positive locking mechanisms

[warywoda]

Hello
I know this is a topic that has been discussed extensively, but I have a few questions I haven't seen asnwered yet.

The rules say that "All critical bolt, nuts, and other fasteners on the steering, braking, driver's harness,
and suspension must be secured from unintentional loosening by the use of positive
locking mechanisms." What exactly constitues a critical fastener? If I am using 9 bolts to mate two components, are these considered critical, or is there enough redundancy there that this rule does not apply?

As well, I have found some bolts on McMaster that have a nylon patch on the threads, for locking purposes. Does anyone know if this is considered a valid locking mechanism?
Thanks

Patrick
McGill FSAE

[HenningO]

Yes, Nyloc nuts are OK for any components that is "far" from a heat source. So don't use it to attach brake discs/calipers as the nylon have a fairly low melting temperature.

Critical components are components that will, in case of coming loose, will endanger the driver or people around the track. As you wrote, all your suspension components, steering, braking systems etc. But not to forget, drive train components can/should be considered as critical.
Examples of non critical components where you could (but you don't really want to) use nuts without any locking is for instance your data aq box, your throttle position sensor, your water pump. etc etc

[moose]

I am fairly certain that nylon patch bolts do not count.

Nylock nuts and safety wire are both good (still need 2 threads showing on both)

there are other locking mechanisms, but i'm not sure which are OK

[VFR750R]

Those aircraft style locknuts that are crimped on three flats work really good, though like all locking nuts, should only be used once. I guess snaprings are considered locking, many teams use those on drivetrain components.

Alot of nascar teams use quick release pins on their shocks, sway-arm links, even splitter struts during practice, but then put proper bolts and locking nuts for the race. Many teams are on 'Wiggins' style oil and water connections, but for the race some safety wire is wrapped around them just to make sure.

We use crazy quantities of safety wire,duct tape, and zipties too.

[Tech Guy]

If you look under the Frequently Asked Questions section on the official FSAE web site at:
http://www.formulasae.org/forums/formula/dispatch.cgi/r...00066/10/def/5779073 (http://www.formulasae.org/forums/formula/dispatch.cgi/rules/folderFrame/100066/10/def/5779073)

you will find this information that was posted in December 2006:

"3.7.2.2 Securing Fasteners
Based on a couple of recent questions, the Rules Committee has decided that in order to be consistent, we need a clearer definition of what constitutes a "positive locking mechanism"� as required by Rule 3.7.2.2.
The definition we will apply is as follows:
1. The Tech Inspectors (and the team members) must be able to see that the device/system is in place, i.e. it is visible.
2. The "positive locking mechanism"� does not rely on the clamping force to apply the "locking"� or anti-vibration feature. In other words, if it loosens a bit, it still prevents the nut or bolt coming completely loose.

Also, "prevailing torque lock nuts"� fabricated by a team will not be acceptable. We have no certainty that they will have the quality control to work all the time."

This should answer your questions, i.e. Nyloc nuts, safety wire, locking tabs are OK. Nylon patches on bolts are not OK.

[moose]

it also probably doesnt hurt to safety wire any really critical external snap rings as well, to make sure they stay on/shut, although I'm not sure if that's required.

[Drew Price]

Patrick,

Regarding your question about 9 fasteners to mate two components, I too had been wondering similar, and just received this rules clarification:

Question:

"Rule 3.7.2.2 states that "All critical bolt, nuts, and other fasteners on the steering, braking, driver's harness, and suspension must be secured from unintentional loosening by the use of positive locking mechanisms. ...."

My question is in regards to the criterion which defines a "Critical Fastener." Is any fastener retaining the above mentioned components a critical fastener, regardless of the number of fasteners retaining the component, or are components in the above groups not considered to be critical fasteners (and are thus exempt from the rule) if there are three or more fasteners retaining the component (one loosens leaving two fasteners to provide location and retention, thus making it a redundant fastener).

For example is a brake caliper permitted to be mounted with three bolts threaded into blind holes with no safety wire, while a similar caliper mounted with two bolts must use one of the above mentioned positive locking mechanisms?"



ANSWERE:

All fasteners in any of the listed systems must meet this rule regardless of the number of fasteners being used. We do not exempt a mounting because it has "redundant"� fasteners, because then we would be involved in many, intense discussions as whether there were redundant fasteners or not. This rule is just formalizing good race car practice.

The only exception we have is for wheel mounting. This is outlined in FAQ # 67 which can be found at:
http://www.formulasae.org/forums/formula/dispatch.cgi/r...me/100066/0/def/bf56 (http://www.formulasae.org/forums/formula/dispatch.cgi/rules/folderFrame/100066/0/def/bf56)

Brake callipers need to meet this rule irrespective whether they have 2 or 3 bolts. The normal method is safety wiring. And yes, drilling holes in socket head bolts can be a challenge.

Rules Committee,
FSAE



Best,
Drew

[warywoda]

Thanks for all the replies.
I have one application where I cannot, for a number of reasons, use a nut. The bolt goes into a threaded part and protrudes from the other end. I want to use countersunk heads, so is it permitted to drill through the threaded part of the bolt and pass the safety wire through this? Or a cotter pin? Also, has anyone tried drilling 10-24 bolts in this way, or is that just too small to do with any success?

[Buckingham]

I have seen many applications in the aircraft industry where they use a deformed thread heli-coil insert. (Sorry, but I don't know specifically where they got 'em). They work on the same principle as the crimped locknuts VFR750R referred to.

While a deformed thread heli-coil is not visible, you may be able to ask for exemption since they work very well and are acceptable for use in aviation seating systems as a positively locking device.

In general, every fastener on your vehicle should be aviation grade, with the exception of OE engine hardware.

[VFR750R]

You should safety wire the head, look up pictures of oil drain plugs that are safety wired, they don't have a nut. Also look at sprocket washers for motorcycles. They have a special washer that has bent tangs or splines that index in the shaft, then the washer is bent around the flats of the nut. This may or may not work for your application, but it might get your gears turning (haha).

[moose]

Drilling the 10-24 shouldn't be too bad, especially if you grind off the threads a little bit. I think I did that for some bolts on something (not sure if they got used), but it wasn't an issue. If you use a nice sharp 1/16" bit i've rarely had issues as long as you make sure the drill bit goes in straight down. If it starts to wander, move over a bit. (I do this in a B-port, clamping the bolt parallel to the Y axis, in a vice).
6-32 is probably the smallest i've gone, but if you're patient and pay attention pretty much any bolt can get a hole drilled in it.

-matt

[jm1495]

On a related note.. Mcmaster also sells capscrews with predrilled heads for safety wire.

[Biggy72]

Mcmaster also sells 1/16" drill bits that easily drill cap screw heads for a fraction of what they cost to buy predrilled. When you go to drill the cap screw you just have to be sure that the bottom side is flat when you go to drill into it. I cranked out a ton of them last year before comp.