Electronics > RF, Microwave, Ham Radio

Printed SMA torque wrenches

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joeqsmith:
Pete Vee had left me a comment about beginners and torque wrenches.   With 3D printers being so common today, we decided to see whats out there and found a couple of torque wrench designs.   The two we settled on are a simple beam and adjustable break-over types.   The models for the beam type uses different thicknesses to get the range of torque you require.  The one shown will reach the top of the scale around 4" lbs.

The adjustable one is made from six parts.   The parts needed some cleaning up to get the drag down.  They are fairly smooth now.   Cost of all three was pennies of material.  These require a compression type spring.  I have a bag of random springs which had a couple that worked well but needed to be cut down.   

https://www.myminifactory.com/object/3d-print-torque-wrench-131619

https://www.thingiverse.com/thing:4344483

joeqsmith:
If you look at the spring they are using compared with what I have, mine is much thicker.  I find it hard to believe they could reach an inch lbs with the spring they show.  Notice how they use the balance to calibrate the wrench but they don't actually show the reading. 

The first parts were printed like they show.   All parts were printed in PLA.  As I was increasing the torque, the plastic handle's tab broke.  In the picture, I have glued it and was able to get 3 in/lbs without it braking a second time.   

We decided to print it lengthwise instead to give it some much needed strength.   This works like a charm. 

A few things to note.  First,  five in/lbs is about the limit before the wrench will deflect enough to spin on the nut.   The beam wrench will slip around 4.  Make sure you get the parts clean before you try and thread in the adjustment bolt.  All the parts should move very freely.   Also, apply a little grease to the moving parts.   
To clean out the bore, oddly enough you may find that the small diameter X-acto handle is a perfect fit.  The knurled end will clean it out with ease. 

I left the orange wrench on my desk and cycled it (fully broke it over ***) I would guess about 100 -150 times.  This wore the cam enough that the wrench is way out of balance now.   If you are going to use one of these rather than spending the $40 for a real wrench, I suggest to check the torque frequently.  Maybe every 10-20 cycles.   

*** I made a few videos on using torque wrenches.  The last one was a destructive test after receiving so many comments about pulling the edge launch connectors off the PCBs.   I did not demonstrate these two types of wrenches.  The break-over type is not designed to be fully broke over.   Make sure you learn how to use one before you actually attempt it.     The only connector I have ever seen damaged by using a torque wrench was when the person didn't ask how to use it..   Well, and the ones I ruined for this video.


coppercone2:
does this have a chance of working with resin printers? I assume its far too stiff, at least the #3, but since I have a full set of all the torque wrenches from micro to truck tire, I think im better off machining that clever adapter you have to interface a normal torque wrench with it, brazing it to a high quality bit so there is a good mechanical coupling to the wrench itself

but this is highly useful for people that want to repair a machine with internal cans anyway, since that will never fit in there

joeqsmith:
I think you would just need to try it.  The brake-over wrenches weak point is the lack of strength and wear.    Making all the parts with metal, grinding the surfaces and maybe hardening them may make for a decent wrench but the cost may far exceed just buying a good wrench.   :-DD     The beam wrench has three different springs and various wrench sizes to choose from.     You may need to play with the spring.   

No doubt, buying a decent wrench and learning to use it properly is really the way to go but I can see the beginner starting with a printed part like these if they already have the printer, materials and they consider their time as free.     

My modified socket has about the smallest footprint but you can only remove so much material.  This limits it to flexible cable.  For ridged, the best thing I came up with was that crows foot.   Of course, I tried to find one but no luck.  1/4" drive small sets must not be very popular.   

The small CDI wrench is a PN# 401SP-CDI.  It's not easily adjustable.  They offer ones that are, for example: 

https://www.amazon.com/Torque-Screwdriver-40-200-cNm/dp/B07SPDJKLB/ref=sr_1_49?crid=2Q8EDLE8Y5AEO&dchild=1&keywords=cdi+torque+screwdriver&qid=1621251060&sprefix=cdi+tor%2Caps%2C181&sr=8-49

joeqsmith:
I have continued to cycle the orange wrench.  Today, it came apart.  There was enough force, it bent the nail before is split at the hole.  This was the same failure I had seen with both wrenches.  This handle had been glued on the opposite side.   

It was set for 3"/lbs but to get that torque, the spring is under a fair bit of tension.  When it came apart, part hit the wall about a meter away with a fair amount of force.  I have not found the missing part yet.    So you may want to wear safety glasses to torque your connectors with one of these!   :-DD

I cleaned up the other Gen II handle and painted it.   I reground the wrenches edges so it should be balanced again (same torque in both directions).   

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