Low budget shield crimping, how I did it, looking for improvements - Page 1
Forum section: electronics / projects

author: Kjelt
author_rank: Super Contributor
timestamp: August 10, 2018, 03:34:34 pm
content: Hi all,I would like a second opinion or alternatives.The goal is to have a decent shield crimp, like NASA describes here in section 2.10 and like in the first picture.https://workmanship.nasa.gov/lib/insp/2%20books/frameset.htmlThe problem I face is that those particular shield crimps are almost unobtanium or you need to buy 100s. And second you need a special crimptool costing $100's. Both not for my hobby purpose.So like everybody else here being on a budget but with plenty of DIY mentality I searched for viable alternatives.I think I found one in copper water piping, cutting small parts of it, sand it so it is not too sharp.For crimping I use the BNC hexagonal crimp die but unfortunately that is just a bit too big, resulting in a non symmetrical crimp, it fits, it clamps , so its ok'ish.I could make the copper thinner so it will be easier to form but this will take quite some time to do it nicely or I should find a perfectly snug fitting milling bit.Just wanted to know if someone had faced the same issues and might have found a better alternative and ofcourse what you think of this?Please remember it does not have to go into space, or be commercially sold as a product, it is for my own hobby projectThanks,

author: Gyro
author_rank: Super Contributor
timestamp: August 10, 2018, 04:01:55 pm
content: Hmm, nice idea but, as far as I can make out, the NASA crimp consist of two metal sleeves - an inner and an outer with the braid crimped between them? I've haven't seen crimping of braid directly onto flexible cable insulation before.I always use the solder approach, bringing the braid wires together and either sleeving of soldering to a ground wire under heatshrink.If you can find two tubes of loose sliding fit it would work though.P.S.In section 4.06 of your link, they show a solder sleeve method - that might be an easier one to emulate, still NASA standard.

author: Kjelt
author_rank: Super Contributor
timestamp: August 10, 2018, 09:30:38 pm
content: Quote from: Gyro on August 10, 2018, 04:01:55 pmI can't see that in the picture I included, so they shove a metal ring under the braid and one above it?QuoteYes that was what I did before but that is forbidden by Nasa since soldering the braid would make it physically weaker to break, and indeed in you solder braid and wiggle it a few times it breaks off there where the solder starts. Still probably good enough for our personal use I just wanted to improve on it.QuoteSeriously it took me a month of trying and looking to find this solution since all available alternative pipes were aluminium which is not a good crimp material due to its oxyde layers.QuoteI will check it out, I could solder the external wire to the pipe before crimping.

author: Gyro
author_rank: Super Contributor
timestamp: August 10, 2018, 09:49:53 pm
content: QuoteYes, it's hard to see - look at the bottom left diagram, the one with dimensions on it, you can see a silver ring, the braid strands and the outer copper coloured ring. Sorry.All the crimp or clamp connectors I know clamp the braid between two metal surfaces, the plastic is going to be too compliant for a gas tight connection.They provide lousy diagrams considering the application.P.S.QuoteTry a model engineering supplier, they do thin walled tubing and stuff, you might have to settle for brass, but I think they do copper too. E.g.https://www.glrkennions.co.uk/brass-copper-tube.htmlbut closer to home.

author: HighVoltage
author_rank: Super Contributor
timestamp: August 10, 2018, 10:04:07 pm
content: I have used "ferrule sleeves" for this purpose before and it was successful.There are so many sizes, usually one fits perfectly.Also, they are cheap and available in many stores.Interestingly, some hex shape crimping tool dies also fitted any one of my crimping needs.When done correctly, it looks and works really good.

author: nanofrog
author_rank: Super Contributor
timestamp: August 11, 2018, 01:04:11 am
content: NASA'sStudent Workbook for Crimping, Interconnecting Cables Harness, and Wiringmight be of use to you. Although it's not pictorial, it's illustrations do show the inner crimp ring for what you're trying to do (Section 16-1 on pg. 50). It's also clearly mentioned in the text, so this paired with the pictorial reference will usually clear up any confusion.Oh, and the actual inner rings used are made of stainless steel (TE connectivity makes them, and they are expensive; i.e. $1.39 per in singles on Mouser).As per tooling, they're typically hex dies suited for the particular coax being terminated. Not rare, but the acceptable tooling is typically from Daniels Manufacturing Corp., and their stuff is pricey due to compliance requirements.That said however, I'd also suggest going with the solder method asGyrosuggested. You wouldn't even need a ring, just use adhesive lined heat shrink to make an appropriate strain relief. It's not NASA standard, but it will definitely provide a good reliable connection. Loom, spiral wrap, zip tie, lace, ... as appropriate if it's in a high vibration environment.If you do decide to use a DIY ring instead of just the soldering method ^, I'd suggest using soft flexible copper tubing rather than the rigid stuff (better electrical properties). Easier to cut, and you can even adjust the inner diameter on a mandrel or even straight punch using a small hammer (no need to machine).Either DIY method is doable and would be affordable vs. truly trying to meet NASA spec.Hope this helps.

author: ConKbot
author_rank: Super Contributor
timestamp: August 11, 2018, 01:25:41 am
content: If you want to terminate into a pigtail, the "cleanest" solution imo, is to get a pick/hook, open up one of the holes in the braid, pull the wire bundle though, then stretch the now empty braid back out. You're left with all the braid intact, no solder making the braid rigid, and a crimpable/solderable pigtail, plus no heat so you can do it with cheap PVC wire no problem.If you can't do that, I like to put my drain wire in place, and lash it on with solid core uninsulated wire. Nothing too heavy, usually 30-26 AWG or so for non-huge cables. After lashing it on, a quick solder job with a minimal amount of solder. Use a high power iron, you don't want the heat to spread, and the wicking to go too far. Glue lined heatshrink until strain relief is adequate, and it's done. Don't try with cheap PVC wire, but some higher temp PVC can survive well enough if you're fast.

author: tpowell1830
author_rank: Frequent Contributor
timestamp: August 11, 2018, 06:07:00 am
content: NASA Standard 8739.4 has good info (link below). However, if you are only doing this for a hobby project, your method works fine. In my job as a harness design engineer I run into this very often. Solder sleeves with a built in drain wire are the easiest method, but solder sleeves are expensive as well.https://standards.nasa.gov/standard/nasa/nasa-std-87394Hope this helps...EDIT: Although I don't recommend this because you can damage your cable, I have used these crimp sleeves, but you need a special crimp tool.https://www.amazon.com/Ideal-2006S-Crimp-Connector-Pack/dp/B000GASBQ4https://www.homedepot.com/p/Ideal-4-Way-Crimp-Tool-C24/300502789?cm_mmc=Shopping%7CG%7CBase%7CD27E%7C27-11_TOOLS_%26_ACCESSORIES%7CNA%7CPLA%7c71700000034238984%7c58700003943782712%7c92700031954542176&gclid=Cj0KCQjw77TbBRDtARIsAC4l83lrGxB_doenNh15rFu-XwB9csyy8ZSZilBDi3lr_7fVodobOfx40MkaAptIEALw_wcB&dclid=CIms_4es5NwCFQkPgQodLDUM6w

author: Kjelt
author_rank: Super Contributor
timestamp: August 11, 2018, 08:22:56 am
content: Thanks everyone for their contributions, a lot of new options to exploreI have thought about ferrules or adereindhulzen as we call them. The problem was this is a 11mm diameter cable resulting in a 50mm2or awg1 / awg0 ferrule, they are not thin (understatement) and my hydraulic crimper would totally destroy the cableFor thin shielded cables they indeed might be a good solution.

author: HighVoltage
author_rank: Super Contributor
timestamp: August 11, 2018, 09:31:33 am
content: For larger diameter ultra thin tubing I have used hollow professional arrows and they seemed to work well, even for crimping. But 11mm is probably even too much for that.You could use a 12x1 brass tube and drill them with an 11mm or even 11.3 mm hole inside.Then cut them to the right size.It would make a good crimpable sleeve.

author: Kjelt
author_rank: Super Contributor
timestamp: August 11, 2018, 12:12:26 pm
content: Quote from: HighVoltage on August 11, 2018, 09:31:33 amArrows, like in bow and arrow? What material are those made from?QuoteThat is my next step with the copper pipe, i have a simple manual metal milling machine so I can slowly thin the sides.

author: Gyro
author_rank: Super Contributor
timestamp: August 11, 2018, 12:21:42 pm
content: QuoteI'd go for thin walled brass, it's easier to work, harder*, and less thermally conductive (faster to solder, less heat transfer).*Possibly the reason that they use brass rather than copper for the olives in plumbing compression joints.

author: HighVoltage
author_rank: Super Contributor
timestamp: August 11, 2018, 02:16:44 pm
content: Yes, it is also my experience to much easier drill and machine brass, compared to copper.Copper is not fun to work with.I am drilling tubes on the lathe and then just cut off, what I need and the drill the next section.And yes, arrows like in archery.They are ultra thin wall thickness, sometimes less than 0.2mm out of aluminum.And the material is crimpable with a hex shape crimp tool, like we used to use inthe 1990s for coaxial cable crimping for network cables and TV antenna connections.I still have all the crimping tools from those days and interestingly, one always fits perfectly.

author: mzzj
author_rank: Super Contributor
timestamp: August 11, 2018, 02:32:47 pm
content: Quote from: Kjelt on August 11, 2018, 08:22:56 amMaybe look for this type of "wire end ferrules"https://nl.wikipedia.org/wiki/AdereindhulsDirt cheap, "sort of commonly" available and thin walled.But I fail to see the point of this exercise, I'll just go along same lines as ConKbot...

author: Kjelt
author_rank: Super Contributor
timestamp: August 11, 2018, 03:24:48 pm
content: Quote from: mzzj on August 11, 2018, 02:32:47 pmIts hobby, you try new things you come across to learn and to fail, to have fun.In my case I had to terminate and ground the shielding, I had several ways of doing this some mentioned above, but I came across the Nasa instructions and then it starts to itch to try it out with the materials that are available to get an improvement

author: mzzj
author_rank: Super Contributor
timestamp: August 11, 2018, 07:41:15 pm
content: Quote from: Kjelt on August 11, 2018, 03:24:48 pmFair enough, that would describe 90% of my hobby projects too.Once I (half-arsedly) master something I fiqure out something else to try.. electronics, machining, welding and fabricobbling.

author: Kjelt
author_rank: Super Contributor
timestamp: August 11, 2018, 07:43:12 pm
content: Exactly, these cables are for my closed loop stepper motors of my new cnc machine

author: Monkeh
author_rank: Super Contributor
timestamp: August 11, 2018, 07:46:32 pm
content: I tend to just strip the cable long and bring the braid out as a conductor itself - use adhesive heatshrink for a little relief. Works fine as long as it's a copper braid.