This guide has been prepared as an aid to those responsible for specifying and purchasing screw machine products and turned parts. Its aim is to promote the understanding of the many factors which affect costs of components produced by
the Precision Turned Parts Industry.

Plating & Heating Treating 

We specialize in machining and rely on outside suppliers for plating and heat treating. However, proper results can be obtained if the specifications are clearly and completely spelled out.

When specifying plating, be sure to advise thickness of plate desired and whether print tolerances apply before or after plating. If possible, use ASTM, Military or Federal Specifications or other recognized sources to remove any doubt as to the requirement. Be sure to advise the supplier of any tests which will be used by incoming inspection

When heat treating is required, avoid general terms such as “Case Harden” or “Heat Treat and Draw”. Give complete details covering depth of case required, core hardness, draw temperature and times, proper hardness scale and tensile ductility requirements

WHAT	HOW	WHY
QUANTITY	Check annual requirements and advise supplier. On re-orders, advise supplier of any changes from the original prints	With annual contract the suppliers can minimize: tooling, set up costs and material costs. Great flexibility for the most economical method of manufacturing is allowed.
OVER AND  UNDER RUNS	Ordering exact quantities increases costs.	Allowance must be made for overage in production which must be prorated in the quoted price. Over/under run quantities in the Precision Turned Parts Industry may vary based on bar length, part size and equipment used to produce the parts
DELIVERY	Allow sufficient lead time for normal planning. Provide your supplier with the best forecast you have.	Quick deliveries involve premium material and labor costs. A longer/better forecast permits more economical manufacturing runs.
PACKAGING	If special packaging, labeling or bar coding is required, advise the supplier of this when the request for pricing is made.	Unusual packaging requirements are expensive due to special material and labor. If advised in advance, a supplier may be able to provide alternative, less expensive packaging.
MATERIAL	Design and application permitting, specify standard sizes of free machining grades	Standard sizes cost less and are more readily available. Free machining material yields greater production, improved finish and closer tolerances
TOLERANCES	Specify no closer tolerances than absolutely functionally necessary. Be sure that the tolerances are shown on the drawing and are practical and consistent with the application of the part.	If required, suppliers of precision turned parts can and will make the parts with close tolerances. However, higher costs can be expected the closer the tolerance requirements.
DIMENSIONAL  RELATIONSHIP	For slotting, cross drilling, milling, broaching, etc., do not specify definite relationships between dimensions unless required. Be sure all dimensions are shown clearly and add up.	Specifying a close relationship requires expensive fixturing and slows production.
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CONCENTRICITY	Concentricity as a dimension should be specified to the maximum allowable limits.	Concentricity of dimensions often determines how a part will be produced. Holding closer limits than required can cause considerable problems in manufacturing and inspecting.
INTERNAL  DIAMETERS	Hole diameters should be specified to the maximum allowable limits.	Suppliers of precision turned parts stock standard drills, reamers and plug gages. Special internal diameters can be produced where required with special tooling.
SHARP  CORNERS	Unless there is a functional need for a sharp corner, specify chamfers or radii at all intersecting surfaces	Sharp corners nick easily and require special handling. It is also more economical to produce a part with "broken corners".
THREADS	Specify standard threads, American National Standards Institute (ANSI) Unified Inch Screw Threads (UN and UNR Thread Form) or other ANSI standard threads. Use class 2a or 2b fits where application permits. For I.D. threads choose the least percent of thread that gives the required strength	Special threads required special tools and gages.   Closer fits may require additional operations. Full threads are harder to tap
BURRS	Do not specify burr removal unless necessary to part function.	Burrs are a natural results of any machining operation involving intersecting surfaces. Burr prevention and removal may require additional machining or a second operation.
FINISH	Clearly specify surface finish no closer than necessary to meet functional requirements	Finer surface finish may require special tooling, slower cycle time or additional second operations and special handling and packaging methods.
QUALITY	Be as detailed as possible with the quality requirements. Specify which characteristics are of greatest importance and product performance. Acquaint the suppliers with any internal quality control requirements, so that production quality methods will be consistent. Indicate initial sample requirements, specialized data requirements and inspection routings as part of the request for quotation.	This will allow the suppliers to focus on what is important and to follow parallel or compatible quality procedures.
GAGES AND  GAGING  EQUIPMENT	Wherever possible, part design should avoid the need for special gages.	Special gages and gaging equipment add to part cost. Customers may supply special gages to eliminate additional gage costs.
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