Anyone know anything about lock nuts?

[shygirl40]

Hi-
I have a task model office chair (from global industries)- it is a fairly simple design and typical of what you might find in many offices with computers. But my chair really sucks because the back of this chair (the manuf. calls it the "back upright"), is held in place by sliding a flat, curved metal bar into a slot in "the seat mechanism" under the seat and then threading a knob, with a flat washer and a tooth washer (in that order) into a hole in the flat, curved metal bar. That sucks because the knob always loosens up (ie. unscrews) after I use the chair a few times, and it causes the "back upright" to become loose as well, and as
you can imagine, the chair isn't fun to use like that. But! I just learned about LOCK NUTS and how they prevent the leveling legs on washing machines from unscrewing whenever the washer moves and I thought, hey, that just might help me with my problem. But! There are -so- many different kinds of lock nuts! Which one would be a good one to
use for my chair? I sure don't know. Could folks here recommend something? Thanks so much.

shygirl

[LazyPup]

Shygirl,

In general lockwashers are a very simple device which relies up a combination of spring tension and friction to hold a nut or bolt in place.

Common lockwashers are made of a spring steel and are cut through on one side, then bent slightly so the two edges of the cut are our of register with each other. At the torque is applied the washer is compressed flat and if the nut or bolt tries to move the cut edge binds into it by friction to prevent movement. Common lock washers are made in many differing metals, steel, carbon steel, stainless steel, brass, bronze, etc. It is always best to match all fasterners by the type of material to prevent electrolosis corrosive effects of dissimilar metals. Common lock washers come in a large variety of sizes from a minor fraction of an inch to 2" or 3". In general, common lock washers offer the best holding power but are not well suited to repeated movements or tensioning.

Internal tooth and external tooth lock washers are generally made in smaller diameters and used in light duty applications such as holding machine screws in an appliance cabinet, electric motor housings and such. Usually the internal tooth type are used under the heads of machine screws and the external tooth type under nuts, but I am not sure if their is a specific reasoning behind that practice.

A jamb nut is normally a nut of the same variety, but slightly thinner. Once the main nut is torqued into place an jam nut is tightened against it to hold it firmly in place. This method is used on very high load demands. (next time your at a shopping mall take a look at the base of the parking lot light poles. You will probably see double nuts used to hold the poles on the concrete pedastal pads). This method is also commonly used on critical parts in an automobile engine internal parts such as rod or crank bearings.

Self locking nuts have a fiber or nylon washer built into the nut which has an internal opening slightly smaller than the bolt diameter. As a bolt passes through the nut it cuts into the fiber material which locks it onto the threads of the bolts. These type are very good in high vibration applications such as on your lawnmower.

The knob on your chair probably has a common lock washer.

Your problem in probably resulting from a couple of conditions which should be fairly easy to fix.

You stated that there is a flat washer between the lock washer and the metal base it rests on. No douth the surface under the flat washer is painted. Quite often in an application like that the paint under the washer breaks down, and the minute granules of loose paint will actualy work as a bearing surface allowing the flat washer to move. You could first try roughing up the painted surface and the face of the flat washer with a piece of sandpaper to remove the loose paint and improve the friction on that surface. If that doesn't solve the problem you may try removing the flat washer and allowing the common lock washer to lock between the underside of the knob and the metal frame.

Common lock washers require a considerable torque in order to work most effectively. You may try adjusting the seat to your liking, then use a pair of pliers to torque the bolt down a bit tighter.

[HayZee518]

Two types of locknuts come to mind. One, if you look at it the hole is slightly trangular in shape and holds quite firmly. The other is called a "nye-lock" and has a piece of nylon embedded within the threads. Either should suffice for your application. When you use these, use two wrenches - NOT PLIERS - to make them up.

[shygirl40]

Wow lazypup! You are amazing- so much good information.
But I need to correct you on something- you misunderstood something about my chair. You said,

"You stated that there is a flat washer between the lock washer and the metal base it rests on."

No, I didn't say that. But first you should know that I definitely do not have a common lock washer, I have something the manufacturer calls, a toothed washer and a plain old regular washer. And the tooth washer doesn't look like the two toothed lock washers you showed in your post. I'm sorry I can't get a picture of it to you, but it looks something like the external lock washer but with some raised ridges on the front and the back of it. And its placement: there is the knob (with a machine screw, I guess you call it), and on that is first the flat washer, and then the toothed washer. So the toothed washer rests between the flat washer and the metal, painted surface.

I've been told by fastenermax.com that I can't use a lock nut because I can't get to the end of the knob/machine screw- but what about a self-locking nut? That sounds real promising. Or I could start first maybe with your two ideas (ie. roughing up the surface and removing the flat washer) and if that fails, then try the self-locking nut.

shygirl

[shygirl40]

Hey HayZee!

quote:Originally posted by HayZee518

Two types of locknuts come to mind. One, if you look at it the hole is slightly trangular in shape and holds quite firmly. The other is called a "nye-lock" and has a piece of nylon embedded within the threads. Either should suffice for your application. When you use these, use two wrenches - NOT PLIERS - to make them up.

These are both self-locking nuts, aren't they? Why is it important to use wrenches and not pliers? That could be a problem for me because I don't have any wrenches (maybe I could borrow something from the hardware store).

shygirl

[LazyPup]

When i suggested using pliers i was envisioning the need to grip the large hand knob on the end of the bolt, in that case you would need something like channel locks to have enough opening to grip the 1 1/2" or 2" knob.

Hayzee is absolutely correct though. One should always use the appropriate wrench rather than pliers to tighten bolts and nuts. Using the wrong tools will result in improper torquing, marred and damaged finishes and skinned knuckles..and take my word for it, nothing is more frustrating than trying to work on something after someone has rounded off all the nuts and bolts with improper tools.

However, in my experience somewhere in the kitchen is a junk drawer jammmed with who know what. An somewhere in that drawer the ladies have a pair of cheap pliers, a bent screw driver, a butter knife and probably a dull steak knife, and through methods that are totally foreign to us guys, they could disassmble a 747 jumbo jet in an afternoon.

I think the girls were getting the McGiver theory of home repairs in Home Ec class while we were goofing off in the shops in school.