polycord problems


I’m Carrie from FRC Team 573, the Mech Warriors. We are using polycord for our pick-up system, but we’ve been having some trouble getting the ends to stick together. We are using 3/16" polycord, which does not seem to melt and fuse well. We’re currently using ferrels, but we also want to glue the joints. Does anyone know the best glue to use and where we can get it? Thanks for the help!

FRC Team 573

We use the heating tool from this kit to weld our belts together:

We went with the 1/4" poly. We used a small 3" vice, put a plate in the middle. We heated the plate hot as we dared and then stuck the ends and let them fuse, letting them cool to room temp. Thus far, no breakages.

How have you been trying to fuse the ends together?

We generally use a lighter to weld our polycord; if we really have to, we’ll use a heat gun, but because heat guns have a wider heat output, we find that they tend to melt too much.

Melding joints together takes a little time; it can take as long as a minute to liquefy ends of just 1/4" polycord.

We usually use an old soldering iron as it keeps the students away from anything involving a torch.

We use a hot knife (essentially an exacto knife stuck in the end of a soldering iron, for those that don’t know). They should be available at most hobby shops. Just let it heat up, stick the two ends of the polycord on opposite sides of the knife, get it all properly aligned, and slide the knife out of the way.

I know you asked specifically about welding the 1/4 polycord together, but, have you ruled out completely using the little metal or plastic pieces to hold them together (McMaster-Carr)?
I asked Warren Hilldebrand (sp?) at Roch Adams about this issue in particular this year before going down this path and he assured me that they have had no problems with using the joining pieces for many years.
If you choose to go down this route and need a few pieces, yesterday?, let me know, we have some at Lamphere High School.

Our team did it with a small torch and skillful hands: a mentor carefully holding the two ends in front of the torch ad pressing the ends together until the fused into one. This left a large lump of melted polycord around the fused point, so we cut off that part with a knife.

It takes practice, but you definitely don’t need to spend $600 to get the results you are looking for.

That’s exactly right. Practice with scraps of polycord until you get the technique down to a science.

One key point to be made is that after they are gooey and stuck together, hold them together for a good 3-4 minutes and DO NOT put stress on them until at least 10 minutes after that. I know that it seems like it is a good bit of time for one belt, but it will hold and not break.

Another good point. We keep a cup of cold water nearby. Once the joint is fused together, we douse it with cold water to ensure it is well cooled before we put any stress on it.

Alright, how about a little secret from Truck Town Thunder. There are two different places we get polycord.

  1. McMaster-Carr A little more choice in color. Seems to have a smooth surface.


  1. / - Doesn’t seem to have a choice other than green but the Polycord has a rough surface that help the balls move up an down.

We haven’t had any problems melting either one. We have used soldering irons, heat guns. The best method we have found is using a soldering gun with a special tip that is flat. It seems to work the best that we have found. Something sort of like this: http://www.google.com/products/catalog?q=soldering+gun+tips&hl=en&prmd=imvns&bav=on.2,or.r_gc.r_pw.,cf.osb&biw=1280&bih=709&um=1&ie=UTF-8&tbm=shop&cid=3604748554759273245&sa=X&ei=vttOT9egEuOu0AGF9YW7DQ&ved=0CIkBEPMCMAE4Hg

A great point… we’ve left samples sit for about 10 minutes (although competition cords sit for longer) and non one on the team - student or mentor - could break them, no matter how hard they pulled.

Please do not use a flame to weld polycord, the fumes are toxic! :eek:

Besides, using a hot air gun works better. Put the cord behind a hole in a piece of aluminum to shield it so only the ends are exposed. When it gets good and soft push it together making a round ball at the joint. Hold it in the ‘L’ of a piece of aluminum angle to keep it straight as it cools, then cut and sand the excess off. Never had a failure.

Good luck, and say hi to Joe and Tom for me!

We use a hot plate like you might find in a high school chemistry lab. We learned the hard way to cover the surface with aluminum foil to prevent the melted plastic from sticking to it permanently and then coking/charring. Agree with all of the other posts; in our experience we found it easiest to work with when the cord is heated to just below the smoke point of the material, allow for some amount of radial extrusion when the ends are pressed together, and give it a nice long cool-down time or accelerate the process with water. We dress the O.D. afterwards using a Dremel tool and abrasive wheel.

We insert the two ends into a short piece of heatshrink of the same diameter, and then use a plastic welding tool to melt the two ends together inside the heatshrink. The plastic melts before the heatshrink burns.

After years of using a soldering iron with a flat tip, last night tried it with a heat gun. Worked great.

1640 uses the magic tool from McMaster. Perfect tool for the job. Makes nice clean joints. Key thing is to read and follow the instructions. Many are loath to do that, but only through the Zen like state of enlightenment from following the directions will you have success.

Use a heat gun, it works much better than a soldering iron. Also try using 1/4", its easier to fuse in my opinion. Be sure to get fully melt the center of the polycord as well. And lastly, be sure not to “over-melt” the ends, if it gets to messy they will not fuse together correctly.

Hope this helps.

we use a sauntering tool and use the edges, melt the ends and then hold them together until the cool down and are tight.