Steel Shock Cord Anchor Question

[GrossApproximator]

I'm aware that some people like to attach a braided steel line to their motor mount (or eyebolt or whatnot) and then a nylon (or whatever) cord to the steel. What size of steel do people like to use? Will the steel deteriorate over time? Do you tie the steel or use JB weld?

[ScrapDaddy]

I'm aware that some people like to attach a braided steel line to their motor mount (or eyebolt or whatnot) and then a nylon (or whatever) cord to the steel. What size of steel do people like to use? Will the steel deteriorate over time? Do you tie the steel or use JB weld?

Unless you are flying HPR steel is not allowed, anyway use kevlar, 6times stronger than steel of the same thickness, and far lighter, it also has a heat resistant quality, it should last longer than your actual rocket.

As for mounting, I would use an eyebolt to the MMT, insert the eyebolt, pull it out and fill the hole with JB and put the eyebolt back in, have you thought about going all Kevlar it will save you trouble in the long run. ;)

BTw these methods are wayyy overkill, you should only use with a HPR

[GrossApproximator]

Just trying to find an attachment method that will outlast the airframe. Also, this rocket may one day go high power--small high power, but high power none the less.

[ScrapDaddy]

Ok then you will have to wait for someone with HPR experience right now I have sratche right under that, my largest engine only being a F42

[GrossApproximator]

Ok then you will have to wait for someone with HPR experience right now I have sratche right under that, my largest engine only being a F42

I've no experience either :D that's why I'm asking so many questions: I need to get a VERY good idea of how to make these things before I start. There can be no foul-ups. But, of course, failure is most certainly an option :bangpan:

[GrossApproximator]

Also, about how long would a 1500 lb test Kevlar cord last if it was epoxied to the motor mount tube? I ask because there's no way I'm ever going to be able to replace this thing without destroying the back half of the rocket (at least not with my current design).

[ScrapDaddy]

You kinda remind mr of me (no offence) kevlar won't give very soon it would outlast steel no doubt

[slogfilet]

Unless you are flying HPR steel is not allowed, anyway use kevlar, 6times stronger than steel of the same thickness, and far lighter, it also has a heat resistant quality, it should last longer than your actual rocket.

Calling Micro... we need some heavy lifting here...


***intermission***


EDIT: But in the mean time, here are a couple very good posts on using braided stainless leaders!

http://www.rocketryforum.com/showpost.php?p=43336&postcount=5

http://www.rocketryforum.com/showpost.php?p=43336&postcount=5

[Gillard]

NCR used the gorilla mount which used a steel loop, i had a motor fail with a blow by which toasted the entire inside of the BT but the loop was fine, because it was steel, the steel was crimped together, a mechanical join is always better than a chemical (glue) join. (hurts to say, as i'm a chemist) but steel loops can be overkill.
On the same hand, I have had Kevlar burn through, granted only on mid power rockets where the kevlar was probably too thin but Kevlar is not fire proof, only fire resistant, i tested Kevlar with a blow torch in my lab at work and it does "go" with enough heat.
on a plus side, i now nearly always use steel fishing leaders with low power rockets, no problems yet, a cheap anchor that is flame proof yet light weight, a big improvement over both elastic cords and kevlar (i still use elastic attached after the steel leader)

[Warthog]

My first HPR rocket was a 4" THOY Phoenix. I flew it on H and I Aerotech reloads. It had a braided stainless steel shock cord that was attached to the forward bulkhead halfway between the 38mm motor tube and the inside of the body tube with an eye bolt. Since it was stainless steel and mostly located away from the ejection charge blast I assumed that it would be fine for a long, long time.

It lasted for 18 flights over a period of 5 years before the shock cord broke. When I looked at it after its last flight the steel cord had corroded through at a point about 2" above the eye bolt. Obviously the combination of heat, burnt black powder and humidity did it in.

On the other hand, I have other HPR rockets with Kevlar shock cords that each have more flights than the Phoenix with no visible damage to the cords.

[RoyAtl]

Unless you are flying HPR steel is not allowed, anyway use kevlar, 6times stronger than steel of the same thickness, and far lighter, it also has a heat resistant quality, it should last longer than your actual rocket.

As for mounting, I would use an eyebolt to the MMT, insert the eyebolt, pull it out and fill the hole with JB and put the eyebolt back in, have you thought about going all Kevlar it will save you trouble in the long run. ;)

BTw these methods are wayyy overkill, you should only use with a HPR

Now ya go jumping off to conclusions the other way. Braided steel cord can certainly be used for a shock cord anchor. Nylon-covered braided steel fishing line can be found in small enough gauge to use, for instance, in a Big Bertha.

Advantage over Kevlar is that it is much more flame resistant. Disadvantage is that its a tad heavier, and is not as flexible.

[ScrapDaddy]

Now ya go jumping off to conclusions the other way. Braided steel cord can certainly be used for a shock cord anchor. Nylon-covered braided steel fishing line can be found in small enough gauge to use, for instance, in a Big Bertha.

Advantage over Kevlar is that it is much more flame resistant. Disadvantage is that its a tad heavier, and is not as flexible.

Ohhh as an anchor, I thought Gross mention the entire cord

[GrossApproximator]

Ohhh as an anchor, I thought Gross mention the entire cord

:roll: Sorry. There's no way 10 feet of steel shock cord would ever get stuffed in this rocket--WAY to skinny. Based on one of the links posted under this thread (really sorry, I'm too lazy to actually look it up, just go a few posts up), I think I want to use steel: my rocket isn't minimum diameter, but it's close. I'd have to mount my Kevlar right on top of the motor mount.

One other option: would an ejection baffle effectively protect the Kevlar? I'm thinking about a 4" long baffle made from a LOC coupler tube and bulkheads with holds in them (sorry about the bad description . . . I might just have to make one). I could probably fit the baffle two inches or so in front of the motor mount tube and attach a Kevlar cord on top of the baffle.

[Micromeister]

Unless you are flying HPR steel is not allowed, anyway use kevlar, 6times stronger than steel of the same thickness, and far lighter, it also has a heat resistant quality, it should last longer than your actual rocket.

As for mounting, I would use an eyebolt to the MMT, insert the eyebolt, pull it out and fill the hole with JB and put the eyebolt back in, have you thought about going all Kevlar it will save you trouble in the long run. ;)

BTw these methods are wayyy overkill, you should only use with a HPR

What the sam hill are you talking about Scrapdaddy! Stainless steel braided fishing leader, and aviation cable are and have been used in and as motor mount Shockcord anchor systems for 20 years. Unless you know what your talking about I do wish you'd NOT post misinformation like that. Use of Stainless or titanium Shockcord Anchor cables is perfectly legal for all forms of Model rocketry.

To answer the thread authors question:
the size and break strength of the steel leader or avaition cable depends entirely on the size of the model being built. To be honest i'm using tiny 49strand stainless beading wire as shockcord anchors in Micro maxx models. 30# and up stainless fishing leader or several diameter stainless avaition cable with crimp connectors in LRP and MPR models. here are some photos of the materials used. these Anchors and generally crimp attached around and between the centering rings on most model motor mounts or can be wrapped around a motor block in minimum dia motor mounts. the beauty of these anchor is they are much more HEAT resistant then the Kevlar line itself. their is a slight weight penelity but on most models these anchors outlast the models motor mount. and can then be reused in another model.

[JDcluster]

Steel cable as an anchor only. You have to make sure that it's shorter than the top of the body tube, otherwise you will end up with a zipper. I have seen some really big rockets use 2 steel cables for attachment ( O & P powered).

I've use it in my Comp4 from Performance Rocketry. You have to use the nylon jacketed type to prevent rust & cutting yourself on the cable ( very sharp). It's best to buy a swag tool to crimp the ferrules onto the ends as a backup encase the glue joints break.

I have also used it on a 3" PML Tomahawk that suffered a CATO back about 4 years ago. I kept the upper half ( the part that survived) of the motor mount with the cable as a souvenir. When used correctly, they work!


JD

[NjCo]

I used some braided picture hanging wire in a modified Big Daddy I built. I wrapped it around the top of the motor mount and then up through the top centering ring. I added some scrap balsa reinforcement where the wire passes through the centering ring. I then put a loop in the wire to secure the shock cord. Here's a picture of the end result:

[NjCo]

30# and up stainless fishing leader or several diameter stainless avaition cable with crimp connectors in LRP and MPR models.

Where do you find those tiny crimp sleeves to fasten the leader ends?

[MarkII]

Where do you find those tiny crimp sleeves to fasten the leader ends?Cabela's. (http://www.cabelas.com/cabelas/en/templates/pod/standard-pod.jsp?id=0011430&navCount=2&parentId=cat20204&masterpathid=&navAction=push&cmCat=MainCatcat20166-cat20180-cat20204&parentType=index&indexId=cat20204&rid=) That's also where I got some 90 lb., 7-strand leader (http://www.cabelas.com/cabelas/en/templates/product/standard-item.jsp;jsessionid=A41SP4HRAQURFLAQBBKSCNNMCAEFAI WE?id=0011246314955a&navCount=42&podId=0011246&parentId=cat20204&masterpathid=&navAction=jump&cmCat=MainCatcat20166-cat20176-cat20204&catalogCode=IK&rid=&parentType=index&indexId=cat20204&hasJS=true&_requestid=120721). I crimp the tubes with vise grips.

Mark K.

[ScrapDaddy]

:roll: Sorry. There's no way 10 feet of steel shock cord would ever get stuffed in this rocket--WAY to skinny. Based on one of the links posted under this thread (really sorry, I'm too lazy to actually look it up, just go a few posts up), I think I want to use steel: my rocket isn't minimum diameter, but it's close. I'd have to mount my Kevlar right on top of the motor mount.

One other option: would an ejection baffle effectively protect the Kevlar? I'm thinking about a 4" long baffle made from a LOC coupler tube and bulkheads with holds in them (sorry about the bad description . . . I might just have to make one). I could probably fit the baffle two inches or so in front of the motor mount tube and attach a Kevlar cord on top of the baffle.

I'm calling you GA becuase your screen name is very long, but to help us all out could you specify if you are refering to a single rocket (give us a size) or just ask it in general.

Not looking things up that can be googled can annoy some of the "more experienced" on TRF, I learned the hard way....... Friendly warning :)

[Micromeister]

Where do you find those tiny crimp sleeves to fasten the leader ends?

Sorry for the interrupted post had a slight emergency near the house last evening.

Crimp sleeves and beads are available for the various cables from the purchase source generally. in the case of Fishing leaders they are generally premade in a variety of lenghts, I've found the 12" leader the most useful in Model and MPR applications. Your local Tackle shop or wal-mark or K-mart sporting goods dept. should have a decent selection.
Because I do lots of other equipment fabrication and other things I buy my Avaition or "Stainless Wire Rope" from where else McMaster-Carr LOL!!! You should be able to fine some sizes at well stocked hardward stores but I find it easier to find on-line.
Stainless Wire Rop comes in a HUGE variety of cable lay-up options and core choices as well as alloy and coverings. Budget is usually the diciding factor on which Stainless steel cable strand count and core choice to make. the 7x19 strand standard core material i'm showing has worked out best for my particular flexibility and strength needs your mileage may vary. I strongly do not recommend vinyl or other coverings on Stainless wire rope as it effects flexibility. Flexibility is paramont for our applications as it determines how well the cable will stand up to repeated bending and flexing during packing and deployments. 7x19 strand is the most flexible Stainless wire rope available at the moment.

Below are the 3- 7x19 and 1x19 strand Stainless cables I'm currently using on most Model and MPR builds with stock numbers and crimp sleeve stock numbers as well. I use a regular pair of terminal crimp pliers to squeeze the sleeves but as Mark mentioned visegrips or plain old pliers can be used.
Another thing that i'm doing after crimping the forward cable loop is to dremel grind the copper sleeve into an oval on both ends removing any snag potential to laundry or kevlar/elastic shockcords added. Take care not to nick the strands of the cable during this process.

That tiny 15 to 21lb test 49 strand Stainless beading wire being used for Micro and 13mm builds is available from Micheals along with the crimp beads and crimp tools. It's some amazingly light, strong, Flame & heat resistant stuff;)
Hope this helps.

[Micromeister]

Lastly a couple more pics of different Stainless Shockcord anchor applications that may help with placement of your Shockcord anchoring system.

Some of these pics are micors but the same anchor installation can be used on larger models.

[NjCo]

Another thing that i'm doing after crimping the forward cable loop is to dremel grind the copper sleeve into an oval on both ends removing any snag potential to laundry or kevlar/elastic shockcords added. Take care not to nick the strands of the cable during this process.

That tiny 15 to 21lb test 49 strand Stainless beading wire being used for Micro and 13mm builds is available from Micheals along with the crimp beads and crimp tools. It's some amazingly light, strong, Flame & heat resistant stuff;)
Hope this helps.

Thanks for the help. The only problem I've seen with using wire leader as a shock cord mount is the potential for snagging the shock cord, shroud lines and chute. Your Dremel solution would solve that for the most part. And I agree that coated wire is a bad choice. They are inherently less flexible and while the wire is heat resistant the coating will not be.

[dixontj93060]

Micromeister,

I need some specific help here. At a Three Oaks launch back in February, I had a wire leader crimp come apart. This is for a Vaughn Bros. ASP and was provided as "standard fare" with the kit. Unfortunately, their quality control apparently allowed a bad crimp to be included in "my kit." In any case, I have searched for small crimps in the places you mention and have not found any as small as this (see picture). The aft end of a 24/40 case is shown for comparison. I mic'ed out the cable at ~1/32". Where might I find a crimp that small to repair this (short of ordering a box of 100 from McMaster-Carr and paying shipping that is 3X the product cost)?

-Tim

BTW, the cable loop connection was to a kevlar cord as you show in another picture in this same thread.


Your local Tackle shop or wal-mark or K-mart sporting goods dept. should have a decent selection.

[Micromeister]

Micromeister,

I need some specific help here. At a Three Oaks launch back in February, I had a wire leader crimp come apart. This is for a Vaughn Bros. ASP and was provided as "standard fare" with the kit. Unfortunately, their quality control apparently allowed a bad crimp to be included in "my kit." In any case, I have searched for small crimps in the places you mention and have not found any as small as this (see picture). The aft end of a 24/40 case is shown for comparison. I mic'ed out the cable at ~1/32". Where might I find a crimp that small to repair this (short of ordering a box of 100 from McMaster-Carr and paying shipping that is 3X the product cost)?

-Tim

BTW, the cable loop connection was to a kevlar cord as you show in another picture in this same thread.

Tim:
The crimp sleeve in your photo looks like the ones I've used from Cabelas in the past. I don't like them much as it's a single tube sleeve allowing cable slip if you're not really careful during crimping.

I'd suggest the dual chamber sleeves shown in the 2nd photo of post #20 they are designed for 1/32" cable. I haven't had any slip problems with these crimp sleeves using a double crimp attachment (one crimp above the other).

Lately I'm happy to say, McMaster has been using US Postal Service and shipping has been a bit better:)

[MarkII]

The double tube variety of crimp tubes is what I use.

As Micro said, look for the leader with the greatest number of strands. For fishing leader, that's usually 7 x 19 (7 strands, each consisting of 19 steel filaments, are twisted or bonded together to make the cable), but in beading applications, it can be up to 49. The 49-strand stainless steel beading cord can be knotted just like string. Michael's carries Beadalon SS beading cord; it is good stuff but it can be a bit pricey. (Watch your paper for coupons!) Use standard beading and jewelry crimp beads (found in the same section) with it. But avoid the very tiny silver crimp beads.

I haven't noticed any problem with nylon-coated SS cord. In the sizes that we are talking about for LPR and small MPR, the coating is very thin. It is there, I think, to make the cable more resistant to fraying, along with giving it smoother and slicker finish. Although SS is fairly corrosion resistant, the nylon coating provides enhanced protection.

Don't think that 20 lb. and 30 lb. Beadalon is for Micromaxx only. It can also be used in smaller LPR rockets, such as Mini Brutes, and up to Alpha-sized rockets. The test strength may not sound like much, but keep in mind that the cord will never degrade, and if it is coated, it will never fray. Because of that, 20-30 lb. strength cable can be suitable for small rockets. On the rare occasions that the cable fails, it is usually because the loop has opened up and not because the cable has parted. Make sure that your loops are well-crimped.

I use SS cable for the first section of the shock cord (the anchor). It goes from the motor mount to the inside top of the tube, where it ends in another crimped loop. Then I attach my Kevlar, paracord or elastic to that. The SS anchor provides peace of mind, because it will last a very long time. (The rest of your rocket will be dust long before it starts to weaken.) I can access the top loop to change the cord that is attached to it by pushing the cable back out the motor mount; it is usually long enough to extend well out of the mount, making the top loop readily accessible.

Mark K.

[dixontj93060]

Micromeister,

Thanks for the info. Based on MarkII's comment, I'll try looking at Michael's before ordering 50 or 100 from McMaster-Carr.

-Tim


Tim:
The crimp sleeve in your photo looks like the ones I've used from Cabelas in the past. I don't like them much as it's a single tube sleeve allowing cable slip if you're not really careful during crimping.

I'd suggest the dual chamber sleeves shown in the 2nd photo of post #20 they are designed for 1/32" cable. I haven't had any slip problems with these crimp sleeves using a double crimp attachment (one crimp above the other).

Lately I'm happy to say, McMaster has been using US Postal Service and shipping has been a bit better:)

[Rocketjunkie]

I braid my loops. This involves unwinding 3 of the strands (I always use 7 x 19) and rewrapping them in opposite directions to form the loop. There is no lump from the sleeve and it won't fail without breaking at least 3 of the 7 primary strands. Pictures of the process are attached, with the rest in the second post.

[Rocketjunkie]

The pictures are of 1/8" cable that I use for rockets in the 10-30 lb range. I drill 2 holes in the top CR, run the cable through one, 1-1/2 times around the motor tube, then out the other hole. The part of the cable going around the MMT is covered with epoxy. I form the loop on both of the free ends and attach the shock cord to both loops via quick link. The loops are a ways down the body tube but long enough to reach easily for shock cord replacement.

[MarkII]

Rocketjunkie, the cable in your pictures is much thicker than anything that I use. What is its load or test rating and what size rockets do you use it in? The reason that I ask is that I am beginning to move up in the size scale (into the 3"-4" range) with my rocket building, and I want to have some idea of when I should change over from fishing leader to another type of cable. TIA.

Mark K.

[Rocketjunkie]

The photos are of 1/8" cable that I use in rockets in the 10-30 lb. range. Larger I use 3/16. If I can reach the forward CR, I usually use a forged eyebolt in the CR, size depending on the size of the rocket. Breaking strength, IIRC, of the 1/8 is about 1700 lb.