>-----Original Message----- >From: Ron Pickard [mailto:rpick...@hypercom.com] >Sent: Monday, March 25, 2002 7:28 AM >To: jo...@exchange.scotland.ncr.com >Cc: emc-p...@ieee.org >Subject: RE: chassis bonding - star washers enough? > > > > >Hi John, > >You wrote: > >>We use screws which have combined hex/posidriv heads with >>serrations under the head, which eliminates the need for star washers. >>We find these work very well for zinc plated parts. On epoxy painted >>parts, they also seem to cut thru the paint and give a satisfactory >>result - you might feel "happier" if you have more than one screw >>for any given part. > >Using these screw types may be "satisfactory" at the time of >production, but what will be expected >when the product is placed into service and into varying >environments? Will the newly exposed >chassis surfaces (I agree that they would very small) become >so oxidized that the oxidation leaches >to the "satisfactory" ground connection? Probably not, but >IMHO, due diligence might prescribe an >evaluation. > >>We also use self-clinching PEM nuts with good results. >>Typically we find that where a grounding conductor has been >>brought to a particular area of our products, we would still >>pass the 0.1 ohm, 25A test when we remove the conductor. > >May I ask how you pass this test when, as you stated, the >conductor is removed (just curious). >Please provide clarification. > >Best regards, > >Ron Pickard >rpick...@hypercom.com
PEM nuts may have their proper place, but I don't like to use them, since they are prone to being driven out by the pressure applied to a bolt during tightening. If the assembler just leans on the bolt a little, the nut pushes out of the clinch, and then spins in the bolt. This can turn into a bad problem if the nut is in a blind area. I prefer to use Rivnuts, which clench with a shoulder on the front surface and a deformation area on the rear. These will not fall out with axial loading. Regards, Ed Ed Price ed.pr...@cubic.com Electromagnetic Compatibility Lab Cubic Defense Systems San Diego, CA USA 858-505-2780 (Voice) 858-505-1583 (Fax) Military & Avionics EMC Services Is Our Specialty Shake-Bake-Shock - Metrology - Reliability Analysis ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list"
