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  1. #21
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    Cool

    Quote Originally Posted by mongobob View Post
    The difference is the single frame is able to be cleaned and therefore lasts longer. Double frames hold the corrosives between them. By the time a problem is visible, it's too late.
    I have seen this too - on more than just firetrucks as bob says. I would also say that a box frame if designed and formed correctly could easily account for fasteners, cross members, and a ready ability to shorten the frame where required (the same as is currently done on c-channel frames in the FS). I also see no reason a boxed frame cannot be properly washed out to prevent corrosion - I have been doing it for years on more than one vehicle.

    ps. Iowa, on a previous posting (another subject) you were as correct in terminolgy as I was when you said "stiffness". It took a while to come to me but "Young's Modulus" is what you were getting at, my appologies, TL


  2. #22
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    Quote Originally Posted by SSIaerialmanTIM View Post
    ps. Iowa, on a previous posting (another subject) you were as correct in terminolgy as I was when you said "stiffness". It took a while to come to me but "Young's Modulus" is what you were getting at, my appologies, TL
    I did notice on the spec I have with the single frame that it talks about MODULUS and RBM I believe are the letters. What are these numbers representing and how do I apply that to our situation? Also, is it possible to have a frame that is to heavy? Once again, thank you all for your insight. It is very helpful.

  3. #23
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    Default Getting technical

    Quote Originally Posted by imafireman View Post
    I did notice on the spec I have with the single frame that it talks about MODULUS and RBM I believe are the letters. What are these numbers representing and how do I apply that to our situation? Also, is it possible to have a frame that is to heavy? Once again, thank you all for your insight. It is very helpful.
    When dealing with truck frames, modulus is usually referred to as SM or Section Modulus.

    Truck frame strength is the structure's ability to resist yielding, buckling, fracture, and fatigue.

    The section modulus (SM) is an engineering term that indicates the strength of a frame by the shape of its section. The SM in truck frames relates to vertical loads on the frame rail, and is expressed in in3. The SM of a typical frame section is calculated by this formula:

    SM=(BxH3)-(bxh3) 6H

    SM= section modulus B=outside flange length H=outside web length b=inside flange length h=inside web length

    RBM (resisting bending moment) is the product of the material yield strength and the section modulus of one sidemember. RBM is used as a means of comparing the relative strength of sidemembers with different geometry and fabricated from different materials. RBM equals SM multiplied by yield strength of material.

    These numbers mean very little by themselves. They become VERY helpful when comparing competitors if they are willing to supply them. It gives you an opportunity to compare the frames "apples to apples" because the numbers are based on the assembled frame, not just a side rail or a crossmember.

    My experience has been that any manufacturer willing to discuss these numbers with you isn't afraid of the long term durability of their product IF they understand the numbers themselves.

    Just to clarify, I'm not an expert. I have however found these numbers to be very helpful in determining a frames ability to hold up to impacts caused by underbody and wing plow mountings. Every frame gives a little. The important thing is, will it return back to it's original shape!

  4. #24
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    Default

    Quote Originally Posted by imafireman View Post
    I did notice on the spec I have with the single frame that it talks about MODULUS and RBM I believe are the letters. What are these numbers representing and how do I apply that to our situation? Also, is it possible to have a frame that is to heavy? Once again, thank you all for your insight. It is very helpful.
    What are the other mfg (custom cab) building for chassis that would meet your spec? Single frame (similar dimensions) or reinf frame (std or as option)? If similar trucks in similar price range are all single frame (with warrenty) that may reassure you.

  5. #25
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    Tim,I invite you up to my section of the woods where I can show you any number of 5-10 yr old box frames that are JUNK.Granted these are small imported pickups but you don't see this damage on C frames.Could they be washed out? Perhaps but you still have that residue sitting in the bottom of the section.I'm prejudiced,I'm NO fan of a box frame and that goes way back to reparing them in the 60's and 70's.I DAMN sure don't want one on my truck for these and other reasons including assembly.If you like 'em,you're welcome to my share.Double/triple frames are prone to the same damage but you can repair those even though it's a tedious job. T.C.

  6. #26
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    Default

    Quote Originally Posted by neiowa View Post
    What are the other mfg (custom cab) building for chassis that would meet your spec? Single frame (similar dimensions) or reinf frame (std or as option)? If similar trucks in similar price range are all single frame (with warrenty) that may reassure you.
    There is only one other manufacturer that shows the numbers on the custom. The numbers for this frame are bout 25% higher being reinforced, but the price is $20,000 out of our price range, so it is not an option. We will have a hard enough time coming up with the 12,500 that is required in the grant. I guess we will have to buy what we can afford and hopefully it will all work out. Thank you all for your help.

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