[jdougn]

I'm new here and plan on thermoforming Jeep Cherokee Fender Flares. The Jeep gets used offroad so the Fender Flares take serious abuse. Jeep Pict in action

I've not built a former yet but am gathering components & information. The former will need to be around 24x48 to accomodate the flare dimensions.

Forming Material: LDPE, HDPE, other options? Ideally, the fender flares would need a considerable amount of flex for random encounters with trail obstacles. I am not well versed in different plastics. I think ldpe is very flexible and might work but it would need to be in black and that I've not found so far. Also, Seaboard® HDPE from Professional Plasitcs might work but it is an extrusion and it doesn't say if it's formable. It would be much more rigid, which is not as good, but is available in colors.

Material Thickness: The product also needs to be thick. I'm thinking at least .25" if not .375". Obviously this will also affect the design needs of the former.

Material Color: White or clear is obviously not an option unless easily paintable. Black is fine. Other colors would be useful in the future.

Vacuum: Any suggestions on the amount of recommended vacuum would be great. Everything I've read so far seems to be for .25" or thinner plastics. There would not be a huge amount of detail needed and the mold would be around 6" high. Based on the material thickness I'm assuming a two stage system?

Vacuum Pump: Has anyone had experience converting an old York style car A/C pump (such as the ER210) into a vacuum pump? The York is an oiled pump with a push/pull design and puts out at least 4.5 cfm on the compressor side.

Molds: Obviously, the flare needs to meet the Jeep sheetmetal properly but I'm not sure of the best way to create the form. MDF would require a lot of scribing and fitting.

Well, this is already long. I'm looking forward to hearing your advice!

Thanks,
Doug

[kayaker43]

Low or high density polyethylene or polypropylene would be my choice. Lexan is still not as tough and too stiff. All the flares I've seen have some detail as far as recessed screw locations etc. Unless you can eliminate those details and keep it a soft roundy shape, then you're a bit beyond borrowed oven elements or crude nichrome and shop vacs here. It will take a better than average system for good results.

Over 1/4 in. will require two sided heating but I'm positive I've never seen flares thicker than 3/16. When you add shape, it feels much surdier than a flat sheet. Start with 3/16 HDPE or poly, LDPE may be too soft?

Oven design will be critical for thicker sheets, The infra-red wavelength should come close to the absorption rate of the plastic. Don't guess here, use a proven oven design. You'll be dissappointed with less than 25 in. Hg, and 27+ would be better, but you'll still get some usability even at 20 in.

A/C compressors have lubrication and rust problems when used in an open system, but may work for a while if you can get them cheap. 4.5 CFM is a bit small for a 2 x 4 but can work OK with a tank. A good two stage would work well using a tank, then direct pump, but your Platen will need to be airtight, not sort of airtight. or the second stage will be inneffective.

I think its a good product idea and it can be done for sure with decent equipment but you'll probably have to spend more than its worth for a couple sets of flares. Entirely feasible if you need to make lots of them.

Warning: I sell plans for VF machines so I could be biased, but check them out if you don't have time to invent your own. http://www.build-stuff.com/1002plans_proto-form.htm

Doug Walsh
Workshop Publishing
(248) 391-2974

[jdougn]

Hey Doug,
I was hoping I'd hear from you on this project and your reply is an encouragment! The Proto-Form Plans look really good so you are allowed to be biased...lol. Does a properly built Proto-Form qualify as a "better than average system" when using your heating elements? How much better are the Build-Stuff heating element kits compared to the typical spiral nicrome design?

Based on your recommendations, 3/16" or 1/4" HDPE Seaboard may be just the product since it's readily available in colors and not too expensive. HDPE Seaboard from Professional Plastics. It is more rigid than prefered but it meets the other criteria very well.

Also, thanks for the advice on the two stage system. A 30 gallon compressor tank is already on hand for the project. The York A/C pump has its own oil reservoir and is very cheap (as in $12 cheap) when teamed up with my existing 1.5hp electric motor. Jeepers use the York pump for onboard-air systems to air-up tires and run air tools in the field. However, based on your input, the York may not produce enough vacuum. Would two vacuum pumps together increase the CFM only or would they also increase the IN.HG?

Thanks,
Doug N.

.......we're missing something but we don't know what....

[kayaker43]

The calrod heaters I use are made to my specs, just a simple rugged system that's been tuned and tweaked to work best with no controls needed. Much better than borrowed oven elements which are never quite right. More elements with the right output and extra perimeter heat. Nice simple buss bar mounting with minimal wiring.

A good coiled nichrome element can work just as well if carefully designed. I actually have some modular "nichrome on ceramic board" type elements coming out soon that will retrofit into the Proto-Form and also be good for homebuilders. Nichrome wire is just cheaper than anything else if you can figure out an effective way to utilize it. I expect them to be around 30% cheaper than my calrod kits.

The york sounds OK with a seperate reservior, but I've heard A/C oils don't prevent corrosion because there's no moisture in a sealed system. Maybe use a different oil? It should pull a very good vacuum but the flow is low for that size machine and tank. Just expect it to run a long time, or add a second one. Is there a cheap source of new ones or do you find them used? Maybe you could spin it faster?

[beone]

You might consider a product call iirc Flexane. It is several viscosities of a polyurethane rubber for molding. Make a female mold, brush or trowell in to the desired thickness, let set and you are done. Get it from most any industrial supply house.
Dave

[jdougn]

...I've heard A/C oils don't prevent corrosion because there's no moisture in a sealed system....
...It should pull a very good vacuum but the flow is low for that size machine and tank. Just expect it to run a long time, or add a second one. Is there a cheap source of new ones or do you find them used? Maybe you could spin it faster?

I will want to go with the calrod system in the future. For now the nichrome will have to do. The York A/C pump uses regular 10w30w in this application. It will turn around 4500rpm (6000rpm maximum per mfg). There are a number of guys in the local jeep club that run York compressors for on-board-air and none have had a problem. I got one today from Pull A Part. The other two I looked at needed rebuilt and I ran out of time.
dn

[kayaker43]

The York pumps sound interesting. I would spin it close to max for best flow. Post some pics when you're done.

I would love to get a flowmeter on it to see what the open flow is. Sometimes they rate them at some medium pressure or vacuum level which is always lower than open flow.

Also it would be good to know how many amps you're pulling to determine the HP requirements. Might be able to use a smaller motor? I'm sure the jeep guys aren't using 1 1/2 hp 12 volt motors?

[jdougn]

You might consider a product call iirc Flexane. It is several viscosities of a polyurethane rubber for molding. Make a female mold, brush or trowell in to the desired thickness, let set and you are done. Get it from most any industrial supply house.
Dave

Well Dave, after spending hours looking at this process this may be an option I hadn't even thought of. I think what I'll do is make the forms first. They will be the same regardless of whether the end product is thermoformed or cast.

I am certainly open to suggestions on the best way to make these Jeep Fender Flares. Of course, the idea is to perhaps sell some to recover the original production costs too.

Thanks,
Doug N

[SCRAPWOTSCRAP]

If you decide to thermoform consider 3/16 black ABS, I would think it would be inexpensive, well suited for the application. Forms easily. Good Luck.

[jdougn]

Got the York & electric motor mounted this evening and rough plumbed the compressor side just to see what would happen. Brought a 20 glln compressor tank up to 100 psi in roughly 2 minutes and this was running at 1/4 speed since I don't have the right pulley yet. I'll have to get a vacuum gauge/controls before I run the vacuum side.

...........Also it would be good to know how many amps you're pulling to determine the HP requirements. Might be able to use a smaller motor? I'm sure the jeep guys aren't using 1 1/2 hp 12 volt motors?

Regular compressor pumps of approximately the same capacity run 3/4hp motors. The 1.5hp was already on hand so that's why it's being used. When using the York pump as on-board-air, the jeepers ditch the oem a/c compressor and mount the York instead. So, the York pump runs off fanbelts from the engine. It is rated to function from 500-6000 rpm. I'll target around 4-5k for the rpms and see what happens. I'll post up when I get a test run using it as a vacuum pump. Hope all goes well!!! lol
Doug N

[jdougn]

If you decide to thermoform consider 3/16 black ABS, I would think it would be inexpensive, well suited for the application. Forms easily. Good Luck.

The ABS would be great if it wasn't so rigid. Ideally, the material needs to collapse before it causes sheet metal damage on the vehicle. Of course, the idea is that it will flex back to shape after most encounters. How UV resistant is ABS? I'll probably use it for proto-typing at least.
Thanks for the help. I am (obviously) new to this!!
dn

[drcrash]

Low or high density polyethylene or polypropylene would be my choice.

I'd be interested in general comments on how to pick between LD and HD and polyethylene and polypropylene.

My understanding is that PE generally stays hot for a long time, and people often have to either hold the vacuum for a long time, or do something drastic to cool it so that they don't have to.

(I've read about people putting towels soaked in ice water over the plastic to get it to harden before their vacuum tank filled up. Yikes.)

Are these plastics particularly hard to heat, or do they just take a long time to heat up? (Do you need especially even heat, or is a reasonably good oven okay, if you just keep heating it?) I realize that for one-sided heating of 1/4" plastic, evenness is very important; I'm just wondering if it's more important for PE or PP than for (say) ABS of the same thickness.

(I'm also wondering if you need strong vacuum during the whole cooling time, because it flows slowly, or if it forms reasonably quickly and you can fall back to low vacuum to hold the shape while it cools.)

[jdougn]

Got the vacuum gauges and tested the set-up this evening. The pulleys were stepped to run the pump at around 4200 rpm. The 1.5hp electric motor off my heavy duty wood lathe, would not get up to speed. Had to go back to the original pulleys.

Running the original pulleys, around 1500 rpm, the 30 gallon tank hit 25hg in 1 minute. It took a total of 3 minutes to hit 28.5hg. The tank was still at 28.5hg 15-20 minutes later so at least the basic parts are leak-proof. Based on my rough math, at 1500rpm the pump moved 3.3 cfm the first minute in a closed system. At roughly 2000rpm the system should put out around 4.4 cfm. How adequate is this cfm for a 2x4 thermoformer that hopes to use .250 materials?

Next step is to plumb a two-stage system. Bought the valves and pipe for that today too.

Doug N

[kayaker43]

30 gallons and 28.5 hg. is usable for a 2 x 4 machine. I would normally go with 2-3 times that flow and a larger tank to minimize vacuum drop and charge quicker, but what you have is a good start. I say try it out and improve if needed.

As a two stage system, the tank is fine and the pump flow is low, but maybe OK if you have a zero leak platen. Even a well sealed wood platen will have enough leakage to make the second stage ineffective.

If your platen isn't leakproof, you can try a second stage tank that will keep up with leakage better.

Sounds like a massively inefficient pump if it takes 1 1/2 hp to get 3-4 CFM!! I have a Gast 30 CFM pump with a 1 1/2 HP motor.

[jdougn]

...Sounds like a massively inefficient pump if it takes 1 1/2 hp to get 3-4 CFM!! I have a Gast 30 CFM pump with a 1 1/2 HP motor.

Yeah, there is a possibility that the electric motor has some issues that I didn't know about...or...it could be a "massively ineffcient pump" that came off a 1983 Volvo! lol
dn

[jdougn]

Does anyone have experience with thermoforming sheets made from recycled car tires? The product is called "Elephant Bark" and is available from www.rubbercal.com
dn

[kayaker43]

Interesting thought, but I'm thinking no, rubber is not a thermoplastic. After its vulcanized, it doesn't soften when heated like plastic does. You can't re-mold vulcanized rubber, they make those mats with ground rubber bits and adhesive

[cod]

On a similar note, it would be neat to make PETG sheet from recycled coke bottles. Not sure how to make a nice flat sheet, and it's prolly not cost-effective for the small shop. Also not sure how to add a glycol polymer.

:rainfro:

[drcrash]

Hmm, I've been thinking that some "rubbers" (rubbery plastics) are thermoformable. I've been meaning to look into which ones... but maybe there aren't any

You can vacuum form EVA foam, which is a rubbery foam, but maybe it's only "rubbery" because it's foamed.

(Solid EVA hot glue is somewhat soft and flexible, but not really rubbery; and maybe it's mostly soft and flexible because of the other stuff they put in it, like wax...?)

EDIT, a couple of hours later:

I guess the term I was looking for was thermoplastic elastomer (TPE). Should have googled first, written later.

http://en.wikipedia.org/wiki/Thermoplastic_elastomer

So now I'm wondering if some TPE would be good for making fender flares.

[jdougn]

Hmm, I've been thinking that some "rubbers" (rubbery plastics) are thermoformable. I've been meaning to look into which ones... So now I'm wondering if some TPE would be good for making fender flares.

So am I! Protoypes will be done in something easy to work and cheap. Maybe HIS or ABS.

Also DrCrash, I was wondering what your source is for your "hefty power diode (which you can get for about $5) and a double-pole toggle switch to avoid having to turn the heat on and off".

Thanks,
dn