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Old 02-15-2013, 03:41 PM   #16
VxZeroKnots OP
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Got some more good information from this thread:

http://www.practicalmachinist.com/vb...re-done-91299/

here is a link in it I still need to explore:

http://www.stanmech.com/HowToWeldPlastics.htm
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VxZeroKnots screwed with this post 02-16-2013 at 07:32 AM
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Old 02-15-2013, 08:19 PM   #17
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I wouldn't weld it and I wouldn't use HDPE. it's tough to get good welds and requires considerable experience. You really don't want a bash plate to break up and there are cheaper and much easier ways to get a plate that will be a lot stronger. if you do go with sheet stock and welding don't get welding rod. Use thin strips cut from the base material you are using. the resins must match exactly and this will do it. Just cut strips that match your welders guide port. Forget a nitrogen rig or even a compressed air gun.. $$$$. A simpler "heatgun" type welder will work fine.It's hotter than an ordinary heatgun and has a special tip. I have one. it works OK but I get more mileage with Fiberglass, including for repairing thermoplastics.

I would also not use HDPE. Too soft. UHMW-PE would be better. (HDPE=High Density polyethelene. UHMW-PE = Ultra High Molecular Weight Polyethelene). The UHMW is more abrasion resistant. But with either one if you hit a rough rock the stone will dig in and you may pitch forward more than sliding over.

I second the fiberglass. Easier to do. An exact fit every time. Easy to maintain as it gets bashed up, fantastically strong, very hard, will slip over things like a metal plate would (althou it will get scraped up. I made a large fiberglass part once, the size of the back end of a small car. It ended up being intentionally run over with an extremely large bulldozer. Didn't even crack (to my dismay, I wanted to destroy it).

You can make a styrofoam form right on the bike and then glass over that and right over your frame tubes as well, then pop the peice off, trim it and get the form out, throw some paint on it and then bolt it up the same way you would a metal plate. it will fit perfectly on the frame tubes and at about 1/4" thick, will take anything you can do to it. You will be using epoxy resin and it has a good shelf life. Easy to sand you plate and ad a layer or three as it gets beat up.

I can go into some more detail about the construction if you are interested. I'm starting a project to make some FG ram air ducts for my RS and I'll probably do a post on that in the coming months.
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Old 02-16-2013, 07:31 AM   #18
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Originally Posted by Plaka View Post
I wouldn't weld it and I wouldn't use HDPE. it's tough to get good welds and requires considerable experience. You really don't want a bash plate to break up and there are cheaper and much easier ways to get a plate that will be a lot stronger. if you do go with sheet stock and welding don't get welding rod. Use thin strips cut from the base material you are using. the resins must match exactly and this will do it. Just cut strips that match your welders guide port. Forget a nitrogen rig or even a compressed air gun.. $$$$. A simpler "heatgun" type welder will work fine.It's hotter than an ordinary heatgun and has a special tip. I have one. it works OK but I get more mileage with Fiberglass, including for repairing thermoplastics.

I would also not use HDPE. Too soft. UHMW-PE would be better. (HDPE=High Density polyethelene. UHMW-PE = Ultra High Molecular Weight Polyethelene). The UHMW is more abrasion resistant. But with either one if you hit a rough rock the stone will dig in and you may pitch forward more than sliding over.

I second the fiberglass. Easier to do. An exact fit every time. Easy to maintain as it gets bashed up, fantastically strong, very hard, will slip over things like a metal plate would (althou it will get scraped up. I made a large fiberglass part once, the size of the back end of a small car. It ended up being intentionally run over with an extremely large bulldozer. Didn't even crack (to my dismay, I wanted to destroy it).

You can make a styrofoam form right on the bike and then glass over that and right over your frame tubes as well, then pop the peice off, trim it and get the form out, throw some paint on it and then bolt it up the same way you would a metal plate. it will fit perfectly on the frame tubes and at about 1/4" thick, will take anything you can do to it. You will be using epoxy resin and it has a good shelf life. Easy to sand you plate and ad a layer or three as it gets beat up.

I can go into some more detail about the construction if you are interested. I'm starting a project to make some FG ram air ducts for my RS and I'll probably do a post on that in the coming months.
Have you used a compressed nitrogen/air welding rig or are you extrapolating the performance of using a heat gun as a welder to be equal? I'd go carbon fiber long before fiberglass just for looks alone, fiberglass is ugly and this piece will be pretty visible. There are already ugly options out there should I decide to be less vain.

I had considered using uhmw-pe but most of the resources state that the more dense the pe the more difficult it is to weld so hdpe seemed like a decent compromise. As to plastic, even soft, not being a good material candidate for skid plate usage simply isn't true, especially when compared to aluminum. Steel is simply too heavy to be considered. Rock crawlers and desert racers have been using UHMW and HDPE over metal skid plates with much success for years. The bike currently has a lower frame/engine skid on it right now made out of something softer than uhmw and it works awesome. I'm just looking to make something with additional coverage.

Another consideration is that metal skids, and I'd assume composites or anything else hard, transfers the force of an impact from the skid directly to the frame and mounding points. On my last bike it even caused the frame tubes to deform a bit. I'm hoping plastic will disperse and absorb the energy from an impact better, it certainly reflects less engine noise back at the rider. I'm not looking for something that will last forever, if I can get a season out of each iteration I'll be happy.
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VxZeroKnots screwed with this post 02-16-2013 at 08:24 AM
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Old 02-16-2013, 08:02 AM   #19
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A book and a little studying first? Haven't seen that book, link was just dropped in my email by someone who has it on order.

{The guys on the MOA forum say it is excellent and
shows you how not to screw it all up.} Quote....!

http://www.amazon.com/gp/product/188...ls_o00_s00_i00


I think I'll go buy it.
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Old 02-16-2013, 08:57 AM   #20
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[QUOTE=VxZeroKnots;20738585]Have you used a compressed nitrogen/air welding rig or are you extrapolating the performance of using a heat gun as a welder to be equal? I'd go carbon fiber long before fiberglass just for looks alone, fiberglass is ugly and this piece will be pretty visible. There are already ugly options out there should I decide to be less vain.

Yes. I started welding with a nitrogen gun (worked in the modeling shop at Rubbermaid Commercial, Pretty big projects like the rolliing garbage bins). They're nice, but costly. The heatgun rig I have now works OK and I've done some projects with it, Sinks, etc.

I agree on transferring force, A rigid GRP plate is just like steel in that respect. But you can soft mount it on rubber bumpers if you want. (maybe something like ethafoam blocks.) it may be a thin flexible peice will work fine. it may flex back far enough to touch the cases but it will prevent abrasion of the metal and spread the blow enough to prvefent puncture of the case.

Carbon fiber is a pain in the ass to work with. (I have some along with some carbon/aramid blends). it is a LOT more difficult to turn a corner with it than glass (often you need special clamping or a vacuum setup) because it is so stiff. it also transfers stresses all over the place making design with it tricky. On top of all that, those slick carbon fiber things you see are complete crap. They are made by taking the resin/fiber ratio way up (to the resin side) to give that smooth glossy surface. This makes for a heavier, weaker part. Properly done FRP has a very spare resin ratio, you should be able to see each strand in the finished surface. of course this doesn't look all that great despite being the strongest way to go. Also, the CF stuff you see has been vacuum bagged, again to give that sheet-of-glass-with CF-in-it look. It's window dressing.

Personally if I was going to use sheet material I would use riveted construction. You can do that very cleanly so it looks right. use big head pop rivits and backing washers. The trick is to work out the shape of your plates so when you assemble everything comes together into the right shape. Use thin cardboard (construction board from the craft shop or some office supply places) or 1/8" foamcore board to sort this out. A combination of thermoforming and riviting can be very effective.

If you're determined to weld having a hot air gun (self contained blower) will definitely do you. And they are handy as a spot heat gun (rusted on nuts) as well. The only trick I can really offer beyound following the directions and using native material as rod, is to use a small planer blade as a scraper to clean up exterior welds. You want one about 1" wide by 3" or so if you can find it. they come in sets of 2 or 3 for portable hand (electric) planers). Stiffer than a utility knife blade and very sharp. I use them for finishing the edges of plexi too.

Kydex is killer stuff. Used to line hockey rinks among many other things, You may have difficulty finding it in thick sheets however. http://en.wikipedia.org/wiki/Kydex You bend nice strait lines with a plexi bender (from platic supply place) or if you have a vacuum source you can vacuum form it in your kitchen (the largest sheet being the size of your oven unless you want to build a heater)
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Old 02-16-2013, 05:50 PM   #21
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Yes. I started welding with a nitrogen gun (worked in the modeling shop at Rubbermaid Commercial, Pretty big projects like the rolliing garbage bins). They're nice, but costly. The heatgun rig I have now works OK and I've done some projects with it, Sinks, etc.

I agree on transferring force, A rigid GRP plate is just like steel in that respect. But you can soft mount it on rubber bumpers if you want. (maybe something like ethafoam blocks.) it may be a thin flexible peice will work fine. it may flex back far enough to touch the cases but it will prevent abrasion of the metal and spread the blow enough to prvefent puncture of the case.

Carbon fiber is a pain in the ass to work with. (I have some along with some carbon/aramid blends). it is a LOT more difficult to turn a corner with it than glass (often you need special clamping or a vacuum setup) because it is so stiff. it also transfers stresses all over the place making design with it tricky. On top of all that, those slick carbon fiber things you see are complete crap. They are made by taking the resin/fiber ratio way up (to the resin side) to give that smooth glossy surface. This makes for a heavier, weaker part. Properly done FRP has a very spare resin ratio, you should be able to see each strand in the finished surface. of course this doesn't look all that great despite being the strongest way to go. Also, the CF stuff you see has been vacuum bagged, again to give that sheet-of-glass-with CF-in-it look. It's window dressing.

Personally if I was going to use sheet material I would use riveted construction. You can do that very cleanly so it looks right. use big head pop rivits and backing washers. The trick is to work out the shape of your plates so when you assemble everything comes together into the right shape. Use thin cardboard (construction board from the craft shop or some office supply places) or 1/8" foamcore board to sort this out. A combination of thermoforming and riviting can be very effective.

If you're determined to weld having a hot air gun (self contained blower) will definitely do you. And they are handy as a spot heat gun (rusted on nuts) as well. The only trick I can really offer beyound following the directions and using native material as rod, is to use a small planer blade as a scraper to clean up exterior welds. You want one about 1" wide by 3" or so if you can find it. they come in sets of 2 or 3 for portable hand (electric) planers). Stiffer than a utility knife blade and very sharp. I use them for finishing the edges of plexi too.

Kydex is killer stuff. Used to line hockey rinks among many other things, You may have difficulty finding it in thick sheets however. http://en.wikipedia.org/wiki/Kydex You bend nice strait lines with a plexi bender (from platic supply place) or if you have a vacuum source you can vacuum form it in your kitchen (the largest sheet being the size of your oven unless you want to build a heater)
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!
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Old 02-16-2013, 07:22 PM   #22
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Originally Posted by VxZeroKnots View Post
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!
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.

Plaka screwed with this post 02-16-2013 at 07:29 PM
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Old 02-17-2013, 06:51 AM   #23
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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.
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Old 02-17-2013, 08:42 AM   #24
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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
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Old 02-17-2013, 11:05 AM   #25
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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.
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.
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