Metal front bumper/tow hook mount

[knochgoon24]

Does it really need to be adjustable? It seems like there are only 2 heights.

 

[greengoblin]

Their Pro/E model was imported from something else, so there is no parametric data associated with it; it's just "dumb" geometry. Not sure I can use it to generate a swept (curved) beam.

Could you even bend it? Aged aluminum does not like to be bent. I pretty sure it has to be annealed and then reheat treated. Heat treating something like that would run what? Around 250 or so.

Does it really need to be adjustable? It seems like there are only 2 heights.

I agree they should just make two different ones. I'd also bet 90% of them would be ordered for a cut front clip.

 

[Calan]

Could you even bend it? Aged aluminum does not like to be bent. I pretty sure it has to be annealed and then reheat treated. Heat treating something like that would run what? Around 250 or so.

I think I ninja edited you Kevin.

I'm willing to bet that it would be really hard to work with. Getting good solid welds or even a smooth bend looks like it would be difficult at best.

Bending it to any degree of accuracy and cleanly would most likely take a special mandrel. This looks like extruded planking (although more complex than most) which is designed to be used in straight sections.

Based on that cross-section, you would have to almost cut it in half to get a bolt or bolt tube through it, at which point it would become pretty weak I think.

 

[turbosax2]

Does it really need to be adjustable? It seems like there are only 2 heights.

So far none of the fixed designs have even met the two height requirement. If we can meet that, I'll be happy. Any other adjustment is just icing on my cake (or pie).

Could you even bend it? Aged aluminum does not like to be bent. I pretty sure it has to be annealed and then reheat treated. Heat treating something like that would run what? Around 250 or so.



I agree they should just make two different ones. I'd also bet 90% of them would be ordered for a cut front clip.

I don't know if I can even bend any of this. Just trying to think outside the box... (catch that pun?)

After all this discussion, I'm honestly kind of fearing even thinking about selling these. Especially with all the welding, the cost is going to be quite high I bet. I kind of wanted the adjustability for myself though. I have the mustache now, but in the future who knows, I might remove it and not want to have to make a whole new bar.

And yes, I know I'm stubborn and picky.

 

[Calan]

So far none of the fixed designs have even met the two height requirement. If we can meet that, I'll be happy. Any other adjustment is just icing on my cake (or pie).

That last one I did doesn't get you there, if you mount the hook to a spacer?

And honestly, I'm not sure I'm following you guys on where the other location is...I don't even know exactly what the "mustache" is referring to.

Freakin' 2g people

And yes, I know I'm stubborn and picky.

No shit? You hide it very well!

 

[turbosax2]

Spacing the hook further would certainly work, but you don't think that would cause strength issues with a 2" spacer?

Red = spot where tow hook will sit if mustache is removed
Yellow = spot where tow hook will sit in stock 2gb configuration (as well as all other bumpers that haven't been hacked)

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[Calan]

Gotcha.

I think you could use a short .25" spacer or so for the red position to clear the bumper cover, and a longer spacer for the yellow position. If the spacer is pretty beefy (like a 2" square block), the net effect felt by the hook will be the same. You'll probably see a bit more vertical force because the hook is lower, but I don't think the spacer itself would be the issue. It would be the same as if you hung the bar lower and used the same .25" spacer.

After talking with some guys here at work and thinking on it some more, I think you can get away with less force in the calculations. If an angry track steward yanks on your buried car from a roll, there isn't much you can do about it. But if you design for a max of say two to three g's of lateral acceleration and assume that for the most part the car will be rolling, you may be able to lower the expected force closer to just the weight of the car.

I still plan on dragging a wheel-locked car around our parking lot with a strain gauge hooked up to it, but it won't happen until next week.

 

[ed1380]

The spacer will act like a lever and it will twist the horizontal bar. So then you have a pulling and twisting motion against the frame rail mounts.

 

[Calan]

So then you have a pulling and twisting motion against the frame rail mounts.

You have that already due to the height of the hook in relation to the tow vehicle. If the hook is lowered, something else will obviously have to be done to compensate, but we haven't reached that bridge yet. The main concern up until now has been preventing excessive stretch and deformation with a pure lateral load applied.

Eric, would it be that big a deal to notch the mustache, so the hook comes out in the same location? It looks like the notch would be virtually invisible even if you didn't have the hook bolted in, since it would only be the thickness of the hook and it's recessed and up at the top.

 

[97gst_spyder]

Or just slot the bumper with no spacers?

 

[turbosax2]

You have that already, as all of the FEA plots have shown. The trick is coming up with materials and dimensions that minimize it and still meet the design criteria...which is what we are trying to do.

Eric, would it be that big a deal to notch the mustache, so the hook comes out in the same location? It looks like the notch would be virtually invisible even if you didn't have the hook bolted in, since it would only be the thickness of the hook and it's recessed and up at the top.

Keep in mind, ALL 2g bumpers sit at the same height. While notching the mustache on a 2gb may not be a big deal to some, I sure as heck wouldn't want to make a notch in a 2ga bumper just so I didn't have to design the part to sit at the proper height.

 

[Calan]

Keep in mind, ALL 2g bumpers sit at the same height. While notching the mustache on a 2gb may not be a big deal to some, I sure as heck wouldn't want to make a notch in a 2ga bumper just so I didn't have to design the part to sit at the proper height.

Well are you designing this for you or someone else? That's their damn problem!

 

[turbosax2]

You can tell that to Brian! (Tip - he's 2ga)

 

[turbosax2]

Ok Craig, with your last model of the 1.5"x3.0" tube, something cool happens. With it mounted as you have it, the bottom of the tube sits 1.75" below the 1.5" square framerail tube, per my specification. HOWEVER, if you take the entire assembly and flip it upside down (as in bolt it in the car upside down), the bottom of the tube is now 2" above where it was before. Nifty

 

[Calan]

Ummm... ok. What does that get us? Didn't you need the second position to be lower and not higher?

I'm headed out of work and about to have some drive time. Call my cell if you want.

 

[greengoblin]

Do you guys know what the OEM bumper weight is? I didn't see that posted anywhere.

 

[turbosax2]

Ummm... ok. What does that get us? Didn't you need the second position to be lower and not higher?

I'm headed out of work and about to have some drive time. Call my cell if you want.

From the factory, the bottom of the bumper is about 1.75" below the bottom of the 1.5" tubing.

So if you offset the 3" tubing down by 0.25" when welding it to the 1.5" framerail tubing, the bottom of the 3" tubing will be 1.75" below the bottom of the 1.5" framerail tubing, thus putting the tow hook in good position for the stock bumper.

But if you flip the entire assembly around, the bottom of the 3" tubing is now 0.25" above the bottom of the 1.5" framerail tubing (2" above where it was before), thus putting the tow hook in good position for non-mustachioed 2gb bumpers.

Do you guys know what the OEM bumper weight is? I didn't see that posted anywhere.

With brackets I estimated 15 lbs. Each bracket weighed 2 lbs. and the bumper itself weighed 9 lbs., but the bumper I weighed was hacked for a FMIC.

 

[knochgoon24]

Wow. Sounds like that's a great solution. And if you make the hook just bolt on, the rest can all be welded. Awesome.

 

[Calan]

I'm still confused.

Doesn't the 1.75" down offset that I modeled put the hook at the red position in your post #131 pic (without a spacer)? If so, flipping it upside down puts the hook above that, no matter which side of the beam it's bolted to.

If what I modeled puts it at the yellow position, then that means that the beam is below the bumper cover; basically where the mustache is...right?

 

[turbosax2]

What you modeled puts it at the yellow. Flip it upside down and you get the red.

The mustache is part of the bumper cover.

 

[Calan]

What you modeled puts it at the yellow. Flip it upside down and you get the red.

The mustache is part of the bumper cover.

Wait... why were we talking about a thick spacer?

If I modeled the yellow and we were using that for both positions (not flipped over), how was a thick spacer going to get us to the red position?

I was thinking I modeled the red, and the spacer gets us down to the yellow.

 

[turbosax2]

Miscommunication. We cool now?

 

[Calan]

Looks like it, based on what you are describing.

Lets get some exact dimensions together and see what happens. Do you know exactly what hook you want to use?

 

[turbosax2]

I won't be able to get exact dimensions for a couple weeks at least. No, I haven't decided on the tow hook. I'm open for discussion on that.

I can give you rough dimensions if you'd like.

 

[Calan]

Rough is good.

Here is what I need off the top of my head, if this makes sense:

1. length of beam, measured in a straight line from inside edge to inside edge (like a bow string).
2. distance from that line ^ to the inside of the curve
3. length of the frame rail tubes
4. location and diameter of the bolts that hold the rails in the frame.
5. center-to-center dim of frame rails (36.5 right?)

No, I haven't decided on the tow hook. I'm open for discussion on that.

If it's .25" thick steel or less, I can plasma cut one that is any shape you want. And I'd probably only charge you like $100 or something.