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Torque callouts

Torque callouts

Torque callouts

(OP)
Is there a particular standard that gives the requirements for calling out torque values on the drawing?  When I worked for a military contractor, we used a table with Roman numerals and their corresponding torque values.  Where I am now just calls the torques out next to the fastener callout.  Please help.

RE: Torque callouts

As far as I know, you just call it out in the notes using whatever units you use.

Chris
Systems Analyst, I.S.
SolidWorks/PDMWorks 05
AutoCAD 06
ctopher's home site (updated 06-21-05)
FAQ559-1100
FAQ559-716

RE: Torque callouts

I've done it by creating a table and placing the values in notes.  I think notes give a little more room for an explanation on the preparation before the bolt is torque.  For example, clean threads before applying anti-galling lubricants (molybdenum disulfide).  But then I've also called out assembly procedures in notes.  I would say follow your company's drawing format but cover all aspects of the assembly process

Best Regards,

Heckler
Sr. Mechanical Engineer
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Never argue with an idiot. They'll bring you down to their level and beat you with experience every time.

RE: Torque callouts

(OP)
Right now, we don't have a set drawing standard.  I'm trying to get one started by using the ASME standards as guides.

Thanks for all of the input.

RE: Torque callouts

Starchief-
Don't forget to provide reasonable tolerances on the torque values!

Tunalover

RE: Torque callouts

So if the drawing call-out states "Torque to 45 to 55 lb ft", what does the technician set the wrench to?

RE: Torque callouts

MintJulep raises an important issue.

A target torque should be identified.  This is what an operator would use.

A torque range can be specified for quality control purposes.  Another person in QC would use this range to inspect the process.

The relationship between target and inspection limits should be developed with actual data from actual parts.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

RE: Torque callouts

Just like any other tolerance, "Torque to 45 to 55 lb ft" would be set at 50 while QC would inspect 45-55. Always shoot for the nom.

Chris
Systems Analyst, I.S.
SolidWorks/PDMWorks 05
AutoCAD 06
ctopher's home site (updated 06-21-05)
FAQ559-1100
FAQ559-716

RE: Torque callouts

We place the torque call out on the fastener right next to the balloon on the drawing.  This makes it easy, as someone looking at the drawing and assembling the product does not have to leave that area on the drawing and locate another table to get the torque info.  Some of our drawings can be quite large and span mulitple sheets.  Also, regarding torque tolerances, keep in mind that a typical torque wrench is only accurate to within +/- 30 to 35%.  Its best to place a torue value on the fastener that is safe for the tool that is intended to tighten the fastener.  Other methods of more accurate tightening of a fastener can be used, but are generally more costly.  I like the approach of designing in an acceptable range so that the least expensive method can utilized and still have a quality design.  Of course, this is different for every company's products and the environment they operate in.

Pete

RE: Torque callouts

Ok, so assuming a micrometer-adjustmet type torque wrench, the wrench setting can be set to the desired "nominal" value of 50 lb ft every time.  So the guy pulling the wrench has no need for a tolerance, he needs to know what to set the wrench to.  Why make him do math?

The concept of a QC torque check on an already tightend fastener is rediculous.

So, the only possible use for a torque range on an assembly drawing is to QC check the calibration of the torque wrench.

RE: Torque callouts

The range on the dwg has nothing to do with QC checking the wrench calibration. If you don't want a tol specified...good luck to you.

Chris
Systems Analyst, I.S.
SolidWorks/PDMWorks 05
AutoCAD 06
ctopher's home site (updated 06-21-05)
FAQ559-1100
FAQ559-716

RE: Torque callouts

I am not advocating a tolerance on the drawing for torques and agree with Mint Julep that having a QC check on torques is a little ridiculous.  I was advocating good design up front, so that you did not have to place a tolerance on the drawing.  But, I can see where highly critical applications might require this type of check.  Again, I think it comes down to each company, their products, and the environment they operate in.

RE: Torque callouts

Everything on a dwg requires some type of tol. Dim's, torque, temp, etc. If there is not a tol, it can cause you trouble later. The tol needs to be in the form of a note or part of the dim. This is the same for all companies. I see companies all the time that do not call out any tol because they think their products are specialized enough for them that they know what they are doing...until the part is outsourced or a new employee starts in the machine shop.

Chris
Systems Analyst, I.S.
SolidWorks/PDMWorks 05
AutoCAD 06
ctopher's home site (updated 06-21-05)
FAQ559-1100
FAQ559-716

RE: Torque callouts

I agree that if you are using torque control for tightening threaded fasteners then the joint design needs to be correctly done.  This includes establishing the minimum and maximum APPLIED torque that the joint can tolerate and still perform correctly.

However, we need to differentiate between design and process and process control.

The process for the guy pulling the wrench should define what to set the wrench to.  In my opinion this should be a single number.

The process controls need to define how much devation between the wrench setting and the actual torque applied is allowed before the wrench goes for recalibration.  The manufacturing engineer needs to know both the joint design and the calibration information to properly define the right number for the guy pulling the wrench.

RE: Torque callouts

I agree, but this information does not belong on drawings. You only call out the range. It's the same as milling, do you call out the speed rate, or how much material is cut before the tool should be changed? Processes do not get noted on drawings, they should be on some type of Job Traveler that is somehow linked to the drawing.

Chris
Systems Analyst, I.S.
SolidWorks/PDMWorks 05
AutoCAD 06
ctopher's home site (updated 06-21-05)
FAQ559-1100
FAQ559-716

RE: Torque callouts

Quote (MintJulep):

The concept of a QC torque check on an already tightend fastener is rediculous.

This is standard practice in the automobile industry.

The concept is that you are checking the process (operator, power tool, air pressure, etc.) and the parts (torque variation might be due to stripped threads, burrs, relaxation due to insufficient strength, etc.)

I think it has limited value, but the auto industry "found religion" with QC, and so QC has a huge inertia (large department workforce, representation on committees, management oversight, etc.).

Taking the QC check to the next level, here is what one company proposes as a QC check to determine torque-tension relationship:

http://www.hexagon.de/tasignat.htm

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

RE: Torque callouts

I like Volvo Corporate Standards 5511,21 & 5511,71 & 8517,3 whenever a torque question arises.

RE: Torque callouts

CoryPad & alexit,
Do those auto stds indicate what to call out on the dwgs for torque?

Chris
Systems Analyst, I.S.
SolidWorks/PDMWorks 05
AutoCAD 06
ctopher's home site (updated 06-21-05)
FAQ559-1100
FAQ559-716

RE: Torque callouts

(OP)
...which was my original question.......

Starchief
Sr. Project Engineer
SolidWorks 2006/Cosmos 2006

RE: Torque callouts

Yes, you read my answer. I'm curious what the auto industry does.

Chris
Systems Analyst, I.S.
SolidWorks/PDMWorks 05
AutoCAD 06
ctopher's home site (updated 06-21-05)
FAQ559-1100
FAQ559-716

RE: Torque callouts

"Everything on a dwg requires some type of tol."

ok, I'll buy that-

Number of active coils on a spring, plus/minus?
Pitch diameter of a gear, plus/minus?
4340 steel, plus/minus?

The first two were actually demanded by an inspection department. But you know what its like arguing with an inspector, ha ha.

RE: Torque callouts

Hey, I can be axxl too.
  Everything specified on a drawing should have some type of tolerance associated with it.  4340 steel is toleranced by it's composition and manufacturing process.  It is not the same as 4130 or 4140.
  A 1/4-20 UNC-2B thread has tolerances determined by "UNC-2B".  If the number of active coils on a spring is critical to the function of the design, then yes, it is specified.  The same goes for the pitch diameter of a gear, even if it is only a partial diameter and only consists of a few gear teeth.
  Fortunately, most of the tolerancing in the above examples is defined in their related specifications, or engineering drawings would be that much more complex.
  You can argue with inspectors all you want, but if you don't have solid evidence to back yourself up, no inspector worth his salt is going to let you win.

RE: Torque callouts

ewh,
thank you.
EngJW, you should have a copy of Machinery Handbook if you don't have one ... and ASME/ANSI standards.

Chris
Systems Analyst, I.S.
SolidWorks/PDMWorks 05
AutoCAD 06
ctopher's home site (updated 06-21-05)
FAQ559-1100
FAQ559-716

RE: Torque callouts

Most auto companies use assembly documents instead of drawings for torque callouts.

The assembly documents will have an assembly torque specification and an inspection torque specification.  Some companies use ranges for both.  For example, if you use an electric power tool, it can be automated to shut off after a certain torque or torque plus angle or angle only.  There will be some variation in these values, so the tool controller is pre-programmed with a lower torque limit, upper torque limit, lower angle limit, and upper torque limit.  Then, each joint on each vehicle can be monitored for quality.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

RE: Torque callouts

The only thing to call out on any dwg is the torque range, nothing else. The rest is up to the mechanic or technician.

Chris
Systems Analyst, I.S.
SolidWorks/PDMWorks 05
AutoCAD 06
ctopher's home site (updated 06-21-05)
FAQ559-1100
FAQ559-716

RE: Torque callouts

I would put the torque spec in a table if you have a lot of them and designate which fasteners are which with some sort of letter designation. Otherwise just put the torque spec in a flag note.
Also, I would put the tolerance in my tolerance block. That way you only have to spec the tolerance once. And besides, whoever is assembling the parts should aim for the torque number spec'd and let QA deal with the tolerances. That is why you have tolerances, so that you can have imperfect people building to a perfect spec and when it comes out wrong, QA decides if it passes or not based on the tolerances.

RE: Torque callouts

(OP)
OK, so back on topic:  Are there any recognized standards that stipulate how torques (regardless of tol.) should be called out on the face of an assy dwg?

Starchief
Sr. Project Engineer
SolidWorks 2006/Cosmos 2006

RE: Torque callouts

As you mentioned above, start with the ASME stds as guides. The same stds apply as if it were a dimension.

Chris
Systems Analyst, I.S.
SolidWorks/PDMWorks 05
AutoCAD 06
ctopher's home site (updated 06-21-05)
FAQ559-1100
FAQ559-716

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