TVP,
Yes, thank you for you clarification. Since the screw is waxed and the hole is drilled, I am assuming that the friction is controlled. I couldn't imagine that 11 in-lb is too much of the seating torque.
MSU2000
Corypad,
My definition of bottoms out is when the underhead screw is seating flush to the top piece part providing clamping pressure to the bottom piece part thru threads generation.
MSU2000
TVP
1. I should mention that I was using manual screw driver to come up with that number while it was using the electric driver that we experienced head fracture. Could you elaborate more on your first sentence please?
2. We tried to control any miss-alligment as best we can, but I undertand...
Gentlemen,
To continue the discussion. Like I mentioned earlier, the prototype testing yield to 16 in-lb of max torque before the head snapped, therefore I set the seating torque to be 11 in-lb (65%).
If the screw head snapped before it bottoms out, it leads me saying that I'm overtorquing...
I would say that lack of confidence resulting in overanalyzing a problem is my situation too. It gets better once you see that your design works.
I'm in my 5th year now (1st on the current job) and finding my self still stumbling across those problems that all of you mentioned. I learned that...
I have an application similar to weight scale that needs to be protected during drop testing (3'). I'm looking into ideas on how to do protect the spring from bending. The mechanism is suspended/canteliver over 2 leaf springs and acts like a weight scale. Cost need to be very minimal. I was...
When the ball end is engaged (inside detent hole)it will be freely to move. If you applied a horizontal force to the ball, the ball can/can't be rotated depending on the friction between mating surfaces and that normal (horizontal force) you apply.
MSU2000
Ok, Let me take it a little furher.
When do I use Thread forming screw instead of sheet metal screw when joining 2 sheet metals. In this case, my sheet metals are .048" and .094" with countersunk for flat head.
Thanks
MSU2000
Coughdrop,
You brough a good point about the hole depth. I haven't checked the actual dimensions on real part. I'd be surprised if they can't hold the depth of one hole to be the same as the rest (it is CNC set up). I found out also that the scews are made overseas. So, this might relates to...
Coughdrop,
The material is Aluminum die casting alloy 383
I believe the casting isn't pre-treated for corrosion protection.
The thing is, when I used manual screw driver. I didn't break a thing. It is only when I used electric screw driver and yes it is random. I tried to align the screw to...
To be honest, that 11 in-lb of seating torque was based on my experiment. I know I need at least 5-6 in-lb torque to drive the screw in ( this is so called prevailing torque, I suppose) and this based on experiment also. Now, I tested up to 16 in-lb before I started to screw head snapped off...
Guys,
What does the move profile of a motor-load system gives you?.
I'm solving a stepper motor-load system and found the acceleration rate of the motor can do given the specified load. I have a given time between t=0 to t=t1. This should give me the move profile of the stepper motor (the...
Limct
You are right about the cost saving feature of tapered hole. Infact we are incorporating that in the production part. I followed the recommeded hole size from the taptite manufacturer. I will look for the website you suggest. I appreciate for the info.
I'll keep you guys posted, I'm...
Ok,
Thanks for the info.
1. Thread forming screw actually forms thread, that means they don't remove material like the thread cutting screw does.
2. Sheet metal screw do not intent to cut or form any threads in the mating material instead it "clamps" the two surface between the screw pitch...
guys,
I'm getting all confused between sheet metal screws, thread forming screws, thread cutting screws, and self drilling screws. What are the differences and usage of such those screws, when to use it, how to choose it, are they interchangeable?
Can you shed some info on this.
Thanks!
MSU2000
Screwman,
It is drill hole and it is set to the recommended size .101 from taptite manufacturer handbook. I do not think that the breakage was caused due to bottoming out of the screw. (The blind hole is .375 and the thread engagement is .300). I will check for the heat treatment spec. The...
Cory,
Screw size is 4-40 x 3/8 taptite 2000 w/short point, made out of alloy steel with case hardening heat treat. It is Pan Torx drive head. The actual torque that caused the screw to broke is unknown. I know that the seating torque was set to be 11 in-lb and prevailing torque is about 5-6...
Taptite is for metal. The screw is clear zinc chromate finish and Since it is thread forming screw, serviceability isn't an that great which by design.
Gensetguy, So you are saying that the torque drive increases as the length of engagement increases?
Thanks
ME2000
