Magnets To Attach Ski Rack To Car Top?

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Quit beating around the bush...

Look man, people have been trying to suggest nicely that you should not do this, but you seem not to be getting the message, so here it is in plain english:


DON"T BE AN IDIOT. DON"T ATTACH A LADDER TO THE ROOF OF YOUR CAR WITH MAGNETS. YOU ARE GOING TO GET SOMEONE KILLED.

Next you're going to say you want to hold the ladder to the ski rack with scotch tape! Jeez! Before you even ask for opinions, here's mine: dont do THAT either!

I_F
 
If I were to do such operation I'd look into decal material. They offer some transparent 0.9mil thick tape to cover your hood angainst rocks, that would prevent the top of the car from getting scratched.

For the holders, there is a special type of universal non permanent holder system that is sold around here by Thule that fit many car and that will securely tighten the current rack to your roof making it perfectly stable just as it was on the previous car which was probably a Volkswagen.

Hope this helps!
Sébastien
 
I'll grant you the ladder didn't fly off quickly, but note, that it did in fact come off. Was this an aluminum ladder or a wood ladder? Mass is going to be your big killer here. I don't remember what you said the original intent was, but I would definately not use magnets for much beyond a ladder or some skis. I don't remember if you said you were thinking lumber or plywood at times as well, but I can guarantee that those WILL slide off. There's a lot of momentum in stopping and starting even at slow speeds. Plus, think about this, you're determined to help the magnets slide by putting a buffer between the two, so it won't scratch your finish!!!

If you insist on doing this, try your experiment of stopping and starting with the heaviest objects you intend to carry. Or better yet, attach the magnets on, put it on your roof, now give it a hard yank sideways.

One other thing to think about, what about the poor kid who chases their ball into the street in front of you? You'll stop in time, but the object flying off the roof will get them.

So, to put it as, I_Forgot did,

DON'T!!!!!

Its just not worth the hassel and money, go buy a rack that fits.
 
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Schaef said:
I'll grant you the ladder didn't fly off quickly, but note, that it did in fact come off. Was this an aluminum ladder or a wood ladder?


Aluminum. A medium duty 8 foot stepladder. It came off, but it took a mile and a half at 40 mph to slide off, and it was entirely unsecured. Not even a piece of scotch tape was holding on the rack. So that indicates that there isn't as much force in the horizontal direction as you might think.


Schaef said:
If you insist on doing this, try your experiment of stopping and starting with the heaviest objects you intend to carry. Or better yet, attach the magnets on, put it on your roof, now give it a hard yank sideways.

Yes, I plan to do all of these things.

One more thing I think I should mention. When I had the car which had a place for the rack to hook onto, on the very rare occasion when I transported a 20 ft extension ladder on the rack I also tied one end of the ladder to the front bumper and the other end to the rear bumper, with the rack in the middle. The racks are only about 3.5 ft apart, so they simply could not secure a 20 ft ladder. I will continue this practice with the magnetic attachment. So we are basically talking a medium duty 8 ft aluminum ladder here, and the occasional plywood which will be transported on city streets at 30 mph.


Schaef said:
One other thing to think about, what about the poor kid who chases their ball into the street in front of you? You'll stop in time, but the object flying off the roof will get them.

That is the pupose of the hard stop and start test-to see if that can happen. If it does, then I find alternative measures to attach the rack to the roof, whether is ruins the finish of car or not. If it doesn't, then I use the magnet method.


Schaef said:
Its just not worth the hassel and money, go buy a rack that fits.

That's just the problem, there is no rack that fits without ruining the finish because this car does not have the place for the hooks to hook onto.
 
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Variac said:
Huge electro magnets- that's the ticket

I don't know if your tongue was planted in your cheek when you wrote that, but that would actually be a very good idea.

One way to do would be the following way.

Take out the interior roof liner and glue large, 1 inch thick electromagnets. Run wire down to the fuse box. Hook up so current is cut off when car is turned off.

On the base of the racks, glue large round donut type piece with the small hole filled up by a real permanent magnet. Make sure the rack pads line up with the electromagnets glued on the inside of the rooftop.

The beauty of this system is the electromagnets will exert enormous pull when the car is running. But to take the racks off the car, simply turn off the car and the racks will be held onto the roof only by the small permanent magnet in the middle of the iron piece at the bottom of the rack pad. After ally, you don't need much force on the rack when the car is parked. Best of both worlds.

There are only a couple of disadvantages here:

A) Cost. I think the electromagnets will be expensive. And I would problably need a bigger alternator to run the current to them.

B) If for any reason the electrical power fails while on the highway, off goes the rack unless you brake VERY slowly and go gradually onto the shoulder. which should make things interesting, if nothing else. :)
 
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Well, maybe I was joking a bit ,but there is no requirement to power them through your ignition. Power them from the battery with a separate switch. Until the battery wears down you are OK ;)

Iguess you need to search the surplus stores online.

Those rack makers are fiendishly clever developing hardware to attach to any car - even going into the crack in the top of the door opening. You might want to more research...
 
kelticwizard,

Lemme get this straight: you are gonna use magnets to hold a rack to the roof of your car, risking the lives of an untold numbers of people in order to not damage the finish on the roof of the car?

I hope the first cop who sees you tickets you and impounds your car. You are truly a menace to society. Get help before someone gets hurt or killed.

I_F
 
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I_Forgot said:
Have you seriously considered the safety aspects of what you are intending to do?


I_Forgot said:
Don't forget to put one arm out the window to help hold the stuff down...


I_Forgot said:
DON"T BE AN IDIOT. DON"T ATTACH A LADDER TO THE ROOF OF YOUR CAR WITH MAGNETS. YOU ARE GOING TO GET SOMEONE KILLED.


I_Forgot said:
You are truly a menace to society.


I have to hand to hand it to you, I_Forgot.

You are enough to make even an Irish-American cry out:

OY, such a noodge!!
 
Well, I'm going to jump back in here for three reasons.

1. Despite the doomcrying by a couple of folk who think that this can't possibly work, apparently on a priori grounds, and who - presumably as good Aristoteleans - don't want to see it tried, I see no reason why this shouldn't be an interesting experiment; provided, of course, it follows the safe methodology kelticwizard described.

2. Early on (post #2), the link I provided points not just to rare-earth magnets, but also to a high-friction material intended to prevent lateral sliding. Using some such material would probably be a good idea - as would making sure that no dust, etc., gets under it.

3. And, despite my interest in this qua experiment, I should point out that my car has no rain gutters and the roof-rack people have no problem providing mounts that hold a rack on while I transport a sixteen-foot boat on top.
 
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Wilfried:

I didn't mean to skip over acknowledging you the first time. Thank you for posting those two links which illustrate the magnetic cartop rack principle is being used in commercial products every day. Am presently looking for a quick freeware program to translate the German site-this is painful to admit because I took two years of German back in college, and all I can remember from it is "Wo ist der Bahnhof"? (Where is the railroad station?)

Your input has been extremely helpful. :)
 
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Aengus:

Thank you for the post above, as well as your previous posts.

When I started this thread, I asked for both pro and con responses to this. I was hoping the con responses, if any, would be from:

A) Engineers who would do a couple of quick estimated calculations of the forces involved and give their honest opinion about whether it would work with materials an amateur can likely get.

B) People who perhaps do not do the calculations but who have worked with magnets extensively. Certainly Schaef's posts, about his lack of success of using magnets to hang a bulletin board on the wall would fall into the category of people with special experience with working with magnetic applications.

In other words, I did not mind responses advising against it, in fact I welcome them, if at least the people advising against it, like Schaef, have some special knowledge or experience dealing with magnetics on some level.

However, the most vociferous opposition and snidest comments seem to come not from the people who have actually worked with magnets, but from people who appear to have no special knowledge or experience with them particularly. I wonder if these fellows plan on giving the Darwin Award to those companies which are already successfully producing magnetic cartop carriers. Especially since the Darwin Award comments came AFTER Wilfried pointed out these products and companies.

Oh well, isn't that always the way.......
 
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Tool49:

Your suggestion to use decal material between the magnets and car surface to prevent scratching is well considered. After all, decals work by friction, so gluing the magnets to the decal material adds an extra demension-friction-to the magnetic force.

The decals I have handled seem to have a vinyl feel to them, which I hope is the case. Most clear flexible plastics are hard to glue, but vinyl is easy to glue. Most glues will stick to it easily. Just as a side note-if you ever have a project which requires clear plastic film for anything, don't use just clear plastic wrap-use Saran wrap. It's vinyl and so most glues stick to it. The normal clear plastic food wrap has few glues which stick to it well.
 
Okay, I'll jump back into this, with a couple of thoughts.

First, I didn't look at the commercial magnetic racks, but a set of skis are a lot lighter than a sheet of plywood (or a ladder) so there are less forces involved.

Second, I'll agree that experimenting in a safe or quasi safe (meaning only the driver is in danger) situation is not a bad idea. In fact, if you do this, I would love to hear the results.

Next, on to the scuff problem, a thought occurred to me, someone had mentioned something about using neoprene as a buffer, this may not be a bad idea. Another thought would be to use something like a router mat or its generic equivalent, namely anti-slip rug stuff. This should provide both the buffer you want and, since its anti-slip, should help with the lateral movement problems. Certainly a better idea than some simply plastic. I'll have to ask some chemical engineers I know that work for a company that makes a neoprene clone what their thoughts are on something like that.

I still have several concerns about this. I'm still not sure about the holding power of even the strong magnets on the thin metal of the roof of your car, and the whole mass and inertia of the cargo on a sudden stop worries me. The starting, not so much, as you can control that, but a sudden stop, you can't always control.

So, if you do try it, let us know the results. Oh, and I still say no, but I tend to over-engineer things.
 
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Schaef said:
I'm still not sure about the holding power of even the strong magnets on the thin metal of the roof of your car.....

I'm leaning toward the idea of temporarily removing the interior roof liner of the car and attaching large magnets of equal or greater size as the carrier pad's magnets to the underside of the roof at the point the carrier pads contact the car. This will double the holding power of the magnet attached to to the carrier pads. Of course, then I reattach the interior liner.

I'll probably attach the magnet on the underside of the roof with Bondo, which will harden and conform to the contour of the roof's curve. Without that, two powerful magnets coming together might tend to flatten the roof at the meeting point!

Also, as this is diyAudio, how appropriate that I just hit the tag sales this weekend and come back with a bunch of people's old speakers and use the magnets from those? Just a thought.....
 
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