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Thread: My experience/how-to on Plastic Welding

  1. #1
    Join Date
    Sep 2012
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    Indiana
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    My experience/how-to on Plastic Welding

    I've been experimenting around w/ plastic welding for some time now, probably not long after I got into the hobby many years ago. My first attempts started w/ a soldering iron and small strips of cut up fenders, which seemed to work, but failed to leave a favorable finish. From there, I upgraded to a Harbor Freight Hot Air Plastic Welder. I've played around w/ this tool now for several months and think I have a process, for the most part, calculated out. I thought I'd share my procedure w/ everyone.

    Tools:

    Hot Air Plastic Welder

    Specialty Convex Finishing Tool

    Dremel

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    My first real attempt at a desirable fixed part is a 85 250R Headlight Shroud. These pics show a crack along the top and extending outward.

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    1) First, I used my trusty soldering iron to position the plastic to the original shape it used to be by tacking several spots on the back side. Once in position, I went through and finished melting the crack back together.

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    2) Next, it was time to move onto the main area. I used a small carbide bit from my Dremel set and slowly routed a V-Groove into the affected areas. After the groove has been machine, make sure it is thoroughly clean and I also use a scuff pad to remove any stray plastic burrs.
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    3) For my filler strips, I used a piece of an old 85 Big Red rear fender that had been cracked and sun toasted. I used a utility blade to scrape this clean and remove any impurities. Then I used the Dremel and cut off wheel to cut thin strips.
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    4) I found the heat setting of 5 to work the best, it seems to heat up quickly, but not scorch or burn the plastic at the same time. To start, I heated the tip of the filler rod until it became soft and also heated the start of the cracked area. I continued going back and forth between these areas until you can notice the plastic just slowing starting to melt on the very outside tips/crack. Once it is hot enough, place the tip of the filler rod into the crack and let it cool such that you have a solid filler rod at the beginning of the crack.
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    5) With the filler rod tacked in place, use the plastic welder to heat the crack and rod simultaneously, sort of in a back and forth motion. If heating correctly, the crack will soften just enough to adhere to the rod, and if the rod is cut thin enough, it will almost fall directly into the groove. I try to keep the filler rod almost in a vertial position at all times, just slightly pointing back the opposite way from the plastic welder and pushing into the groove. This step is hard to explain and I don't have enough hands to capture a pic and weld at the same time.
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    6) When the weld has been completed, I use my "special" spoon and go back and heat up the welded area and "roughly" smooth out the area w/ a spoon. This helps fill in any cracks or crevices.
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    7) Now that the welding and filling is done, the hard part begins. Sanding and finishing. I use a 120 grit drum sander for my Dremel and attempt to remove the high areas. This can be difficult to do w/o going to deep or gougin the material. I got a little too agressive on a few areas on this. I'm hoping most the of the imperfections will come out in the wet sanding steps.
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    8) I also picked up some fine sanding wheels for my Dremel. I belive I received a 180 and 220 grit wheel? Shown is the coarser of the 2. After the drum sander, I use this wheel to fine tune the area a little. It will still look rough after this is done, but it should start to come back to life after a 180 grit wet hand sand.
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    9) After these steps, its onto a wet hand sand and buff process. This is as far as I have made it on this area. I have a few pics of an area I already performed. In my opinion, it turned out well. It's hard to see where the filler material was added, but up close you can see it. It's also extremely hard to finish these small contoured areas. If it were on a big rear fender and not curved so much, it would be easier to sand and make it look even better.
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    I hope to add more pics in the next few weeks of more finished results. I wouldn't claim this is a process for a showroom restore, but it's better than stitching or a soldering iron. I think it will just fine shined up and from 10 feet away.

  2. #2
    Join Date
    Aug 2008
    Location
    devore,ca
    --
    1,015
    Good write up.
    I got one of those HF plastic welders at a yard sale for 5 bucks. Used it to fix a crack in my RV water tank. Sealed the crack but looked like crap.
    YAMAHA 450 HYBRID
    85 350X- RED
    85 350x -BLACK
    86 350x-WHITE (with Goki)
    85 250r
    83 atc 70
    84 atc 70
    84 atc 110
    09 yfz 450
    2006 Arctic Cat Prowler
    RZR XP 900

  3. #3
    Join Date
    Nov 2009
    Location
    vt
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    143
    Your work looks awesome, no doubt!

    But I think the best plastic welding method is called zip ties and a drill

    I think plastic welding works well for things that NEVER move (as in they aren't attached to anything that is ever going to move, or have any sort of pressure on it.)

    I did a LOT of research on this, and the common theme was this:

    Over time, the plastic weld will likely fail at some point, or at least SOME of your welds will fail.

    I don't think this has anything to do with how good you are at plastic welding either.

    Even if you weld a fender (etc.) on your bike that has no direct pressure or weight on it, it will STILL have some sort of pressure on it (just from driving the bike, hitting bumps, the WIND at 40+ MPH, etc.) That, and the constant vibration of the bike while it is running.

    The problem with plastic is that NOTHING wants to make a GOOD/Permanent bond with it. Not super glue made for plastic, plastic JB weld, not "Rapid Fix", not even fiberglass (but MAN does fiberglass work awesome on metal!!)

    Plastic is a REAL B*TCH to try to make anything permanently bond to. Plastic is a weird thing... for example, certain acids that can melt metal will NOT melt plastic.

    I know zip ties look like crap compared to plastic welding, but they NEVER fail (unless your zip ties suck or something

    Did I mention how bad plastic pisses me off?

  4. #4
    Join Date
    Sep 2012
    Location
    Indiana
    --
    455
    I can't say I have any real world usage on average to severe abuse on plastic welded repairs. Any repairs I make on my personal machines will merely be for cosmetic purposes. I drive them around the yard or around town, and would never see any action that would put them under any serious stress. I would be curious to know how well it would hold up over time for someone who races or trail rides quite a bit. I can say just from a hand test, that it is quite a noticable difference in how much "flex" this shroud has from before to after the repairs.

  5. #5
    Join Date
    Aug 2008
    Location
    devore,ca
    --
    1,015
    I would think a repair like that would hold up fine on a headlight bezel. I've seen people use a plastic mesh type stuff you get at a hobby shop plastic welded to the underside of fenders to reinforce the weld.
    YAMAHA 450 HYBRID
    85 350X- RED
    85 350x -BLACK
    86 350x-WHITE (with Goki)
    85 250r
    83 atc 70
    84 atc 70
    84 atc 110
    09 yfz 450
    2006 Arctic Cat Prowler
    RZR XP 900

  6. #6
    Join Date
    Jan 2012
    Location
    Carthage NY 250r rules
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    2,345
    Iv done similar repairs on plastics and they held up fine riding and racing.I use a heatgun,soldering iron and a old flatiron.I think Newby200x is doing a great job.
    250r rules

  7. #7
    Join Date
    Mar 2010
    Location
    Slidell, LA
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    4,737
    Very nice job plastic welding that headlight. One of the nicer plastic weld jobs I have seen! Keep up the good work!
    Feedback for yaegerb: Click Here

    Need something blasted or polished or both? Send me a PM

  8. #8
    Join Date
    Nov 2009
    Location
    vt
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    Yea I guess that plastic weld will probably hold, considering it is only used on the headlight plastics.

    Hey atc300r, did you plastic weld actual fenders on your bike (the ones that held up to riding / racing)???

    Or just headlight plastic and other areas that don't get much movement/stress/wind force?

  9. #9
    Join Date
    Jan 2012
    Location
    Carthage NY 250r rules
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    2,345
    I welded fenders.
    250r rules

  10. #10
    Join Date
    Mar 2013
    Location
    Baldwin, Wi
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    603
    https://www.youtube.com/watch?v=W7icuxY2lC8&t=112s

    Did this almost 4 years ago. The fenders have cracked in many new locations but all my welds are holding strong.
    85 Tri-z Power valve on Inverts
    85 Tri-z Basket Case
    01 gsxr750 engine/Tri-z frame (long long way from complete)

  11. #11
    Join Date
    Sep 2012
    Location
    Indiana
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    Looks like you did quite an impressive job. My goal is to provide a repair that is strong, yet almost unnoticeable that it had ever been done. I think this process gets that very close. If the "fill" area wasn't a few shades darker red than the original, it would be hard to know that it had ever been welded.

  12. #12
    Join Date
    Jan 2012
    Location
    Carthage NY 250r rules
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    2,345
    X2 . Its hard to get the color to match with heat to much heat and it gets dark.
    Quote Originally Posted by newby200x View Post
    Looks like you did quite an impressive job. My goal is to provide a repair that is strong, yet almost unnoticeable that it had ever been done. I think this process gets that very close. If the "fill" area wasn't a few shades darker red than the original, it would be hard to know that it had ever been welded.
    250r rules

  13. #13
    Join Date
    Mar 2013
    Location
    Baldwin, Wi
    --
    603
    Thanks. for that quad i didn't care about how it looked. what the video doesn't show is that i flip the fenders over and do the top side also. This past weekend I had these fenders back off for more repair. One of mt horses kicked the front right fender off. It is now whole again with all the new cracks fixed.
    If you zoom in on these fenders you can see all the battle scars.
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    Last edited by NeverLift; 12-05-2017 at 04:09 PM.
    85 Tri-z Power valve on Inverts
    85 Tri-z Basket Case
    01 gsxr750 engine/Tri-z frame (long long way from complete)

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