Torque callouts

[Starchief]

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.

 

[ctopher]

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
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ctopher's home site (updated 06-21-05)
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[Heckler]

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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[Starchief]

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.

 

[Tunalover]

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


Tunalover

 

[MintJulep]

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

 

[CoryPad]

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.

 

[ctopher]

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)
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[pdybeck]

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

 

[MintJulep]

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.

 

[ctopher]

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)
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[pdybeck]

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.

 

[ctopher]

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
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ctopher's home site (updated 06-21-05)
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[MintJulep]

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.

 

[ctopher]

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)
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[CoryPad]

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.

 

[alexit]

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

 

[ctopher]

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

 

[Starchief]

...which was my original question.......

Starchief
Sr. Project Engineer
SolidWorks 2006/Cosmos 2006

 

[ctopher]

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