Not sure how long these wrenches will last, but only take 15 minutes to print and use about 3 grams of filament. ![]() Three perimiters (wall line count), four top and bottom layers, and 40% infill. We recommend 4 in-lb sma torque wrenches for Brass SMAs, 5 in-lb sma torque wrenches for lab testing with Stainless Steel. My settings for the print is for PLA filament. It also makes it easier to get the cables on and off than just using my fingers. With this value I appear to be getting more consistant readings than I hade before, and have a handy stylus for the touch screen. Then by adjusting the number of top and bottom layers, along with number of perimiters I got the torque to be somewhere around 4 in. I measured how much force I had to apply for this slip to happen. Just place over the connector nut and turn until the wrench slipps around to the next flat. I printed a couple with different printer settings and tried them out. I also added a small hole 2" from the center of the wrench opening, so you can use a small luggage scale to compute the actual torque. While I was working on the design I decided to taper the other end of the wrench so it could be used as a stylus for the touch screen. This wrench is made from stainless steel to last a lifetime and is small enough to keep in your pocket. I also put a wide enough slot in the end of the wrench to allow it to slide over cables easily. For my use it would be adequate to have it somewhere near that value as long as it was consistant. Looking as the specifications for SMA connectors, I found that they shold be tightened to 5 in. I looked around, and found a couple examples of torque wrenches that looked easy enough to model one on for SMA connectors. Each style of adapter cable is available in 3' or 6' lengths. Thorlabs’ Premium Microwave Adapter Cables have an SMP female connector on one end and either a male or female SMA connector on the other. I wondered if it would be possible to 3D print someting that would be usable. Available with SMA Male or Female Connector to SMP Female Connector. 1 x Crows foot torque head for SMA, 2.92 and 3.5mm connectors. The TT-01-SM comes with: 1 x Anodized TT-01 Adjustable Torque Tool for the range of 1-6NM. Looking around I found that even the cheapest torque wrench for SMA connectors cost nearly as much if not much more than the NanoVNA. The TT-01-SM is an Adjustable SMA Torque Wrench which is compatible with all SMA Male, 2.92mm and 3.5mm connectors. After watching several Youtube videos and reading soome instruction manuals on much more expensive VNAs, I decided I need some form of torque wrench to help eleviate the problem. ![]() After a some checking, it appears that having the connectors 'finger tight' is not quite good enough for getting consistant readings. Table 1 Common SMA connector torque values Connector material Torque N-m (lb-in) Brass 0.34 to 0.56 (3 to 5) Stainless steel 0.79 to 1.13 (7 to 10) 4. Using the NanoVNA, this has shown up a little more often. I have been using SMA connectors on most of my projects, and have occasionaly gotten a slightly different reading than I had expected.
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