Practical Insights for Machining Really Big Pieces

Recent News - July 9, 2014

What is a really big piece?

by Geoff Ginader
President American Hollow Boring

That’s a question without a universal answer. There are many ways to define a really big piece. A large work piece could be described as any that is really heavy, or one that is too large to fit in a typical machine.  Parts may be very long, or large in diameter.  Sometimes “large” is a relative term by material.  For example, a large piece of pure copper of a given size may be more uncommon and expensive than a steel bar many times that size.  Also, while tubing is common, there are limits to what’s available in seamless tubing, especially with extra heavy wall thickness.  With the many factors to consider, the definition of what’s really big varies from machine shop to machine shop based on their own internal capabilities.  This article is a resource for anyone who must buy or specify large machined parts.

For most machine shops a typical large piece is any piece that is over 3000 pounds, with a length of over 80 inches. This can vary from machine shop to machine shop. For instance, American Hollow Boring Co. in Erie, PA has unique capabilities because they are able to handle parts up to 20,000 pounds and a length up to 390 inches.  So, large for them is far outside the typical range.  Demand for machining large parts exists in many industries.  Oil & Gas, Heavy Equipment, Machinery Builders, and Aerospace industries, all have requirements for large pieces that need machining.  Metal service centers, as well as other metal producers, are also in the market for this service.  Projects can vary from one large piece to truck load quantities.  The volume and mix really depends on the customers and their unique needs.

Planning is Necessary

When handling a large work piece, a lot of planning needs to go into the project approach. If you want to put a hole into the piece, you first have to consider the capacity of the machine you select to do the job.  In most cases, you need to prepare the work piece properly to run.  Some pieces must be round or balanced to run smoothly within the machine and to be held properly during the machining process. Once in the drilling process, the approach can be more or less aggressive depending on your goals and the needs of the customer. Small workpieces can be drilled right at size while large parts often require two cuts or more.  All these elements need consideration, because of the risk of a heavy cut developing chatter or developing a problem during the process.  Time estimates for processing can be complex with high metal removal rates balanced with demands of finishing large surface areas.

Preventing Obstacles

The biggest obstacle to many machining projects is being able to get a clear, detailed definition of the process, and what is needed by the customer. Project definition (scope) is very important; it clearly sets up the buyer and the manufacturer for success with the project, rather than experiencing problems through the process.  To achieve this goal, it is necessary to have a well-defined project from the beginning. Questions need to be asked and answered to assure the project runs smoothly.  Some common questions are:

  • What machining service needs be performed on the part(s)?
  • What is the quantity of pieces/parts required?
  • What material is required or supplied?
  • What is the heat treatment or hardness?
  • What is the weight of the part
  • What is the length?
  • What is the diameter?
  • What does the outside look like?

Typically these details are handled and communicated through a sketch or drawing.  A good drawing can answer a lot of questions completely.  The quality and detail in the drawing make a big difference.

The Right Machine for the Job

In most cases, you want a machine that’s a little larger than the work piece at hand.  A more powerful machine for larger pieces is a good idea. If there is a lot of material to remove then it is better done with an 80 horse power machine, rather than a 50; or a 50 horsepower than a 25.  It’s always important to select the right tool for the job.  When it comes to drilling holes that are very deep, a smaller machine may be feasible if you select the right process.  The trepanning process allows a very large hole to be made on a smaller machine with less power because a core is left uncut.

The Right Shop for the Job

When it comes to selecting the right shop for your job, a lot of thought and consideration should go into the question of whether or not the shop is qualified. Simply stated, does the company have a track record with machining large parts of your required size and shape?  Good communication between the buyer and the shop is very important to determine this.  Although there are a lot of shops out there, you really want to gain a good level of understanding and trust with a machine shop you plan on utilizing.  This becomes more critical when buying large work pieces so you should ask many questions and be sure you are in accord with what is required.    

  • Does it have a range of capabilities that encompasses your work piece requirements?  Or are you on the very edge of the capabilities of the shop you’re working with or considering to work with?
  • Can the shop point to specific examples of work completed of a similar nature

Is the shop quality system ISO certified?  For example, suppose you have a 6 inch hole to drill.  You want to work with a shop that can deep drill a lot smaller than 6 inches and a lot larger than 6 inches. Then the shop is more apt to have the tools, methods, gages, and experience to complete the work properly.  You want to be confidently within the “core” capabilities of the shop.  This is a good decision criteria for a buyer that is considering a machine shop – find the shops core!

Final thought

When machining large work pieces, it comes down to the customer’s detailed specifications.  The details of the project need to be prepared and clearly communicated, preferably in a detailed drawing. The customer should ask questions and make sure the answers work within the defined plan and needs. Finally, remember that not only does it have to be the right machine to machine the part, but also the right machine shop as established by the “core” of that shop’s capabilities.  If, by really big parts, you mean GREAT parts, you need a great machine shop to make them.  We make great big parts at American Hollow Boring Co.

Geoff Ginader is the president of American Hollow Boring Co., an independent machine shop specializing in deep-hole drilling and large part machining for industrial applications that range from heavy machinery to defense projects. He enjoys solving complex machining problems, and experts at AHB are available to review specific projects.