I agree with safety first and I have a question: What is a cake joint? I've never heard that term before.
Fish plating the side of the frame is almost a waste of effort. The fish plates, if you want to strengthen the frame in bending, which is where it sees the most load, needs to be on the top and the bottom of the frame rails. the most important side is the side of the rail that is in tension from the bending forces. Doing them on the side is easy, looks nice and almost worthless. Rex
fish plates are a joke. if you can not weld two pieces of tubing together you should not be building a frame I can`t believe people do this it looks like a child's first grade project when I see that crap
There should be a special place in hell for professional drag and oval track shops that utilize fish plates on their frame joints, right? Not to mention the sanctioning bodies that require them in certain incidences. Pussies, all of them. Frank
There was a thread on this a while back. very nice way to ad a pice of steel to the joint that isn't cut and welded in the same plane as the original cut/weld. I believe it was stated to be an aerospace approved way to do it. I've plated and not plated. I TIG them all so I know I have penetration. v'd- out the edges. The plates were diamonds and the diamond was offset to have the joint run though the middle. Kind of like a circle, only square. My latest frame I did not plate for appearance reasons. I also sanded the welds off completely smooth. I've seen lots of guys "sweep" frames by making multiple cuts through 3 1/2 sides of the tubing to get this done and mig them and sand them out and not have any issues. I'm gonna have to say it depends on your welding skills and machine. A 110 volt mig ain't gonna be the right machine here. "If you put enough metal on it, it'll hold just fine". That seems to be a motto of a lot of unskilled welders who's work I am called on to fix quite a bit. If you are unsure about your skills either get more skills or hire a pro to help you through that part.
Amen Brother! I already stated that the NHRA requires fish plates on all butt joints. Obviously these guys know more than the NHRA officials...LOL...
3/21/09 Rex, are you sure about that? Think about this. The load on the frame rail of a vehicle places the top of the frame under compression and the bottom of the frame under tension. Think of a fishplate on the sides of a welded frame as acting like the web of a structural I-beam or wide flange beam. It's the vertical web that provides the "strength" and most resistance to the downward bending forces. To prove it, support a 2x4 at each end with the (3 1/2 ") face of the 2 x 4 facing up. Then stand on the middle of it and watch the deflection. Then flip the 2x4 on its (1 1/2") edge, stand on the edge and observe the deflection. In reality, the fishplates welded to the inside and outside of frame rails provide much more resistance to the bending forces created by the downward load than the (top plates) or top of the frame since the fish plates act as a type of web, similar to that of a structural I beam. Welding fishplates inside and outside the top and bottom of the vehicle frame would also provide more resistance to the bending forces induced by side impact. I realize modern car design employs "crumple zones". Also, I am not implying that fishplates or gussets should or should not be used when building a tubular frame although I do see lots of tubular frames with gussets welded in. I am referring to subframing of a typical car.
ugh that earlier picture with the wing whale was eye traumatizing ugly should have fishplated the door to her refrigerator
Right on. The NHRA takes into account that cars are frequently home-built and that they are mig welded and maybe sometimes not so well so they are better off requiring it to be safe.
I have worked with some great dragster chassis builders and that would be extra weight and a waste of time unless they required it but on all these model a frames it says I don't know how to weld two pieces of tubing together
19forty, Without trying to insult you, you don't know what you are talking about. If the web provided the strenght then why can you drill a beam axle and not loose any strength? The web of an I beam or the side plates of a piece of box tubing, when in bending, only carry the shear stress which is approximately 1/2 of the tension or the compression stress that the beam flanges carry. There is a book called "The Theory of Stress and Strain" by a guy named Tiemisenko, read it and then get back to me. Rex
Well I just learned something too, I didn't know about the straight lines being a no-no. When you make one of these plates do you grind the weld on the chassis flush or do you grind a channel for the weld in the back of the fish plate so it lays flush? Or is there another way I'm not thinking of?
duallys ok ...but not tow trucks or big rigs ..those get sleeved with another frame and are bolted together
Actually, for vertical loading, the beam web provides shear strength, the top and bottom flanges resist bending via tension and compression. I'm still mulling over the whole fishplate thing from a theory perspective... .
3/21/09 Rex, Thanks for the reply. I am not insulted. Think of this. The number and size of the holes you can drill in an I-Beam depends on the size of the beam, the load it is supporting and the number and size of the holes you drill. There reaches a point where the strength of the I beam decreases significantly if too many holes are drilled. Think of this way. What would happen if you drilled a series of large holes so close together in the web so that there was almost no web left? The axle would be weakened and bend easily. And the extreme example would be in you drilled so many large holes that there was no web left at all. All you would have is the top and bottom flanges with no supporting web. Hence a very weak axle. As for the "Theory of Stress and Strain" in a beam the site below offers a clear example regarding the relationship between the shear strength and the tension and compression forces in a loaded box beam. Keep in mind that the downard force is measured in pounds and the shear strength is pound per square inch. In the example shown in the site below using a 2 " x 4" hollow beam (similiar to a car frame) the 10,000 pound centered load is easily supported. Click on the other links too at the bottom of the page. http://physics.uwstout.edu/statStr/statics/Beams/bdsne49a.htm It would be interesting to have a mechanical engineer from Super Bell or Magnum axle clarify this.
19forty, I happen to have a degree in mechanical engineering and have designed machine tools, bigger than most peoples houses, and weldments that weighted in the hundreds of tons, I do stress analysis both the old way with pencil and paper and the new way using finite element analysis (FEA). I have done it for 40 years. If you go to the site you recommended you should notice that their calculations for horizontal shear at the beam center line is only 937 PSI which is far under the shear strenght of mild steel which is approx. 30,000 PSI but if you go the the link "4.7B bending stress" you will see that the maximum stress in the top and bottom surfaces of the beam are 112,500 PSI which is approx two time the maximum tensile strength of mild steel, which is approx 60,000 PSI so what did they do? they made the beam THICKER which reduced the bending stress. This is the same thing you would do if you added fish plates to the top and bottom surfaces of the beam. You will notice the term they use "moment of inertia" and its valvue is based upon the width of the beam times the height CUBED. From this you should immediately see in our case that if you add the fish plates to the side the "moment of inertia" of the beam will only increase by the percentage of increase to the width, but if you add the fish plate to the top and bottom surfaces the moment of inertia will increase by the CUBE function of the increase. Thanks for the link. Rex
Rex, thanks for the flashback to statics and other classes I can't remember (metallurgist myself). All I remember is "you can poke holes in the web, but leave the flanges alone... And yes, this post is of no real value
I realize this thread is older but just saw it. If you are adding a fish plate to a welded area on the frame, Do you grind the weld down on the frame or do you cut a small channel of the plate to fit over the weld? May be a silly question but you can't know if you don't ask.
Here ya go. 69 Tans Am front clip top a 51 Merc. You make sure the weld has deep enough penetration so you can grind it smooth so fish plates have a secure fit. Notice thick plate on inside of frame with plug welds plus plates all around. Those welds are critical. If VIN # is stamped on frame don't grind it or cut it off.
Someone posted that "we" box frames for beam strength and that the top and bottom flanges should be augmented instead as it is more efficient in strengthening a beam (against vertical loads). To the contrary, I think "we" typically box our C-section frames to minimize twisting of the frame rails...
This roadster had the 2x4 frame “zeed” in 1981 to lower and lengthen it. The frame was built in 1969. The welds were done by a certified steam fitter welder with a DC stick. I’m sure the roll cage does not hurt it’s strength. It has no plates on either side. It’s been over 200 quite a few times.
Jimmy This thread reminds me of a saying I heard once........ "If you can't weld good, weld lots". Long before I had a number of friends that welded, mostly with TIG machines I thought that "fish plates" were a good idea, I've had some of them weld for me when I wanted something nicer than what I could MIG weld and asked them if fish plates were necessary. Their responses were mostly "if you don't trust my welding why are you bothering me".
Found this article while building a car trailer. https://mechanicalelements.com/mounting-trailer-axle-springs/ Quote from article; "Combine these ideas of stress distribution with the fact that welding weakens the areas immediately around the weld. (I won’t go into the heat distress of welding.) If we weld in areas of high stress, we effectively decrease strength of the beam."
The Jalopy Journal
