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09-21-2013, 02:18 PM   #16
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QuoteOriginally posted by pacerr Quote
For those new to the JIS topic:

https://www.pentaxforums.com/forums/maintenance-repair-articles/119344-cross-...s-caution.html

The increased radius of the Phillips driver ensures that it will not seat properly and can damage the screw head under more than moderate torque.
And that is the beauty of the Phillips. It will cam out by design.
List of screw drives - Wikipedia, the free encyclopedia

09-21-2013, 09:17 PM   #17
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>> Wiki refs:

- " Phillips . . . purposely designed to cam out when the screw stalled,[citation needed] to prevent the fastener damaging the work or the head, instead damaging the driver."

- "The JIS B 1012 is commonly found in Japanese equipment. It looks like a Phillips screw, but is designed not to cam out and will, therefore, be damaged by a Phillips screwdriver if it is too tight. " <<

Phillips design is certainly a worthy feature when installing steel fasteners with a steel bit in an assembly line fashion as intended.

Unfortunately, installation isn't the problem in this application. The broader head of the steel Phillips bit doesn't seat fully into the JIS-type screw causing it to ream out the head of soft brass or aluminum camera and lens screws if they don't turn freely when unscrewing them -- which many don't as they're often corroded or a thread sealant has been used.

Once the cross point head of these tiny screws is damaged it's almost impossible to remove them with a screw extractor. If a JIS-type screw doesn't turn freely with a substitute Phillips bit you're better off to file a straight-slot type bit to a suitable point rather than risk reaming the head with a poorly fitting Phillips bit. Better yet, use the JIS bit with anything you plan to reassemble or repair.

H2

Last edited by pacerr; 09-21-2013 at 09:32 PM.
09-21-2013, 11:19 PM   #18
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QuoteOriginally posted by Ex Finn. Quote
And that is the beauty of the Phillips. It will cam out by design.
...in a Phillips cut head. With JIS, it merely mangles the screw.


Steve

(...doesn't want to talk about how this knowledge was acquired...)
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