Screw Screw ThreadsThreads

Manufacturing TechnologyManufacturing Technology

Bayside Secondary SchoolBayside Secondary School

HPEDSBHPEDSB

Basic Thread ProfileBasic Thread Profile

Thread DesignationThread Designation

ImperialImperial

MD – Pitch UNF or UNCMD – Pitch UNF or UNC

Ex.Ex.

¼-20 UNC¼-20 UNC

¼-28 UNF¼-28 UNF

MetricMetric

M(MD) x PitchM(MD) x Pitch

Ex.Ex.

M10 x 1.5M10 x 1.5

M10 x 1.0M10 x 1.0

Threaded HolesThreaded Holes

Created in a 3-Step Process:Created in a 3-Step Process:– Center Drill in desired locationCenter Drill in desired location– Drill to correct Tap Drill SizeDrill to correct Tap Drill Size– Create threads using a TapCreate threads using a Tap

Finding TDS on a chartFinding TDS on a chart

Calculating Tap Drill SizeCalculating Tap Drill Size

TDS = D – TDS = D – 1 1

NN

Where Where D = Major DiameterD = Major Diameter

N = # of threads per inchN = # of threads per inch

TDS Calculation ExampleTDS Calculation Example

Find the TDS for a 3/8-16 UNC boltFind the TDS for a 3/8-16 UNC boltTDS = D-TDS = D-11

NNTDS = .375” – TDS = .375” – 11

1616TDS = .375” – 0.0625”TDS = .375” – 0.0625”TDS = 0.3125” or 5/16”TDS = 0.3125” or 5/16”

It is important to know that drills come in It is important to know that drills come in fractional, numbered and lettered drill bits and fractional, numbered and lettered drill bits and you must cross reference your answer to the you must cross reference your answer to the appropriate size and typeappropriate size and type

Threaded Hole TipsThreaded Hole Tips

• Countersink the hole slightly to Countersink the hole slightly to give yourself a lead-in for your tapgive yourself a lead-in for your tap

• Use Rapid Tap or other cutting fluid Use Rapid Tap or other cutting fluid to help the tapping processto help the tapping process

• Always start with a taper tap Always start with a taper tap

TapsTaps

External ThreadsExternal Threads

• Most commonly created using a Most commonly created using a Die and Die HandleDie and Die Handle

• Material Diameter = Major Material Diameter = Major Diameter of the ThreadDiameter of the Thread

ExampleExample

• If the material on the left is ½” If the material on the left is ½” diameter, you can thread it with a ½”-13 diameter, you can thread it with a ½”-13 UNC dieUNC die

Questions?Questions?