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: internal teeth or external?
: internal teeth or external? -- dalecyr	Post Reply	Top of thread	Engineering Forum

Posted by: dalecyr ® 01/05/2011, 12:49:48 Author Profile eMail author Edit

I never really understood the reasoning behind the split lock washer. It doesnt seem like it has any significant gripping surface, (with just the one cut) and I've always doubted the effect the offset at the split has. Star, or toothed, lock washers intuitively have more of a locking effect, due to more teeth. But, I've always wondered which is better for a particular application. If we can't come up with a sound engineering principal, I could always ask my wife... ;) dale

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: internal teeth or external?
: internal teeth or external? -- dalecyr	Post Reply	Top of thread	Engineering Forum

Posted by: Kelly Bramble ® 01/05/2011, 08:17:37 Author Profile eMail author Edit

Good question, I just looked in my data and found that there are four basic types of Tooth Lock Washers. Internal Tooth, External Tooth, External Tooth Countersunk, and Internal/External Tooth Lock Washers. No data was given on specific application, however the sizes are fewer and smaller than the split type.

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: : internal teeth or external?
: : internal teeth or external? -- Kelly Bramble	Post Reply	Top of thread	Engineering Forum

Posted by: Kelly Bramble ® 01/05/2011, 09:19:14 Author Profile eMail author Edit

Oh ya - /hardware/tooth-washers-external-internal.htm

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: : : internal teeth or external?
: : : internal teeth or external? -- Kelly Bramble	Post Reply	Top of thread	Engineering Forum

Posted by: Pinkerton ® 01/05/2011, 18:38:44 Author Profile eMail author Edit

Oh Kelly, what a cop-out. Dave

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: : : : internal teeth or external?
: : : : internal teeth or external? -- Pinkerton	Post Reply	Top of thread	Engineering Forum

Posted by: Pinkerton ® 01/05/2011, 19:08:00 Author Profile eMail author Edit

Hi Dale, As with all things in life and Engineering it is all about compromise, but first let me comment on the ubiquitous spring washer. If correctly used and installed for an application there is nothing that will do the job better than a single-break spring washer. The break is intended to be harder than the base metal and the bolt. As such it bites into both metals and forms a strong mechanical connection. The break-cut is angled such that any movement to un-do the bolt/nut will increase the cutting angle into the metals of both parts, thus encouraging even deeper mechanical engagement. It will continue to shear it's way into both metals until the "bite" is so deep it cannot proceed further without deforming (opening) the washer. Nuff said. Now to the star washers in general. They are intended for much lower torque applications and usually where the base material is softer than the screw material. The multiple spikes are intended to dig into both materials, but unlike the spring washer, once that locked-integrity has been breached there is no follow up action to regain or maintain control as with the spring washer. Now, to the internal versus external it is application dependent. Usually an external is used for plastic materials to spread the locking load and engagement "cuts" over a wider area. With the external one, the screw head has to be as large as the washer and that is not always desirable or possible. Often the internal one can present a better "look" as it is nice and round, smooth and flat from an outside view. With the internal one the clearance hole for the screw has to be quite tight in the base material otherwise there is good locking to the screw but poor locking to the base material. This is what lead to the internal/external type Kelly pointed out. The external locks to the plastic, the internal to the screw head. Also it is noteworthy in spring v star, that star washers tap out around the 1" diameter whereas spring lock washer run to 2" diameter or more. That alone tells some sort of story??? No? Dave Modified by Pinkerton at Thu, Jan 06, 2011, 09:32:45

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: : : : : internal teeth or external?
: : : : : internal teeth or external? -- Pinkerton	Post Reply	Top of thread	Engineering Forum

Posted by: dalecyr ® 01/06/2011, 17:06:49 Author Profile eMail author Edit

ah, ok thanks, that makes sense. although it seems obvious when you say it, the nuances are just obtuse enough to be non-intuitive. thanks for the clarification.

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: : : : : : internal teeth or external?
: : : : : : internal teeth or external? -- dalecyr	Post Reply	Top of thread	Engineering Forum

Posted by: dalecyr ® 01/06/2011, 17:15:11 Author Profile eMail author Edit

HEY!!! Wait a second... so... that means that there is a correct, and an incorrect, way to install split washers. Right?

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: : : : : : : internal teeth or external?
: : : : : : : internal teeth or external? -- dalecyr	Post Reply	Top of thread	Engineering Forum

Posted by: Pinkerton ® 01/07/2011, 09:31:36 Author Profile eMail author Edit

Yeah ... and ... right hand bolt threads become left hand threads if you turn the bolt over end-for-end in your hand. LOL Dave

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