It sounds like you could use the square notch like you described without any problems, Or you could use the round notch and reinforce the inside with a couple of plates if you really feel that it needs the strength. I am a big fan of over engineering.

I won't C notch anything more than 1/2 the thickness of the frame, and that depends on where the load is. If a frame needs a notch and the crossmember that supports the weight is located a relatively long way from the notch, I use less of a notch.

I have cut plates and welded them inside of the frame if I wanted to reinforce it. If I can't reach inside of the rails I drill holes and plug weld the reinforcing plate to the main rail. (same as what you said you'd do with the 1" box tube )

With what you are doing I don't think that any kind of notch, round or square will hurt. The load is almost right above where your notch will be, (it isn't like the spring mount is 2 feet away and the load is on the opposite side of the frame from the notch.

I don't think the pivot end of the I beam takes alot of abuse, think of it as the end of the crowbar that is in your hand. It takes a relativly small amount of strength to hold it where it needs to be.

A notched beam is ultimately as strong as it's thinnest section. The rounded shape spreads the stresses out along the whole notch, and it has no stress risers that you would get from the corners on a square notch. So in effect it really isn't that much stronger, just tougher, and able to "spring back" better.. But, if the notch is close to the load, it won't matter.

BTW, don't use "pipe" to reinforce anything. Pipe is usually low carbon, crappy steel. Use "tube". I like using hot rolled flatbar, bent over a pipe to shape it. That way I know what kind of steel I'm getting.

I hope all that makes sense to you.

Notch it! :thumbup:


Later,
mikey

 

Rather than notching the frame why not 'Z' the frame just behind where the twin 'I' beam axles mount? This will enable you to lower the main section of the frame as much as you want while not reducing frame strength at all.

 

BTW, don't use "pipe" to reinforce anything. Pipe is usually low carbon, crappy steel. Use "tube". I like using hot rolled flatbar, bent over a pipe to shape it. That way I know what kind of steel I'm getting.

Thanks for this tip and also the rest of your analysis. Exactly the info I was after.

 

Rather than notching the frame why not 'Z' the frame just behind where the twin 'I' beam axles mount? This will enable you to lower the main section of the frame as much as you want while not reducing frame strength at all.

If I understand what you are saying correctly(Z the frame up OVER the I-Beams rather than under-slinging the frame) that's how I did it on the roadster chassis. But I was never totally happy with that "look". A little cumbersome and cluttered to me. That's why I wanted to attempt an under-slung frame on this project...to see if I could make it safe, simple, and a little better looking than the roadster chassis. (And add a bit more to Twin I-Beam knowledge base.)

I know you were one of the folks warning against the perils of notching frames in some of the other threads, so I'm glad you jumped in on this one. My inclination at the moment is to continue ahead with the under-slung concept and reinforce the inside of the frame rails with 1/4" plates as outlined by Mikey. Do you see a major catastrophe ahead with that plan?

 

My inclination at the moment is to continue ahead with the under-slung concept and reinforce the inside of the frame rails with 1/4" plates as outlined by Mikey. Do you see a major catastrophe ahead with that plan?

Mikey gave excellent advise for "C" notching the frame and using the correct material.

If I understand your original post; the only thing mounted forward of where you want the notch to be is the radiator and a bracket to mount the pivot end of the 'I' beam. If that is so, I am concerned about the forces on the bracket for the 'I' beam working against the "C" notched section of the frame. I wouldn't use a square notch. It wouldn't be as strong and looks bad.

 

it isn't like the spring mount is 2 feet away and the load is on the opposite side of the frame from the notch.

I don't think the pivot end of the I beam takes alot of abuse, think of it as the end of the crowbar that is in your hand. It takes a relativly small amount of strength to hold it where it needs to be.

Unless I am thinking wrong; this is exactly what CBOY will have with the twin 'I' beam setup. See picture below of his original twin 'I' beam setup with the previous frame.

The pivot end will also be subjected to side loads as the suspension comes in contact with irregularities (potholes) in the road surface.

Adding plates on the inside of the frame to provide additional support would help in an up and down direction but add little support to any side to side forces.

Just some things to consider. Not saying what is being considered is incorrect.

 

I agree, Frisco. I could be misunderstanding just what Dewey is doing. (say that out loud, haha)

I wish there was a picture or drawing. I would like to see just where the notch needs to be, what is in front of it and what is behind it. . My powers of comprehension get taxed pretty easily on this kind of discussion.

I'll bet this discussion could use a structural engineer, ( I'm strictly shadetree), maybe a PM to willys36 is in order.


Later, mikey

 

I wish there was a picture or drawing. I would like to see just where the notch needs to be, what is in front of it and what is behind it. .

I've got to head out to a meeting tonight but I'll try early tomorrow to draw and post something to describe what I'm attempting to do. My hand sketches might be more confusing than helpful at this point since I'm about the only person that can understand them.

One possibility to counter Frisco's concerns about the side loading is to place a cross member (probably a 1x2 box tube) at the point on the frame where the pivot bracket is welded. I'd have to look the design over in more detail but I don't think it would interfere with anything except possibly the lower radiator hose. I could then even weld a small triangular brace from the cross member up the pivot mount bracket.

 

You guys have pretty well analyzed this question already but here are a couple quick drawings to make sure we are on the same page regarding what I want to do. The first sketch is the total frame side view which shows the position of the axle pivot mounts. The second sketch is a close-up (not to scale BTW) showing the driver's side frame rail, pivot bracket, and proposed notch in the frame. I did not include a passenger side frame rail sketch because that pivot bracket mounts to the frame BEHIND the notch (when viewing from the front of the chassis to the back)...thus the notch should not carry any particularly heavy loads.

Does this help visualize things?

 

And just for the fun of it...here's a sneak preview of the project:

 

Does this help visualize things?

That's what I assumed you had in mind when you mentioned an "underslung" frame.

The notch would apparently be for clearance of the axle when the axle is deflected down (primarily when under acceleration due to weight transfer).

I don't think that much of the suspension travel will be in a downward direction, but rather will be inclined to get compressed (upward direction).

That being the case, do you really need as deep a notch as you suggest?

Have you enough ground clearance up front to install the brackets that the twin 'I' beams mount to up higher? This would give you more clearance between the bottom of the 'I' beams and the frame. Increase the distance of where the 'pivot center' is located.

The problem I see with the notch is that the portion of the frame in front of the notch will be supporting much of the weight of the entire front end. ( engine, radiator, frame, steering, all frontal suspended weight) That's a lot of force and the notch would be a very weak point.

 

Where does the upper spring mount go, and how is it tied into the frame rail?
Can you make an upside down hoop that connects to either side of the notch, and straddles the I beam with the shock mount directly above the I beam, that would relieve any stress on the c notch.

Now that I see the pic, I don't think that the weight itself is an issue to the notch, but how you mount the spring may put some twisting forces on it.

I could see if the upper mount is far enough away that it would act as a big lever,with the c notch as it's fulcrum.

More info please sir.. :thumbup:

Mikey

 

Here is what I am talking about

What do you think?..Dewey? Frisco?

Mikey

 

What do you think?..Dewey? Frisco?

Mikey

Mikey, that would give the additional strength, but would probably not give the clean appearance that Dewey is looking for.

I just did a search on "underslung frame" hoping to find a picture or two of a few I've seen on-line using semi-elliptical springs. I didn't find them but found some interesting reading. Links below. The article on the Healey is very interesting pertaining to "body roll" and frame interference. The other articles are written about the "Underslung" car from the early 1900's. Seems that it could actually tilt up to 55 degrees to the side and would not roll over. Had monster tires though for ground clearance. What's old is new again.

Underslung #1

Underslung #2

Underslung #3

Underslung #4

 

I don't think that much of the suspension travel will be in a downward direction, but rather will be inclined to get compressed (upward direction).That being the case, do you really need as deep a notch as you suggest?

That's a VERY interesting question. Maybe I don't need a notch at all. I had assumed I would need as much travel down as up (potholes etc.). The stock F-150 had the snubber set at 2 1/4" above the axle (for upward travel)...so I was shooting for about 2" for downward travel. If I only need 1" of travel, I think I could do it with no notch at all (see sketch below)

Have you enough ground clearance up front to install the brackets that the twin 'I' beams mount to up higher? This would give you more clearance between the bottom of the 'I' beams and the frame. Increase the distance of where the 'pivot center' is located.

This will probably be more explanation of Twin I-Beam geometry than you ever wanted to hear. I've put together this little sketch which will hopefully help visualize the parameters I have to work with.

Note that the position of the axle pivot hole is set in stone by the spindle center line (imaginary line between the two front spindle centers). This position of the pivot hole keeps the camber correct.

The scrub line is set by the outer edge of the rim, which in my case (15"rims) is 8 1/8" below the spindle center line. This fixes the axle pivot point 6 1/8" above the scrub line.

Then if I subtract out the height of the frame rail (3") and the distance the bottom half of the axle extends below the center of the pivot hole (1 1/4"), the absolute maximum downward axle travel is 1 7/8" before striking the top of the frame rail. HOWEVER, that assumes zero leeway for the scrub line, that is, the bottom of the frame rail would be right at the scrub line height. And in my mind, to be safe, I need to raise the bottom of the frame rail (which will be the absolute lowest point on the car) at least 1/2" to 1" above the scrub line. Assuming I used 7/8" of tolerance, that would give me 1" of downward travel for the axle with NO notch at all.

The big question then is, would 1" of downward travel be sufficient? The other question is, what about a snubber? If I set the tip of the snubber 1/4" about the frame, that now limits downward travel to only 3/4". I suppose I could split the difference (5/8" of scrub line tolerance and 1/4" of snubber) and that would get me back to 1" of axle travel.

 

All of those measurements sound like more than enough road clearance. From the ride height position, I always try to get 1 " of downward travel for every 2" of upward travel.

If you use a conical or wedge shaped snubber, it will let you keep some of your travel, and will dampen the movement as it compresses.

Mikey

 

Where does the upper spring mount go, and how is it tied into the frame rail?

The spring mount position is totally up in the air at this point so I think I can pretty much adjust it to stay out of trouble. In fact, I'm not even sure what type of springs I am going to use. I'd really like to try a quarter eliptical set up hidden on the inside of (and parallel to) the frame rails. Another option is to mount the quarter eliptical's perpendicular to the frame and parallel with each axle. If I went this route I'd have to make certain the mounting point would not place any stress on the notched section of the frame rail (I think this is possible but I have a lot of sketching to do to make certain it will work.)

Can you make an upside down hoop that connects to either side of the notch, and straddles the I beam with the shock mount directly above the I beam, that would relieve any stress on the c notch.

I think before I would do that I'd simply go back to the Z'd frame idea. I have difficulting visioning how the loops could be designed to really look good.

 

c notch

c notch and build a step over box. you could than use the step over box to hold your quarter leaf spring. and make a small modified push rod suspension with it.

 

The spring mount position is totally up in the air at this point so I think I can pretty much adjust it to stay out of trouble. In fact, I'm not even sure what type of springs I am going to use. I'd really like to try a quarter eliptical set up hidden on the inside of (and parallel to) the frame rails. Another option is to mount the quarter eliptical's perpendicular to the frame and parallel with each axle. If I went this route I'd have to make certain the mounting point would not place any stress on the notched section of the frame rail (I think this is possible but I have a lot of sketching to do to make certain it will work.)


I think before I would do that I'd simply go back to the Z'd frame idea. I have difficulting visioning how the loops could be designed to really look good.

Gotcha :thumbup:
If you use a 1/4 eliptical spring, then the load (where the spring is anchored to the frame),is way behind the notch,(not in front of it), and attached to a point closer to the motor mounts. Which puts your bending moment right where it needs to be most
( I think I used that term correctly)

If you put the 1/4 eliptical springs perpendicular to the frame, you will have to engineer it so the frame doesn't twist.
That will be easy.

Also, most of the forces from braking will be loaded back into the frame at the point where the radius rod or 4 bars mount, SO,

The notched frame member will have even less work to do. AND less chance of breaking.

Does any of that sound right?

Mikey

 

All of those measurements sound like more than enough road clearance. From the ride height position, I always try to get 1 " of downward travel for every 2" of upward travel.

What's your take on the scrub line issue? Is 5/8" leeway enough (that is, the lowest point of the chassis/body will be 5/8" above the scrub line)? If I went with 1" downward travel (to snubber and then 1/4" of snubber compression before the axle could strike the frame) and 5/8" tolerance on the scrub line I don't have to notch at all.

 

What's your take on the scrub line issue? Is 5/8" leeway enough (that is, the lowest point of the chassis/body will be 5/8" above the scrub line)? If I went with 1" downward travel (to snubber and then 1/4" of snubber compression before the axle could strike the frame) and 5/8" tolerance on the scrub line I don't have to notch at all.

How often do you plan on driving it with 2 bare rims?

If I see the frame level with the scrub line I'm calling it good.

just my opinion..

Mikey

 

c notch and build a step over box. you could than use the step over box to hold your quarter leaf spring. and make a small modified push rod suspension with it.

The drawback I see to this alternative is that the step over box would have to be fairly tall in order to accommodate the upward travel of the axle. Below you can see how high I had to go with a Z to clear the axles when I built the roadster project.

One of my big aims with this new chassis is to try to clean up and "streamline" the I-Beam suspension to a much great extent than I did with the roadster. I think the "box over" idea is a good one from an engineering standpoint, but I'm having a little trouble with how it might look visually.

 

How often do you plan on driving it with 2 bare rims?

Hopefully never. But I know that technically the scrub line assumes a catastrophic situation where you shred off the tire completely and run on the rim. Then I just figured a person really ought to provide a bit of fudge factor for when you start bouncing off the pavement... (Also, we don't want Centerline to bust us for violating the rat rod code of ethics. Lol).

Barring any other's who might join the thread in the next 24 hours and put the nix on this plan, I'm tending to think I will put this thing together with 1/4" to 1/2" of scrub line tolerance and about 1/4" of snubber sticking up above the frame. That gives me at least 1" of clean downward travel on the axles and keeps the front end pretty clean looking.

 

i know this post is old but i would do this and use it to make you quarter leaf spring holder on top

this is a the beginning of the rear suspension of a lotus europa i am doing for a customer.the final geometery has not been drawn . the pick up point will be to the rear of the c thru the the reinforcement by about 3 inches. the c clears the axle from the trans axle.