Basic Mechanics for Letterpress: Machine Maintenance
Types of Bearings
With "lubricated for life" bearings being very commonplace these days, it's easy to overlook the need for proper lubrication in letterpress machinery. Given the ubiquity of ball bearings, it's easy to forget that there's a variety of different kinds of bearings. Low cost ball bearings are a fairly recent innovation, most of the bearings you find in letterpress machines are plain bearings. Plain bearings rely on two surfaces in direct meter-on-metal, sliding contact. Running without lubrication, this arrangement is a recipe for disaster. However, if a film of oil is introduced between the two surfaces, a reasonably usable bearing surface is formed.
The lowest common denominator in bearings is the integral bearing, a sometimes hardened steel shaft rotating in a cast iron hole. They are easily spotted by the simplicity of their design; a form fitting hole is made in a casting and a shaft is passed through the hole. This kind of bearing is unfortunately very common in letterpress equipment.
Bronze Sleeve Bearings
Bronze sleeve bearings are usually machined as a hollow bronze cylinder, or (surprise) sleeve, which is then press-fit in the machine or secured in some other manner. They can easily be re-made from scratch and replaced when worn.
Babbitt bearings are cast from babbitt, an alloy of various metals including lead, tin and copper, the alloy varying depending on application. Babbitt bearings can be replaced by melting the old babbitt metal out with a torch, and pouring a new one in its place, using the existing shaft as a form.
Ball bearings appear on some more modern pieces of letterpress equipment, or in the case of the Linotype, on more modern additions to the Linotype platform.
Most modern ball bearings are sealed for life, a crafty definition that actually means sealed for the life of the bearing, not the life of the machine containing the bearing. Older non-sealed bearings need to be packed with grease. Sometimes this needs to be done manually, sometimes screw-down grease caps are provided to help force new grease into the bearing.
Plain, Bronze Sleeve and Babbitt Bearings
Left un-lubricated, an integral of bearing will fail quite rapidly. If this kind of bearing becomes significantly worn, your machine will need to take a trip to a machine shop to be repaired. Bronze sleeve bearings and babbitt bearings are plain bearings, they need to be lubricated or they will fail. Because of the softer bearing material, they won't fail as quickly as a plain bearing, but they will get sloppy over time and seize up under load.
In their simplist form, this kind of bearing is lubricated by putting a drop of oil on the shaft close to the bearing. Capilliary action will draw the oil into the bearing. The next step up from this is the oil hole, which is a hole drilled into perpendicularly the bearing, into which a drop of two of oil can be placed. Another common thing you will find are small oil cups covering the oil holes. These have spring loaded covers that you can open and put a few drops of oil inside. Some presses (Heidelbergs) have a central one shot oiling system, that feeds oil to all of the critical oiling points via pipes. On larger shafts, you'll sometimes come across screw-down grease caps. You'll see these on the main cam shaft bearings on a Linotype, for example.
The Importance of Proper Lubrication
When a plain bearing runs dry, there will be metal-on-metal contact. This immediately leads to wear, which results in sloppy bearings, stiff operation and seized shafts. Considering that the difference between good impression and no ink being transferred to paper at all, the difference a few thousandths of an inch of wear can make is significant. Given that the manufacture of most letterpress equipment pre-dates the proliferation of "e;sealed for life"e; bearings, you can automatically assume that you're going to need to oil things periodically.