallel pin'.

Configurations

There is a limited number of dowel pin types. Locating pins, cotter pins, and spring pins have their own unique Engineering360 selection guide and specification filter. A straight pin with metric or SAE threads is called a threaded rod.

Resources

ABC Article Directory - Technology - Dowel Pin Handbook

Wikipedia - Dowel

McMaster-Carr - Dowel Pins

E & T Fasteners - Molder Plastic Dowels

Tooling U - Overview of Non-Threaded Fasteners - Class Vocabulary

Groov-Pin Corp. - Groove Pins

Warwick Fasteners - Dowel Pins 

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