Adding "fish plates" to a welded joint?

[astroracer]

Does anyone think I need to fishplate the welded joints on my rear frame? I haven't welded anything yet (tomorrow) but have been thinking about the neccessity of adding the reinforcements.

The plates will prevent the wheel tub from sitting flush to rail. I guess I can hammerform a pocket into the tub to accomodate the plates.

What is the recommendation?
Thanks
Mark

[parsonsj]

I think you mean to weld a chunk of plate over top of the welded joint? Morrison does it when they joint tubes in similar fashion.

Another suggestion: cap the ends of the tubes before welding them together. It will help prevent the failure mode of the tube collapsing and breaking the weld. And it's hidden from sight.

jp

[Rod]

fishplate? cool word, and yes reinforce the weld, always

[astroracer]

I think you mean to weld a chunk of plate over top of the welded joint? Morrison does it when they joint tubes in similar fashion.

Another suggestion: cap the ends of the tubes before welding them together. It will help prevent the failure mode of the tube collapsing and breaking the weld. And it's hidden from sight.

jp

Thanks John, you've got me thinking now. Reinforcing it is... I'll get some pics today.
Mark

[astroracer]

Well, this is what I've come up with for my frame reinforcements. I am going to fab up these small "H" sections to weld inside the joints.


I will grind a 1/4" relief into each tube section to allow the welds to be below surface to eliminate the need to grind them.


I will weld the H inside the tube as best I can before assembling the joint for tacking and final welding.

Final welding will fill in the "slot" so a little bit of clean-up with a grinder will smooth it off...
Will this work okay?
Mark

[parsonsj]

Oh, hell yeah. I think it will work great!

A lot of work... but it will work better than fish-plating, I think.

jp

[astroracer]

Oh, hell yeah. I think it will work great!

A lot of work... but it will work better than fish-plating, I think.

jp

I think so too. Your "cap the end of the tube" suggestion hit home and this was the best method I came up with to get maximum weld footprint. The strap between the tube sides will add a LOT of cross-sectional rigidity. These joints should be bullit proof. I will be fabbing this stuff today...
Mark

[69stang]

astroracer,
I like this idea. I'm going to cut apart some of my joints and redo them using the "H" pieces. I currently just have some small pieces plug welded to the inside of the joints.

[astroracer]

astroracer,
I like this idea. I'm going to cut apart some of my joints and redo them using the "H" pieces. I currently just have some small pieces plug welded to the inside of the joints.

Thank you Roger, I guess that is the ultimate compliment isn't it? I think this will be worth your while and it's not that difficult to fab up. I made all of my pieces in about three hours today.
I am going to take this back to my Bad Ast built thread. If you want to follow along further go here...
https://www.pro-touring.com/forum/sh...t=20086&page=8

[68sixspeed]

Well, this is what I've come up with for my frame reinforcements. I am going to fab up these small "H" sections to weld inside the joints.


I will grind a 1/4" relief into each tube section to allow the welds to be below surface to eliminate the need to grind them.


I will weld the H inside the tube as best I can before assembling the joint for tacking and final welding.

Final welding will fill in the "slot" so a little bit of clean-up with a grinder will smooth it off...
Will this work okay?
Mark

nice, but on a high strength area I'd still do the 'diamonds' over the outside, the idea being to get back away from the tube-to-tube weld joint and get some different material. You'll never break a good weld, but you'll tear the material next to the weld, in the model you made, if you tear the tube next to the weld, the inner piece isn't going to help. Now if you made it wider and drilled a few holes in the side of the tubes you could plug weld it to get some more strength. Just my $.02 though. -Dan

[flangehead99]

Tack your joint together, take your grinder and grind a groove in the seam, weldit up, grind it smooth and diamond plate the sides or cut pieces of plate to fit the ID of your box tube to use as backing , seperate the ends of two pieces to be welded about 1/8 to 3/16 weld up and grind flush. It doesn't get any stronger than a full penetration weld and when ground flush has that finished look.

[L & H Kustoms]

even with your H plates you still need to bevel all the edges to get full penetration. and bevel the edges prior to making any tack welds.

[astroracer]

Thanks for the input guys, everything you are suggesting has been taken into account. The "H" plate will do the same job as a "diamond" on the outside. It eliminates the tube to tube weld and provides an excellant backer for full penetration welds. All of the seams will be beveled before welding and I will be adding top and bottom backers as well.
I want you to know your suggestions and advice have made me think this through and I feel the design is sound and will work well.
Thank You!
Mark S.

[Jim Nilsen]

nice, but on a high strength area I'd still do the 'diamonds' over the outside, the idea being to get back away from the tube-to-tube weld joint and get some different material. You'll never break a good weld, but you'll tear the material next to the weld, in the model you made, if you tear the tube next to the weld, the inner piece isn't going to help. Now if you made it wider and drilled a few holes in the side of the tubes you could plug weld it to get some more strength. Just my $.02 though. -Dan

I have seen plug welds used to put fish plates on the inside of pieces that were prefabbed for assembly as a slip fit that needed to look good on the outside for cosmetic reasons. It is also used to make some types of catwalks for ease of assembly except they use bolts in one half of the joint and bridge the two pieces like he has done in the pic to keep it from crushing.

[redss86]

Just some food for thought, this is what I did to reinforce my tube joints. I is a backing plate that extends 3" in each tube, and has three plug welds on either side of joint. Then I completely welded all the way around the joint, and ground it smooth. Here is a before and after pic.




Sorry for the size if they are too big, I know the top tube in the first pic isn't the same size as the second, but I had to change it. After I got it all together, the 2x4 top didn't leave me enough up travel to be comfortable with. Second pic isn't very close but you can still see what it looks like finished.

Just what I did,
Joe

[Jim Nilsen]

Once you get the wheel well steel,trunk floor and all the other components in that area it should hold the world and more.

Looks good!

[snackbar]

Holy Crap! I just learned a ton! Thanks men.

[Johnny C.]

Great information and cool ideas.

[Mathius]

The plates will prevent the wheel tub from sitting flush to rail. I guess I can hammerform a pocket into the tub to accomodate the plates.

Are you going for a stock... full frame separate body design, or more of a unibody construction where the body is welded to the frame? If that were the case, you could modify the wheel tubs and make them part of the re-enforcement. Just make the re-enforcement area out of the thicker plate and weld the tubs to it.

It sounds like you're wanting to be able to take the body back off though. I tend to agree with this approach myself. Body bushings were invented for a reason, but I still think modifying the wheel tubs is in order to do what you want and I'd want that frame to hold up before I ever worried about my wheel tubs not fitting.

Mathius

[astroracer]

Are you going for a stock... full frame separate body design, or more of a unibody construction where the body is welded to the frame? If that were the case, you could modify the wheel tubs and make them part of the re-enforcement. Just make the re-enforcement area out of the thicker plate and weld the tubs to it.

It sounds like you're wanting to be able to take the body back off though. I tend to agree with this approach myself. Body bushings were invented for a reason, but I still think modifying the wheel tubs is in order to do what you want and I'd want that frame to hold up before I ever worried about my wheel tubs not fitting.

Mathius

The Astro Van platform is unibody with a front bolt-in subframe and welded "hat" rear rails. I am building a full "bolt-in" frame that will tie everything together.
Thanks for looking
Mark