What size drill to use for undersized Cuetec 3/8-14 tap?
- Thread starter fab944
- Start date
Looks like you're tap drill is severely too small. There should be a flat on the crest of the thread,,,,, those are ragged because of the sharp edge.
Real machinists use the simple calculation of Diameter - Pitch to determine tap drill size. For 3/8-14 that would calculate to .303",,,,,,,,, try an N drill (.302") then tap it.
Real machinists use the simple calculation of Diameter - Pitch to determine tap drill size. For 3/8-14 that would calculate to .303",,,,,,,,, try an N drill (.302") then tap it.
Is it possible that he's using a full size 3/8x14 tap instead of a tap designed to fit the undersized Cuetec joint screw?
Well, from what I can determine, the difference is stated as being a .360 OD as opposed to a .375 OD. But what else is undersized? 30 Degree threads load on "pitch diameter", not OD. My statement earlier was based on standard .375 od. Who knows why Cuetec would fool around with that when a 9mm is practically identical OD but here we are. So did the Pitch diameter change as well? I honestly have no clue. BUT! The formula I stated works for all 60 degree threads, imperial as well as metric, so maybe go with an "L" drill,,,,,,,,, or a 7.3mm,,,,,,,,,,,,HA!
Ok guys, so I found the pic from Cuetec of their 3/8-14 tap they sell, below. So it looks just like any other standard screw thread except they reduced the OD by .015". To me, since proportionally it looks normal, my guess is everything else about the diametrical aspects of the tap have reduced equally. If they altered OD only there would be a big land on the OD of the tap and screw, which does not appear to be the case. Therefore, the pitch diameter and minor diameters must have reduced as well. That being the case, .288 mathematically would be the ideal tap drill. As shown before, the .265 leaves ragged sharp crests, so we know that's too small. Someone should try around a .288 or so and let us know what it looks like. I would, but I have no need for that tap so I can't.
When KJ hung out here......god I miss Him, he sold a 3/8x14 tap that he modified, so the edges were, more rounded, which fit the pins perfectly. So if you look at the above picture of the tap....the edges are rounded, not sharp....makes a very large difference.
It does make a difference, in that all Unified V threads should be radiused 1/8" of the pitch of the thread for strength, so much better than sharp V thread. If your point was that sharp threads are good enough for cues, you may be right.
Thank you for the explanation(s). I will look for an L drill bit to use on the next go around. I appreciate the detailed information received.
Frank