All the kings horses

Have you ever found extra screws laying on the floor after you have assembled something?  If not, they were probably already lost underneath the table or discarded with the trash.  The point is, that without detailed step by step assembly instructions, a properly assembled part is not guaranteed.  In the modern world of manufacturing there is a methodically organized way of assembling where all parts are brought together, laid out in proper order and assembled with the proper tools to assure a quality product.  In the everyday world of repair, it is quite a different story.  A typical repair bench is a lot different from the factory where the part was originally assembled.  Knowing that you have this disadvantage you must take action up front to avoid problems later.  In the last “Maintenance Messenger” we concentrated on driving home the following point:  Disassembly procedure is crucial to assuring a properly assembled part.  Assuming that the part was taken apart properly and repairs have been made or parts replaced it is now time to reassemble.  Will it take all the “Kings Horses and the Kings Men” to it together again?

Any assembly project can be simplified if an organized procedure is in place and followed.  Although the use of force is often required to disassemble, we strongly discourage the use of force in the assembly process.  Proper assembly procedures require the use of temperature variation (Fire & Ice).  Metals react like your body and shrink with cold temperatures and swell with hot temperatures.  For example:  A .002”/ .004” interference fit will fall together if you shrink a bushing using dry ice and apply heat to the hole with a rose bud (torch).  Bushing size and material type however can greatly affect these numbers.  For ease of installation of ball and roller bearings onto shafts, hot oil baths are highly recommended.  Hot oil, however, can be extremely dangerous and should be done by professionals.  (For some hints on proper fits see the issue of the “Maintenance messenger” entitled “Fits Like a Glove”.)  Now utilizing information from our last newsletter, detailing the disassembly process you are now ready to assemble.  Below we have listed a helpful checklist for assembling various types of components.

Bearings

Clean out bore or shaftCheck dimensions and finish conditionUse proper sized insertion toolA hot oil soak will expand I.D. for assembly easeIf lube is required, verify proper lube & clean pathways

Slides

Check surface finishCheck oil provision, clean & working orderRun slide all the way in and outUse bluing on gib to check amount of contact

Wear Plates

Check surface finish conditionCheck lubrication provisionCheck for proper height or engagement point contactUse bluing to check amount of contact
Splines, Universals, Gears, Etc.

Check surface finishLook for wear patterns. Check lube provision. Gearing can sometimes be turned around for opposite wear

Bushings

Clean and check hole diameterCheck O.D. of bushing to assure proper interferenceUse dry ice to shrink O.D.Recheck O.D. of bushingInstall and check I.D. / Hone if necessary

Assembly can become an expensive ordeal even if the part is assembled correctly the first time!
Some things to keep in mind to help keep your costs down.Keep tools clean and organizedKeep ample supply of fasteners, gasket material, compounds, etc.Inspect incoming parts prior to assemblyAssign specific tasks to each person involved in the assembly processKeep people involved to a minimumKnow what skills are involved and match-up personnel accordingly

After all the different machines that we have designed and built over the years, the assembly time estimation is still the most difficult part of the quotation.  I hate to admit it, but some of my estimates have been one third of the actual time spent on the assembly procedure.  I believe quoting assembly work is so difficult because of the many different skill levels required by assembly personnel.  From bolting up a bracket, scraping a gib, running a wire harness, installing a PLC. etc., time estimation is a composite of skill, character, and organization of your assembly department.  If your estimation is lower than the time that it actually takes, take a look at the above checklist and see if you can make some improvements to save time and improve the quality of the work being performed.