10-32 screw / 10-24 tapped hole

[bernardg]

Hello,

Our motors call for a 10-24 tapped hole on the endframes, and a 10-24 screw is driven into it to mount the motors into the unit.Accidentaly, we used a 10-32 screw instead of a 10-24 screw. (Because the torque wrench was powerful enough, this was not inspected during the assembly process.)

Our customer says that this unit would face some amount of vibration during itz application in the field.

Questions:
(1) what is the worst case scenario that we are looking at becos of the faulty screw.
(2) What will be the retention properties of this screw? will this give way?

Feed me with your comments also.

Regards,
bernie

 

[CoryPad]

(1) The worst case scenario is that the internal and external threads have sheared and there is no joint preload. The joint has no resistance to external forces and will disassemble immediately after force application.

(2)The joint will have no retention properties since the threads will have been damaged during installation. The joint will give way.

You need to inspect all products. You will need to remove all screws, repair the internal threads (e.g. thread insert like Heli-Coil), use new screws, and reassemble using the proper technique (torque, angle, etc.)

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[strokersix]

Agree that you should probably assume worst case.

However, it is certainly possible that the screw may have deformed the housing threads, forming it's own threads in the process. If this is the case, and there is adequate thread length, the joint could be reliable. Thread forming screws are commonly used in softer, ductile materials and can be quite resistant to loosening because there is very little or no clearance in the threads.

I offer the above comments for discussion only, not a recommendation.

 

[CoryPad]

strokersix,

If a non-matching external thread is forced into a tapped hole, new threads may be formed. However, this is not analogous to a thread forming fastener. In this case, even if new threads are formed, they will be incomplete, full of cracks, and very prone to stripping.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[arto]

Helicoil it, like Corypad sez. These rank up there with WD-40 & Duct Tape, as the greatest inventions known to man! ;-)
They will be better than the original!

http://www.emhart.com/products/helicoil.html

or the equivalent, from Australia:

http://www.recoil.com.au/default.htm

 

[strokersix]

I figured there would be a response to my comments!

Helical thread inserts are a preferable solution. Here's another possibility: If there is enough material can the hole be drilled and tapped deeper and a longer fastener used? Be sure to remove all the damaged threads with a clearance drill though. What about using a larger fastener? Obviously both of these approaches require hardware different from design intent.

Mike