2 More frame/weld questions - Strong enough?

[Sam_Fear]

Since I'm not doing the welding, I gotta get this figured out 100% before hand. I don't want to have to deal with it again!

Well, after some more thought and research of some past threads, I'm going to go with 3x3 1/4 square tube for my rails. 3x2 3/16 is no where near the strength of 4x2 3/16, but 3x3 5/16 is close. That 1" less height will make a big difference for my plans.

The next problem I still have is how to deal with the rear Z. I'm very limited space-wise front to back. I have to cut the frame ahead of the lower link mount, but the rear passenger area is only 22" from the rear wheel center. So the less room the Z takes the better. My idea is to use steel plate. Is 1/2 steel plate strong enough? Bad idea? 3/4"?

This rear Z will depend on butt welding the frame to the rear side of the plate steel and butt welding the 3x3 rails to the front side. I can gusset some of it, but not really fishplate much. Will this be OK from a weld strength stand point?

 

[Unkl Ian]

You don't want to weld 1/2" or thicker on to
a frame made from much thinner material.

Bad practice.

 

[Unkl Ian]

Well, after some more thought and research of some past threads, I'm going to go with 3x3 1/4 square tube for my rails. 3x2 3/16 is no where near the strength of 4x2 3/16, but 3x3 5/16 is close.

What size are the stock rails ?

How are you calculating strength ?

 

[Lightning]

Any butt joint welding of stock frame rails to 1/2 - 3/4 plate would be a very weak connection - the frame will have more give than the plate in flexibilty and will eventually develope a crack. A better connection would be a lap weld , more surface area, but this also would have it's lack of strength, it might last longer, but the torsional twist of the stock frame on the plate would eventually rip that welded section out. Best to use basically the same material as the stock frame, in this case the 3x3x1/4 " tubing and gusset with your 1/2 " plate and cap off the short tubes for strength.

 

[Gearhead10]

I'd use the same thickness of metal as the frame rail tube. Where you are z'ing it I would use a web gusset, made from the tubing you are using for the frame, to support the Z. It would be alot stronger than plating it. JMO

 

[Daman]

You don't want to weld 1/2" or thicker on to
a frame made from much thinner material.

Bad practice.

+1

How much are they charging for a welder out there? Maybe you could rent one.

 

[Bonehead]

On your drawing, the front looks pretty good from what I see. The back could be stronger, if it lapped, instead of just butting in. I know you have seen similar rears done on lighter frames and light weight builds. But what you are going after is a little more complicated, using that style of frame.

 

[moronthethrottle]

I can't see your first two pics on this thread, but based upon your earlier thread, I think I see what you're going for. FWIW, here's what I would consider doing if I were you (and I don't like to pretend I am).

Can you get a couple pieces of 3 1/2" x 3 1/2" x 1/4" sq tube? They would sit vertically in the rear frame-you would have to notch out the bottom (only) of the frame to allow it to hang under down to where your 3x3 will meet it. Notch the 3 1/2 x 3 1/2 to allow the 3x3 to slide into it.

Before doing all this, you will want some holes in the rear frame and the vertical 3 1/2" tube for plug welding. Plug weld the frame to the tube and around it as much as possible. Then slide the 3" tube into it, plug weld it and weld all around it. You may want to put a 10 gage cap on the bottom of the 3 1/2" tube for appearance and additional strength. I've made one assumption on this-that this new vertical tube will clear the trailing arm bolt...if not, you may have to cheat it ahead a bit, or notch it again to make clearance.

Try to find a local guy who races modifieds or street stocks. They know these frames better than anyone and will probably give you some great advice.

 

[Sam_Fear]

Thanks for all the input fellas. I finally found what I was looking for I think. And I was, of course making it too difficult. Found this on that hamburger site. Cut it father to slide a rail inside and drop down from there. Should be fairly easy for a good welder to figure the rest.

Notice the plug welds on an inside sleeve.

I also spent some serious time re-measuring and figured out I'll have a few extra inches (4) ahead of the lower link mount. I'm gonna go with this general idea and just drop it down where needed. And I found out the 3x3 the guy had was only 5-1/2' long. Not enough, so I'l plan on getting 3x2x.25.