I took my torque wrenches in to work and had a standards lab friend check the calibration on my inch # torque wrench,sears 20-250 clicker. I told to him I would be using it to build my plane with. When I picked it up he had a chart of calibration for it and it started at 50 in #'s, I told him the first torque was at 20-25 in. #'s. He said "and your building a plane with this?" yes says I. He goes into a verbal treatise on torque that went on for about 10 minutes. He says there is know way I can use this wrench for 20-25 in. #'s, the bottom 20% of scale cannot be used,he was getting in my face over this. I see on Avery's cat. they mention this also,but then Cleveland says there WT-1501 wrench 20-150 is best for RV's. He says I need a 0-50 in. # wrench to do this correctly and if I use my 20-250 in.# wrench I am off scale out of calibration and I really have know way to know what torque I put on the AN 3 bolt. I see others have used the same or similar wrench and there planes haven't fallen out of the sky,but it looks like he is right and I need another wrench, 0-50 in. #. When it comes to something like this I think erring on the safe side is prudent. What say those that have gone before me? Gene
Van's Air Force
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Metrology chewing out on torque wrenches
- Thread starter gbumga
- Start date
cytoxin
Well Known Member
http://buy1.snapon.com/catalog/item...8&group_ID=961&store=snapon-store&dir=catalog this is a good one as well. no ratchet mechanism,
so it can be a little less than user friendly.
so it can be a little less than user friendly.
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AlexPeterson
Well Known Member
Sometimes experts are a real pain.
Get a fish scale, set up a little moment arm, and see what it actually is when your torque wrench is set to 25. It is probably within 20%. Big deal. Most people, if not using any torque wrench, probably over torque AN3 bolts by about 300% or more. The torque wrench you have is probably just fine.
The standards lab folks are certifying to various standards. You are building an airplane instead.
How close was it at 50 in-lbs?
Get a fish scale, set up a little moment arm, and see what it actually is when your torque wrench is set to 25. It is probably within 20%. Big deal. Most people, if not using any torque wrench, probably over torque AN3 bolts by about 300% or more. The torque wrench you have is probably just fine.
The standards lab folks are certifying to various standards. You are building an airplane instead.
How close was it at 50 in-lbs?
Alex, what it was at 50 in #
Alex, it was 51.100 at 50. I don't understand what you mean by they use different standards. They pull to 50 and see what there calibration equipment says, the standard is what are the tolerances ie. +/- 4% for the sears wrench and quality of exceptable calibration equipment,unless I'm missing something,which is a frequent event. I agree most people over torque,but 300 % over torque and you have stretched the bolt,what would be the failure point? I work at a nuclear plant and we nit-pick to the inth [is that a real word?]degree and I see failure of stuff all the time,where QA watches the manufacture and the paper costs more than the part and its still wrong sometimes and fails sometimes. I complained about the cost of a 0-50 wrench and he said theres a reason they cost so much,repeatable accuracy. I agree it would be ok,those flying that have done this is proof. After all the failure of fasteners I've seen in 30 yrs of being a wrench monkey I'm just looking to build not a perfect plane but built to specs plane. Thanks for reading my post and replying,that golf buddy metrologist friend of mine did said the screw driver type is best for little stuff like AN3 bolts. regards Gene, glows in the dark
Alex, it was 51.100 at 50. I don't understand what you mean by they use different standards. They pull to 50 and see what there calibration equipment says, the standard is what are the tolerances ie. +/- 4% for the sears wrench and quality of exceptable calibration equipment,unless I'm missing something,which is a frequent event. I agree most people over torque,but 300 % over torque and you have stretched the bolt,what would be the failure point? I work at a nuclear plant and we nit-pick to the inth [is that a real word?]degree and I see failure of stuff all the time,where QA watches the manufacture and the paper costs more than the part and its still wrong sometimes and fails sometimes. I complained about the cost of a 0-50 wrench and he said theres a reason they cost so much,repeatable accuracy. I agree it would be ok,those flying that have done this is proof. After all the failure of fasteners I've seen in 30 yrs of being a wrench monkey I'm just looking to build not a perfect plane but built to specs plane. Thanks for reading my post and replying,that golf buddy metrologist friend of mine did said the screw driver type is best for little stuff like AN3 bolts. regards Gene, glows in the dark
AlexPeterson
Well Known Member
clarification
Well, what I mean is that since they are part of a nuke power plant organization, they may have to calibrate to tolerances much tighter than what we aircraft builders need. For example, they may have a blanket requirement of +/-1% or whatever. If your wrench is only 2% off, it is probably quite good for a non-professional quality wrench. If we torqued our bolts to +/- 20% of true value, we would probably do better than many repair shops. The drag on a nyloc AN3 nut is around 15 in-lbs, so 60% of the tightening torque of 25 is just to overcome the nut's locking features. It would be interesting to know where your wrench actually is at 25 indicated. I'll bet is is reasonable.
Well, what I mean is that since they are part of a nuke power plant organization, they may have to calibrate to tolerances much tighter than what we aircraft builders need. For example, they may have a blanket requirement of +/-1% or whatever. If your wrench is only 2% off, it is probably quite good for a non-professional quality wrench. If we torqued our bolts to +/- 20% of true value, we would probably do better than many repair shops. The drag on a nyloc AN3 nut is around 15 in-lbs, so 60% of the tightening torque of 25 is just to overcome the nut's locking features. It would be interesting to know where your wrench actually is at 25 indicated. I'll bet is is reasonable.
Kevin Horton
Well Known Member
The whole point of a specified torque is to achieve a certain amount of clamping force, so we need to compensate for the drag torque on the nut. E.g., if you want 20-25 in-lb on the bolt, and the drag torque on the nut is 15 in-lb, you need to set the wrench to 35-40 in-lb.
