minimum wall thickness for tapped hole 2

[lodhss]

Trying to figure out how to calculate the minimum wall thickness of a tapped hole. I’ve seen stuff for sheet metal, but not for a solid block. Right now, the wall thickness is approx 0.25 x set screw diam. The set screw would be torqued to max holding power. If you have any helpful info, that’d be greatly appreciated!

 

[MikeHalloran]

ISTR a general rule like 1.0 x nominal diameter to begin developing the screw strength, depending on the female part's material.
Upper limit is around 3.0 x nominal diameter, at which depth a Delrin nut can break a steel screw.
I.e., 0.25 x D is generally not enough.


Mike Halloran
Pembroke Pines, FL, USA

 

[TVP]

Mike is referring to the thread length or depth. Based on the attachment, I believe the OP is asking about the wall thickness in terms of how close to the edge of a part (edge margin) can the thread major diameter be. The wall thickness can be as little as D/4 for standard nuts, but usually is greater for bosses or straight sections in parts (castings, sheetmetal, etc.). A common rule of thumb is that the wall thickness must be > 3 times thread height.

 

[johnchrc]

What is the application? What pressure is this holding? Do you have to tighten to max. torque? It it just a bleed port or does it hold near critial pressure and if it bursts will it but a bullet in someone? I think it will work depending on your application/

Have you looked at smaller size pipe plugs? How about a straignt thread with o-ring on end built to your exact requirments.

Parker Plugs?
CJ


- CJ

 

[lodhss]

the set screw and hole would be CoCr or titanium alloy. It would be rather small. Looking at possibly 8-36 UNF set screw. Hand tightened. The set screw will be used to hold a transverse axle in place. No bursting in this application

 

[johnchrc]

I'm sorry. I thought you were installing NPT plugs.

Either your thread shears or the outer tubeshears. You have thin wall on one side but enormous wall on the other. I don't think the tube will fail. Try FEA or run calcs with the average wall 360 degrees around. It has to be supported by the thicker tube.

If I was unsure I would run a quick cheapt test. Test it in a press. For the materials, use HT Alloy Steel and same set screw material. Apply axial load in press. Repeat as required.

Pre-torquing may help relieve thread shear as its loaded but I dodn't think you need to do anything except make-it up to shoulder, tighten per spec and apply blue loc-tite so it doesn't come loose.

Just some suggestions...

Let me know what you find do and find out.

CJ

- CJ

 

[MikeHalloran]

I should have mentioned this: I hate setscrews. I tend to fire designers who use them.


Mike Halloran
Pembroke Pines, FL, USA

 

[johnchrc]

Set screws for this don't seem appropriate and almosy always back off. Use loc-tite and torque shoulders where applicable.

For holes you need to drill #20(.161) or #19(.166) #10 -32 ta x X dp (or tap thru)

You could also epoxy or weld ends into the frame that may be much stonfer and firmer to fit one of the transverse axles against. I'm not really familiar with the axles but I like to ask questions to see if I can helop and learn soehting. Lord knows I need to.

Chris


- CJ

 

[mfgenggear]

I agree, set screws are workable to hold objects that are not under stress.
such as tooling balls or pins which need to be held in place but are not under load.

Mfgengear

 

[lodhss]

can't use locktite (medical application so it needs to be sterilized), and the set screw needs to be able to be removed if the axle needs replacement. The set screw isn't meant to hold down the axle, rather prevent it from sliding in and out of a transverse hole. I was going to add a c-clip to the set screw to prevent it from backing out.

 

[MikeHalloran]

Use a bigger c-clip. ... to retain the axle. Forget the setscrew.


Mike Halloran
Pembroke Pines, FL, USA

 

[FACS]

It's going to come down to the material you are threading, and if it will deform when you cut the threads. That said, the wall thickness for a small portion of the threads can be as thin as the depth on the threads. If a smaller set screw will do the job, then go with it.

If you are worried about the set screw backing out (not the intent of the original post) then see if it's possible to add another set screw, and try it as a jam nut. Otherwise, use your retaining ring to hold it in.

Charlie

http://www.facsco.com