Don't buy SMA cable assemblies from CentricRF

[KE5FX]

A sane person follows the manufactures procedures. 

I was expecting  you to follow their instructions below, but you would need to ditch the cheap torque meter for a peak reading meter.   Of course, the absolute values are meaningless but at least you could get some relative data.    Then, don't cover up the handle with your hand as you show.  Maybe just use a finger and work your way up the handle in one inch increments. 

• To improve performance of a wrench that hasn’t been used recently, actu-
ate the wrench by clicking the wrench head back and forth several times
before use. This will spread the lubricant through the internal mechanism.
• Click type tools require smooth consistent application of force. Each torqu-
ing action should be completed within 2 seconds. Slower or faster torquing
action will detract from accuracy.


***
Maybe measure at six locations.   You did later state anywhere on the red handle, but with the 3 closer to the pivot point, I expect you will measure a big increase.  While you asked about where the pivot point was for your wrench, I think once you place your finger in the far left location and apply force, you will have answered that one for yourself.

Sounds like you have your work cut out for you.  Looking forward to your video (which if it's like your others will certainly be worth watching.) 

For what it's worth, my 1-minute clip shows about 10% of the experiments I actually performed, and for the record, yes, you can apply much more than the rated torque if you intentionally hold the wrench near the pivot point. 

News flash #1: tools can be misused.  Ric Romero has more on this late-breaking story at 11.  News flash #2: you have to go out of your way to misuse this particular torque wrench in a way that results in significant overtorque.

The digital torque wrench is actually pretty decent for the price, and it does have a peak-reading feature, but I found that the impulse imparted during breakover made the measurement less repeatable rather than more.  The peak-hold feature appears worthwhile at higher torques, but this was very close to the lower end of the wrench's range.

[joeqsmith]

A sane person follows the manufactures procedures. 

I was expecting  you to follow their instructions below, but you would need to ditch the cheap torque meter for a peak reading meter.   Of course, the absolute values are meaningless but at least you could get some relative data.    Then, don't cover up the handle with your hand as you show.  Maybe just use a finger and work your way up the handle in one inch increments. 

• To improve performance of a wrench that hasn’t been used recently, actu-
ate the wrench by clicking the wrench head back and forth several times
before use. This will spread the lubricant through the internal mechanism.
• Click type tools require smooth consistent application of force. Each torqu-
ing action should be completed within 2 seconds. Slower or faster torquing
action will detract from accuracy.


***
Maybe measure at six locations.   You did later state anywhere on the red handle, but with the 3 closer to the pivot point, I expect you will measure a big increase.  While you asked about where the pivot point was for your wrench, I think once you place your finger in the far left location and apply force, you will have answered that one for yourself.

Sounds like you have your work cut out for you.  Looking forward to your video (which if it's like your others will certainly be worth watching.) 

For what it's worth, my 1-minute clip shows about 10% of the experiments I actually performed, and for the record, yes, you can apply much more than the rated torque if you intentionally hold the wrench near the pivot point. 

News flash #1: tools can be misused.  Ric Romero has more on this late-breaking story at 11.  News flash #2: you have to go out of your way to misuse this particular torque wrench in a way that results in significant overtorque.

The digital torque wrench is actually pretty decent for the price, and it does have a peak-reading feature, but I found that the impulse imparted during breakover made the measurement less repeatable rather than more.  The peak-hold feature appears worthwhile at higher torques, but this was very close to the lower end of the wrench's range.

I'll leave it to you to prove your own statements with math.

[KE5FX]

Math without the right model is a waste of time.  Models that involve tying a string to the wrench and applying a normal force to a single point in the middle of the handle are not useful for describing how the tool will actually work, because they don't reflect how the tool is actually used. 

Likewise, models that involve grasping the moment arm near the pivot point are only useful for demonstrating what happens during intentional, negligent misuse.

The problem is, the .PDF warns that holding the wrench anywhere other than the very end of the handle constitutes misuse.  That's simply wrong, and I'm satisfied that I've shown that.  I'll leave any remaining work to those who continue to assert otherwise.

[joeqsmith]

Math without the right model is a waste of time.  Models that involve tying a string to the wrench and applying a normal force to a single point in the middle of the handle are not useful for describing how the tool will actually work, because they don't reflect how the tool is actually used. 

Likewise, models that involve grasping the moment arm near the pivot point are only useful for demonstrating what happens during intentional, negligent misuse.

The problem is, the .PDF warns that holding the wrench anywhere other than the very end of the handle constitutes misuse.  That's simply wrong, and I'm satisfied that I've shown that.  I'll leave any remaining work to those who continue to assert otherwise.

So you want others to show you the math but feel that is has no value?   While I am sure many a free energy Tesla believers also are satisfied with what they show.   They too always ask the public to run the test. 

Seems you are trying to constrain how users hold the wrench now rather than your original comments that it doesn't matter.   Progress....

[KE5FX]

Yep, I was out of line to suggest that it didn't matter at all.  It clearly does, in the sense that grasping the wrench well away from the end of the handle can apply significantly more torque at breakover.

Someone reading what I wrote would come away with the impression that you can't misuse a torque wrench.  That wouldn't serve students any better than the overly-conservative advice in the .PDF does.  Like I said, I wouldn't defend that hill any further.

[joeqsmith]

While most hams tell me that torque wrenches are pointless, here is a ham with several.     

[KE5FX]

You'd never catch me saying they're pointless, wearing either my ham hat or my professional hat. 

The .PDF triggers me because I have to write documents like that.  If I tell people to do something obviously goofy, not only will they not do it, they will start to wonder what else they can safely ignore.

[G0HZU]

To help try and resolve this issue, I waited until I was back at work today.   ....

Does your company have a set of gages to repeat the OPs measurements?   Or, I wonder if you or your company has seen a similar trend? 

***
I'm curious if your company produces any products that use RF connectors during testing, and it so do they torque them?

In terms of pin depth gauges for various RF connectors and stuff like that I doubt the company has these but I might be wrong.

I'm curious if your company produces any products that use RF connectors during testing, and it so do they torque them?

I work for a very large defence company that makes lots of RF based equipment so lots of RF connectors are involved during manufacture and test. Obviously, torque wrenches are used and this is why there are various torque tester stations to check the torque wrenches

RF cables generally get made by Suhner (and similar companies) to the company drawings. This is why I doubt there will be any pin depth gauges. If there are any, they will probably be securely locked away for special occasions. I'm not aware of any issues when Suhner make cables and these cables are typically used at high RF power levels up at many GHz.

[joeqsmith]

You'd never catch me saying they're pointless, wearing either my ham hat or my professional hat. 

The .PDF triggers me because I have to write documents like that.  If I tell people to do something obviously goofy, not only will they not do it, they will start to wonder what else they can safely ignore.

In general, people will not take the time to read or do their own research.  I don't believe I'm biased from interacting with the hams and hobbyists.  A good example is TV ads where dad assembles some furniture, kids toy...  Parts are left over and they fall apart...  Maybe entertaining on some level but I suspect it's closer to reality.   

On the flip side, how many times have you had to contact the creator of a document  to determine what they meant.   Datasheets,  standards.....   In the age of so many companies trading hands and marketing getting involved with changing datasheets, it hasn't gotten any easier.

Recently reached out to viewer's to proof a document I am working on for some software I wrote.  I was surprised by the amount of good feedback they provided.   So there are a few of us out there who still read.   

[joeqsmith]

To help try and resolve this issue, I waited until I was back at work today.   ....

Does your company have a set of gages to repeat the OPs measurements?   Or, I wonder if you or your company has seen a similar trend? 

***
I'm curious if your company produces any products that use RF connectors during testing, and it so do they torque them?

In terms of pin depth gauges for various RF connectors and stuff like that I doubt the company has these but I might be wrong.

I'm curious if your company produces any products that use RF connectors during testing, and it so do they torque them?

I work for a very large defence company that makes lots of RF based equipment so lots of RF connectors are involved during manufacture and test. Obviously, torque wrenches are used and this is why there are various torque tester stations to check the torque wrenches

RF cables generally get made by Suhner (and similar companies) to the company drawings. This is why I doubt there will be any pin depth gauges. If there are any, they will probably be securely locked away for special occasions. I'm not aware of any issues when Suhner make cables and these cables are typically used at high RF power levels up at many GHz.

Thanks,  this is some good insight.  Can they not achieve consistent results by hand tightening?  If that is not the problem, care to elaborate on the reasons for their use?     

It would be interesting to check if they did have gages for male SMA connectors.   Maybe then you could check a few cables and post your results.   

I mentioned I have an assortment of manufactured cables.  Some of these were made by Digi-Key.  I have some really cheap ones from Amazon.   I thought about measuring what I have on-hand and providing that data.   I wrote CentricRF and provided them a link to this thread.  I offered to test some of their cables independently.  If they take me up on it, I'll put some sort of test together. 

[G0HZU]

I think a lot depends on the intended application. For cables using N connections that have to withstand vehicle use it's possible to use N connectors that can support a torque tool.
See below for a typical example. This is obviously going to be better than hand tightening.

For general bench use, it's generally fine to hand tighten N connectors.

I have seen issues with SMA cables that have been hastily assembled by technicians (using Suco 141 cable) where the male pin ends up at the wrong depth. I've seen it where is it obviously wrong even with the naked eye. No need for any gauges!

However, the cable issue I see most often is when thicker RF cables aren't crimped well at the connectors. This can cause leakage issues and suckouts up at many GHz. It's easy to spot this if the cable is measured on a VNA and the cable is wiggled near its ends. This generally happens if cables are ordered (to a custom length) from alternative suppliers if someone needs the cable(s) quickly. It's always very disappointing to see this when it happens.

[tautech]

I think a lot depends on the intended application.
.........
For general bench use, it's generally fine to hand tighten N connectors.

Advanced VNA afficiardos will disagree.

[G0HZU]

I think a lot depends on the intended application.
.........
For general bench use, it's generally fine to hand tighten N connectors.

Advanced VNA afficiardos will disagree.

I'm really referring to operation (evaluation)  of the same (vehicle based) equipment on a bench. It's generally fine to attach N cables or N attenuators to it and just hand tighten them. Often the cable or attenuator won't support a torque tool anyway.

[tautech]

I think a lot depends on the intended application.
.........
For general bench use, it's generally fine to hand tighten N connectors.

Advanced VNA afficiardos will disagree.

I'm really referring to operation (evaluation)  of the same (vehicle based) equipment on a bench. It's generally fine to attach N cables or N attenuators to it and just hand tighten them. Often the cable or attenuator won't support a torque tool anyway.

Real results have suggested otherwise and now I alway tighten N type.....especially for a VNA.
SMA are a quite different beast but both benefit from torquing to provide repeatable results.

[G0HZU]

I think a lot depends on the intended application.
.........
For general bench use, it's generally fine to hand tighten N connectors.

Advanced VNA afficiardos will disagree.

I'm really referring to operation (evaluation)  of the same (vehicle based) equipment on a bench. It's generally fine to attach N cables or N attenuators to it and just hand tighten them. Often the cable or attenuator won't support a torque tool anyway.

Real results have suggested otherwise and now I alway tighten N type.....especially for a VNA.
SMA are a quite different beast but both benefit from torquing to provide repeatable results.

I wasn't referring to VNA use I was referring to general benchwork using N connectors. This could mean connecting a general test cable to an attenuator or a spectrum analyser. The connectors often don't have flats on them for a torque wrench.

However, I have used N type VNA cal kits without a torque wrench many times. A torque wrench is obviously better but often it isn't necessary. This is based on decades of experience working in RF labs. Not all measurements have to follow metrology guidelines just like not everyone has to measure stuff using metrology grade equipment whilst following metrology grade procedures.

Often, I'll re-use stored cal setups months later. I do this to save time on occasions where I don't need great accuracy or low uncertainty.

Also, for the more critical applications, the dominant uncertainty/errors will often be due to cable wear issues and cable flexing (during the cal process) and issues with the test fixture and the limitations of the VNA hardware itself.

[joeqsmith]

I think a lot depends on the intended application. For cables using N connections that have to withstand vehicle use it's possible to use N connectors that can support a torque tool.
See below for a typical example. This is obviously going to be better than hand tightening.

For general bench use, it's generally fine to hand tighten N connectors.
...

I would have guessed that your production test fixtures would be a similar environment to general bench use.  Which gets back to why does your company torque connections for production?  Consider the costs not just the operation, but tracking, calibration... 


Attached is an interesting memo on the use of SMAs.  A few quotes related to connector torque.   

However, at both organizations, SMA connectors are routinely torqued to the recommended torque, "plus a bit", the extra "bit", which is deemed important to long term reliability, being at the discretion of the assembler. This is not sufficiently well defined for use as an ALMA standard procedure.

[/i]

Galen Watts [14] writes: "...I use a procedure where I bring the SMA to full torque (wrench click), wait a couple seconds, full torque again, wait a couple seconds, full torque a third time, all while counter torquing with a plain wrench when possible or pressing lightly on rigid/semi rigid coaxial cable counter to the torquing direction when applicable. Following this procedure I have not yet seen loose SMA connectors in cryogenic applications after multiple temperature cycles..." He notes that "...the  SMA  shell  will  frequently  turn  a  little  farther  on  the  second  and  often  the  third application of the same torque."

Suggestions for ALMA
(i) The connector should be tightened to a torque of 8 in-lb (88 N-cm) unless otherwise specified by the manufacturer.
(ii) The torque wrench should be applied three times in succession.
(iii) A second wrench should be used where appropriate to prevent rotation of the body of the connector. This is facilitated by the use of male SMA connectors with a hexagonal section behind the nut and female SMA connectors with a hexagonal section behind the thread [8].
(iv) Striping or gluing SMA connectors should not be done unless it becomes clear during early ALMA operation that it is necessary.

[G0HZU]

I'm not sure where this is all leading... at work, there is a difference between 'general bench work' and production ATE procedures. The ATE stuff is very strict for obvious reasons.

General bench work might involve the manual checking of a unit that has failed a phase noise or a spurious test or maybe it has some other issue. If it can't be sorted by the test engineers I would typically get called across to look at it if it was something I was involved in the design of.

Other bench work might involve R&D work. It generally isn't necessary to use torque tools for stuff like this especially when rapidly cable swapping between analyser types or a scope or something else.

I really just joined this thread to try and prove that the Keysight torque tools are meant to be held a certain way or the accuracy (and repeatability) of the torque will begin to degrade. It should be obvious with this type of tool that uncertainty will creep in if the pressure points on the tool are poorly defined across various fingers and a thumb. I couldn't back any of this up using real tests with the relevant hardware until I was at work on Monday.

The repeatability is really impressive if used the way suggested by Keysight as this defines how and where the force is applied by the user. Any attempt to use a different type of grip will result in impaired repeatability and the torque can be greater or lower than the torque the tool is calibrated for.

However, it generally doesn't make a great deal of difference unless the tool is gripped in an unnatural way or if it is used nearer the pivot point. But the difference is real and easy to demonstrate. Keysight do describe this stuff in the various cal kit manuals. It's up to the individual if they want to strive for the most accurate torque each time they use this tool. I don't have a Keysight torque tool here at home, just the little Suhner torque tool.

[joeqsmith]

I'm not sure where this is all leading... at work, there is a difference between 'general bench work' and production ATE procedures. The ATE stuff is very strict for obvious reasons.
....

I have read numerous times how finger tight is repeatable, good enough, torque wrenches are pointless......  Assuming any of that is true,  I am asking specifics of why you can't get away with finger tightening your connections in production.  Maybe you expand on what these obvious reasons are.     

Looking at my old HP VNA, the N connectors do not have a flats.  Even the APC-7 connectors are finger tight only.  That setup's upper limit was only 2.6GHz, and really, what's the accuracy of a grease pen on the screen....   

I don't believe the lack of requiring a torque wrench was just because of the low frequency.   I have an old Adam Russell N style cable rated for 18GHz.  It is marked at both ends "DO NOT WRENCH CONNECTOR". 

[Someone]

It is marked at both ends "DO NOT WRENCH CONNECTOR".

In some industries/settings tightening a fastener is done until it yields, so I can fully appreciate the need for such a warning.

[joeqsmith]

It is marked at both ends "DO NOT WRENCH CONNECTOR".

In some industries/settings tightening a fastener is done until it yields, so I can fully appreciate the need for such a warning.

[mark432]

Wow there's a lot of gibberish in this thread.

1) You cannot reach the recommended torque for an SMA with your fingers.  Use a wrench.  If you insist on being fast and imprecise, spend $5 on a hasco SMA finger wrench.
https://www.hasco-inc.com/tools/sma-3-5mm-2-92mm-2-4mm-1-85mm-connector-finger-thumb-wrench-blue/
That will at least increase the diameter to a size where you can apply the required torque.

2) Type N connectors were designed back when dinosaurs roamed the earth.  They were designed to be hand tightened.  It is at least possible to hit the right torque without a tool.  Since those days, the precision grade parts available today benefit from repeatable torque.  Please don't be one of the clowns that grabs a pair of cannon pliers and tries to put 60 ftlbs on it.  You'll find different hex sizes and torque specs for type N. 

3) MIL-STD-348 is just an interface spec.  If you expect it to tell you everything about the SMA connector you're being lazy.  You need to go hunt through 39012 and relevant "slash" sheets and quite likely commercial specs as well depending on what you're doing.

4) Connector gauges are generally comparators against a reference standard.  Check your reference.  Is it good?  This is easy for SMA but harder for N.  Either way, I didn't notice any reference to zeroing the gauges.

5) If your torque wrench appreciably changes its delived torque based on where your fingers are on the handle, it is a POS and belongs in the trash.  Typical RF connector torque wrenches do not have this property.  Don't use a $10 beam torque wrench with a crowsfoot or whatever nonsense.  It looks like you can buy a knockoff for $35.

6) I've definitely had batches of bad cables from pros.  It happens. There's still a lot of hand labor in RF cable assembly.

7) I don't think I'd ever buy used RF cables.  Cables get abused.  Pulled.  Twisted.  Kinked.  Run over by office chairs.  Thermal cycled.  Shaken.  Etc.  A multi thousand dollar VNA cable can look great visually, and still be toast electrically.  I think I'd rather buy a rental car.

[Smoky]

That little blue wrench is perfect

https://www.hasco-inc.com/tools/sma-3-5mm-2-92mm-2-4mm-1-85mm-connector-finger-thumb-wrench-blue/

[joeqsmith]

Wow there's a lot of gibberish in this thread.

And thank you for taking the time to add even more gibber jabber.

1) You cannot reach the recommended torque for an SMA with your fingers.  Use a wrench.  If you insist on being fast and imprecise, spend $5 on a hasco SMA finger wrench.
https://www.hasco-inc.com/tools/sma-3-5mm-2-92mm-2-4mm-1-85mm-connector-finger-thumb-wrench-blue/
That will at least increase the diameter to a size where you can apply the required torque.

I have some open end wrenches I could use if the goal was to over torque them.  I assume you are suggesting that is not possible with the tool you are recommending. 

4) Connector gauges are generally comparators against a reference standard.  Check your reference.  Is it good?  This is easy for SMA but harder for N.  Either way, I didn't notice any reference to zeroing the gauges.

I can easily remedy that.  See attached image.  Feel better now?

Now, how good is that standard?

5) If your torque wrench appreciably changes its delived torque based on where your fingers are on the handle, it is a POS and belongs in the trash.  Typical RF connector torque wrenches do not have this property. 

I really don't know what "appreciable" changes are or what a "typical" wrench would be.   No matter, finger placement has been covered but rather then posting gibberish,  feel free to prove me otherwise.  Plot the six or so data points I previously asked for.   

https://www.eevblog.com/forum/testgear/dont-buy-sma-cable-assemblies-from-centricrf/msg5752031/#msg5752031

[mark432]

Wow there's a lot of gibberish in this thread.

And thank you for taking the time to add even more gibber jabber.

Gee.  I can't imagine how your interactions with manufacturers didn't go the way you wanted them to.
 

1) You cannot reach the recommended torque for an SMA with your fingers.  Use a wrench.  If you insist on being fast and imprecise, spend $5 on a hasco SMA finger wrench.
https://www.hasco-inc.com/tools/sma-3-5mm-2-92mm-2-4mm-1-85mm-connector-finger-thumb-wrench-blue/
That will at least increase the diameter to a size where you can apply the required torque.

I have some open end wrenches I could use if the goal was to over torque them.  I assume you are suggesting that is not possible with the tool you are recommending. 

You do know what happens when you assume right?
That tool means that you will at least apply enough torque to mate the reference planes and compress any gasket.  The basic, bare minimum requirement. 
It will remind you that these are just SMA connectors as it starts to slip, but they's nothing to stop you from just acting like a fool and tightening your grip.

If you have to make a quick check on 100 units, it's just the ticket.  An open end wrench will be slower and more prone to over torque.

4) Connector gauges are generally comparators against a reference standard.  Check your reference.  Is it good?  This is easy for SMA but harder for N.  Either way, I didn't notice any reference to zeroing the gauges.

I can easily remedy that.  See attached image.  Feel better now?

Now, how good is that standard?

Quit being lazy and tell us.  What number are you zeroing to? 

I said "check you reference" not " blindly trust it."

5) If your torque wrench appreciably changes its delived torque based on where your fingers are on the handle, it is a POS and belongs in the trash.  Typical RF connector torque wrenches do not have this property. 

I really don't know what "appreciable" changes are or what a "typical" wrench would be.   No matter, finger placement has been covered but rather then posting gibberish,  feel free to prove me otherwise.  Plot the six or so data points I previously asked for.   

https://www.eevblog.com/forum/testgear/dont-buy-sma-cable-assemblies-from-centricrf/msg5752031/#msg5752031

If you can't define an appreciable change in torque perhaps you should leave the discussion alone.  Go look at the torque spec.  It's a range.  All torque specs produced by serious people are.

Commonly 8-10 in lbs
https://www.centricrf.com/torque-specifications/

Thus a change of 0.2 in lbs would be insignificant whereas a change of 2 in lbs would.

This is obvious, common sense stuff.
If you insist on not using common sense you could go buy yourself a copy of a torque wrench standard like ISO 6789.


As for "typical" you do at least seem to speak English.  You should know what "typical" means.  Go do some searching as if you were going to buy an SMA torque wrench.  What are the most common types?  That's typical.  Typical is a "clicker" style.

This is not hard stuff.  Maybe twisting a male connector onto a female connector is just not for you.  Maybe you should just use SMB connectors.

[nctnico]

5) If your torque wrench appreciably changes its delived torque based on where your fingers are on the handle, it is a POS and belongs in the trash.

It has been proven mathematically that torque wrenches based on a click mechanism are sensitive to position of where the force is applied due to the difference in arm length between the rotation point of the jaw and the pivot point of the click mechanism. I'll admit it is something that takes some time & thought to wrap your head around but this is basic physics.