I SUPPOSE start read article will say yourself Well heres another article full technical jargon could probably just want tell what know about drilling tapping leave can relate attitude inasmuch think about some technical articles read Nevertheless feel person wants develop certain skill should know basics first Therefore going talk about threads tap drill sizes number screws clearance drills etc case wondering guy goes Ive machinist about ten years recently started teaching Machine Tool Technology Hayward Regional Occupa tional Center Hayward California also teach part-time Chabot College Hayward Ive modeler five years have great success modeling think related experience machinist Lets start wing hold-down bolt use usually -20 first part sign refers major diameter largest part thread second part refers number threads per inch TPI Now have thread 250 major diameter 20 TPI able find tap drill size dont have tap drill chart dont have drill press getting drill ab solutely straight can problemso suggested impose buddy drill press make some simple jigswhen clamped down work hole through material underneath will precisely aligned have find pitch pitch thread refers distance crest crest point point pitch computed dividing number threads per inch inch See Fig 1 As can see pitch 20 threads per inch works Out 050 knowledge what pitch constant factor 649 can compute tap drill size size hole should before tapped can done dont have tap drill chart pictured run across thread standard such -32 can also compute tap drill size metric threads Metric threads anything afraid fact metric thread pitch already indicated 8X125 thread 8 mm major diameterX 125 mm pitch Before compute tap drill size numbers talking about want talk about thread form Basically thread unified national metric made up series equilateral triangles having equal angles equal sides See Fig 2 angle 600 sides pitch whatever thread using thread form pictured Fig 2 what call sharp V thread looks very nice functional very practical industry standards because tap tool used cut thread wears especially point Therefore time would take cut tap tool would have replace sharpen OW viously very economical industry has come up modified V thread See Fig 3 thread form tool wear kept minimum Reading might say have tapped hole flat crest thread looks too wide thread looks too shallow might think yourself Ill just drill hole little smaller get deeper thread necessary go smaller tap drill tap drills based making hole sized tap cuts 75% full thread depth has found industry 95% full thread depth 5% stronger 75% full thread depth Now lets get back pitch constant factor 649 find out what tap drill use -20 thread find depth thread take constant factor 649 multiply pitch double threads both sides screw multi ply again 75 subtract major diameter will come out correct tap drill size Lets work out Major diameter250 Threads per inch20 Pitch 1 20 Depth thread 649Xpitch 050032 Double depth thread064 75% double depth thread 75X064048 Subtract major diameter 250048202 have tap drill chart will note -20 thread calls *7 tap drill 201 formula works virtually thread dont have chart handy Now information well good works fine threads like -20 i-16 5/16-18 because major diameter clear defined fraction what about threads use motor mounts wheel collars devises etc Threads like 2-56 3-48 4-40 632 8-32 10-32 know second number represents threads per inch what hell does other number mean Say 632 thread just what does 6 mean screw sizes indicated whole number such 6 8 10 use two different constants 060 013to find major diameter screw major diameter computed multiplying 013 number screw adding 060 results 6X013060138 major diameter 8X0 1 3060 164 major diameter OXOL 3060 190 major diameter Now know about threads ha ha lets talk about drilling tapping times have asked about what can done drill tap gets stuck and/or breaks off aluminum motor mount stock answer throw away start over again Now some might have some real good ways remove broken drill tap hopefully after reading wont have use First have get drill tap started straight have drill press easy thing dont have drill press youre tired imposing buddy has heres what can Impose people familiar tap wrenchif inserted hole jig block drilling tapping material cutting fluid oil should used Besides lubri cating drill chips lubricated preventing packing galling can jam break drill tap Wrench takes different sizes taps August 198037 us proper use tap fuzzy matter Heres valuable briefing expert machinist U Norman Jensen U e time impie jigs jig placco whatever ep e ana ping C Ilimr 38 Model Aviation
Edition: Model Aviation - 1980/08
Page Numbers: 37, 38
I SUPPOSE start read article will say yourself Well heres another article full technical jargon could probably just want tell what know about drilling tapping leave can relate attitude inasmuch think about some technical articles read Nevertheless feel person wants develop certain skill should know basics first Therefore going talk about threads tap drill sizes number screws clearance drills etc case wondering guy goes Ive machinist about ten years recently started teaching Machine Tool Technology Hayward Regional Occupa tional Center Hayward California also teach part-time Chabot College Hayward Ive modeler five years have great success modeling think related experience machinist Lets start wing hold-down bolt use usually -20 first part sign refers major diameter largest part thread second part refers number threads per inch TPI Now have thread 250 major diameter 20 TPI able find tap drill size dont have tap drill chart dont have drill press getting drill ab solutely straight can problemso suggested impose buddy drill press make some simple jigswhen clamped down work hole through material underneath will precisely aligned have find pitch pitch thread refers distance crest crest point point pitch computed dividing number threads per inch inch See Fig 1 As can see pitch 20 threads per inch works Out 050 knowledge what pitch constant factor 649 can compute tap drill size size hole should before tapped can done dont have tap drill chart pictured run across thread standard such -32 can also compute tap drill size metric threads Metric threads anything afraid fact metric thread pitch already indicated 8X125 thread 8 mm major diameterX 125 mm pitch Before compute tap drill size numbers talking about want talk about thread form Basically thread unified national metric made up series equilateral triangles having equal angles equal sides See Fig 2 angle 600 sides pitch whatever thread using thread form pictured Fig 2 what call sharp V thread looks very nice functional very practical industry standards because tap tool used cut thread wears especially point Therefore time would take cut tap tool would have replace sharpen OW viously very economical industry has come up modified V thread See Fig 3 thread form tool wear kept minimum Reading might say have tapped hole flat crest thread looks too wide thread looks too shallow might think yourself Ill just drill hole little smaller get deeper thread necessary go smaller tap drill tap drills based making hole sized tap cuts 75% full thread depth has found industry 95% full thread depth 5% stronger 75% full thread depth Now lets get back pitch constant factor 649 find out what tap drill use -20 thread find depth thread take constant factor 649 multiply pitch double threads both sides screw multi ply again 75 subtract major diameter will come out correct tap drill size Lets work out Major diameter250 Threads per inch20 Pitch 1 20 Depth thread 649Xpitch 050032 Double depth thread064 75% double depth thread 75X064048 Subtract major diameter 250048202 have tap drill chart will note -20 thread calls *7 tap drill 201 formula works virtually thread dont have chart handy Now information well good works fine threads like -20 i-16 5/16-18 because major diameter clear defined fraction what about threads use motor mounts wheel collars devises etc Threads like 2-56 3-48 4-40 632 8-32 10-32 know second number represents threads per inch what hell does other number mean Say 632 thread just what does 6 mean screw sizes indicated whole number such 6 8 10 use two different constants 060 013to find major diameter screw major diameter computed multiplying 013 number screw adding 060 results 6X013060138 major diameter 8X0 1 3060 164 major diameter OXOL 3060 190 major diameter Now know about threads ha ha lets talk about drilling tapping times have asked about what can done drill tap gets stuck and/or breaks off aluminum motor mount stock answer throw away start over again Now some might have some real good ways remove broken drill tap hopefully after reading wont have use First have get drill tap started straight have drill press easy thing dont have drill press youre tired imposing buddy has heres what can Impose people familiar tap wrenchif inserted hole jig block drilling tapping material cutting fluid oil should used Besides lubri cating drill chips lubricated preventing packing galling can jam break drill tap Wrench takes different sizes taps August 198037 us proper use tap fuzzy matter Heres valuable briefing expert machinist U Norman Jensen U e time impie jigs jig placco whatever ep e ana ping C Ilimr 38 Model Aviation