TheRocketScientist
Mechanical
- Feb 19, 2009
- 20
I am looking for exact specifications for the #2 drill tip of a TEK type self drilling screw. I am securing a plastic block to 0.090" thick aluminum extrusion with 3/4" long stainless steel #10 TEK type screws. Currently using #10-16 screws with a #2 drill tip, which strip at about 70-80 in-lbs, allowing easy secure assembly to a good seating at about 25 in-lbs using Atlas-Copco auto shutoff assembly tools.
Purchasing wants to change to a fine thread #10-24 with a #2 drill tip. Evidently, any of these have to be special ordered because the manufacturer generally produces a #3 drill tip on this size screw. We must have a #2 drill tip [shorter length] because the screw cannot be located further inward lest it hit another surface [see photo]. There's only enough room, as it is, to get 2 or maybe 3 threads past the anchoring surface before the drill tip encounters the far wall.
Initial samples of the fine thread 10-24 screw provided good results, stripping at 80-90 in-lbs. However, the samples from the first major purchase of these screws perform very poorly, stripping at 45 at best, or as low as 27 in-lbs in one case- barely greater than the seating torque. Consequently we can't select or adjust a tool to seat but not strip these.
Nominal screw diameter is 0.190, and the samples match this well, except the outer 3-4 threads are more like 0.180" OD. I ran some fine thread samples in to just the drilling depth, effectively making a tapping pilot hole with the sample screw, then gaged that hole with number drills, to find that the drill tips were making holes 0.161-0.169" dia., as crudely measured in this manner. In comparison, Machinery's handbook suggests 0.148-0.154" tap hole for #10-24 _machine screw_ threads.
Close examination of the currently used [coarse thread] and the sample finer thread screws shows that the finer thread samples have very little protrusion of the thread beyond the diameter of the drilling tip. I suspect that the #2 drill tip is not formed correctly to spec, or perhaps the spec is not suitable for fine threaded fasteners into AL substrate. Not enough material left for a proper grip, with a 0.170" hole and 0.180" threads.
Bottom line, the early samples held much more torque than the present samples, and I suspect the reason is an incorrectly manufactured #2 drill tip- but I cannot find any EXACT specificatons showing what the drill tip should look like and measure.
I did find a thread here at Eng-Tips [via Google]:
Which, for some reason a search here for "TEK" or "TEK screw" will NOT find...
From that thread, I visited the recommended link:
which has no such information, so I submitted a request via their handy link.
I have yet to try to find the NASPEC information that was mentioned in the previous thread. I thought perhaps someone here has been thru this already and has a readily available pointer for me to find the specs of this type of screw drilling point.
Purchasing wants to change to a fine thread #10-24 with a #2 drill tip. Evidently, any of these have to be special ordered because the manufacturer generally produces a #3 drill tip on this size screw. We must have a #2 drill tip [shorter length] because the screw cannot be located further inward lest it hit another surface [see photo]. There's only enough room, as it is, to get 2 or maybe 3 threads past the anchoring surface before the drill tip encounters the far wall.
Initial samples of the fine thread 10-24 screw provided good results, stripping at 80-90 in-lbs. However, the samples from the first major purchase of these screws perform very poorly, stripping at 45 at best, or as low as 27 in-lbs in one case- barely greater than the seating torque. Consequently we can't select or adjust a tool to seat but not strip these.
Nominal screw diameter is 0.190, and the samples match this well, except the outer 3-4 threads are more like 0.180" OD. I ran some fine thread samples in to just the drilling depth, effectively making a tapping pilot hole with the sample screw, then gaged that hole with number drills, to find that the drill tips were making holes 0.161-0.169" dia., as crudely measured in this manner. In comparison, Machinery's handbook suggests 0.148-0.154" tap hole for #10-24 _machine screw_ threads.
Close examination of the currently used [coarse thread] and the sample finer thread screws shows that the finer thread samples have very little protrusion of the thread beyond the diameter of the drilling tip. I suspect that the #2 drill tip is not formed correctly to spec, or perhaps the spec is not suitable for fine threaded fasteners into AL substrate. Not enough material left for a proper grip, with a 0.170" hole and 0.180" threads.
Bottom line, the early samples held much more torque than the present samples, and I suspect the reason is an incorrectly manufactured #2 drill tip- but I cannot find any EXACT specificatons showing what the drill tip should look like and measure.
I did find a thread here at Eng-Tips [via Google]:
Which, for some reason a search here for "TEK" or "TEK screw" will NOT find...
From that thread, I visited the recommended link:
which has no such information, so I submitted a request via their handy link.
I have yet to try to find the NASPEC information that was mentioned in the previous thread. I thought perhaps someone here has been thru this already and has a readily available pointer for me to find the specs of this type of screw drilling point.
