1. Home
  2. Electronics Design
  3. SMA / SMC Tightening torque

SMA / SMC Tightening torque

I'm not sure what you mean by "that" imperative, but I do know that torque values are specified to keep ham-fisted operators from OVER- tightening things, which could distort the dielectric, and worst case, strip the threads. When I had occasion to use those type of connectors in the military (USAF), we generally hand-tightened them, and used a

1/4" open-end wrench with just a little more than a feather-touch. Less force at the end of the wrench than it takes to push a telephone keypad button. We got, for all practical purposes, 100% reliability.

Get a little bitty torque wrench and a "crow foot", if you're really nervous about it or have a PHB breathing down your neck. :-)

As to where to get one, I know nothing about the UK other than that Brit teeth are an endless source of humour - do you have anything like a "Yellow Pages?"

Good Luck! Rich

Reply to
Rich Grise
Loading thread data ...

According to the service manual for my spectrum analyzer: "when replacing semi-rigid pipe connections it is imperative that the following torque settings are used: SMA: 99 - 106 N-cm; SMC: 42 - 49 N-cm"

  1. Is it really that imperative?
  2. Does anyone know where I can buy suitable torque wrenches in the UK?

Thanks, Andrew.

Reply to
Andrew Holme

I haven't used SMC much so the following applies to SMA.

You could probably hook a spring balance (or just a spring with a known extension at the required tension) to the other end of the spanner.

If the connectors are too loose, they may fall off or give unreliable contact after exposure to vibration. If you do them up too tight you can damage the connectors (I have read that the pins can be compressed too much amongst other things). If you do them up just tight enough that you think they won't come loose of their own accord, and no tighter, then you should be fine. The 7% or so tolerance that they specify in your manual is probably unnecessary for normal purposes. When using a network analyser, in my experience I have never been able to see any electrical difference between finger-tight (i.e. done up with my fingers and no spanner) and torque-wrench tight. The advantage of using the torque wrench is that I can then do them up tighter so that I have more confidence that the cables won't come loose later. If you'll be around to re-tighten the connectors then finger tight would probably do.

Chris

Reply to
Chris Jones

I once tightened an SMA with a TDR attached (at the other end of a cable).

There was a little spike of higher impedance that became narrower as I tightened the nut. It disappeared (roughly) when the correct torque was reached.

Regards, Allan

Reply to
allanherriman

I vaguely remember seeing connectors with a lockwire hole in the shell, in case you have a mission-critical, high-vibration application (like a fighter airplane).

Cheers! Rich

Reply to
Rich Grise

RS Components sell the torque wrenches (certainly for SMA, I'd guess SMC as well). By default I' d say therefore that Farnell do too - they both have US distributors if you're over there. Mind you those distributors are hideously expensive (we get them from Nera for less!) but it should give you a manufacturer's name.

Cheers.

Ken

Reply to
Ken Taylor

I can't find any on either's web site. Can you post the order code? Thanks.

I've found a few US companies on the web e.g.

formatting link
but this is 0.35 Nm for SMC when I thought it had to be .42 - .49

Thanks to all the posters for your responses.

I've gone and tightened the damn things up by hand now - but I would still like to buy the proper tool for future use.

Reply to
Andrew Holme

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.