15/32 -18 ??? Thread size

[Froneck]

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Ground 55° tool with sharp point, didn't try to radius it. Machined a blank .468" with a .412" pilot. Used the Starrett protractor set to 27.5° and used the chuck face that I know is square with no run-out to position the tool that is on center height. Threaded the blank using the nut as my gauge. Threaded until the tip touched the pilot and checked fit. continued but increasing depth .001 thread depth knowing the the sharp point would have to go deeper. Nut finally started but 1 turn, cut another .001" nut went on more. Continued until OD was reduced to .465" Nut will only go on 3 turns then stop indicating pitch is wrong. Checked with thread gauge and 18TPI fits perfect! Checked the Delrin I threaded with the nut and it too fits the 18TPI gauge perfect.Checked Delrinr again with 1.5mm thread gauge and still the same after 10 threads the alignment is at least .75mm off! Colored the screw threads with Magic Marker, rub off is at the leading edge of the 3rd thread. Indicating he 18TPI is not enough lead. So it must be 1.5mm though the Delrin threaded with the nut is 18TPI! I guess the best thing is to get a 12mm X 1.5mm tap. Any other suggestions?

 

[franco]

A couple of questions.
!. Was the strut also replaced?
2. If so was it a genuine BMW part, or after market Chinese?

If Chinese, all sorts of variations are possible: if genuine BMW, I really can't see why, on a fitting like a strut, assuming it is for a hood or trunk support, there could be any reason to depart from one of the appropriate ISO preferred pitches for a 12mm rod, in this case 1.25, 1.5 or 1.75. It just doesn't make sense.

Did you also check the thread pitch on the strut rod and/or try the original nut on the new(?) strut?

By the way, my 60 year old Moore and Wright thread gauges do have a 1.4 mm gauge, so it may have been used in the past: from China anything is possible.

Just to confuse things further, 17 TPI is very close to 1.5 mm pitch.

franco

 

[Froneck]

The strutt looks original but I have no idea where the top attachment came from, as I mentioned a friend wants it done. The Strutt is 14mm X 1.5mm. The end of the shaft had a hex hole for a hex wrench to hold the shaft. It broke at the end of the hex hole. The other nut will extend into the mount and is longer so additional threads are needed. Best would have been to re-thread the nut but that's hind sight since I did mount and indicate the shaft in the lathe, center drilled the end and took a skim cut. The shaft is now slightly over 1/2", I stopped to check the threads size in the nut before going too far on the shaft. I found a tap and die set 12mm X 1.5mm on ebay. The tap will confirm thread size in the nut but if it don't I'm going to use it to cut new threads in the nut and use the die to thread the shaft. Estimated delivery date is Friday 09/10

 

[Froneck]

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12mm X 1.5mm tap and die came today. Tap fits the nut I have so it is 1.5mm! Turned the strut rod to 12mm and used the die to cut the threads, came out perfect! I guess my thread measurement using the nut as a die to thread Delrin so I could check size was not a good way. I have done it with wood a number of times but I guess plastic is not a good method!
Thanks for all the help guys!!