Eric Arthrell | 11/07/2017 08:06:13 |
47 forum posts 19 photos | Hello Can anyone advice on how to work out the depth of cut required for cutting a 1-7/8" x 8TPI whit form thread please. I get a value of 0.100" "not confident that this is correct " not the brightest bulb on the tree Regards Eric
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Hopper | 11/07/2017 08:12:39 |
![]() 7881 forum posts 397 photos | Whitworth thread depth = .6403 x pitch. Pitch of an 8tpi thread is one eighth of an inch, or .125. .6403 x .125 = .080" So thread depth is .080" But don't trust my math, I majored in English Lit at college so check it yourself to make sure. |
Eric Arthrell | 11/07/2017 10:33:09 |
47 forum posts 19 photos | Thank you for your reply Hopper . confirmed my calculation, the extra .020" is for crest and root addition using a pointed cutting tool profile. ie P x 0.160083 = 0.020". Kind Regards Eric |
Bazyle | 11/07/2017 10:52:35 |
![]() 6956 forum posts 229 photos | There are various tables to save you the maths for depth but the tricky bit is deciding on the max diameter of the blank to start with to avoid the pointed crests fouling when you try the nut. I can confidently suggest you make it out of metal or something not liquid or gas as I majored in Metallurgy & Materials Science. |
Howard Lewis | 11/07/2017 14:38:26 |
7227 forum posts 21 photos | If anything, machine the blank very slightle undersize, (in this case say 0.010" Somewhere in my Apprentice Notes there is a formula to to calculate by how much the thread should be truncated. Found it! For WHITFORM threads truncation should remove (0.160083 x Pitch) from the crest of the thread, which looks like 0.020" for 8 tpi. So I was erring on the side of caution, above. Truncated dia of SCREW = Nominal Dia - 0.1478 / TPI (1.835" in this case) Truncated dia of NUT = Nominal (Core) Dia + 0.1478 / TPI BUT allowance needs to be made for the truncation when setting depth of cut, so maybe the depth of cut on a 1.875 x 8 TPI thread would then become 0.060" ( If the blank were not truncated, the tool would make contact at 1.875", but the truncation has removed 0.020" already, so the tool should only be fed in 0.060" to achieve a full depth of thread. Howard |
richardandtracy | 11/07/2017 16:26:57 |
![]() 943 forum posts 10 photos | For info, on metric external threads, with a sharp point cutter, DOC = 0.7578 x P where P= pitch. Source, Kempes Engineers Handbook, 1988, page E6/3 Fig 3, calculated from thread height H = 0.866025404P x 7/8 to allow squaring off of the ends. For metric internal threads, it's DOC = 0.6495 x P. Regards, Richard.
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Eric Arthrell | 12/07/2017 16:15:31 |
47 forum posts 19 photos | Thank you for your replies now feel more confident to have a few trial runs before machining back plate for my four jaw chuck. Regards Eric |
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