Metal front bumper/tow hook mount

[turbosax2]

You ask hard questions. Hope these are close...

1. 45"
2. 4"
3. 10" on long edge
4. 10mm bolts / 2" and 6" away from edge that goes in frame rail
5. 38.25"

 

[Calan]

4. 4" and 6" from the back surface of the rail tubes (closest to rear of car)? Vertical, centered in the tubes?
5. I knew that.

 

[turbosax2]

Correct.

 

[Calan]

Cool. I'm adding the weld material now, and will get the tubes in place for the bolts and start playing with some more numbers.

How thick of a spacer do you need to clear the lower edge of the bumper cover?

Do you want me to just wing something on a hook and spacer that I could plasma cut for you? Pay the shipping to get it to you and we'll call it good.

 

[turbosax2]

Try 1/2" spacer. I can send you the model of the tow hook I made. What kind of file do you need?

 

[Calan]

1. 45"
2. 4"
3. 10" on long edge
4. 10mm bolts / 2" and 6" away from edge that goes in frame rail
5. 38.25"

With an inside beam length of 45 inches and 38.25" centers on the frame tubes, the beam overhangs on each end by 2.625". Does that sound about right?

 

[turbosax2]

Keep the 38.25", reduce the inside beam length to reduce the overhang. Unless the overhang can provide any benefit, I'd just as soon have less material for less weight! The 45" was a pure guess.

 

[Calan]

Ok. I'll leave just enough for a good weld.

 

[greengoblin]

When you flip it over will it still fit under the bumper cover? I.E. not contact the upper inside edge?

If it fit that would be a great solution.

 

[Calan]

When you flip it over will it still fit under the bumper cover? I.E. not contact the upper inside edge?

If it fit that would be a great solution.

Looks like it will according to Eric's bumper measurements.

 

[turbosax2]

When you flip it over will it still fit under the bumper cover? I.E. not contact the upper inside edge?

If it fit that would be a great solution.

In the lower (stock position), the bottom of the bumper is 1.75" below the 1.5" tube. In the upper position, it is reversed (1.75" above the 1.5" tube).

1.75 + 1.75 + 1.5 = 5

We measured the stock bumper at 5" height. So ya, I'm hoping it will fit.

 

[turbosax2]

Craig, we discussed adding a fuse to system, or rather designing a certain part of the assembly to break first thus preventing undue damage to the car. I discussed this with the engineer here at work and he suggested something along the lines of a "shear bolt". I'll have to search around a bit to see if something along those lines is available, but I found this from a quick search indicating it's possible:
EDGE

These would be used at the two hook mounting points to prevent damaging the crash bar, and maybe even higher rated shear bolts at the four frame rail mounting points as an additional fail-safe to prevent damaging the frame rails in the car.

I emailed you pictures of the tow hooks for specs, by the way.



We'll also need to figure out a way to attach the frame rail tubes to the car. If we go with steel this will be easy; weld in two threaded tubes that span the whole 1.5" tube so the piece can be bolted in either way (when the assembly is flipped upside down). However, if we use aluminum I wouldn't feel comfortable doing the same thing with aluminum (steel bolt in aluminum nut = ). But we could do that and use a TimeSert to reinforce the threads. I'm open to other ideas!

 

[greengoblin]

These guys make nice thread inserts.

Avdel Global :: Threaded Inserts

 

[Calan]

Eric... would this basic design work?

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If so, I "think" you could rate it at somewhere around 4500 lbs of towing capacity, and a weight of around 12 lbs made from aluminum.

That is a 1 x 1 x .12 reinforcement tube running along the back, and it does a lot to help distribute the load and lower the stresses and bending in the main beam.

 

[snowborder714]

The bar behind the curved one is right where my FMIC is.

 

[turbosax2]

^ Yup. Check out the pictures here, Craig.

Bumper pictures by turbosax2 - Photobucket


There might be room for something like that if it sat right against the FMIC. But I'm guessing that's pushing it. If we make the piece in front straight rather than curved, does that improve the strength at all?

 

[Calan]

There might be room for something like that if it sat right against the FMIC.

Yeah... that was kind of the idea. I figured the curve was to match the bumper cover, and the inside edge where the curve starts would be close to the corner of the IC; although I'm not exactly sure where everything falls once assembled.

Let me rephrase the question: Can you make something like this work?

 

[turbosax2]

Well, we could remove the FMIC and make it work...

But, without being at the car I can't say for sure whether or not that we could make that work. My money is on no.

 

[Calan]

Well, we could remove the FMIC and make it work.

There ya go! You would cut down on more useless weight also.

My money is on no.

Too bad. That is a pretty strong design based on what I've seen so far.

I'll keep thinking on it.

EDIT:

What if it was a piece of angle instead of square tube? In the pic above, the angle would replace the top and right side of the square tube.

Would the top leg of the angle sit above the FMIC? Where is the top of the FMIC in relation to the bottom of the frame rail tubes?

 

[turbosax2]

I don't have measurements, but I'd guess the top of the FMIC is about 0.5" above the top of the frame rail tube. Keep in mind what happens to that piece when the assembly is flipped upside down.

 

[Calan]

What is your IC core thickness? And how far is it from it to the inside of the bumper cover?

 

[turbosax2]

Did you see my question in post 166?

3.5" thick. How close it is to the bumper cover depends on which point of the curve you're asking about. At the edges of the FMIC, it's 1.5" (hence the 1.5" tubing max).

 

[Calan]

How close it is to the bumper cover depends on which point of the curve you're asking about.

At the upper middle of the IC, center of the 5" high bumper.

If we make the piece in front straight rather than curved, does that improve the strength at all?

Making it straight would help with a lot of things, including fabrication. The biggest issue with doing that is that you now have a pretty significant upward force to deal with, due to the longer hook.

It's weird that you asked that; my reason for the above question is because I was considering running the 1.5" beam flat against the IC, and then building out and reinforcing a front area for the hook to mount to... since the rear brace won't fit.

 

[turbosax2]

I don't have the distance at the middle. Just guessing by the pictures, maybe 3.5" from the FMIC to the bumper cover.

Flat is not preferable for many reasons in my opinion. But if it's significantly stronger, it's worth considering.

 

[Calan]

That doesn't leave much wiggle room.

What are your reasons? It would be easy to weld some simple support brackets or pads to the flat bar to support the bumper cover, if that was one of them.