Pipe Notch

[SCOTI]

Originally Posted by kieth

Hey Lake Roadster, read this thread and your analysis with great interest, the information is invaluable and I would just like to ask a question about the beam analysis. You state that most of the strength is being added by adding material above the frame, I would say it is also being added by the double wall material in the tubing ?

1. If one built a 2.5" notch kit that had upper and lower frame flanges inside and outside of the frame lets say 5/16 110,000 psi yield strength material bolted in with grade 8 bolts couldn,t we pick up enough strength to equal the old frame. (I do not ask this to be critical just a different way of looking at the problem)

2. What is the section modulus of the stock 60-66 frame and the yield strength of the material.

thanks in advance. Kieth

I'll let Lakeroadster answer your question specifically, but he & I discussed a similar scenario. I proposed wrapping the inside, outside, plus the top & bottom lip of the frame rail w/.375" material. The rail itself was 5" tall w/a 3" .250" thick pipe c-notch. It was close....

[lakeroadster]

Originally Posted by kieth

Hey Lake Roadster, read this thread and your analysis with great interest, the information is invaluable and I would just like to ask a question about the beam analysis. You state that most of the strength is being added by adding material above the frame, I would say it is also being added by the double wall material in the tubing? Kieth

What I wrote....

Originally Posted by Lakeroadster

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.

Section height drives strength.

If you look at the moment of inertia calc. below you will see the height of the member is to the 3rd power. It is the overwhelming driving factor for strength. Small changes in height therefore make drastic strength changes.

Properties of various sections.

The strength of a c-channel isn't doubled by adding a boxing plate. Sure it helps, but not nearly as much as you might think:

For our stock c-channel style frames the Moment of Inertia above the axle based on b = 3", d = 4.50", h = 4.18", t = 0.16" is:

Stock C-Channel type frame section Moment of Inertia = 5.49 in^4

vs.

Rectangular (Boxed) frame section Moment of Inertia = 6.47in^4

Boxing the frame helps, but only about 15%

Here is the Diagram and the Formula for calculating Moment of Inertia for a Rectangular tube (Note that "h" in this sketch is different than "h" in the above sketch: b = 3", d = 4.50", h = 2.68", k = 4.18")

Bolted Notches

Bolted notches do not transfer loads nearly as well as welded in notches. I personally would not use a bolted in notch unless it was welded in after installation, but I am conservative and I have a welder. I always prefer welding instead of bolting when it is an option. Having designed and worked at fabrication shops since the early 1980's and witnessing first hand failed bolted joints I just don't see the need for risking it on a part that will never really need to be unbolted.

With regards to other "design specific" questions, due to liability issues, I don't want to get into any member specific designs other than the ones I have already looked at.

John

[SCOTI]

Originally Posted by lakeroadster

Actually I said:

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

Section height drives strength.

To be more specific to everyone else about what I wrote.... I was amazed that when cutting >1/2 of the frame height for the c-notch, even using the .375" thick material doubled on top, bottom, inside & outside of the frame, the strength still wasn't equal to just the original c-channel.

This is why I have opted to skip the bolt-in c-notch on my Dually & build a short step notch using the same amount of material above the frame that is being removed where the c-notch is going.

[Mike Bradbury]

Originally Posted by lakeroadster

I reviewed this thread and was concerned that some of the information that was posted would be taken out of context and misused. To prevent this from happening I deleted my posts and reworked the data into the following:

Frame Notch Based On Strength

Lakeroadster, How does the suspension placement effect the strength? Meaning that if the notch is aft of the spring perches, then the notch is cantilevered and the stress is applied downward on the notch. But if the notches are before the perches the the notch is stressed in a completely different geometry.
To clarify I used coil overs that are behind the rear axle, so the notch is not absorbing the same kind of stresses, true? love to here your thoughts on this. My notch is boxed but no re-enforcing plate on the outside.





Mike

[61_FL_Apache]

Is the notch above really gonna gain you much drop? I would like to do this too but go at least half way into the frame so its not too deep of a notch.

[lakeroadster]

Originally Posted by Mike Bradbury

Lakeroadster, How does the suspension placement effect the strength? Mike

Mike,

First things first.... neat set-up. I have admired your work. How does the truck ride, smooth or harsh? I have coil overs on my Model A Tudor fenderless hot rod.. it's pretty darn harsh.

For your front trailing arm attachments are you using something with rotational movement like a heim joint or rubber bushing? If not are you at all worried about it binding up due to axle movement , or are you thinking the tube will allow torsional twisting?

Ok, back to topic.

You are right, location of the spring (lower fulcrum) changes the analysis in your instance.

Your set-up will be different because the fulcrum is moved back behind the rear axle. Your frame in the notch area will see all suspension related stresses, a standard trailing arm frame doesn't see suspension "spring" related stresses in the frame notch area, 'cause the spring is ahead of the rear axle.

The FEA I used for the previous posts 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. If hauling and towing loads are not present the trailing arm suspension frame has almost no load at the rear axle.

[Mike Bradbury]

When I started it was a C20 with the big unsprung weight a Dana 60, and very stiff leaf springs. So it is hard to say how much better the ride is from a stock C10. I think the ride is very smooth and drivable. The other day I needed to get out in front of other cars while we were at a stoplight because I had a right turn coming up soon after the light. I punched it at green and laid a nice consistent peel with no chatter or hop until I got full traction. I need to put a sway bar in the back but still in the design phase.

O.K. back to the question, I used the Sphon spherical joint and there is very little bind during articulation. The suspension only moves 3 up and 3 down so with that range it has no problem with binding.


I think I will weld up a fish plate to the outside of the frame just to give it a little extra strength. As you can see the notch is pretty mild and I still have a six in drop in the back. Not sure if the C20's have more of an arch in the frame over the axle or not. I might have been able to get away with not notching the frame but then I might have contacted my axle on a severe bump.
Mike

[lakeroadster]

Boy those Sphon spherical joints are the cats meow, that's great, and grease fittings too! The extended sleeves should allow for more articulation then you will ever need.

Thanks for posting up the photo.

[SCOTI]

Originally Posted by lakeroadster

Boy those Sphon spherical joints are the cats meow, that's great, and grease fittings too! The extended sleeves should allow for more articulation then you will ever need.

Thanks for posting up the photo.

That's what I'm using as well. They're the only way to go if using a solid T/A vs the original I-beam style IMO.

[N2TRUX]

The information provided by lakeroadster is now immortalized in our FAQ. Thanks for your awesome write up John.

To view this FAQ go here- Frame Notch Based On Strength

[1beatnik]

Truck is sooo nice

[lakeroadster]

Originally Posted by N2TRUX

The information provided by lakeroadster is now immortalized in our FAQ. Thanks for your awesome write up John.

Thanks N2TRUX!

We all do what we can, and collectively we can do some pretty awesome schtuff!

John

[N2TRUX]

Let me know when you are ready to do another one. The FAQ forum is undergoing a complete frame off restoration. We are looking for some new FAQ's to compliment the old ones already there.

[SierraMtns]

Has anyone done a notch like the one Lakerodester did?

[Lowkash]

I am in the process of attempting that style of notch. I will post some pictures when I hopefully accomplish the task.

It's being done to a 68 so the frame rails are quite different in the area that this notch is done at. It's not a nice straight shot as shown in the FEA but I beleive is doable. I am also using 4" x 2" x 0.25" instead of the 3.5" x 2.5" x 0.25" shown. It should give me about a 4" drop when I am done.

Regards,
Adam

[made2drag]

lakeroadster, I liked the link with c-notch strengths compared to stock. It would seem to me that once the bed is mounted and bolted up, the frame would have more support?.... Are your % figures with the bed on or off? thanks

[chevy_mike]

Originally Posted by made2drag

lakeroadster, I liked the link with c-notch strengths compared to stock. It would seem to me that once the bed is mounted and bolted up, the frame would have more support?.... Are your % figures with the bed on or off? thanks

lakeroadster's account was suspended a looong time ago so do not expect any replies from him....