Get bent, Building a better mousetrap Options

[mitchntx]

IN an effort to lose weight off the race car, I want to cut the SFCs off. However, I use them to jack up the car.

After seeing several "pro" teams use a receiver/stab setup off the roll cage, I began fabricating this kind of rig.

I used 1" square tubing as the receiver and gusseted the hell out of it to keep deflection to a minimum. I have some 3/4" solid bar stock I was using as the stab.

After welding the receiver portion to the cage and mocking up the stab with plenty of gussets, I tested the rig and ... it bent. (IMG:http://www.frrax.com/rrforum/style_emoticons/default/mad.gif) 3/4" solid bar stock bent like a pretzel.

And it yielded right at the end of the gusseting. Think of it as a pry bar.

I opened the door and placed the jack on the end of the receiver and lifted the car without an issue ...

So help me out here ... what can I do to the bar stock I have to increase it's strength or what kind of 3/4" bar stock can I source that will lift 1500lbs?

[FBody383]

So help me out here ... what can I do to the bar stock I have to increase it's strength or what kind of 3/4" bar stock can I source that will lift 1500lbs?

The idea is certainly sound.
I have one of these for the M3 and it works great. My guess is you need a harder steel than the mild bar stock you have. Call your metal guy or one of the online shops - I've bought from Metal Depot and Online Metal.

[StanIROCZ]

So help me out here ... what can I do to the bar stock I have to increase it's strength or what kind of 3/4" bar stock can I source that will lift 1500lbs?

Throw a picture up here with dimensions (length of the "pry bar" etc). It is a pretty simple stress calculation. If you are limited to 3/4" square your only choice will be to increase the strength of the metal. The stress calc can tell you if there is even a chance of you getting there with that size.

You might be able to flame harden and quench the piece you have. By doing this the steel will get stronger but might be more brittle and could break before bend, so you will need to be careful.

[mitchntx]

The stab ...

(IMG:http://www.lawmotorsports.net/Pics/Mitch/stab.jpg)



The stab fully inserted.

(IMG:http://www.lawmotorsports.net/Pics/Mitch/stab_receiver1.jpg)

After closer inspection, it appears the end of the receiver is deformed as well, just beyond the gusset on top.

Again, the stab was a mock up in order to find the weakness. I didn't spend a lot of time on it.

I added in about 10* off vertical because I realized that as the car goes up, the angle change would add leverage.

Maybe I didn't add enough angle?

Maybe I under built the whole rig?

[StanIROCZ]

I assumed a 6" lever arm and 1600 lbs of load and came up with 364 ksi stress. Regular off the shelf mild steel is good for ~50. I don't know of any steel that can handle 364 ksi.

If you take the gussets out completely you can slide that 3/4 stock in farther to reduce the 6" lever arm that I mentioned above. If you can get the vertical bar within .5" (zero would be better) of the end of the square receiver your stress goes down to 30.3 KSI. To do that your verticle tube will be almost touching the rocker panel.

But really, you should have the gussets because your failure mode will probably shift to the weld (or atleast it would scare me).

Maybe I under built the whole rig?

Yeah, I think so. I would probably use 2" next time and you wouldn't need a solid bar stock. A .250 wall will be pleanty. And keep the lever arm to a minimum.

[StanIROCZ]

I assumed a 6" lever arm and 1600 lbs of load and came up with 364 ksi stress. Regular off the shelf mild steel is good for ~50. I don't know of any steel that can handle 364 ksi.

If you take the gussets out completely you can slide that 3/4 stock in farther to reduce the 6" lever arm that I mentioned above. If you can get the vertical bar within .5" (zero would be better) of the end of the square receiver your stress goes down to 30.3 KSI. To do that your verticle tube will be almost touching the rocker panel.

But really, you should have the gussets because your failure mode will probably shift to the weld (or atleast it would scare me).

Maybe I under built the whole rig?

Yeah, I think so. I would probably use 2" next time and you wouldn't need a solid bar stock. A .250 wall will be pleanty. And keep the lever arm to a minimum.

I have a better idea for your design that will reduce the amount of mass on the car and increase the strength. If I get time tonight I'll sketch it up and post.

[mitchntx]

Thanks, Stan .... Learning by doing, I guess ... glad I didn't cut the subs off first. (IMG:http://www.frrax.com/rrforum/style_emoticons/default/wink.gif)

[RichardP]

(IMG:http://www.lawmotorsports.net/Pics/Mitch/stab_receiver1.jpg)

Good stuff Mitch. I've been wanting to add a jacking point to my car but haven't gotten around to it.

Reducing the moment arm is the best way to strengthen your setup.

I'm a little confused, though. By adding the diagonal back down to the rocker sill, you have effectively added an additional attachment point to the cage. That would make this not CMC legal. Is that what you were going for???


Richard P.

[rmackintosh]

I used small trailer hitch recievers and made a stab out of the insert. Will look for some photos

(IMG:http://farm4.static.flickr.com/3188/3059876322_da9d9a4349.jpg)

I don't have a clear pic of the passenger side, but you can see a bit of the triangulation in this photo.....I do not attach to the body of the car on EITHER side...except for the tab running down on the back side you can see in the pic....just a flat bar strap.

....no pics of the stab....will have to go out to the trailer and take one.....hold on....

This post has been edited by rmackintosh: Nov 25 2008, 09:34 PM

[rmackintosh]

Here is the stab. As stated it is a small sized trailer hitch. The one side is for normal jacking....the short side is for when I have a flat tire or something....
(IMG:http://farm4.static.flickr.com/3021/3059056615_199b678893.jpg)

[JKnight]

Can't find a pic at the moment, but JR Smith on his AIX Camaro had part of the roll cage that came down through the rocker panel that he could use to jack the car. I've always thought that would be a nice thing to have - although jacking the wife's car via the subframe connectors is quite simple.

The jacking plate for BMW factory jack points shown above doesn't work terrible well on my BMW (quiet Randy!) as I can't get my jack and a jackstand to be in that same area simultaneously, and the factory jack point has been known to be not the strongest point.

Jason

[mitchntx]

(IMG:http://www.lawmotorsports.net/Pics/Mitch/stab_receiver1.jpg)

Good stuff Mitch. I've been wanting to add a jacking point to my car but haven't gotten around to it.

Reducing the moment arm is the best way to strengthen your setup.

I'm a little confused, though. By adding the diagonal back down to the rocker sill, you have effectively added an additional attachment point to the cage. That would make this not CMC legal. Is that what you were going for???


Richard P.

You know, when I discussed this with a series director, it was concluded that it was in fact and by the strict letter, technically, an additional "mounting point" but it added no rigidity to the structure. I also noted that someone was gonna say something and he said, "nah ... no way." (IMG:http://www.frrax.com/rrforum/style_emoticons/default/dry.gif)

I needed something to brace deflection. I only have a single bar on the passenger side (and yes, the factory crash bar is still in the passenger door).


Randy, that's a good idea. My goal was to keep everything as light as possible. Adding both those hitch receivers sorta negates the reason for cutting off the subs. I'm sure they are lighter, but not by as much as I was hoping to gain. Looks like I'm back to square one ...

[rmackintosh]

Not THAT much heavier. Granted it is much thicker wall than the thin wall tubing you are working with but the 6-7" of it is no big deal.

It is not the same size as the hitch on your 2500 truck.....it is the itty bitty reciever and hitch....1 1/4" square I think.

This post has been edited by rmackintosh: Nov 26 2008, 01:43 AM

[StanIROCZ]

Good stuff Mitch. I've been wanting to add a jacking point to my car but haven't gotten around to it.

Reducing the moment arm is the best way to strengthen your setup.

I'm a little confused, though. By adding the diagonal back down to the rocker sill, you have effectively added an additional attachment point to the cage. That would make this not CMC legal. Is that what you were going for???


Richard P.

Aww Crap, there are mustang guys hanging out on this forum (IMG:http://www.frrax.com/rrforum/style_emoticons/default/banghead.gif)

Here's roughly how I was planning to do it when it comes time to do my cage. I think this would add the smallest amount of mass to the chassis by putting most of the mass in the receiver.

(IMG:http://i116.photobucket.com/albums/o33/StanIROCZ/stab_receiver1.jpg)

The verticle part could be made from a 2 pieces of flat stock and then weld in the square "hole" to receive the receiver. You might want to box in the back side of the verticle with another piece of flat stock, or just start out with a square tube and cut the square hole in it. There's more than one way to do it.

I wouldn't think that you would need anything more that 3/16" steel on the chassis side. Might be able to go thinner but I'd have to throw some math at it first.

Center the verticle at the CG or maybe slightly rearward since that will allow more height which will reduce the stress on you cage tube.

This post has been edited by StanIROCZ: Nov 26 2008, 02:16 AM

[StanIROCZ]

Not THAT much heavier.

I don't mean to pick on you Randy but I've been thinking about this a lot as I am trimming out a wire at a time out of my wiring harnesses. There are probably hundreds to even a thousand little things that you touch on the car over the years. If you scrutinize every 0.1, 0.2, .5, 1lb, it adds up. Not right away, but over the years each little detail x100 or x1000 gives you some significant savings. This isn’t something that hasn’t been said before, but I just thought I’d say it again.

[nape]

You can accomplish the same thing with about 8" of 1 1/4" schedule 80 pipe per side (or at least that's what I think it is. I found it on a job). I'll see if I have any pictures of it at home.

Make a 6" wide x 2" high T out of the pipe and weld it to the rocker panel and floor pan right underneath the rear most of the two floor pan seat rails. It jacks the car almost perfectly.

They maybe weigh a pound each?

[mitchntx]

Aww Crap, there are mustang guys hanging out on this forum (IMG:http://www.frrax.com/rrforum/style_emoticons/default/banghead.gif)

Not so fast ... he's bi!

(IMG:http://www.frrax.com/rrforum/style_emoticons/default/nutkick.gif)

[rmackintosh]

Not THAT much heavier.

I don't mean to pick on you Randy but I've been thinking about this a lot as I am trimming out a wire at a time out of my wiring harnesses. There are probably hundreds to even a thousand little things that you touch on the car over the years. If you scrutinize every 0.1, 0.2, .5, 1lb, it adds up. Not right away, but over the years each little detail x100 or x1000 gives you some significant savings. This isn’t something that hasn’t been said before, but I just thought I’d say it again.

Oh...don't think I don't know it. I have spent lots of $$$ and hours trimming from my elephant!

I am saying that 6" of trailer hitch (total weight maybe 2 lbs) is not that much. You need to make the thing strong enough to support jacking up a 3000 lb. car after all. You will put another 1+ lb. gussetting up that sucker to hold the car.... (IMG:http://www.frrax.com/rrforum/style_emoticons/default/blink.gif)

You could make a contraption like yours to make it pin on and removable true enough. But in this case, something that is used every day and takes a lot of stress doing it, I like simple. I don't have to open the door to access mine, it buts right up to the door and I can slip it in and be jacking in like 3 seconds....that is an important feature to me. I like simplicity and functionality for such a critical, much used part! (IMG:http://www.frrax.com/rrforum/style_emoticons/default/cool2.gif)

[StanIROCZ]

Not THAT much heavier.

I don't mean to pick on you Randy but I've been thinking about this a lot as I am trimming out a wire at a time out of my wiring harnesses. There are probably hundreds to even a thousand little things that you touch on the car over the years. If you scrutinize every 0.1, 0.2, .5, 1lb, it adds up. Not right away, but over the years each little detail x100 or x1000 gives you some significant savings. This isn’t something that hasn’t been said before, but I just thought I’d say it again.

Oh...don't think I don't know it. I have spent lots of $$$ and hours trimming from my elephant!

I am saying that 6" of trailer hitch (total weight maybe 2 lbs) is not that much. You need to make the thing strong enough to support jacking up a 3000 lb. car after all. You will put another 1+ lb. gussetting up that sucker to hold the car.... (IMG:http://www.frrax.com/rrforum/style_emoticons/default/blink.gif)

You could make a contraption like yours to make it pin on and removable true enough. But in this case, something that is used every day and takes a lot of stress doing it, I like simple. I don't have to open the door to access mine, it buts right up to the door and I can slip it in and be jacking in like 3 seconds....that is an important feature to me. I like simplicity and functionality for such a critical, much used part! (IMG:http://www.frrax.com/rrforum/style_emoticons/default/cool2.gif)

I agree, its worth 2 lbs esp when you are going to save about 30 by removing the SFCs. But if you can save a couple more, why not (IMG:http://www.frrax.com/rrforum/style_emoticons/default/cool2.gif) With the Nascar door bars the way you have them on the drivers side I agree that it doesn't add too much weight and it is more robust. But with an X-bar I think the way I have it has more of an advantage. Also, I plan to keep my windows and door panels since I drive on the street, so thats the only way for me to do it.

One thing I should mention about my contraption is that you want to make sure you have a good clean fit between the receiver and the square hole. You don't want it to be loose. That detail might mike this version a bit more difficult to fab.

[rmackintosh]

But with an X-bar I think the way I have it has more of an advantage. Also, I plan to keep my windows and door panels since I drive on the street, so thats the only way for me to do it.

Yeah, my passenger has an X like Mitch's and what you describe....and actually its roots are much like yours...trailer reciever buts up to the flat bar coming down from the X much like your drawing....but instead of the "pin box" my reciever juts out from there. Two small round tubes up to the X for support. (IMG:http://www.frrax.com/rrforum/style_emoticons/default/cool2.gif)

This post has been edited by rmackintosh: Nov 26 2008, 04:12 AM