Plastic Welding Newb

Discussion in 'The Garage' started by VxZeroKnots, Feb 11, 2013.

  1. VxZeroKnots

    VxZeroKnots Long timer

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    Sweet info man thanks! Looks like CF is out. I'm not making this particular skid for the engine, as I already have one of these
    and it is killer. It gouges pretty easy but compared to the Aluminum skid I had on my last bike it is brilliant. It is 1/4" and the "wings" are folded up from the bottom piece and then welded at the bend so the part that sees the most abuse is all one bit. I bought a Hyde racing skid plate and was very unimpressed with the fit and quality of it given the price.

    The Hyde is made from 1/8" and the parts are joined via the pop-rivet method you outlined. I ended up cutting it up to where just the pipe guard bolts to the AXP skid plate and then mounts to the pipe with the included band thingies. It has a bunch of little rubber nubbins which isolate the pipe from the skid portion and it seems like those coupled with the shape of the guard are what provide the protection more than the thickness of the material.

    My plan is to build a faceted pipe guard which integrates better with the AXP plate out of 1/4" HDPE seaboard and try to use as few separate pieces as possible and weld as little as possible.I already have a rivet gun so I might make some gussets for the major seams and pop-rivet them over the seam to reinforce it, but was thinking of using 1/8" HDPE for that. My research today didn't turn up any UHMW that was black or UV resistant so if you know a source for that I'd love to hear about it. Also, I think the rubber nubbins Hyde uses are silicon rubber for heat resistance because they spend their whole life in contact with the pipe. I don't know where those are sourced from but if you have any insight for a solution there I'd appreciate it.

    Thanks for all your input!
    #21
  2. Plaka

    Plaka Brevis illi vita est

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    I get my plastics from the scrap bin at Tap Plastics or scrounge them (I just tore down an old wheelchair, got two nice slabs of thermoplastic, black to use in some project and a LOT of nice bushings and connectors for 1"tube.. You can sometimes get smaller pieces from McMaster Carr, (online or local depending on where you are). Also McMC on rubber bumpers. But you could also make your own. Take a short peice of pipe and lube the inside up well with vaseline. Set it on a flat surface also lubed with the vaseline. Squirt in some high temp black silicone from the auto parts place. Do not fill your mold to the top. let it set up (days). Then take a small bolt and thread on a nut so when the bolt heat reats on the top of the silicone the nut will be just above the top of the mold. Secure that nut with read locktite (stud locker). Put the bolt back in the mold and top the mold up with more silicone. When it's done Push it out of the mold. Now you have a silicone bumper with a "stud" sticking out of it and a wrench flat on the stud to hold while you tighten on another nut on the other side of whatever you are fastening to.

    You can also cast in a coupling nut (Used for joining threaded rod, hardware store) and leave that sticking out just enough to get a thin wrench on (Thin wrenches from bicycle shop). Coupling nuts can be an inch long, depending on size, and you can saw or grind them to the ideal length. This gives you a bolt (A nice rounded button head rounded allen capscrew please) on the outside.

    UV resistance is a non issue on something you expect to last a season, even at high altitude. 5 years in the sun and you get surface oxidation, nothing more. Spray on some 303 all or similar if you want. Has sunscreen in it.

    Thermoplastic sheet will stay where you put it if you bend it hot. Polyethene is difficult to hot bend because it transmits heat poorly. Hard to get heat penetration to make a stress free bend. Not a problem with Kydex. Another resin to consider is lexan. VERY tough, Comes in smoke or you can dye it to a dark smoke (Use RIT), or just paint it. usually easy to get scraps and 1/4" is a common thickness. You can solvent weld it but the welds are weak. best simply thermoformed and let it go at that...or use mechanical fastenings. it has poor chemical resistance. Keep it away from gas, oil, sticker glue, etc.

    For ease of fabrication little beats fiberglass. Use epoxy resin rather than polyester if you can (less toxic, allows you to use the lost foam technique). Invest in a couple rollers (like three for $25) because you will be thinking up more projects to do with it.if you have some part that you know will get trashed then make a regular wood mold so you can turn out more parts whenever you want.

    For your particular application it sounds like you want some shock absorption behind a very rigid plate. Use the silicone bumpers.

    if you work with 1/8 or even 1/4" foamcore; make a strait bend by marking your bend line then drawing the ass end of a bic pen along the line to crush the bend line on the inside. The board will then fold nicely on that line. A hot glue fun is your friend. It is well worth your time to model the part in cheap foam core before you cut costly plastic.
    #22
  3. VxZeroKnots

    VxZeroKnots Long timer

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    damn good info, I was planning on prototyping with cardboard, but I guess i can go high zoot and use foam baord. :D
    #23
  4. oldebike

    oldebike Olde and classic

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    I have a plastic welding kit from Urethane supply company. The kit is pretty complete, and comes with a couple of interchangeable tips, different rods for different plastics, a temperature control for the welder, and the most important accessory of all, a really complete instruction guide. You can achieve good results, what I would call structural results, if you know what you are doing in advance and have the right tools and the right materials. You can imbed additional structural material such as a wire mesh into your material to give it added strength. In fact I just used it yesterday to repair a plastic mount for a drawer slide in my kitchen. It wasn't pretty, but gave me the satisfaction of fixing it myself, plus I saved a trip to the hardware store along with a few bucks, I'm pretty sure I'll never have to mess with it again, it's stronger than the original because I used wire mesh to reinforce it. As in anything worth doing, there is a learning curve involved. Your first efforts might not be what you'd hope for, but give it a shot and learn a new skill. Be careful though, because if your buddies find out you can plastic weld you might end up getting a lot of phone calls to fix fairings and fenders and the like. YMMV
    #24
  5. Plaka

    Plaka Brevis illi vita est

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    Cardboard will work. It just bends differently depending on whether you are bending with, across or at an angle to the corrugations. Again you do a crush on the inside of the bend line. A super dulled pizza wheel works pretty well as does some hammering on a narrow strip of metal (wide putty knife). More often with cardboard I just cut pieces and tape them with wide masking tape. I made some metal brackets for a radar detector setup on a guy bike last summer and I modeled in cardboard for peices that were eventually bent steel. I just didn't have any foam core handy (I usually scrounge it used).

    As an aside, Acrylic (plexiglas) comes in bending grade and glazing grade. The difference is one is extruded sheet and the other is cast sheet. they look the same but if you try to hot bend glazing grade it don't work well---to much internal stress in the sheet. I dunno about lexan but I would mention what you are doing to whomever you get your plastic from and get their advice.

    Parts of all sorts often have features on them that have nothing to do with the final use of the part. they are there just to make the part easier to manufacture. You see them all the time but are seldom aware of what they are or why they are there. On molded plastic parts there may be little posts on the inside. These are zero draft pins and serve to pull the part out of the mold. On cast metal parts there may be special machined surfaces somewhere that serve to register the part in a machining fixture. On all sorts of parts there may be holes or slots that are used to bolt the part into a machining or finishing fixture. You can play this too. if some part is being a bitch to clamp (like over a bending fixture) you drill a couple little holes and screw it to the fixture.. You might make one or more sides larger so you can screw up the edge with clamps or holes and then trim those edges off later. Holes near the center of a part can be filled or just ignored.

    Once you have a prototype you like you cut it apart to get you flat patterns. Then put it back together and lube the inside with vaseline. Stuff it with bondo (buy it by the gallon). You will get a little shrink but not much. Peel off the now trashed prototype and you have a male plug to fabricate your finished part over. Stick on you pieces of plastic (Hot glue, DF tape, screws) and everything is held in position for welding. You can also make a female plug. just make a little cardboard "box" (more like a collar) to go around your prototype, lube the outside, etc. make it plenty thick.
    #25