ken98k Posted February 4, 2008 Report Share Posted February 4, 2008 Anybody know what size drill bit for a 9/16 - 24 tap? Link to comment Share on other sites More sharing options...
rdfrench31 Posted February 4, 2008 Report Share Posted February 4, 2008 try here looks like different sizes for different materials Link to comment Share on other sites More sharing options...
Ron J Posted February 4, 2008 Report Share Posted February 4, 2008 My machinerys handbook says the minor diameter is .517" - .527". The calc they use is based on engagement length, but basically: Hole size = Basic major (.562") minus {1.08253 x % of full thread (normally 75%)} divided by threads per inch. I came up with .528". Seems large to me. .500" seems small. I would experiment with 33/64" (.515") it will probably cut .518 or so. Link to comment Share on other sites More sharing options...
z1r Posted February 4, 2008 Report Share Posted February 4, 2008 My calcs also came out to around 527" assuming 75% fit. But I'm sure you could use a 33/64 (.515"). Link to comment Share on other sites More sharing options...
carzngunz Posted February 4, 2008 Report Share Posted February 4, 2008 An easy formula to remember is: Tap drill size = O.D. (of bolt) - pitch (of threads) Pitch = 1/ threads per inch This gives a decimal size drill. An example would be 3/8-16. 3/8 - 1/16= 5/16 or 0.3125 1/4-20 would be 0.250" - (1/20) or 0.050"= 0.200" a #7 drill is 0.201" This gives a good fit and easy to remember, works for metric also. Link to comment Share on other sites More sharing options...
ken98k Posted February 5, 2008 Author Report Share Posted February 5, 2008 An easy formula to remember is: Tap drill size = O.D. (of bolt) - pitch (of threads) Pitch = 1/ threads per inch This gives a decimal size drill. An example would be 3/8-16. 3/8 - 1/16= 5/16 or 0.3125 1/4-20 would be 0.250" - (1/20) or 0.050"= 0.200" a #7 drill is 0.201" This gives a good fit and easy to remember, works for metric also. .562-24=538? Link to comment Share on other sites More sharing options...
rdfrench31 Posted February 5, 2008 Report Share Posted February 5, 2008 .562-24=538? .562-(1/24)=.520 I think I would just use the 33/64 drill Link to comment Share on other sites More sharing options...
Ron J Posted February 6, 2008 Report Share Posted February 6, 2008 carz, that is a good formula. Much easier than anything I've come across in 25 yrs! Thanks. Link to comment Share on other sites More sharing options...
carzngunz Posted February 6, 2008 Report Share Posted February 6, 2008 I used to remember a real easy one for cutting speeds too but my memory lets me down sometimes! I've got some notes somewhere but I probably couldn't find those either. Link to comment Share on other sites More sharing options...
ken98k Posted February 7, 2008 Author Report Share Posted February 7, 2008 I used to remember a real easy one for cutting speeds too but my memory lets me down sometimes! I've got some notes somewhere but I probably couldn't find those either. I think I got this from Don Markey CUTTING SPEED MULTIPLIED TIMES 4, DIVIDED BY CUTTER DIAMETER, EQUALS SPINDLE RPM For a quick reference you can use the formula of Cutting speed (CS) X 4/Diameter of cutter (D). cs is around 125 with carbide and low carbon hardened alloy steel. 125X4/.5=1000RPM. If the steel is softer use 300 for a cut speed. Depending on the steel you can go up to 600cs, but if your chips are black or dark purple slow it down until they are amber. Feed rate depends on the # of flutes on the cutter. Link to comment Share on other sites More sharing options...
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