Best Way to Tie Off Surgical Tubing
 

Hello CD world,

We are planning on using surgical tubing this year for our launching mechanism. We have been tying the surgical tubing in knots, but with the extreme stress we are putting it under the knots are slipping bit by bit. I was wondering if any people with a lot of experience with the stuff could advise us and other FIRST teams on the best way to tie the stuff. I have seen a few posts mentioning zip ties and hose clamps, but can't be certain if there is any trick to securing this stuff.

Thank you

Re: Best Way to Tie Off Surgical Tubing
 

The method that the teams I have been on is to use zip ties to hold them together. The trick is to stretch the surgical tubing so that the zip tie is tightened when the tubing is as thin as it will be so it doesn't slip.

Re: Best Way to Tie Off Surgical Tubing
 

Using zip ties with a zip tie gun ensures that they are tight. Pretty easy to find one relatively cheap.


http://www.uline.com/Product/Detail/...A&gclsrc=aw.ds

Re: Best Way to Tie Off Surgical Tubing
 

Hose clamps might be the way to go for a COTS component. The ability to have them adjust tensioning with minimal effort is a solid way to go. Also, replacements for new surgical tubing in the same clamps would take much less time than with zipties.

The only issue I could see with them is that they would be too sharp and the recoil might sever the tubing which would drastically increase performance overtime. However, adding some material to reduce the catching of that edge can certainly be done.

In addition, clamping the tubing after a point where it has attained some friction is much better than to the final stretched position.

Edit: Apparently the end of my third sentence was cut off.

Bolt two flat blocks together. Sandwich the surgical tubing in between.

Re: Best Way to Tie Off Surgical Tubing
 

Zip Ties work great. We have put lots and lots of stress on our surgical tubing and the Zip Ties have not shown any real weaknesses.

Re: Best Way to Tie Off Surgical Tubing
 

What Cory is getting at is make a capstan of sorts;
http://en.wikipedia.org/wiki/Capstan_equation

Wrap the surgical tubing a few times around something and the clamping force required afterwards is a fraction of the loaded tension.

Re: Best Way to Tie Off Surgical Tubing
 

In 2011 when we balanced our arm with tubing, we doubled back the tubing about six inches and installed several zip ties, pulling them all tight with pliers. The system never slipped, just be sure those zip ties are TIGHT.

Re: Best Way to Tie Off Surgical Tubing
 

What kind of knot have you been using? We haven't had any problems using a euro death knot. Also, you can reduce the load on whatever joint you use by using more individual strands in parallel.

Re: Best Way to Tie Off Surgical Tubing
 

Don't tie knots in surgical tubing, they are nearly impossible to remove. Zip ties work just when you pretension the surgical tubing, and are much more easily removed when compared to knots.

Re: Best Way to Tie Off Surgical Tubing
 

What's wrong with the obvious way?

(do NOT lubricate)

Re: Best Way to Tie Off Surgical Tubing
 

I agree with the zip tie solution. Knots can be incredibly difficult to remove, plus, in my experience, creates wear on that point of the tubing due to the tension of the knot itself, making it weaker as time goes on.

Re: Best Way to Tie Off Surgical Tubing
 

We have also been using the "Pre-stretch, ziptie really tight" method for years.

Re: Best Way to Tie Off Surgical Tubing
 

Can anyone provide pictures of their zip tie surgical tubing method?

Re: Best Way to Tie Off Surgical Tubing
 

I concur with the multiple ziptie method. One way we've used to prevent pull-out is to insert the largest set screw you can into each open end of the surgical tubing. You may have to work it a little bit to get it in all the way. Then when you ziptie your tubing in place, make sure at least one ziptie is across the set screw area of the tubing. The threads act as a bit of a hose barb feature to resist slippage.

Good luck to all this year!

Re: Best Way to Tie Off Surgical Tubing
 

We are using 6mm or 1/4 studs, screw eyes, etc. with a nylock nut on ends.
The domed nut inserts into the tubing ID (can't be too big of ID) and enough tubing is pushed past the nut to allow 3 zip ties or a hose clamp to lock the tip from sliding past the nut.

We also, on higher stress schemes, add some urethane adhesive (Shoe Goo) but only when there is plenty of drying time available, as it is solvent based.

Protecting the the tubing from sharp edges of hose clamp with a few layers of Gorilla tape, or something similar, is a good idea too.

-Dick Ledford

Re: Best Way to Tie Off Surgical Tubing
 

On the boat I use tubing as an anchor snub to slow the jerking motion in waves. Knot of choice is the Ossel Hitch. Rather than putting the end under the loop, I push a loop under, that lets me pull the free end to untie it.

I use the same knot with the smaller Vex tubing since where we attach is limited in space.

Since in your case this may be a once and done, double wrap around the support and then using zip ties like you would clamps on a wire cable would be my second choice.

Re: Best Way to Tie Off Surgical Tubing
 

Take a look at how a wrist rocket uses round stock to join the tube to the sling shot. Making precut tube into large rubber bands and using carabiners to attach more or less bands is a good method to adjust your mechanism.

Re: Best Way to Tie Off Surgical Tubing
 

#10 screws attached with two nuts, one on each side of whatever you're attaching the tubing to (be sure to use a lock nut on the back), such that the head is about 1/2" above the closest nut. Push the tubing over the head and onto the screw. Zip-tie behind the screw head. The screw head acts like a barbed hose fitting, which the tubing grips more tightly as it is tensioned, like Chinese handcuffs. The zip-tie is insurance.

Re: Best Way to Tie Off Surgical Tubing
 

http://www.mcmaster.com/#push-on-hose-fittings/=qe24fd

When I was on 27, we used something like the couplings here with zipties in 2008 for our launcher with surgical tubing worked well and was pretty easy, like everyone else said, just get the zip ties tight.

Re: Best Way to Tie Off Surgical Tubing
 

This is what we did to tie off the surgical tubing on our prototype (on one side). We tied the lose ends with zip ties just like everyone else. It seemed to work fine, although it takes up more tubing than some other options.


http://www.geospectra.net/kite/knots/knot09.jpg

Re: Best Way to Tie Off Surgical Tubing
 

Several zip ties is definitely the way to go. It even works okay for some thicker ropes if you don't want a knot for some reason.

Untying knots isn't always impossible, but you have to fiddle with the tension of each section of tubing manually as you do it and thus it takes a few minutes. More importantly, knots are kind of a weak point.

Re: Best Way to Tie Off Surgical Tubing
 

WARNING! - If you are using THICK WALL surgical tubing, like spear fishing guns use, and also are extending it to 3X the initial un-stretched tubing length, the zip ties will be UNable to hold something internally gripped inside the ID of the tubing. The tubing's OD shrinks with the decreasing wall thickness as tube stretches, but the zip ties maintain their same ID, and they cannot be pulled tight enough at pre-stretch to still have enough grip compression when the wall thickness decreases and tube OD shrinks so much at full stretch.

We tested 5/8" OD X 1/8 inch tubing (1/4" wall thickness) with 1/4-20 threaded screw eye inserted ~1-1/2". Three strong cable ties pulled very tight & necking in on the tubing OD would not work, since we could not pull them tight enough to handle how much the tube wall gets thinner as the length extends.

We then added a screw type hose clamp, crushing hose wall even more, and included two zip ties (one on each side of hose clamp), but the screw eye still pulled out.

Only by adding a nylon insert nut to the tip of the screw eye (the domed nut end helps for inserting into 1/8" tube ID), and countersinking the tubing end hole ID about 3/16" deep, could we then get the nut deep enough into the tube ID so that we could get a hose clamp adjacent to the nut (nearer tube end) and thus have the nut being wedged against the hose clamp ID as screw eye starts to pull out of the hose clamp. This wedging effect seems to finally be effective enough to prevent the eye bolt from slipping out. Will not be shure thugh until wee complete a lot more winding/shooting cycles than we have so far. More to follow.

Two cable ties were also used; one on either side of the hose clamp. Will post PICs in a day or two. Initial shooting was excellent, and we still have more options for improvement/

We are also looking to shrink our ram shooter length, and the overlapping/protruding h/w from surgical tubing ends only forces having longer tubing pieces greater spread between the winder cord pulley wheels. So we are revising how we transition with shortest distance from winder rope, to surgical tubing, and then to tubing anchor point.

-Dick Ledford

Re: Best Way to Tie Off Surgical Tubing
 

I assume that's a typo? "unable".

Re: Best Way to Tie Off Surgical Tubing
 

Yes -error & now fixed. Thnx.

BTW, you may get away with zip ties only if you stretch tubing a lot just as you are cinching down the zip ties two-man job), but my concern would be that the zip tie latching flap may get over stressed and crack, and we are not going to risk that kind of exposure to failures.

We are going with 6mm threaded rod having a nylon insert locknut at tip which gets inserted into tubing ID just beyond the hose clamp location. In addition, a pair of cable ties adjacent to the hose clamp will be added, and the assembly will also be glued with no-solvent fast set urethane adhesive.

Then if we can keep the total ram shooter length down in the 24-28" range, all will be good (at 30" right now).



-Dick Ledford

Re: Best Way to Tie Off Surgical Tubing
 

With the amount of potential energy these bands are storing there is a real possibility for injury - - similar to springs. If your method of securing the tubing works well I hope you will post a picture for safety reasons at least. Thanks!
Jim

Re: Best Way to Tie Off Surgical Tubing
 

Here in Hawaii we use the surgical tubing for spear fishing.

Please refer to the youtube link below on how to tie them off properly.
http://www.youtube.com/watch?v=zvV1JjoAnhU

Instead of using the pre-made beaded string you can just use any high tensile strength string and just tie a knot in it. A waxed type string is best to use during the constrictor knot.

Please refrain from using hose clamps or metal wire as it will cut into the rubber. And once it does snap you now have a deadly projectile on the end. Zip ties may work, but it is difficult to get the tension down hard enough.

Re: Best Way to Tie Off Surgical Tubing
 

This is fantastic. We are using 1/2" OD 1/8" ID spear gun tubing and everyone runs for cover when the catapult is pulled back because they are all worried that the ties will break. None have broken yet but I am glad there is a better method out there (other than hose clamps)

Re: Best Way to Tie Off Surgical Tubing
 

Is there universal agreement among the speargun community concerning the wisdom of using silicone lubricant to insert the plugs?

Or do some promote the use of alternative compounds which will not permanently reduce the friction between the plug and tubing?

Re: Best Way to Tie Off Surgical Tubing
 

Maybe they want to reuse the plug?

Re: Best Way to Tie Off Surgical Tubing
 

If that is what is driving the decision, it sounds penny wise and pound foolish.

Re: Best Way to Tie Off Surgical Tubing
 

It's not the friction of the plug inside the tubing that's responsible for holding tight.
The plug is trapped by pulling up tight against the outside cinch.
It's the cinch of the Kevlar thread outside keeping the monkey's fist inside the jar.

Re: Best Way to Tie Off Surgical Tubing
 

Yes. If the plug is lubricated, as shown in the video, then what you describe above is the main thing keeping the tubing from pulling away. All (or most) of the stress is concentrated at the tie circumference where the tubing is crushed by the Kevlar thread biting into it.

With a less effective lubricant, the tubing would grip the plug and distribute the load over a much greater area.

My question was not whether the cinch should be eliminated, but whether there is consensus agreement in the speargun community concerning the wisdom of using such an effective and permanent lubricant. Or are there some who advocate using a less effective lubricant (for the reasons stated above).

Re: Best Way to Tie Off Surgical Tubing
 

FORGE THEM IN THE FIRES OF MOUNT DOOM!!!!!!!!!!

In all seriousness, though, use zipties and nuts. The zipties are great for holding it down, but a nut will keep it stuck on there for good (it is also reusable, whereas zipties only last for one use).

Re: Best Way to Tie Off Surgical Tubing
 

On the other hand...
... as will the sharp corners of metal nuts