Frame Welding Do's and Dont's (Thanks Nick)

[ntsqd]

So you prefer concentrated loads to distributed loads? Interesting.
Mind explaining why?

[BDKW1]

Something more like this. When they do a 90* bend at the bottom and run the tube strait into the frame, that's where cracks start to form. It either rips a round hole out of the frame or if your added plate is thick enough it starts cracking the tube. This will prevent all of that.......

Although, had I done that one I would have made the tube land all the way at the bottom of the frame.........

[ntsqd]

The two problems that I see with that are that it results in a vertical stress riser in the web of a mostly bending loaded member and that if it were done the way that you wanted you would have been welding on a bend in sheet or plate. Both are no-no's. I will grant that by boxing in the tube that you do get some load distribution and lower stress on the weld bead due to it's increased length.

Look at it this way, those fancy lugs on older steel bicycle frames are not ornately shaped purely for cosmetics. Sure, some get pretty carried away, but cosmetics is not the root cause of their shape. The cheap frames with square cut lugs always failed at the edge of the lug. Using a non recta-linear shaped load spreading plate of the same approximate thickness as the frame rail does the same type of thing. Same with when reducing a tube size in a run. The ends of both the larger tube and the tube slipped into it are not, when properly done, cut square. Different instances, but all are the same basic issue.

[BDKW1]

Well, having seen it done both ways, the way I posted has held up WAY better than other methods. As for welding on the bend, I see no problem with that. Having the tube attach on a rib versus in the middle of a flat plate greatly reduces flexing of the plate and everything involved.

The lugs on Bicycles hold little value hear as they were done for brazed frames................

[ntsqd]

I'm sorry that you can't see why the lugs on brazed bicycle frames is a good example of cross sectional change induced stress risers and the need to not make them function as 'cookie cutters'. Bolted, brazed, welded, or bonded the change in cross section is still there and is still a stress riser.
If the web is such a bad place to attach a load and welding is preferred to bolting, why is it that OTR truck frames only allow bolting to the frame, and only allow it to be placed on the web and never on the flanges? (The load can sit on the flange, but it can't be attached there.)

There is a difference between what works, this time, and what is good practice. I'm hoping to promote good practice instead of wet thumb in the wind "it worked this time".

[BDKW1]

OTR truck frames are heat treated hence the bolting. I don't have anything against bolting on cages. I actually prefer it with urethane bushings on pre-runners. The lugs on bike frames are a poor example because their purpose was to locate the tubes and surface area for the brazed joint. Strengthening of the joint was a byproduct and the scallops in them were for weight reduction. How many lug frames do you see built anymore?

If this mount were just supporting weight in the middle of a span you would have a valid point. Since it's and integrated load bearing member which is turning a ladder frame into a space frame things are a little different. It will see loads in more directions than strait down and it will take some of the loads.......

[ntsqd]

So a straight edged lug would be just fine then? Is the idea of not creating a 'cookie cutter' in the design of the reinforcing plate/tube/lug/gusset/whatever not registering? That would be the same thing as cutting sleeves in a butt weld square, or in cutting the ends of the tubes in a OD reduction joint square, or in cutting the fish plates of a frame extension but-weld square. The holes in the lugs were for weight, the scalloping is not. It was a case of function dictating form, which was then turned into a cosmetic feature. That the scallops may have saved weight was incidental to the original goal of not creating a stress riser.

No argument on the loads in other planes. Where your loosing me is the justification for not following good practice for loads in the vertical plane. I see no reason that a load spreading plate would fail to spread the load when applied from any direction in it's quadrants (obviously if the load direction has a vector component pulling the plate away from the frame then it's not doing a lot).

[BDKW1]

I see no reason that a load spreading plate would fail to spread the load when applied from any direction in it's quadrants (obviously if the load direction has a vector component pulling the plate away from the frame then it's not doing a lot).

It does spread the load out on the frame. The problem is the tube attachment. Just running the tube into the plate and welding it on will develop cracks on the tube. While the boxing I posted earlier might not be the best thing for the frame rail itself but it's effects are minimal enough not to be a factor. It does however increase the load carrying capacity of the tube to where it will not be a concern.

Another good way I have seen of doing it was on an old Bronco built by UMP. They cut oval holes in the frame that the tube would go through and land on the bottom rail inside the frame. They were then welded to the outside of the frame and to the bottom rail on the inside. They also took all the tubes that landed on the top rail and ran them through to the bottom rail. For as little tube as the truck has on it, I'm surprised it's still together after all these years.

[Rednek Renegade]

Ok, I have read both pages of this discussion and the whole second page is just confusing. I have a 94 F150 that has a crack 1" from the top of the frame rail that goes all the way down the face to the bottom and wraps around the "C". This crack is located smack dab behind where the factory radius arm mount goes. If I were to make a 3"x1" plate and drill and mount said plate to the bottom of the frame rail (bolts toward the floor pan) and thin fishplate the side of the frame rail making my plate/welds not run perfectly vertical and fashioning the plate in a trapezoid like shape I should be fine?

Need Input!!!!!

[SteveG]

Have you drilled the end of the crack so it stops spreading?

[Rednek Renegade]

Have you drilled the end of the crack so it stops spreading?

It had a factory drilled hole and the crack spread past that hole

[philofab]

Have you drilled the end of the crack so it stops spreading?

It had a factory drilled hole and the crack spread past that hole

Drill the ends of the cracks with a 1/4 drill bit. Grind a valley in the crack using the edge of the grinding wheel. Weld with a decent mig machine (220v). Should be good for a while. Grind flat and add a coupon with v style ends if you want for reinforcement of the area.

[Rednek Renegade]

Have you drilled the end of the crack so it stops spreading?

It had a factory drilled hole and the crack spread past that hole

Drill the ends of the cracks with a 1/4 drill bit. Grind a valley in the crack using the edge of the grinding wheel. Weld with a decent mig machine (220v). Should be good for a while. Grind flat and add a coupon with v style ends if you want for reinforcement of the area.

its at the welding shop right now, they are welding the actual crack and then fishplating the face with non vertical beads, I also made a bracket for the bottom of the "C". The crack extended all the way through the bottom of the C so there was no end to drill on the bottom. After its all done I might go back later and Box that section for added strength if that makes since. I will get pictures after I get the truck back to the shop

[Rednek Renegade]

Got the frame fixed. Welded a fishplate to the face of the frame, then welded the seam of the actual crack on the inside of the "C" channel, I then took 2 pieces of 3/16ths steel and made a bolt in "sandwich" style reinforcement at the bottom of the frame to take any of the stress that caused the initial crack

I also got some pics of the lift Using the 99-up superduty Radius arms and springs if anyone is still interested in that swap.

http://fullsizebronco.com/forum/showthr ... ost2438629