Peter, Be careful about producing a lightweight jig. If it isn't stiff enough you'll end up wasting a lot of time and money. The tables on vibration machines are normally made from magnesium alloy which I believe has a slightly better stiffness/weight ratio than aluminium. However the real reason for using mag alloy is that is has a lower loss tangent than aluminium. I think you have three options: 1. Decide your current fixture overdesigned and either redesign it or start cutting chunks off it. 2. Decide it isn't overdesigned but redesign it in carbon fibre - you won't achieve a great increase in stiffness/weight ratio by moving to another metal. 3. Take the easy option and start phoning test houses.... Regards, [log in to unmask] wrote: > > Hi T-Nagers, > > I know that this is a largely Mechanical question, but I need your > recommendations for light-weight materials that I could use in place of > aluminium to make a vibration test jig. I have been landed with designing > an ESS jig to take a 14.5kg (32.5lbs) box that will be attached in three > places - by a wedge-shaped tongue into a groove arrangement along the rear > bottom edge, and by two ARINC fasters at the bottom of the front panel > below all the interface connectors. > > The ESS Vibration test is 10 minutes Random vibration in one axis. > Frequencies range between 20Hz and 2000Hz, with the vibration profile > ramping up between 20Hz and 80 Hz at 3dB/octave to an acceleration spectral > density of 0.04g^2/Hz, then ramping down again between 350Hz and 2000Hz at > -3dB/octave. The vibration table we have will take a maximum theoretical > weight of 82 lbs at a spectral density of 0.04g^2/Hz before it self-aborts, > so allowing for some oscillation around the max s.d. figure of the profile > and a margin of safety for the weight of the Unit to be tested, I reckon I > have a maximum weight allowance for the vibration test jig of 37.5 lbs. > > The jig we have, designed by someone else without a lot of science or math > involved, weighs in at around 26kg (58lbs), so it has to lose a lot of > weight before we can use our own vibration table. > > If I can't put the jig on an effective diet, I'm faced with relying on > renting expensive time at an outside facility that's already pretty > popular, so my windows of opportunity are unlikely to match the times when > I need to use the vibrator without a lot of dead waiting time. > > Hope someone out here knows what I'm talking about and can help. I've never > known this forum to be be completely stumped for an answer to anything yet. > > Peter > > [This e-mail is confidential and may also be privileged. If you are not the > intended recipient, please delete it and notify us immediately; you should > not copy or use it for any purpose, nor disclose its contents to any other > person. Thank you.] > > --------------------------------------------------------------------------------- > Technet Mail List provided as a free service by IPC using LISTSERV 1.8d > To unsubscribe, send a message to [log in to unmask] with following text in > the BODY (NOT the subject field): SIGNOFF Technet > To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) > To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest > Search the archives of previous posts at: http://listserv.ipc.org/archives > Please visit IPC web site http://www.ipc.org/html/forum.htm for additional > information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 > --------------------------------------------------------------------------------- -- Eric Christison Mechanical Engineer STMicroelectronics 33 Pinkhill Edinburgh EH12 7BF tel: +44 (0)131 336 6165 fax: +44 (0)131 336 6001 --------------------------------------------------------------------------------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8d To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/html/forum.htm for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ---------------------------------------------------------------------------------