Nubo

I'm looking to make a grille for the RX-8, and thought I'd share my experience so far.

Like the Miata, the RX-8 also leaves some sensitive areas unprotected -- namely the A/C condenser and the oil coolers. Given reports already in this forum of impact damage to the A/C condenser I decided it was important to have grilles to protect these areas. Member Hymee has already designed some grilles for these areas and offered to provide them to other interested members. You might want to find those threads if you are interested in an already-fabricated solution. I wanted something a little different. I don't think I'll be producing more than just my own copy but in case anyone's interested in this alternative here are some details. I started out looking at stainless steel but then it took an interesting turn.

I'd had good results with my Miata grille, which I'd purchased back in 1990 or so. It was a stainless-steel mesh with 1/2-inch openings. Large enough to permit generous airflow and avoid bug-blockage but small enough it seemed to stop anything capable of significant damage to the radiator. Thanks to its corrosion resistance it was maintenance free, and since it was unpainted there were no issues of chipped paint, etc. The material is strong and rigid due to each intersection being electro-welded.

It took some time to find a source for this material. It is known in the industry as "#2 mesh", meaning there are 2 openings per inch in each direction. One thing about these meshes that surprised me was the actual percentage of "open area" in the mesh. You may be surprised when looking at the pictures below that the stainless steel mesh pictured is only about 76% open area. This reinforced my decision not to go any smaller with the mesh; open area tends to drop as the number of wires per inch increases. Thickness of the wire, of course, is also important but you don't want overly thin wire from strength as well as an aesthetic perspective.

Most sites I found were geared towards industrial sales and had very large minimum orders or had forms to "get a quote", which implied pretty much the same thing. Finally, I found twpinc.com, which has minimum order sizes that are reasonable enough for this project, considering that I may also end up replacing the main radiator grille as well. Their minimum order for the #2 stainless mesh is 12 square feet (3x4). see: http://www.twpinc.com/twp/jsp/product.jsp?type=14

This is where the project took a twist. While perusing the twpinc.com website, I noticed they also had similar sized mesh manufactured in other metals - including bronze. These meshes have a more interesting shape because they're actually woven instead of being welded together. It also occurred to me that the bronze mesh might be very attractive if it were to develop a green patina such as you see on old bronze statues. I thought this might be very handsome in conjunction with a yellow RX-8. Much of the rest of this post will be concerned with the bronze option. Not much to say about the stainless - it will work and should be problem free. I really wanted to see what could be done with the bronze though, now that I had this idea in my head.

Twpinc.com allows you to purchase small samples of the material, and so I ordered a sample of each, bronze and stainless. Both in the #2 mesh, and in each case I opted for the .063 inch wire sizes.

Here's an initial picture of both types. I've already subjected the bronze to some "processing".

Nubo

As mentioned earlier, the stainless mesh is welded at each crossing. This makes for a very strong and rigid material. If you wanted to cut a grille from it all you would have to do is mark off your shape and start cutting - the resulting piece would be ready to fit. The bronze is different. Since it is woven, the wires are all free to move. The crimp design helps to hold the wires to a grid pattern but you can push and pull from the edges somewhat like an accordion, changing the shape of the "holes" from square to parallelogram in both directions. This also results in a fairly "floppy" structure -- not rigid at all. The effect was very noticeable on the 6x6 sample. For a larger sheet it would be more pronounced. This is not a defect of the material - the manufacturer explains the property in the specs and it's up to the end-user to determine suitability and devise any necessary methods for holding the desired shape.

In order to stiffen and stabilize the sample, I began wrapping the crossings at the edges with thin copper wire and soldering. This was rather time-consuming until I realized I could probably just solder the crossings directly, so that's what I did, using rosin-core electrical solder.

The solder stiffened up the sample very nicely. For a larger sheet though, I think you could do even better by soldering complete "boxes" around the edge. There was very little evidence of shifting under pressure and my initial worry about potential rattles was relieved somewhat.

Step 2 - how to get the "green" finish without waiting 20 years or enlisting a flock of pigeons. An internet search turned up some suggestions. The easiest and safest appeared to be use of ammonia. Note - In the U.S. the term "ammonia" in this context refers to "household ammonia", or aqueous ammonia, rather than the pure substance.

First, I cleaned the bronze sample by scrubbing with hand soap and a scotch-brite pad, then rinsed with water and dried. The metal took on a very bright coppery finish. I took a large plastic container and set a thin cylinder of plastic on end inside it. Then I poured about 1/2 cup of ammonia into the container. Finally, I placed the sample on the cylinder and sealed the container. The idea is to let the ammonia vapors do the work, and not to pour the ammonia directly on the metal.

I checked the sample about 2 hours later and it had already turned black. Wanting green, I re-closed the container and let the ammonia do its magic.

The next morning the sample still appeared primarily black. In the evening the appearance hadn't changed. Finally, the next morning I decided to take a picture of the "black" bronze, and took the sample out of the container and placed it in the sink. By the time I returned with the camera, the whole thing had turned green! Yay! By the way, this green surface is referred to as "verdigris".

Here's a picture of the result.

Nubo

And, here's a close-up.

Nubo

I don't know if anyone is into this, but this weathered surface has a really strong appeal for me. I also think the verdigris would be a fabulous contrast with the yellow vehicle. It also seemed to add another bit of stability to the "weave" - all of the intersections now seem to have "mated". I don't know how strong or permanent this effect would be on the road. And, I have the same questions about this application in the larger sense.

Although I love the look, I'm worried about several items. Foremost, I'm wondering what effect this could have on the aluminum radiator and condenser coils. Some of this surface compound will wash off as the metal ages and I don't know what this would do to the aluminum over time. Any metallurgists or chemists out there?

Second, I don't know how permanent this patina would be in service, or how it would hold up to the rain blast at highway speeds. If it just reverts to plain dark bronze, the attraction may not be there for me. I suppose I could "preserve" the finish somehow, but not sure what to try that wouldn't detract from the wonderful "natural" look it has now.

Third, I'm still not sure about the structural properties. For smaller or "thinner" areas like the oil coolers and A/C duct, I don't think it will be a problem. But I'm not sure about a larger area like the radiator grille. I'd hate to end up with rattles and certainly don't want the material bowing in and out. This might be resolved by soldering the edges more thoroughly as mentioned previously. It might help also to solder a few select crossings in the "viewable area" as well, but I don't think I want to go that route. I suppose it would also be possible to fabricate a rigid frame for the edges that could hold the material in tension.

Well, I will be using one or the other of these materials. It's an interesting choice between the indestructible and problem-free (yet cold) stainless steel and the potentially troublesome yet soulful and ephemerally beautiful bronze.

BVD

Hi Nubo,

Interesting idea. I’m not sure how you could preserve the finish, but giving it a blast with a decent hosepipe should give you some idea of how it would stand up to rain at speed. At least that’s how I rather crudely tested the black paint I put on the grille I made for my yellow RX8. It seemed to stand up to both the hose test and the rain. Hymee has his grilles powder coated black – very strong and weather resistant.

I also made my own grille, with stainless steel mesh that’s finer than yours, but also woven like the bronze you have. In our area the risk is not so much from large rocks but from small sharp stones that are regularly kicked up by passing traffic. Harmless at rest but lethal enough if you hit one at full speed. I’ve lost 3 or 4 windscreens from cracks that developed from stone chips, and sustained innumerable paintwork chips over the years. I achieved even more strength and rigidity by making the grilles in a sort of box shape – bending the sides into an L profile all round. Invisible from outside the car.

I did a fair bit of pondering before I fitted mine – how to attach it, whether it would have an effect on cooling etc.

Of course, if you fit any mesh across an airflow path there must be some risk of reducing the flow, but it’s by no means a given that will cause any problems. Firstly, the limiting factor may well be elsewhere in the system, such as the amount that can flow through the two ‘radiators’. I’ve no reason to believe that the air available from the front is already anywhere near some critical limit. If so, the decision by Mazda to block off the bigger percentage of the diamond shapes on the upper grill would seem somewhat odd.

Also, a temporary restriction such as a wire may not actually reduce flow much, if at all – it depends on a great many other factors, including air pressure and speed at the front of the car, flow potential through the radiators, what happens around and behind the rads, etc. For instance, if you look at a river that has to travel through a narrow pass, under normal conditions the water simply speeds up through the restriction, and then slows down again when it widens out again.

I came to the conclusion that the only way I could tell what effect my mesh would have was to simply do some before and after tests under varying conditions, and increase mesh size if I saw any negative results. So far, I’ve seen no difference whatsoever in the temperature gauge, which simply gets up to working temperature and stays there.

Despite some good hot weather (it’s summer here in West Australia) and doing things like running the car up a long steep hill with the aircon full blast, and as much engine load as I could practically muster – all seems fine. I’ve tried different speeds, gears etc but the needle just doesn’t budge past its normal operating temperature position.

No doubt I could engineer some more testing special conditions – such as sustained high rev racing, or whatever – but I’m really only interested in making sure that it’s 100% OK for the way I actually drive the car, not some circumstance I’ll never see. I’ll be keeping an eye on it this summer, but so far it’s absolutely fine.

Anybody else had experiences with fitting grilles to cars – good or bad?

All the best with your project Nubo,

Chris.

Nubo

Thanks BVD, I suspect you're probably right and the restrictions of the radiator and other coolers probably exceed any effect of the grilles. Another argument in support of that is the huge amount of obstruction that happens when someone puts a license plate over the radiator grille - apparently that works out ok.

In another thread someone commented on this also, said not to worry and that "it's not rocket science". I understood his reasoning but the reality of it is - turbulence and fluid dynamics are pretty tough subjects and actually at the center of "rocket science" in the classical sense :D. I know I don't have the math for it so I best be as careful as I can.

I stuck with the #2 mesh since that's what I've been using on my current vehicle with no cooling problems for 150,000 miles.

BVD

I absolutely agree. It's a complex and fascinating subject, and the tantalising thing is that there is no single or simple answer to the effect of any particular grille size. What is happening will change constantly as the speed of the car changes, and the numerous flow and pressure variables keep altering. Not to mention the effects of a heap of heat variables in various parts of the system.

It would be intriguing to have something a little more sophisticated than just the car's temperature gauge to be able to monitor what really happens. But I suppose, in the end, the only really practical outcome of interest is whether the car is overheating or not as a result. And I've certainly not seen anything to suggest that's going to happen.

And I'm already glad that I've fitted the mesh. Today, when I washed the car (it just reached 1000kms, so deserves a clean..) I found a stone chip on the windscreen. Already!! If the grille hasn't fended off a stone or two, I'm sure it will eventually. Nice to have the peace of mind.

Hope you find a way to preserve that unique look.

Cheers, Chris.

Hymee

iTrader: (1)

Nice work Nubo!

I like the verdigris look. I wonder why it only turned green after you removed it from the amonia gas. Maybe the presence of oxygen? I wonder if the amonia removed the surface impurities, and as soon as the oxygen hit the pure bronze the oxidation (greening) took place.

I made my grills out of grade 304 stainless steel woven wire mesh.



I also made one for the oil cooler.

It was good you could solder the bronze. I tried that with SS, but of course it would not solder with normal solder. I ended up hiring a spot welder to tack some of the wires together in certain points. This strengthend the shear of the grills quite a bit

The powder coating process strengthened the grills even more, as it effectivley bonds each wire crossing.

The mesh I chose has a 5.3mm aperature, with a 1.0mm wire diameter. 12mm is about 1/2 inch, so 5.3 is less than 1/4 inch. I think that is the same size as what BVD used.

Would love to see the verdigris bronze on the yellow car!

Cheers,
Hymee.

Nubo

I'm not sure what happened after removing from the ammonia. From what I've read, verdigris is copper sulfate, copper chloride, or both. I didn't think our house had high concentrations of chlorine or sulfide in the air. Maybe it only takes a little bit though?

The bronze was definitely not in an elemental state in the presence of the ammonia fumes. (the bronze was never in direct contact with the liquid ammonia) The surface of the bronze was black and wet, and the wet, black stuff came off readily on my fingers where I touched it. Whatever that stuff was is what turned into the verdigris.

I might run the process again, and when removing from the ammonia fumes, put in a second container with a bit of bleach in the bottom and see if I get a more intense green. Adequate ventillation of course!

All that being said, I am now leaning away from using the stuff. It's very pretty but I just don't know if it would have adverse effects from leaching into the coils over time. I think I'll have to find some use for bronze out in the yard to satisfy my craving. I'll probably go for the stainless after all. If I want color the powder coating sounds like a good way to go.

Your installation looks great .

Omicron

Couldn't you just paint the stainless steel mesh to match the green of the verdigris, and "weather" it with carefully applied bits of the different colors of the weathering patina? Just a thought....

Nubo

My mom used like to apply "antiqueing" to lots of stuff. Sorry to say, it never quite looked "antique" to me and I formed negative opinions on applying coatings to mimic natural effects. If I went with a color, I'd probably just get the stainless powder coated a solid color. On the other hand I guess that accelerating the ageing process with ammonia constitutes a fakery of its own...

Omicron

Well, twas just a thought. Keep us posted on what you work out, and if you tackle the entire grille (as I'm thinking of doing myself next summer) let us know how it goes.

Nubo

just adding an attachment to see if it pulls the old attachments back in. I lost those pics...