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Quantity. Check annual
requirements. Order as larger a quantity as possible.
Why. Large quantities reduce prorated tooling, setup
costs, materials costs and provides greater flexibility for the most
economical method of manufacturing.
Materials. Physicals permitting, specify
standard size of free machining grades.
Why. Standard sizes of materials cost less and are
more readily available. Free machining material yields greater production,
improved finish and closer tolerances. Consult your supplier on material
recommendation.
Tolerance. Specify no closer tolerance or surface
finish than absolutely necessary.
Why. If close tolerance work is required, your screw
machine supplier can and will make the parts to your specification,
but the tolerance requirement is a very important factor in determining
the overall cost of the part.
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Threads.
a. Special Threads. American National Standard Institute
(ANSI) Unified Inch Screw Threads UN and UNR Thread Form) or other
ANSI standard threads.
b. Thread Class Fit and Percent of Thread. Use class
2 fits where application permits. Choose the least percent of thread
that gives the required strength.
Why.
a. Special threads require special tools and gages.
b. If closer than class 2 fit is needed, it may require
additional operations. The percentage of full thread should be in
accordance with generally accepted standard practice.
Internal Diameters
Hole diameters should be specified to permit the use of standard reamers,
drills and plug gages.
Why.
Your screw machine supplier stocks standard drills, reamers and plug
gages. Special internal diameters can be produced where required.
Surface Finish.
Specify surface finish no closer than necessary to meet functional
requirements.
Why.
Close surface finish may require special tooling, slower cycle time
or additional second operations.
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Gages & Gaging Equipment.
Wherever possible, part design should avoid the need for special gages.
Why.
Special gages and gaging equipment add to the cost. If special gages
are required, they should be provided by the customer.
Burrs.
Do not specify burr removal unless necessary to the function of the
part.
Why.
Burrs are a natural result of any machining operation involving intersecting
surfaces. Burr prevention and or removal may require additional machining
or second operations.
Sharp Corners.
Unless there is a functional need for a sharp corner, specify chamfers
or radii at all intersecting surfaces.
Why.
Sharp corners nick easily and require special handling. It is also
more economical to produce a part with 'broken corners.'
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Concentricity.
Concentricity as a dimension, should be specified to the maximum allowable
limits.
Why.
Concentricity of dimensions often determines how a part will be produced.
Holding closer limits than required can cause considerable problems
in manufacturing and inspecting.
Dimensional Relationship.
For slotting, slabbing, cross drilling, milling broaching, etc., do
not specify definite relationships between dimensions unless required.
Why.
Specifying a close relationship requires expensive fixturing and slows
production.
Inspection.
Do not specify 100% inspection except where critical dimensions demand
it.
Why.
Quality assurance can most economically be provided through sampling
plan inspection. If you have adopted AQL standards, be sure to provide
them to your supplier.
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Deliveries.
Allow sufficient lead time for normal planning. Do not ask your supplier
to spread delivery over an extended period of time.
Why.
Quick deliveries involve premium material and labor costs. Extended
deliveries involve inventory costs.
Over & Under Runs.
Ordering exact quantities increases costs.
Why.
Allowance must be made for overage in production which must be prorated
in the quoted price. Standard practice in the Screw Machine Products
Industry is quantity variation of plus or minus 10%.
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MAKE OR BUY? - An All Important Decision
Deciding whether to make or buy precision machined products is a complex
decision involving the consideration of not only cost, but also many
other factors. It requires a team effort with input from those responsible
in the areas of purchasing, costing, finance, manufacturing, corporate
planning, and policy making.
Your evaluation will involve the interrelationship of many departments
and functions of your business. The checklist below will be a good
starting point for you to consider many of the factors involved in
operating a precision machined products department.
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CHECKLIST
SKILLED/KNOWLEDGEABLE EMPLOYEES REQUIRED
- This is by far the Industry's greatest challenge.
 Are skilled operators
and set-up/operators available to operate the equipment?
Are engineers
and other individuals for management and supervisors available?
How will a pool
of skilled labor be built?
What training will
be offered, at what cost and where?
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CAPITAL INVESTMENT
Machinery
How many and what
type of machines will be needed?
Will secondary
or other equipment be needed?
How will this
equipment be maintained and by whom?
ADDITIONAL WORKING CAPITAL REQUIREMENTS
Inventory - How much inventory will be needed of:
General supplies?
Tooling?
Material?
In-process and
finished parts?
Payroll Requirements (hourly and supervisory)
Wages?
Benefits?
What Outside Services Will Be Needed?
Heat treating?
Plating?
Others?
Other Expenses
Insurance?
Taxes?
Capital loan payments?
Supporting Services - A variety of supporting services
will be needed in plant, including:
Quality control
Tooling
Material storage/handling
Turnings storage
Parts cleaning
Metalworking fluids
- storage and processing
Environmental
controls and issues, i.e., noise, oil, mist, etc.
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PLANT INVESTMENTS
How much and what type of floor space will be needed for
all of the above?
Equipment Installation - What will be the requirements for:
Electrical wiring?
Floor loading?
Plumbing?
Lighting?
HVAC?
Air (compressed)?
OTHER ECONOMIC CONSIDERATIONS
- A variety of other items need to be considered when evaluating the
establishment of a precision machined products department, including:
How will scheduling
be handled - both internally and when outside services are needed?
How will our personnel
be trained to make the correct decisions when purchasing material,
tooling, machine tools and supplies?
How will the processing
of turnings and metalworking lubricants, and potentially hazardous
materials be handled?
Who will
be sure that we meet OSHA and other regulations for:
- Noise?
- Personal protective equipment?
- Mist control?
- Disposal of wastes?
- Standards on part cleanliness?
- Quality?
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CONCLUSION
The ultimate question is: What is the best method your company
can use to improve its profit position by reducing manufacturing costs?
By establishing a precision machined products department can there
be cost savings?
OR
Can a properly equipped purchasing department more profitably
serve your company through the selection of the best suppliers? 
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