Author Topic: SMA torque wrench  (Read 3917 times)

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Offline taydin

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SMA torque wrench
« on: January 26, 2019, 04:30:52 pm »
I'm in the market to get an SMA torque wrench. Pasternack has an 8 in/lb wrench for $200, and aliexpress has an 8 in/lb torque wrench for $20 dollars.

I'm going to use the wrench for assembling the HP 8592B SA that I'm trying to fix Given that this SA is not a terribly accurate SA to begin with, can I get by with the aliexpress wrench or should I go for the Pasternack?
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Online KrudyZ

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Re: SMA torque wrench
« Reply #1 on: January 26, 2019, 04:47:45 pm »
I would say get the cheap one.
They are adjustable and easy to check by hanging a 2 lb weight with a thread or wire four inches out on the lever arm.
The better ones might hold their calibrated value better, but for what you are doing that's not really needed.
BTW, torque is a product of perpendicular force and distance, so its in*lb not in/lb


 

Offline TheSteve

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Re: SMA torque wrench
« Reply #2 on: January 26, 2019, 05:09:06 pm »
For SMA you might want to go for 5 in/lb. The 8 in/lb spec is more generally used for 3.5mm. If mating the two the torque spec follows the male connector.
I'd also recommend the cheaper wrench, just give it a quick verify when you get it.
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Offline EVS

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Re: SMA torque wrench
« Reply #3 on: January 26, 2019, 06:08:37 pm »
For SMA you might want to go for 5 in/lb.
This is true for brass SMA connectors. For stainless steel - no.
 
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Offline taydin

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Re: SMA torque wrench
« Reply #4 on: January 26, 2019, 06:13:01 pm »
Damn, the 8592B has both stainless and brass :) Won't be so bad when I get them from aliexpress. I can definitely test them and confirm that they exhibit the rated torque.
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Offline TheSteve

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Re: SMA torque wrench
« Reply #5 on: January 26, 2019, 07:04:09 pm »
There seems to be quite a few torque specs for SMA. I'm sticking with what is recommended by Keysight:
https://www.keysight.com/main/editorial.jspx?cc=US&lc=eng&ckey=1000004245:epsg:faq&nid=-11143.0.00&id=1000004245:epsg:faq
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Offline 0culus

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Re: SMA torque wrench
« Reply #6 on: January 26, 2019, 07:09:30 pm »
Man, I was just looking at these the other day and then I saw the prices for good ones.  |O
 

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Offline EVS

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Re: SMA torque wrench
« Reply #8 on: January 26, 2019, 07:20:34 pm »
For example, Radiall produces two series of SMA connectors - brass (R124 series) and stainless steel (R125 series).
The commercial SMA connectors (R124 coupling nut torque recommended 60 Ncm - 5.2 inch pounds) have been specially designed for applications where low installed costs are of the utmost importance.
The stainless steel SMA connectors (R125 coupling nut torque 80 to 115 Ncm - 7 to 10 inch pounds) have been designed for applications where reliability, durability, robustness and high frequency are very important.
 

Offline TheSteve

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Re: SMA torque wrench
« Reply #9 on: January 26, 2019, 07:40:13 pm »
https://www.eevblog.com/forum/projects/diy-sma-torque-wrench/

That was a great thread. I bought myself some Utica torque wrenches last year and did a DIY cal on one for SMA and one for 3.5mm(they were $13 each shipped). I have since purchased an official Keysight one for 3.5mm. If I needed more though I'd just get the chinese ones that look 95% the same as the Keysight ones. They are lightweight and break the same as the Keysight ones, and are less then $30 shipped.

If in doubt I'd use the lower torque on connectors, it is pretty easy to verify the mating is reliable/repeatable. More torque also accelerates connector wear.
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Offline KJDS

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Re: SMA torque wrench
« Reply #10 on: January 27, 2019, 10:48:27 am »
Go rock climbing, tighten with fingers

Spend torque wrench savings on beer.

Alternatively, use a very short spanner and press gently.

Offline tggzzz

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Re: SMA torque wrench
« Reply #11 on: January 27, 2019, 11:00:57 am »
Cheap, flexible, suitable for many purposes...
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Offline taydin

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Re: SMA torque wrench
« Reply #12 on: January 27, 2019, 12:39:27 pm »
Ordered an $18 wrench from aliexpress. It's adjustable with a hex socket screw between 05N/m and 3N/m covering all possible SMA types :)
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Offline rastro

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Re: SMA torque wrench
« Reply #13 on: January 28, 2019, 08:30:45 pm »
I bought a couple of inexpensive ones on ebay SMA & 3.5 for around $40 each.  They seemed accurate and repeatable. 

These are useful when connecting between systems with RF cables. 

However when working on tight spaces inside a piece of test equipment it seems like all bets are off to get a torque wrench on many connectors.  A good example is trying to replace the ACLU on an HP 8566.  It's on an assembly with 2 other RF components in totem pole arrangement.  |O

Maybe there are some good suggestions and tricks for getting torque wrench to work in tight spots.  Usually your lucky to find a or make a basic non torque wrench that will fit.

rastro
 

Offline tggzzz

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Re: SMA torque wrench
« Reply #14 on: January 28, 2019, 08:44:12 pm »
Find a way to get something, anything on the connector (other than your fingers!). Then use the spring balance  plus lever trick. The lever could be a pair of locking pliers, a screwdriver, whatever fits and is available.
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Offline TheUnnamedNewbie

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Re: SMA torque wrench
« Reply #15 on: January 29, 2019, 05:52:02 am »
I bought a couple of inexpensive ones on ebay SMA & 3.5 for around $40 each.  They seemed accurate and repeatable. 

These are useful when connecting between systems with RF cables. 

However when working on tight spaces inside a piece of test equipment it seems like all bets are off to get a torque wrench on many connectors.  A good example is trying to replace the ACLU on an HP 8566.  It's on an assembly with 2 other RF components in totem pole arrangement.  |O

Maybe there are some good suggestions and tricks for getting torque wrench to work in tight spots.  Usually your lucky to find a or make a basic non torque wrench that will fit.

rastro

I can relate to that. In my experience, however, there is generally a certain 'order' in which you can atatch all the connectors and still use a torque wrench on each. Figuring out what that order is however...
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Offline EVS

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Re: SMA torque wrench
« Reply #16 on: January 29, 2019, 09:03:27 am »
Maybe there are some good suggestions and tricks for getting torque wrench to work in tight spots.
maybe this
https://kendonpark.com/store/KCR-3125S-8C
 
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Online coppercone2

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Re: SMA torque wrench
« Reply #17 on: January 29, 2019, 05:10:18 pm »
If i had non ressurected equipment i would get that. Unfortunately its night of the dead in my lab. Its like putting a three peice suit on a zombie.


This forum has powerful necromancers on it. Kelthuzad would be proud.
« Last Edit: January 29, 2019, 05:12:28 pm by coppercone2 »
 

Offline tggzzz

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Re: SMA torque wrench
« Reply #18 on: January 29, 2019, 05:43:35 pm »
Maybe there are some good suggestions and tricks for getting torque wrench to work in tight spots.
maybe this
https://kendonpark.com/store/KCR-3125S-8C

This came from somewhere, probably an evaluation kit of some sort.

The cable can go along the centreline, and a spanner can grip it anywhere along its length.

There are lies, damned lies, statistics - and ADC/DAC specs.
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Online coppercone2

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Re: SMA torque wrench
« Reply #19 on: January 29, 2019, 05:45:48 pm »
Keep in mind that causes torque error because its an interface lever.
 

Online IanB

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Re: SMA torque wrench
« Reply #20 on: January 29, 2019, 05:51:46 pm »
Why is torque important in these connectors? Is it critical?

I can see that over tightening could cause mechanical damage or strip threads. Leaving it too loose means it could come undone with vibration and degrade the signal. But how big is the region in the middle, between too tight and too loose?
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Offline tggzzz

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Re: SMA torque wrench
« Reply #21 on: January 29, 2019, 06:10:50 pm »
Keep in mind that causes torque error because its an interface lever.

Please disambiguate "that", "error" and "interface".
« Last Edit: January 29, 2019, 06:12:29 pm by tggzzz »
There are lies, damned lies, statistics - and ADC/DAC specs.
Glider pilot's aphorism: "there is no substitute for span". Retort: "There is a substitute: skill+imagination. But you can buy span".
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Offline Bud

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Re: SMA torque wrench
« Reply #22 on: January 29, 2019, 06:27:50 pm »
It is important for repeatable measurements using a VNA for example. Using a torque wrench helps minimise reflection variations on the connectors.
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Offline TheSteve

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Re: SMA torque wrench
« Reply #23 on: January 29, 2019, 06:51:30 pm »
And if you just spent 13k USD on a Keysight 85052b 3.5mm Cal kit you wouldn't want to damage it by over torquing and damaging the threads.
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Offline Mechatrommer

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Re: SMA torque wrench
« Reply #24 on: January 29, 2019, 07:55:01 pm »
Why is torque important in these connectors? Is it critical?
i guess its critical near double digit GHz band. for single digit, i hardly see any difference between sligtly tight, tight to over tight.

I can see that over tightening could cause mechanical damage or strip threads. Leaving it too loose means it could come undone with vibration and degrade the signal. But how big is the region in the middle, between too tight and too loose?
i bought this https://www.ebay.com.my/itm/1N-m-3N-m-opening-8MM-SMA-torque-wrench-RF-connector-opening-spanner/292927697475?hash=item4433d9f243:m:mUI4KC35S8i5GEGn7qQWynA:rk:1:pf:0 and the torque is too much for my taste i guess at its default setting (1Nm iirc) it can chip away some metal on the thread, so i loosen it to minimum level before the spring comes off, but its still too tight it brings the permanent sacrificial N to sma adapter along to turn with it on my VNA (which i tightened with "the hand" quite hard). not wanting further damage by using it, in the end i use back "the hand". maybe i can use that wrench later for my all-metal real-steel CNC project.
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