Printed SMA torque wrenches  - Page 1
Forum section: electronics / rf-microwave

author: joeqsmith
author_rank: Super Contributor
timestamp: May 11, 2021, 01:32:35 pm
content: 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-131619https://www.thingiverse.com/thing:4344483

author: joeqsmith
author_rank: Super Contributor
timestamp: May 17, 2021, 12:12:04 am
content: 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.

author: coppercone2
author_rank: Super Contributor
timestamp: May 17, 2021, 03:55:31 am
content: 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 itselfbut this is highly useful for people that want to repair a machine with internal cans anyway, since that will never fit in there

author: joeqsmith
author_rank: Super Contributor
timestamp: May 17, 2021, 12:00:59 pm
content: 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.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

author: joeqsmith
author_rank: Super Contributor
timestamp: May 18, 2021, 12:31:19 am
content: 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!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).

author: joeqsmith
author_rank: Super Contributor
timestamp: May 19, 2021, 02:37:27 am
content: To reach the higher torques, I used two springs. This is what was in the other 4"/lb blue wrench. With the wench wearing so badly, I cut two strips of metal and epoxied them to the plunger and wrench edges. I tried to find some shipping strap but I think even an old soup can would wear better than the plastic. I had tried to hot glue the metal but with the force required, it would pull loose. The cheapo wrench is starting to get a bit too complex.

author: joeqsmith
author_rank: Super Contributor
timestamp: May 19, 2021, 11:35:05 pm
content: The epoxy seems to hold the metal straps in place if you decide to try and reinforce one.

author: joeqsmith
author_rank: Super Contributor
timestamp: May 26, 2021, 12:46:56 am
content: I've been cycling the metal reinforced wrench by hand for the last few days. The wrench now will hold calibration and with the handle printed long way, there has not been another fracture. This is starting to look like a usable wrench.

author: 2x2l
author_rank: Contributor
timestamp: August 01, 2021, 05:52:00 am
content: Ahgghghh damnit Joe I had a real long comment drafted, figured it merited getting on the forums, didn't remember my password, had to reset it, check my handful of email accounts to find whichi email tied to my user, and reset it. By which point you had addressed some of my comments. It's still on my clipboard so I'm going to paste it despite you addressing things like cycling.A plug spring, is wayy more elegant than what I was thinking. Remember buddies, k is only constant within the linear region, you'll go into the plastic (that is, region on the stress/strain curve, not material) failure zone well before you see a fracture failure (just like metal - the permanant deformation region of yield comes before the fracture). and game over. But yeah, that's really a insanely elegant idea (I think) since even if one of the two springs approaches permanent deformation, the other one will compensate? I think? Not even close to someone in materials science. My experience with springs are limited to legos and struct coils and..I think that's it so, grain of salt. Or, maybe it will just introduce 2^n variables, since you now have to material combinations with two diameters, with different loading profiles. Someone in materials or metals should jump in here.Adding two metals in a plug form and playing around with them will almost certainly keep you in the elastic zone (say 1.5 to 10 as k performs 100% linear, for at least a few hundred cycles. I bet you can get a bag of chinese springs for a couple bucks on ebay, and benefit entirely from their lack of quality control. Then you can play around with the material combinations, and mayb get you something which will perform for a few thousand cycles before the fatigue profile changes.Just a tangential point: Fictive.com has a service that uses something similar to a sintered metal process which will 3d print your Solidworks models (I think, I don't do all that fancy art stuff). It';ll likely be way out of the 'cost/result' region, but it'd be really really fun to play around with, which I presume is what most of us are here (edit: this was a comment from Joe's original youtube thread)People are 3d printing custom intake headers for performance cars with the entry/mid level (500k-ish?- no idea at all- the platform looked no bigger than 24x36) metal printing. Beforehand, the company has to manually work with you/do a lot of manual geometry analysis (since I think their production volume at this point is so low that it hasn't merited automation yet, some brief FEA just because COMSOL is super cheap, compared to a field failure -> customer&reputation loss. I digress - 3d printing green-> sintered metals is going to be suppppppper cool. I expect to see hackaday post of any day now from some dude who "borrowed" metal grains from work-------- You benefit from the material variance to for *your* setup. But the inconsistency, would you go into production, would introduce so many variables that you'd be banging your head at the table. Especially because you don't know which component is responsble of the variance in the assembly. At which point, just bring in COMSOL and order from some place that has batch reports for tracibility-- so there's that downside of Chinese materials-- you now-- the whole tracability thing that any competent manufacturer will deliver to you in the packing slip

author: joeqsmith
author_rank: Super Contributor
timestamp: August 01, 2021, 03:00:08 pm
content: I should have linked it here. The springs were just what I had on-hand. If one of the springs becomes damaged, the second one is not going to help. Using the twin spring just kept me in that small package size with the torque level I was looking for.

author: Marsupilami
author_rank: Frequent Contributor
timestamp: August 02, 2021, 12:50:33 am
content: This is really cool.

author: neilhao
author_rank: Regular Contributor
timestamp: August 07, 2021, 02:09:05 pm
content: Thanks Joe for sharing this. I just printed mine, looks great.

author: joeqsmith
author_rank: Super Contributor
timestamp: August 07, 2021, 06:01:34 pm
content: Personally, I would be more interested in how the different plastics, settings, dimensions, effect the torque range. If you can reach 4" lbs or does the wrench slip on the nut? Does it break... Basically how well it works, not how it looks. Lets hear some details.Does look nice though.