Boxing plate fish mouths
 

I was reading threads and looking at galleries, it was late at night and I came across some diagrams for fish-mouthing the boxing plates. I can't remember where the pictures were. I believe they were in a members gallery. Does anyone know who has them in their gallery?

I don't recall, but there's 2 basic ways to make a plate........>_<......or....<_>.........

The basic idea is to avoid square corners which can localize stresses and lead to cracking.

Bobby

Was it this one? It is from my gallery.
https://www.ford-trucks.com/user_gal.../54978.520.390
The fishmouth should be 1-1/2 deeper than it is high.

Fish Mouths
 

Bingo. Bob, tell him what he wins!!


Thanks a lot. That was the one I was trying to find.

Boxing plates...
 

I am curious WHY HEIDT'S ($$$!), TCI, & other suppliers never offer

fish-mouthed ends to their plates...only square cut ends...

This is data I will be needing to put to use soon...

IF the plate is used at the end of a rail, should it remaim squared off?

IF the plate is used away from the end of a rail then obviously it SHOULD

be fish-mouthed...am I correct??? :confused:

What about using the cut-outs to weld to the top & bottom of the rail

for additional support...or is this just overkill...?


-Thanx...

A fully boxed frame needs no fishmouths. The idea of the fishmouth is to transition from a very stiff (boxed) section to a more flexible (unboxed) area at the end of the plate. A square-cut box plate concentrates the stress at its corners and causes cracking of the frame rail at the end of the plate. All of this applies where the stress is spread over a continuous length of frame rail. There are no stresses at the end of the rail. That plate can be cut square.

Although continuous welding of the box plates always looks nice, it can be very problematic by distorting the rail with the weld heat. Care must be taken to skip around with welding, allowing welded areas to cool before adding more welds near that area, and continuously checking the frame squareness. Typically, the box plate can be slightly recessed into the rail channel and stitched to the rail by using 1' long welds every 2-3 inches. That is sufficient for strength.

Also, the box plate can have oval holes spaced thru it's length without any appreciable reduction in the stiffening. This is a very nice looking touch to boxing and allows easy routing of electrical wiring and hydrauic lines thru the boxed area. The space between the oval cuouts should be half of the oval's length.

Actually for the TCI front end I just installed, their plates are cut non-square

https://www.ford-trucks.com/user_gal...id=177980&.jpg

Sam

yeow.. the boxing plates I made for my volare ARE square on the back end near the firewall.. now you worry me..

Sam

Boxing woes...
 

THANKS...AGAIN...

I guess I'm just gettin' a little fired-up the closer I get to rippin' this

truck apart down to the frame...

I'm confusued about boxing the whole frame. With a 302 & a C4 I dont

know IF that will be required since the truck was originally built with a V8 &

Fordomatic...MIGHT upgrade to an AOD later IF funds allow...

So...basically...any type of a concave shape will reduce stress???

I just need to be concerned IF I do not box end-to-end...

If you are keeping the stock suspension, no boxing should be done. Henry's design of the frame was to allow it to flex as part of the solid axle suspension. The whole thing works together. The long leaf springs and channel frame flex together, spreading the axle loads out and allowing for rougher roads and deep axle travel.

If you are going to an IFS, you should box the front of the frame back to the cab mounts (firewall). An IFS's springs are supposed to do the flexing and require a more rigid frame to work properly. The IFS's springs and A-arms concentrate the road loads into a small section of the frame. The frame flexing defeats the spring action and results in frame cracking where the IFS is attached. Frame boxing came about after folks tried grafting IFS onto unboxed frames.

Whether the boxed frame will crack really depends on what you put it through. Daily cruising doesn't produce much stress, while Street or drag racing does.

While it is true that any sort of fishmouthing will help distribute stresses, the more depth, the better. The idea is to transition from stiff to flexible.

IMHO, I would deepen the TCI fishmouths on Sam's frame, and I would prefer to see the boxing go back farther toward the cab mounts, but I'm not TCI, so what do I know?

we are going to fully box the frame with the TCI in it..

I am worried about the volare/460 combo where the back of the boxing plate is square.. but.. I don't intend to race at all (well, gotta see what it can do once or twice)..

sam

I wouldn't worry about fishplating the boxing plates on a weld-in front end, torsion would be minimal after the crossmember is installed.

Frame boxing continued...
 

How about the rear? I have the Air Ride Technology triangulated 4-link with the Shockwave 8000.

Should the rear be boxed also or does that suspension need the flex the stock frame offers?

I am considering boxing the entire frame. I don't plan to race it regularly but do want to "see what it can do" from time to time.

I would think the air ride should soften the stiffened chassis as far as ride quality is concerned.

Important to know before I start welding as the rear end is where I am starting. (I figure if I screw it up I can still put the leaf springs back on and tow it somewhere to get fixed.)

BACA -

Basically, I would suggest that boxing the frame is a good idea anywhere that the suspension isn't the stock leaf spring type. If you examine the stock frame and suspension, you can see what the designers had in mind. The leaf springs are long and attach to the frame at their ends, which divides the spring load and applies it to the frame at two points. At the end of each leaf spring support, there is a crossmember. This design allows torsional movement of the frame, but retains the frame's geometry and width. The whole system is the suspension.

A triangulated 4-link will use springs (bags) that put road loads into the frame at one point on each side, like an IFS, at the end of that crossmember. Boxing will stiffen the frame and allow the springs (bags) to do the work without frame flex. Without boxing, the concentrated springs loads will work the frame hard and dampen the spring's function, resulting in frame cracks.

With the suspensions you have in mind, I would box the entire frame.

Thank you. That makes perfect sense explained the way you did.