Tech Tip #64 - Bridge and Car Reamers – Kennametal
“Bridge” and “car” reamers are older terms that refer to a time when misalignment of holes in structural steel components were more common than they are today.
Misalignment of holes for bolts in bridges, early automobiles and railroad box cars required a method to create a usable hole from two or more holes that were not aligned properly.
This method was developed: A rotating tapered reamer is inserted to a depth that creates a usable diameter into which the fastener will fit.
Bridge and car reamers are designed to cut on their sides, as opposed to conventional reamers that cut on the chamfer. Both styles are heavily webbed for strength and are right-hand cut and left-hand helix to push the chips ahead of the tool.
A bridge reamer typically has 3 flutes with a long lead. A car reamer typically has 5 flutes and is slightly shorter, making it more rigid.