Glue/Epoxy on Kevlar?

I know a lot of us use wood glue or epoxy to to secure knots that are tied attaching the Kevlar to an eye screws or nose cones, but are there other methods of doing this?

I thought maybe using some heat shrink around the knot might work well instead. It will also give it a cleaner look. I have heard on this forum and others that the wood glue or epoxy will actually shorten the life of the Kevlar/Knot causing it to fail.

I wanted to bring this up because I know that the directions in some kits say it's perfectly ok to do this?

Any feed back on this??

If you tie a good knot, you don't need any glue. A good knot will get tighter the harder you pull on it. Glue on a knot is like a screen door on a submarine.

jeffgeraci said:

If you tie a good knot, you don't need any glue. A good knot will get tighter the harder you pull on it. Glue on a knot is like a screen door on a submarine.

Click to expand...

What about heat shrink over knot? Pros / Cons?

Dan I like the heat shrink on the end of the line to keep it from unraveling-makes a prettier knot too. Guess you could shrink the knot-can't hurt! One of my buds uses that Dip-It rubber stuff for handles and what ever-but I don't like that heat resistance (none) but it may not make any diff 'cuz it's KEVLAR, huh? ( funny image: flaming knots!)

fyrwrxz said:

Dan I like the heat shrink on the end of the line to keep it from unraveling-makes a prettier knot too. Guess you could shrink the knot-can't hurt! One of my buds uses that Dip-It rubber stuff for handles and what ever-but I don't like that heat resistance (none) but it may not make any diff 'cuz it's KEVLAR, huh? ( funny image: flaming knots!)

Click to expand...

Can you use a hair dryer to get the heat shrink to work? Just curious? I may have to borrow a heat gun or buy one...tools on a low since I left my ex..she got the tools.

29 cent Bic lighter...no tools required!

fyrwrxz said:

29 cent Bic lighter...no tools required!

Click to expand...

LOL I may have to try that...I have one of those candle lighters.

Save myself from burning my fingers.

have to Join Jeff in saying
Proper knot choice and knot tying require nothing else to stay where you put them. Any Kit manufacturer who makes such a statement is only looking to sell more of their kits. IT IS NOT EVER OK to glue any line.

It is not advisable to use Glue or epoxy on any knot as it will causes the knotted line, not matter what the material, to fail AT the edge of the glue or epoxy. Adding glue to knots is like adding shards of glass or razor blades to the material of the line. As the line flex back and forth the dried adhesive acts like the edge of a knife..weaking the fibres until they fail. Add just a little strain..like an ejection charge throwing a nosecone to the end of the line or a chute opening... and SNAP!

Can you embed kevlar in glue or epoxy? Sure; many including myself do. We do so with the understanding that the kevlar, or whatever material will eventually fail at that point unless it is somehow "Strain releaved" so no pressure is put on the embedded section of the line. I do this mostly by running my shocklines to the outside edge of the airframe/centering ring joint, keeping the line as far away from the heat as possible.

Also keep in mind KEVLAR does not burn but it does decompose a bit every time it is subjected to temperatures of 482°C/900°F and above. Keeping you kevlar lines as far as practical away from our ejection charges vastly increases the over all life of the shockcord.

jeffgeraci said:

If you tie a good knot, you don't need any glue. A good knot will get tighter the harder you pull on it. Glue on a knot is like a screen door on a submarine.

Click to expand...

I've been using a non-slip mono loop knot to attach my kevlar harness (shock cord) to the screweyes and quicklinks in my rockets. Some websites claim that this knot maintains 100% of the strength of the cord while others claim that it maintains about 80% of the cord's strength.

Other knots with similar claims (100% and/or 80% strength) are the Bimini Twist knot and the Duncan (Uni) knot.

https://www.animatedknots.com/

What is your opinion on these knots suitability in rocketry?

Do you have a better suggestion as to what type of knot to use to attach kevlar shock cord/harness to screweyes and quicklinks?

I agree, the right knot doesn't need any glue.

I do remember in kit instructions they'll tell you to place a drop of glue to set the knot.
Years back I once tried thin CA on a shroud line knot. The glue stiffened up the string as it ran up the line away from the knot!
Not recommended.

Shroud lines supplied in some Quest kits seem to untie themselves!
That's probably the only time I felt the need for a small drop of glue to help "set" the knot.

RocketManDan said:

LOL I may have to try that...I have one of those candle lighters.

Save myself from burning my fingers.

Click to expand...

I set heat-shrink tube over a candle, keeps both hands free to manipulate the work.:wink:

Mine are all finger-trapped and sewn, as this doesn't create a stress point like a knot does. No knot maintains 100% of the strength of the cord -- they all create a stress point, just some are better than others.

Some refer to a finger trap as a "DeHate Loop", as Robert DeHate posted pictures of how to do it.

After you do the loops like Robert shows, then run some stitches through the line where the end is trapped inside. This keeps it from slipping when it's not under tension.

Finger traps are heavily used in skydiving.

-Kevin

I totally agree...no glue
I always wrap around the eyehook/bolt twice before tying off.
habit

RandyT0001 said:

I've been using a non-slip mono loop knot to attach my kevlar harness (shock cord) to the screweyes and quicklinks in my rockets. Some websites claim that this knot maintains 100% of the strength of the cord while others claim that it maintains about 80% of the cord's strength.

Other knots with similar claims (100% and/or 80% strength) are the Bimini Twist knot and the Duncan (Uni) knot.

https://www.animatedknots.com/

What is your opinion on these knots suitability in rocketry?

Do you have a better suggestion as to what type of knot to use to attach kevlar shock cord/harness to screweyes and quicklinks?

Click to expand...

Randy:
Don't believe Any that claim 100% line strength...that's totally bogus! just putting a bend in any line reduces the line strength. 80% is likely a more approperate number. Knot selection depands on a lot of factors.

I use a lot of 2 and 3 half hitch knots, sheet bend, Bowline and improved clinch knots depending on placement, expected stress on the line and differing line sizes.

When you say no glue, are you are also meaning at the MMT as well? I have seen instructions that say to glue the shock cord on to the MMT.

Thanks

the shock cord won't "wiggle" at the MMT like it would at the other end
it's that back and forth wiggle against the glue edge that will want to saw thru and weaken the cord.
I've never had one give at the motor mount

**not to say it won't happen**

Micromeister said:

Randy:
Don't believe Any that claim 100% line strength...that's totally bogus! just putting a bend in any line reduces the line strength. 80% is likely a more approperate number. Knot selection depands on a lot of factors.

I use a lot of 2 and 3 half hitch knots, sheet bend, Bowline and improved clinch knots depending on placement, expected stress on the line and differing line sizes.

Click to expand...

I use the non-slip loop knot because it is 'non-slip'. I had searched the internet looking for knots that would not untie (slip open) themselves under dynamic loads. This one looked to be the easiest to tie and would tighten under loads. I knew that no knot would carry 100% of the rope/cord's breaking strength. Even an 80% load capacity is probably under 'ideal' laboratory conditions.

To revisit an old thread... I used the bowline knot, and I'm not concerned about the knot, but what about using epoxy or glue on the loose end to stop it from flaying. If not glue, then what?

There is nothing wrong with using glue at that point.

Titan II said:

There is nothing wrong with using glue at that point.

Click to expand...

ditto! but I'd either whip the end with thread or burn/melt the free end with a lighter, depending on the line type. Whipping the Loose ends of rope and line is something pick-up as a Scout. Takes a little more time then glue but generally looks better

I'll go the glue route until you teach me how to whip my ends....................

Try a sewn harness..
You can't beat them for maintaining the strength of the material...
They make for a super clean looking finished product....
And there'a a cool factor in them as well...
Once you try them,,
You'll be hooked....

Teddy

I was totally thinking of buying some one bad hawk harnesses... First time building high power.
Hey, I haven't started my Arreaux or my PML AMRAAM 2 yet, recommendations?

Wow,,
If I remember correctly those are both mid sized rockets...
Your best bet would probably be either the
1/2" Flat Kevlar or the 9/16" Tubular Nylon....
If they are a bit larger then mid the 11/32" Tubular Kevlaris it for sure...
But contact me through the "Contact Us" page on my site and tell me specifics about those rockets,,, I don't want to guess,, right ??

Teddy

troj said:

Mine are all finger-trapped and sewn, as this doesn't create a stress point like a knot does. No knot maintains 100% of the strength of the cord -- they all create a stress point, just some are better than others.

Some refer to a finger trap as a "DeHate Loop", as Robert DeHate posted pictures of how to do it.

After you do the loops like Robert shows, then run some stitches through the line where the end is trapped inside. This keeps it from slipping when it's not under tension.

Finger traps are heavily used in skydiving.

-Kevin

Click to expand...

+1 on what Kevin said.

I started using the DeHate method of making loops after looking at the difference in strength compared to tying knots.

https://rocketmaterials.org/datastore/cord/Shock_Cords/index.php

I have made a knot that exceeded the strength of the tubular Kevlar braid line that I used. It snapped the shock cord right in the middle. I don't know if the finger trap style would have worked on such a large cord though, what with much smaller sub strands relative to the diameter of the tube, and the larger inner area compared to the actual cross sectional area of the cord.

I used a doubled figure eight to create a harness loop, and then loosened that knot and back fed the main shock cord between the two ends of the loop.

onebadhawk said:

Wow,,
If I remember correctly those are both mid sized rockets...
Your best bet would probably be either the
1/2" Flat Kevlar or the 9/16" Tubular Nylon....
If they are a bit larger then mid the 11/32" Tubular Kevlaris it for sure...
But contact me through the "Contact Us" page on my site and tell me specifics about those rockets,,, I don't want to guess,, right ??

Teddy

Click to expand...

I'll do that!

CzTeacherMan said:

I'll go the glue route until you teach me how to whip my ends....................

Click to expand...

KNOT a problem It is quite easy even on very small diameter lines. I use 2-strand 13lb Kevlar thread for Mod-Roc use on braided and twisted Kevlar shock lines. Works like a charm and stays in place.
Sorry the GIF file wouldn't upload for some reason? it converts to a single frame jpg with I try to attach it. If you'll go to https://www.meritbadge.ord/wiki/index.php/Whipping it will show the exact process in a moving Gif file.

Micromeister said:

It is not advisable to use Glue or epoxy on any knot as it will causes the knotted line, not matter what the material, to fail AT the edge of the glue or epoxy.

Click to expand...

I agree that proper knots do not need glue but, I have worked with epoxy and fabrics of all kinds. I have never had kevlar fail at the edge of epoxy. I would have no issue epoxy over a knot but again there are knots which don't need it.

I would think that the Kevlar would become brittle if it absorbed/was coated with epoxy. From my experience, laminated composites (ie kevlar+epoxy) tend to shatter when subjected to a sufficiently high deflection. Non-laminated materials (ie plain ol' Kevlar) do just fine under the same deflection. For a tie-off point for shock cord, the latter seems optimal, so I would want to reduce the incidence of epoxy on Kevlar as much as possible.