The Importance of Proper Fixturing
Selecting the way to fixture a part is most critical in achieving the required end result. In turn, the fixturing process should be viewed as being equally as important as the selecting of the actual machine and tooling.
There are still many chucks manufactured fifty years ago that are still working today, making quality parts.
The 3-Jaw Chuck has been the norm of every shop since the beginning of Lathes and the Turning of Round Stock. Initially, there was the Manual Chuck which for years was the staple for work holding on lathes.This eventually led to the Power Actuated Chuck and its various style Master Jaws, with or without thru-holes.
Multi-Spindle Chucks available in various styles for specific processes
Just as the auto industry’s car models were made to suit people’s needs, various models of chucks entered the shops designed for particular manufacturing needs. All were arguably improvements…Self Centering Chucks, Compensating Chucks, Pull-Back Chucks, and Anvil Chucks.
These also came in an assortment of Master Jaw designs such as Tongue & Groove, Acme Serrated, Square or “Vee” Serrated. Others came with extended jaw strokes.
With changes in manufacturing came the demand for higher speeds and feeds, improved surface finishes and tighter tolerances.
Manual lathes were replaced with CNC Controlled Machines. Coated Carbides were developed by the tooling industry to attain the demanded higher speeds and feeds. To reach these goals, chuck manufacturers had to respond with work holding devices to meet these demanding situations.
Today, the situation for Work Holding has taken on a whole new meaning.
High Speed Counter-Centrifugal Chucks, Index Chucks, Chucks with shifting centers, Compensating Chucks with Collets or Mandrels are becoming the norm on lathes.
As lathes take on the look and capability of a “Universal Machine”, the situation requires versatility in the way a part is gripped. Today, manufacturers have to meet new demands and whole-new challenges.
Originally, production requirements were for high volume. The situation allowed multiple operations over a number of machines. Each machine was somewhat specialized in the sense that changeover required a great deal of downtime to achieve. When a changeover was required, it was limited such as to not disturb the production. In turn, this caused machines to not work efficiently at the available speeds or feeds. because the tools were “OK” or the chucks could hold a variety of parts efficiently at the lower speeds and feeds.
Typical set-up with sub-spindle and live tooling to completely machine part in one process
Options now allow for many parts to be completed in a single operation, with one setup and one clamping.
Not only do lathes now have the capability to turn parts at high speeds and feeds with better accuracy and repeatability, they also have the capability for drive tools… milling capabilities…automatic gaging…tool offsetting…automatic load/ unload…spindle positioning…back working.
To accomplish the above it is necessary to go through the thought process required to determine the best possible method to safely hold the parts to allow accessibility of the aforementioned options.
The obvious goal is to make your product in a single setup, at the fastest time, with the least cost, and of the best quality. It sounds simple. However, that is one loaded objective. In most situations, all the ingredients are not available. The machine may not have all the needed capabilities. The costs may not be justifiable, or the quantities may determine the process. The variables go on and on.
Initially, the Chuck size has to be established. Make sure the part will fit safely and securely within the envelope of the Chuck. Like everything else, there may be exceptions. The part may not always be round, or may have an extended arm, which will require a counterbalance.
Next, the type of chuck has to be determined. A common 3-Jaw Chuck is appropriate for most turning applications. However, for particular parts rectangular in shape, a 2-Jaw Chuck may suit the part better for gripping. Another option may be a Collet Chuck or Mandel to maintain concentricity requirements between operations.
Reviewing the part print and the tolerance requirements will define the process method(s) to obtain your objective…a consistent quality part in the least amount of time. To accomplish this goal is to establish the best process suited to the part’s dimensional and finish requirements. Datums are established for a reason. Know where they are and use them accordingly in your setup.
Production will dictate the process and tooling more than anything. Major volume jobs, will require a power actuated fixture to allow ease and quickness of loading/unloading in the shortest possible time. If only one or two pieces are going to be made, a Manual Chuck would be used with top tooling capable of holding the part at the speeds and feeds necessary to cut the part. However, this is probably not the most efficient method.
Selecting the proper work holding method is just as critical as determining the correct cutting tools, speeds & feeds, and process. Like the previously mentioned items, there are references, recommendations and many vendors with expertise to assist in the selection process. When planning and selecting work holding, it would be most beneficial to use their resources, knowledge, experience and guidance.