From mwest_at_cdsnet_dot_net Sun Jun 21 14:26:04 1998 Received: from mail-01.cdsnet_dot_net (mail-01.cdsnet_dot_net [206.107.16.35]) by yiff.azaccess_dot_com (8.8.5/8.8.5) with SMTP id OAA14423 for <vintagebus_at_type2_dot_com>; Sun, 21 Jun 1998 14:26:01 -0700 Date: Sun, 21 Jun 1998 14:26:01 -0700 Message-Id: <199806212126.OAA14423_at_yiff.azaccess_dot_com> Received: (qmail 14572 invoked from network); 21 Jun 1998 21:09:16 -0000 Received: from d01a8554.dip.cdsnet_dot_net (208.26.133.84) by mail.cdsnet_dot_net with SMTP; 21 Jun 1998 21:09:16 -0000 X-Sender: mwest_at_mail.cdsnet_dot_net Mime-Version: 1.0 To: VintagVW_at_listproc.sjsu_dot_edu From: mwest_at_cdsnet_dot_net (Mike West) Subject: Re: RFC: Torque, and tools. and what not to do... Cc: type2_at_type2_dot_com, Vintage Bus <vintagebus_at_type2_dot_com> . > >when I started working on VW's, I was told by a very competent mechanic >that whenever one uses an extension on a torque wrench, to set the wrench >to 5 lbs higher than you would normally. 5 lbs for each extension. > >Later, I asked him about deepwell sockets. He looked at me for a minute, >then said he saw no reason to change for them. the 5 pounds is not for >the length, but for the flex that happens in each socket joint. > >I've been using this for a few years now with no noticed problem...anyone >have any comments? > >...david > >-- >David Raistrick '69 Westy-Itchigo keen_at_finally.atlasta_dot_net > '82 Westy-Baby Maxine (Mom's) > '66 SO-44 Westy (coming soon!) in Augusta Ga > - - - - - - - - - - - - - - Raistrick put you guys up to this didn't he . . ? :-) First he goes by with the bait, then a couple of you throw rocks. Then you get "physicsdude" AKA "thingguy" to light a smoke pot near my hole . . OK . . . I'm awake and totally pissed off . . . ! :-) That A/A+B = Torque is if you put a crows-foot on the end of the torque wrench . . . "old handle/new handle . . ? a ratio Another example is the "slugging wrench" for the rear axle nuts. It has a 1/2" drive socket in it that is 3-1/2" from the center of the nut. . . . need to do that ratio thing that "thingguy" brought up . . Assuming the 6" from "thingguys" example, a 200 ft-lb torque on a 6" extension would give you 285 ft-lbs . . . It's a way to get more torque from your wrench than it's rated for. Putting an extension or "cheater bar" on the handle end is not the same . . for that, you continue to read the gauge . . (bad) David, however, was talking about an extension for the socket. . That which gives you an offset position for the wrench from the socket . . For that we would have a torque loss equation . . . You apply 50 ft-lbs of torque to a six inch extension to the socket . . the extension is steel and steel is still the most "elastic" material we have . . . . Elasticity is defined as the amount of load that can be applied to a material under certain constraints and the material will return to its original shape . . . So that extension is a spring . . . in our case, it is a "torsion spring" . . . When you apply your force, the "spring" starts to wind up . . When the spring rate reaches equalibrium with the force required to move the nut, then torque will be applied to the nut . . As it gets harder to turn the nut the spring must first "wind up" or deflect radially until a new equalibrium is reached. . . The amount exerted to the nut will always be "less the amount used to deflect the shaft around it's axis" . . . The torsion spring rate is relative to material spring rate times the cross-section of the shaft times the length of the shaft. . You notice this when you are trying to loosen a nut with a long extension . . you get a lot of angular movement before you get the damn thing wound up enough to break that nut loose. . . Makes it almost impossible to use an extension on a impact-wrench. I have this friend who is a power tool freak . . he's pulling a tranny from a ford SUV . . . he's clear behind the car, with about a four foot extension made up of about five pieces and he'e got an impact wrench on it to break a bolt loose up on the tranny. . . :-) Might as well beat it with a flower . . . :-) He doesn't take well to criticism so I left him to it . . :-) So the spring is relative to the material of the extension and the diameter of the shaft and the length of the shaft times the force. Going thru the numbers for a standard 1/2" shaft and 6" long, 5 lbs might be a good number for the 50 lbs in . . . Only when you apply ten pounds or 150 lbs . . the number needs to change . . . Without resorting to math, I'll tell you how to figure the spring rate for your extension . . For a 1/2" drive torque wrench, get a 1/2" bolt and nut . . Get some lock washers and flat washers, 2 or 3 . . . If you have a pipe spacer, throw that in too . . Get a bolt about as long as you can set in the jaws of your vise. No vise . . ? well you're SOL aren't you . . ? :-) The idea of the longer bolt is that it's a spring when it's pulled too . . the longer it is the more movement for a given force . . Put the nut in the vise . . thread all that garbage on the bolt, put a flat washer between each lock washer and the faces of the nut and bolt-head . . . Get a pair of calipers and your 12" extension bar . . Put the extension on the torque wrench and torque the bolt down to a good number for a 1/2 or 13mm bolt . . . 50-80 ft-lb . . Now take a measurement over the head to nut with the calipers. Take the extension off and using the same number for tightening, see if you move the nut . . . bets are you will . . If you can't tell if it moves, mark it with an index mark, nut to bolt . . . Also take another measurement over-all. . . it got shorter. Now start adding a pound or five to the reading/extension and testing with the real number w/o extension till it stops moving . . the measurement stays the same . . You will have to do a series of tests relative to the torque to work out a sliding scale you can use. As in "add a pound for each 20 lbs of torque" . . . Let's forget the whole thing and go get big heavy extension. I have this maybe six inch extension for wheel nuts, etc. . . It's 3/4 inch and looks like a nose-tackle . . :-) Then I got a 3/4 X 1/2 short adapter to get me to my socket. Has a spring rate of about 150 lbs on an 8 ft cheater bar. . Oh, the number of socket connections is just slop to a torque wrench, no big deal other than the thing wants to bend all which way . . To an impact wrench it would be important if the spring rate didn't already defeat its purpose . . None of this could be categorized a "sin" . . A sin is if you cause another un-necessary pain . . causing yourself pain is just stupid. :-) west :-)