Frame Notch Strength Testing

Discussion in 'Suspension' started by K2, Jul 23, 2012.

  1. K2

    K2 Administrator
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    Thread content copied from http://67-72chevytrucks.com/vboard/showthread.php?t=457037
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    A lot of guys are notching their frames to lower the trucks stance. As a Mechanical Engineer some of the photos these guys have posted on various websites reflect notches that are scary.

    Please note that I don’t have a dog in this hunt; I am not selling anything. Don’t shoot the messenger, I am merely trying to help.

    How you notch your truck frame should depend on its original factory design and how it will ultimately be used by you or any future owner. My personal philosophy has always been any change to the frame should restore the original strength, but that is me. I always assume that just because I may never push the envelope of my truck to its rated capacity doesn’t mean the next owner won’t.

    Things to consider:

    How do you plan to use the truck? If those plans include hauling loads in the truck or pulling a trailer with the truck the frame will see these loads and frame strength will be very important.

    Long bed trucks load the rear frame section more than short bed trucks.
    A look at various designs using Finite Element Analysis
    A Stock Frame (based on a 65 C10) is the baseline for all of these designs. The FEA assumes a factory stock standard coil spring / trailing arm type suspension, circa '65 (I have been told that the suspensions from 63-72 were all very similar) and assumes a bending moment from hauling and towing loads. Worth noting is that if hauling and towing loads are not present the trailing arm suspension style frame has almost no load at the rear axle, only the weight of the frame itself and the truck bed.

    A Stock Frame (based on a 65 C10) is the baseline for all of these designs.

    [​IMG]

    Commercially Available Notches

    Bolt In
    This model replicates the popular bolt in notch, it gains you about 3-1/2" additional clearance. It captures the bottom and the outside of the frame and is ¼” thick. The frame is not boxed. FEA reveals the frame is 80% weaker than stock.

    Bolt In Type Notch

    [​IMG]

    Add a welded in boxing plate to the back of this design and the FEA reveals the frame is still 60% weaker than stock.

    [​IMG]

    Weld In (Dim. data was taken from this website: http://www.suicidedoors.com/notches/...step-notchkit)

    The half circle notch is slightly stronger than stock (about 10%) and gives about 8" more travel.

    Half Circle Notch FEA

    [​IMG]

    The Step Notch is slightly weaker than stock (about 10%) and gives about 8" more travel.
    Step Notch FEA

    [​IMG]

    DIY Weld In Notches

    Pipe Notch. This yields 2" more travel than stock and is as strong as a stock frame. It utilizes a 3/8" reinforcing pad and a 1/4” boxing plate to accomplish this.

    Pipe Notch FEA

    [​IMG]

    Deep Pipe Notch. I saw this being done on one of the websites. It was a boxed installation and it is about 76% weaker than stock!

    Deep Pipe Notch FEA

    [​IMG]

    [​IMG]

    Step Notch made from rectangular tube. Here is one I developed that is made from mitered 3-1/2” x 2-1/2” x ¼” wall tubing. It is about 10% stronger than a stock frame and gains you about 3-1/2" additional clearance.

    Tube Type Step Notch FEA

    [​IMG]

    Tube Type Step Notch as viewed from inside

    [​IMG]

    Summary

    If you want the frame to be as strong as stock and you want a frame notch deeper than the 2" there is simply no substitute for adding some sort of truss structure, or replacing the frame section with another structural member that has the same or greater section height as the original frame.

    Whenever someone starts talking about a deep frame notch (> 2” nom.) and state that just by adding thicker plates to the sides of the frame rails this makes the frame stronger than it was in its original condition, yet they are and not adding vertical height, they do not understand beam analysis.

    Some final thoughts

    The implementation of any design affects its strength. The final fabrication can only be as good as the welder – fabricator performing the work.

    I have yet to see a bolt in notch that will restore the strength of the frame to the factory condition.

    I have not seen any manufacturers “certifying”, via a signed document, the strength of their notch kits.

    The information posted here is for reference only. Results will vary based on actual dimensions, materials used and the quality of the implementation and fabrication.
     
  2. Whitebeauty

    Whitebeauty New Member

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    Excellent work.....i definetly agree with your thought process. Make better or the same but dont degrade it...
     
  3. revobreaker

    revobreaker Moderator
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    So how are you gonna notch it klint?
     
  4. babyboi2284

    babyboi2284 BaggedXR2284

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    So according to this (totally different vehicle and frame I know)...adding the DJM notch even welded in will still be alot weaker than the frame un-notched. Even though everyone says the DJM kit is a well made kit the stock frame will eventually suffer with the notch bolted and welded in.
     
  5. Gadget

    Gadget Well-Known Member

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    There you go getting all technical.

    I could of told you right from the start that is a bad deal without all the fancy colors....

    G
     
  6. babyboi2284

    babyboi2284 BaggedXR2284

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    I was thinking that I have 2 1/4" blocks and still have the stock bump stop brackets on. If I go 3/3 then I can just cut off the stock brackets and that will make up for the extra 3/4" of the new blocks so I will still have the same ride quality. I still plan to go DJM but maybe with a different notch since I still plan to eventually bag my truck
     
  7. K2

    K2 Administrator
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    This doesn't necessarily change my decision to notch the truck and drop it. Just something that I came across in my research and, as stated, while not the same truck or frame type - I thought it was good information worth sharing.

    The reality is that I don't plan on getting rid of my truck for a good while (assuming engine #2 lasts at least as long as engine #1). So I don't mind compromising some structural integrity for the sake of aesthetics. I also rarely use my truck as a truck now that we no longer have the jet skis to tow so this would again be more for looks than anything. But hopefully paired with a set of XII stock height coils and XII sways, the drop would also be semi-functional performance-wise in the twisties.
     
  8. Gadget

    Gadget Well-Known Member

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    I already gave you my opinion on what kit to go with and what kit to not go with....

    G
     
  9. babyboi2284

    babyboi2284 BaggedXR2284

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    I don't use my truck to tow or haul but it is my daily driver so I want to have a reliable setup.
     
  10. x20Runner05

    x20Runner05 New Member

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    Great info.....I nominate this for a STICKY
     
  11. revobreaker

    revobreaker Moderator
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    I also wonder... assuming you use a bolt in notch, at what point (either towing or loading the bed) will you exceed the "20%" strength left in the frame?

    I did a weld in step notch on my bagged sonoma. Im pretty sure that it is now stronger then the stock frame because we also boxed the inside in...but im not an engineer so:dontknow:
     
  12. blackx-runner

    blackx-runner "White Flash"

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    If all else fails weld and brace the shit out of it. :biggrin:
     
  13. Torspd

    Torspd Moderator
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    Very well presented. In that last picture, of the rear end of the truck, I completely see that back most portion of the frame folding up. Or down for the matter.
     
  14. K2

    K2 Administrator
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    One thing that I don't understand... the data says that the deep pipe notch is 76% weaker than stock while the bolt-in is 80% weaker than stock. Logically that makes no sense to me. Looking at the colors on the output, the entire frame around the pipe notch is yellow. Also the pipe notch easily cuts out 90%+ of the frame while the bolt-in cuts out maybe 70-80%. I mean I know that pipes are structurally sound due to their design but is that still the case when you cut the bottom out of one and have it braced on nothing?
     
  15. babyboi2284

    babyboi2284 BaggedXR2284

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    Doesn't just welding on the frame make it weaker?
     
  16. K2

    K2 Administrator
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    In my educating myself on this process I have read that using a plasma cutter or welding on the frame could weaken it due to the large amount of heat imposed on the steel.

    Keep in mind too - that in all my time on this website I've never heard of anyone having a problem with a DJM c-notch.
     
  17. babyboi2284

    babyboi2284 BaggedXR2284

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    I have no doubt in the notch....but I do have doubt in the frame lol
     
  18. Reverend_d

    Reverend_d New Member

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    this all great info for sure. but as gadget said weaker it will be that is just a given. it is not going to fall off the back of the truck just get it done right by the right person and yes you can do it yourself if you know what you are doing.
     
  19. Coupe

    Coupe Active Member

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    While, I believe the output of the FEA graphs (the results look right), these are still in localized area. To get the big picture for an X-Runner, you would need to do both sides with the x-brace.

    Another thing that effects the output, is the grade of the steel. These are probaly done with a mild steel. There are higher grades of steel available.
     
  20. sdxrunner619

    sdxrunner619 Active Member

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    I see why frame notching is illegal in formula d......no djm for me. :/
     

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