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Old 02-11-2013, 08:37 PM   #1
VxZeroKnots OP
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Plastic Welding Newb

So after adventures in trying to get a skid plate to fit on my oddball bike I can't help but feel like I could make something better.

I'm looking mainly to weld HDPE and am looking to get a reasonably priced plastic welding starter kit and it seems like there are lots of sources online to get welding rod and sheet.

What are everyone's recommendations for a good starter setup?

Anyone got any cool projects or wisdom they'd like to share?
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Old 02-12-2013, 02:44 AM   #2
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It won't work ?, well, not the way you hope.

If you can bend stuff so none of the welds are critical for strength, maybe, but typically plastic doesn't 'weld' like metal. The joins won't be as strong as the bulk material. Not saying plastic is bad, some of the moulded plastic guards are excellent, but they aren't made with welds.

I've certainly fixed things like indicator housings and handguards, but 'structural' strength is going to be a hard ask.

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Old 02-12-2013, 06:34 AM   #3
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Quote:
Originally Posted by PeterW View Post
It won't work ?, well, not the way you hope.

If you can bend stuff so none of the welds are critical for strength, maybe, but typically plastic doesn't 'weld' like metal. The joins won't be as strong as the bulk material. Not saying plastic is bad, some of the moulded plastic guards are excellent, but they aren't made with welds.

I've certainly fixed things like indicator housings and handguards, but 'structural' strength is going to be a hard ask.

Pete
The stock skid plate which came on my bike appears to be HDPE and it is most certainly welded, the Hyde Racing skid plate also looks to have some welds on it at well. I think the key to strength is to make it all one piece and score the material at the bends so the weld only holds the material in place. I've never been one to be dissuaded by whether something was thought possible or not.

Quote:
Originally Posted by NJjeff View Post
Plastic welding (when you know how) is a very stable joining method with strengths equal or greater than the base material.
Though the technique is somewhat different than gas welding or brazing the concept is there.
Countless tanks, fixtures, and structures are routinely fabricated from plastic and joined by hot gas welding. When done properly there is no concern for failure.

How well will a plastic skid plate function, I don't know. I think I'd call it a splash shield or stone guard and hope for the best. None the less it can be fabricated though it will most likely look bulky due to the material thickness required for strength.

I'd suggest you try here: http://www.usplastic.com/catalog/sea...=welder&page=1
They offer multiple units.

A few points for the actual welding. Cleanliness of the base material and gas (air or N2) is utmost critical. Your not going to get away with an oil type air compressor with excessive moisture mixed in. A diaphragm type compressor with a method of moisture removal is good start.
This is what I want to hear! cheers! By they way, it is quite common these days in rock crawling is to use plastic skids, I expect some deformation under impact but am not worried about it, I just need to dissipate most of the energy. As to a source of gas, it looks like nitrogen is the way to go.
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VxZeroKnots screwed with this post 02-12-2013 at 06:47 AM
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Old 02-12-2013, 08:10 AM   #4
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Go for it. You will learn something along the way.

Worst that can happen is you will burn your finger on some hot plastic.
Best you can do is become an expert and sell us something cool you made in the Vendors forum.
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Old 02-12-2013, 08:15 AM   #5
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Originally Posted by NJjeff View Post
Go for it. You will learn something along the way.

Worst that can happen is you will burn your finger on some hot plastic.
Best you can do is become an expert and sell us something cool you made in the Vendors forum.
That's the idea! My motto is there is no possible way to waste money on tools or learning.
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Old 02-12-2013, 11:14 PM   #6
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Quote:
Originally Posted by VxZeroKnots View Post
The stock skid plate which came on my bike appears to be HDPE and it is most certainly welded, the Hyde Racing skid plate also looks to have some welds on it at well.
The Hyde racing skid plate on my DL is moulded, not a weld anwhere. I'm *very* happy with how tough it is, no problems with the right plastics being strong enough for this. The welding, not so confident.

I have plastic welded stuff, and the joins are weaker than the bulk material, it's a polymer - 'long chains of shit' holding it together, not metal - which is just irregular crystals jammed into one another. The problem is getting the 'long chains of shit' to bridge any gaps sucessfully, just melting it together is not guaranteed to work.

Not sayng you can't make a welded skid plate, just warning you that unlike metal welding where the joins can be as strong as or stronger than the bulk metal that's unlikely to be true with a plastic weld.

I'm happy for you to prove me wrong - but you asked if anyone had any experience - that was mine.

Pete
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Old 02-12-2013, 03:28 AM   #7
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[QUOTE=VxZeroKnots;20705236]So after adventures in trying to get a skid plate to fit on my oddball bike I can't help but feel like I could make something better.QUOTE]

Grain shovel and a hammer.


Depending on what kind of plastic you are using, some weld better than others.
I do what’s called (solvent welding) with MEK on ABS plastic with great success. ABS is what was mostly used on street/sport bikes fairings. I wouldn’t want to make a skid plate out of it thou.
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Old 02-12-2013, 05:21 AM   #8
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Plastic welding (when you know how) is a very stable joining method with strengths equal or greater than the base material.
Though the technique is somewhat different than gas welding or brazing the concept is there.
Countless tanks, fixtures, and structures are routinely fabricated from plastic and joined by hot gas welding. When done properly there is no concern for failure.

How well will a plastic skid plate function, I don't know. I think I'd call it a splash shield or stone guard and hope for the best. None the less it can be fabricated though it will most likely look bulky due to the material thickness required for strength.

I'd suggest you try here: http://www.usplastic.com/catalog/sea...=welder&page=1
They offer multiple units.

A few points for the actual welding. Cleanliness of the base material and gas (air or N2) is utmost critical. Your not going to get away with an oil type air compressor with excessive moisture mixed in. A diaphragm type compressor with a method of moisture removal is good start.
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Old 02-12-2013, 05:04 AM   #9
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I am also interested in buying a plastic welding iron. I gave it a try with a soldering iron and that works well enough that I'm prepared to buy the real gear. My polyethylene repair may not be as strong as original, but the original broke and the repair has held through multiple drops off-road.

The "trick" as far as I understand it is to prevent burning while also getting good penetration. Welding and brazing metal have helped me learn about plastic. I used plastic shaved off another piece -- my hypothesis being that it would be a similar material with similar melt point and a good chance of melding together.



Yes it's ugly. Yes a real plastic welding iron would probably make it look better. (It is not visible at all from the outside.)

The two things I'd look for are interchangeable tip shapes and adjustable temperature with a guide to setting the temperature for different types of plastic. I THINK that you can shave welding rod off the pieces you're using to make a project though that may not work for all types of plastic.
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Old 02-12-2013, 08:20 AM   #10
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If you are repairing a broken HPDE or other thermoplastic part, then welding is a good path IMO. However, if you want to make a skid plate from scratch, I would consider taking a piece of thin plywood as a base to make one out of fiberglass. The basic idea is to cover the plywood in epoxy and fiberglass cloth. Curves, etc. for the base plate can be made by adding molding material, such as modeling clay, and layering the fiberglass cloth on the mold. While it will take more time than welding, repairs can be made to restore the plate to original condition using the same technique.

However, learning to weld plastic would be more fun. Harbor freight sells an inexpensive hot air welder. Good luck!
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Old 02-12-2013, 09:00 AM   #11
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Look up kydex, you can buy a large sheet then cut and shape it into the shape you need. The only tools you'll need are a heat gun and some good scissors. It comes in a variety of colors and thickness too.

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Old 02-12-2013, 09:46 AM   #12
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Depending on the application....been using the "Solder-it" paste type weld the last couple days on small test projects. All good so far and only needs 195F to set.

Sure good at filling holes and joints. Yep....drilled one of them holes at the wrong place, had to fix that.

http://www.solder-it.com/shop/category.aspx?catid=24

Bugger...can't find the plastic weld paste on their website.Discontinued??? Maybe but I know where there is some.
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Old 02-13-2013, 04:14 AM   #13
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Consider Carbon fiber.

It's infinitely customizable too.

Very forgiving, strong as hell, mostly hand work and some grinding or sanding. Wear a mask. There are some great carbon fiber threads on ADV

(get it, Carbon fiber "threads" ? )
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Old 02-13-2013, 04:28 AM   #14
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Fill one of these bait tanks with water and fish parts and you'll want a really strong tank even if it's welded plastic. Put that tank on a boat tossing on the ocean and the stress will be high although different from impact stress.

I have seen these guys at the local fair and they make rectangular tanks far larger than the 10 bushel tanks shown.

http://sullivanplastic.com/ "If you can make it out of plywood, we can make it out of plastic."
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Old 02-13-2013, 07:29 AM   #15
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Here is a lot of good information on the process. I'm still on the fence as to what equipment I'll be buying, but HDPE still seems like the material of choice.

http://www.wegenerwelding.com/pdf/09_Guidelines.pdf
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