Can I drill a 2" hole in a 5" C Frame?

Cut a shirt cardboard (remember this matl?) template for the inside region. Bob suggests a good way of plating, to strengthen it. I still like the idea of flanging a min. size hole, but this section of the frame is stressed.

 

An unreinforced 2" hole in a 5" C-channel reduces it's ability to withstand the forces applied to the frame through the leaf springs. All you're left with is 1-1/2" of frame above and below the centerline of the hole. I wouldn't recommend this approach, not sure why anyone would. Is sleeving and boxing so difficult? I think it's pretty simple, and adds lots of strength and safety.

 

ah ha now there is an interesting approach....hmmm?

 

Just what I was gonna say...

 

There isn't a lot of stress behind the front spring mount and the largest bending moment will be between the front and rear suspensions. Why do you think severely notched frames work just fine.

 

Now we are talkin!

 

Make a "C" shape piece with a hole in it that bolts inside facing the frame C where the new hole will be.

 

This guy knows what he is talking about! You will only lose about 10% of your strength with a 2" hole in a 5" "C" channel. (The flanges are where the strength is) If you are still worried weld a short piece of tubing of the same wall thickness as your frame channel into the hole.
Do not weld in plates, or box a short area!!!!!!!!!!!!!! You will form stress risers at the ends of the plates that can start cracks.
Assuming leaf springs I address the guy that says directly above the axle is the highest stress point, I disagree, it is at the front spring hanger. The spring is carrying half of the weight resting on the rear axle. Where the weight carried by the spring and the weight carried by the rear of the frame converge, (at the front hanger) is the most highly stressed point on the back half of the frame. This is why many medium duty truck frames are tapered from the spring hanger to the rear of the frame.

 

Quote:
<TABLE cellSpacing=0 cellPadding=6 width="100%" border=0><TBODY><TR><TD class=alt2 style="BORDER-TOP: 1px inset; BORDER-RIGHT: 1px inset; BORDER-BOTTOM: 1px inset; BORDER-LEFT: 1px inset">Originally Posted by pitman
Could you drill the hole in a smaller diameter, and flange the hole (increasing the dia to 2") ?
This would lessen the loss of strength in the C rail.
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Just what I was gonna say...


I don't understand what you mean.

Nic

 

I'm "that guy". The leaf spring is attached to the frame fore and aft. Those 2 points carry the weight that you speak of, not just at the front hanger.

If cutting an un-reinforced 2-inch hole in a 5-inch frame at the midpoint between these 2 points is safe, how about a 3-inch hole? How about 4-inches? Are these safe as well? I say it's not, just my opinion though. Where do you draw the line? The vertical "web" of the C channel provides the resistance to the moment forces. If it didn't, the frame would be 1-inch tall, not 5-inches tall. Hotrodding is about making cars faster and better. Not faster and worse. If you're going to cut a hole like this, at least be safe and reinforce it with a sleeve, and box it. Just my $0.02.

Here's a calculator to simulate the point: http://civilengineer.webinfolist.com/mech/bmcalcp.php

Enter difference values for the location of the moment reaction and tell me where it's greatest. Dead center between the spring hangers.

 

For the alarmists posting on this thread........do whatever you want to your vehicle.....overbuilding won't hurt.....but obviously structures are not well understood here.

Look at space frame structures, i.e., skeletal roof joists, bridge girders, aircraft wing spars. The latter is aluminum, full of holes and quite light weight. The web DOES NOT have to be solid to provide beam strength for many applications, including this one.

 

No one is saying it has to be solid. If it's properly engineered, a structure with holes works just fine. That's all I'm saying.

 

x2. And a frame section with a 2" belled hole wont give up ant strength at all. Honestly, if it were mine, I'd just cut the hole and not worry about it.Belling the hole would be overkill, but if it really bothers you, do that. This idea of boxing a 6" section around the hole? Uh, yea...

 

Ole Don>>>Make it fit available space.>>>

I agree. And if it were mine, I'd look real hard for another way of doing it to avoid a drilling a hole in the frame. Even if it means it'll be a slow drinker. Gates & other mfs have a bunch of different universal rubber filler hoses that can be made to fit thru minimal openings.

Jack E/NJ

 

Any problem with putting the filler under the bed, with a chrome access cover ? I'd think it's better than cutting the frame.


4TTRUK

 

Dirty Dave>>>It has been through the bed since 2007 because I couldnt stomach drilling a hole in a brand new steel fender. Now I can.>>>

40FordGuy>>> Any problem with putting the filler under the bed, with a chrome access cover ? I'd think it's better than cutting the frame.>>>

Chrome, yeah! He oughta go for chrome. Or maybe not. I think he's now really ready to cut a hole in his 7 year-old fender. But now he can't stomach cutting a hole in his frame to do it. What a dilemma! 8^)

Jack E/NJ



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Jack, Be sure that I have no problem with drilling the frame. I have all winter to accomplish this as part of a list of small stuff so I thought I would get some other opinions.

Appreciate all comments and suggestions.

ate up now that is funny!

 

Engineered wood I beams are stronger than traditional lumber and the center section is just osb that you can take huge chunks out of. The flanges are what give it strength. The dilema with a frame rail is that you are giving it a weak spot for the twisting action to focus on and thats what causes cracks. Your not off roading or even hauling a heavy load so it shouldnt be a problem . But if you are concerned about it I would probrobly just weld a ring of some sort around the hole. a piece of thick wall pipe would be fine or a piece of round bar bent in a circle. like others have said boxing it will be worse because it stresses the flanges at the ends of the box.

 

Belled hole...

 

A C channel is a basic truss. The flanges carry the load and the web maintains the distance between the flanges. The more distance between the flanges, the stiffer the truss. That is why you avoid modifying the flanges. A 2" hole in the center of a 5" channel won't effect it's ability as a truss.

Boxing in a section of frame will transfer stresses to the end of the boxed area.

 

You should be ok with a 2" hole in a 5" rail if you center the hole in the frame from top to bottom. At that location there is no significant load in the form of either compression or tension. The general rule in most engineered wood framing is to avoid cutting a hole in the webbing of a load bearing joist if the hole is greater than 1/2 of the overall frame height. I'm not certain how that translates to steel structures.


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Wow !!!

 

I have no desire to start a pissing match, but I have studied some engineering and because of that know some things that not everyone has thought about. (I didn't say I was an engineer) In a beam (frame rail) there are what is called extreme fiber(s) and neutral fiber, Google those terms and read about them, it will help you understand why a 2" hole in the side of a truck frame does very little to reduce strength.

 

I'm not looking for a pissing contest either. I'm a registered professional (mechanical) engineer with 30 years of experience in mechanical engineering, and am just answering the OP's question with my opinion about drilling this large hole into a truck frame that's 50+ years old.

If you all want to recommend doing it without some simple reinforcement, go right ahead. I wouldn't.

Over and out.

 

^^BAD example!!!

 

Well I don't know what they teach in professional engineering school in Noo Yawk, but you don't understand beam design, if you are arguing with me about this strength issue!

 

Probably the same stuff I was taught in Illinois, and that is that removing material from near the neutral axis minimizes the loss of strength in bending, but there is no question it reduces the stiffness in bending there. Right over the axle is the worst place to do it, too. Will it fail if he drills it there? I doubt it, but if he reinforces the frame there, he can be sure it's safe.

The C-notch posted earlier, which does not appear to have any reinforcing plates, is real scary. If it is 1/2 the original flange-to-flange distance as it appears, it is 1/4 the stiffness of the original frame there.

 

Oh... Got it. Thanks

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Not if you use a boxing plate with scalloped shaped ends....as opposed to just a rectangular shaped boxing plate.