Hi Hal I won't quarrel with your figures...they seem about right.
The issue is the definition of specific stiffness... Steel has about three times the modulus of aluminum, but it is also three times the density! Specific stiffness is the ratio of those two parameters, so they are about the same. This is true for most alloys, hardened or unhardened. One way to think of it is an identically dimensioned bar of different materials. The material with the highest specific stiffness will ring with the highest note when struck. FYI the highest specific stiffness of the common metals is beryllium. OK? :) Les Leslie M.Watts L M Watts Furniture Tiger Georgia Main page: http://www.lmwatts.com Engineering: http://www.lmwatts.com/shop.html Cnc surplus for sale: http://www.lmwatts.com/forsale.html Carved signs: http://www.lmwatts.com/signwp.html -----Original Message----- From: Hal Eckhart [mailto:[EMAIL PROTECTED] Sent: Monday, October 25, 2004 8:19 PM To: [EMAIL PROTECTED] Subject: RE: [CAD_CAM_EDM_DRO] Re: sourcing motion control parts - steel vs aluminum On 10/25/04 6:23 PM, Leslie Watts wrote: >Aluminum and steel are virtually identical in specific stiffness. I don't think that's true. The modulus of elasticity for steel is 29,700,000 psi and it's 10,000,000 psi for aluminum (this will vary based on type and temper, but it's the best info I can find). For example, a 2" square steel tube with a 1/8" wall would deflect 0.11" with 100# load in the middle of an 8' run. For aluminum, it would deflect 0.33". This info is from the cheesy calculator I hacked together at <http://metalgeek.com/static/deflection.php>. If you want to quarrel with my conclusions, I've posted my sources there. I am NOT an expert on this, although I do bend a lot of metal. And my limited testing seems to support the accuracy of the calculator. But I'm certainly open to other ideas. And one note about 8020. I've used it, although I wouldn't recommend it for framing (for a hobbyist). Unless you're going to be reconfiguring it later, it's awfully pricy. However, they do sell a slick little sliding dohickey for it that seems like it would work fine for a plasma Y axis. Hal Eckhart - Casa Forge - Minneapolis MN - <http://www.casaforge.com> Addresses: FAQ: http://www.ktmarketing.com/faq.html FILES: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/files/ Post Messages: [EMAIL PROTECTED] Subscribe: [EMAIL PROTECTED] Unsubscribe: [EMAIL PROTECTED] List owner: [EMAIL PROTECTED], [EMAIL PROTECTED], [EMAIL PROTECTED] Moderator: [EMAIL PROTECTED] [EMAIL PROTECTED] [EMAIL PROTECTED] [Moderators] URL to this group: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO OFF Topic POSTS: General Machining If you wish to post on unlimited OT subjects goto: aol://5863:126/rec.crafts.metalworking or go thru Google.com to reach it if you have trouble. http://www.metalworking.com/news_servers.html http://groups.yahoo.com/group/jobshophomeshop I consider this to be a sister site to the CCED group, as many of the same members are there, for OT subjects, that are not allowed on the CCED list. NOTICE: ALL POSTINGS TO THIS GROUP BECOME PUBLIC DOMAIN BY POSTING THEM. DON'T POST IF YOU CAN NOT ACCEPT THIS.....NO EXCEPTIONS........ bill List Mom List Owner Yahoo! Groups Links Addresses: FAQ: http://www.ktmarketing.com/faq.html FILES: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/files/ Post Messages: [EMAIL PROTECTED] Subscribe: [EMAIL PROTECTED] Unsubscribe: [EMAIL PROTECTED] List owner: [EMAIL PROTECTED], [EMAIL PROTECTED], [EMAIL PROTECTED] Moderator: [EMAIL PROTECTED] [EMAIL PROTECTED] [EMAIL PROTECTED] [Moderators] URL to this group: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO OFF Topic POSTS: General Machining If you wish to post on unlimited OT subjects goto: aol://5863:126/rec.crafts.metalworking or go thru Google.com to reach it if you have trouble. http://www.metalworking.com/news_servers.html http://groups.yahoo.com/group/jobshophomeshop I consider this to be a sister site to the CCED group, as many of the same members are there, for OT subjects, that are not allowed on the CCED list. NOTICE: ALL POSTINGS TO THIS GROUP BECOME PUBLIC DOMAIN BY POSTING THEM. DON'T POST IF YOU CAN NOT ACCEPT THIS.....NO EXCEPTIONS........ bill List Mom List Owner Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
