Mold Components Pages 39 to 50 Pg. 5 What You Need to Know About Leader Pins and Bushings By Jim Fattori Leader pins are often referred to as guide pins. They lead or to four decimal places prior to machining the holes in the guide one half of a mold into the other. The outer diameter mold base — just like you should be doing for ejector pins and of a leader pin is typically . inch below nominal with a sleeves. tolerance of +./-. inch. A leader pin bushing typi-If you ever receive pins or bushings that are out of speci-cally has an inside diameter of . inch above nominal ication, you have three options: You can ask that they be with a tolerance of +./-.. Therefore, the pin has replaced; you can return them for credit; or you can machine a close sliding it in its mat-ing bushing with a clearance of between . and . inch total. A close sliding it is intended for the accurate loca-tion of parts that must assemble without perceptible play. It is well worth taking some time to become familiar with the various types of its, if for no other reason than to use the cor-rect terminology when speaking with others. The major categories of ANSI B.--R its are: • Running or Sliding Fits (RC1 through RC9) • Locational Fits (LC, LT, LN) • Locational Clearance Fits (LC – LC) • Locational Transition Fits (LT – LT ) • Locational Interference Fits (LN – LN ) Straight (top) and shouldered (bottom) leader pins. • Force or Shrink Fits (FN1 – FN5) The majority of leader pins offered by mold component suppliers include a small shoulder the bore holes in the plate according to the actual pin dimen-at the head end, which is . inch above nominal with a sions. If you choose this last option due to the required tolerance of +./-., as shown in the image above mold delivery date, be sure to number the pins so they are (top). The purpose of this oversized shoulder is to provide an reinstalled in the corresponding holes during any routine interference it at room temperature in a mold plate — typi-maintenance. cally a medium or heavy drive type of it. Technically, the The length of the oversized shoulder varies with the pin’s amount of interference should be proportional to the diameter diameter and length. They are usually adequate for most of the pin and the amount of desired pressure to install, as per molds. one of the ANSI class ratings, but that is basically overkill for FOR MORE INFORMATION our application. Still, you need to keep in mind that pin and bushing sizes Injection Mold Consulting LLC / injectionmoldconsulting.com and tolerances are catalog speciications. To avoid any unwel-Jim Fattori, Founder come surprises, it is imperative that you measure every pin 50 MoldMaking Technology — — JULY 2023 Image courtesy of Jim Fattori.