Whiz-Lock Screw 3

[dik]

I'm looking for design information for a 1/4-20 X 0.75 Whiz-Lock Screw as manufactured by MacLean-Fogg Co. Anyone have a link that gives design load capacity? I assume that the material is Grade 5 or equivalent.

thanks, Dik

 

[Screwman]

The Whiz-lok design is only the serrated feature on the underside of the head. the balance of the fastener is open to any design that the engineer requires. You need to know if it is grade 5 or grade 8, since that will make a huge difference in it's performance and capacity.
In my experience (almost 30 years) the Whiz-lok feature is more Marketing than actual performance. If you take a standard head design on a threaded fastener and load it up to the proper clamp load it works just as well. One situation where the Whiz-lok works well is bearing against softer die cast surfaces, where the serrations really dig in and prevent rotation. In most cases you can obtain better resistance to loosening if you use a thread rolling screw like a Taptite, plus you eliminate cross threading and the cost of tapping.

Dick

 

[dik]

Thanks very much... I was almost thinking that no one had ever heard of them. I didn't know it was just a feature of the serrated head. It is my understanding that the bolts are Grade 5 and that they should be treated as such. The bolts are in tension; does the serration have an effect on reducing the head thickness to possibly reduce tensile capacity?

Dik

 

[Tmoose]

1/4-20 ends up with a disproportionatly small minor diameter and a thus relatively weak bolts. I worry a lot about adequate initial torque/tension, and good bearing under the bolt and nut heads to prevent embedment and loss of torque. Serrations on a fastener or washer face would seem to me an invitation for embedment and loss of torque, which then unnecessarily subjects the bolt to fatigue if my loads are varying.

If loads vary then keeping the fastener from rotating may
instill a false sense of security.

http://www.boltscience.com/images/boltf6.jpg

http://www.boltscience.com/pages/vibloose.htm

 

[dik]

Thanks for the additional information; I'll pass this on to the client... although I use them, fasteners are not my area of expertise...

Dik

 

[Screwman]

Like Moose said, the serrations can cause embedment, with a resulting loss of clamp load. The head cross section is such that head yielding is not a failure mode though.
If the client is having such a problem with loosening, then you need to first make sure that the parts are truly being tightened to their full capability. If they are still loosening, then you may need to resort to "band aids" to help prevent (not solve) the problem. Some of the things I would try would be lock nuts (nylock or deflected metal), or a thread adhesive (preapplied by the manufacturer is much less messy). Don't even contemplate using a 'lock washer' because they don't (lock that is). On joints that have small L/D ratios (less than 4 : 1) you sometimes are forced to use the band aid approach since there is not enough effective stretch avaiable in the bolts to keep them from loosening.

Dick