I am cutting down a 51 ford frame and welding it back together. Which is better using a MIG welder or a stick welder (using 7018 rods). I was told by a welder that modified big trucks and he said that the 7018 rods were the best way to go. I have read in magazines that a MIG welder was preferable. Any advice? Does it make any difference?

 

IMO a stick welder gives better penetration for frame work, is less fussy about cleanliness and the welds can be ground down.
A MIG is easier to use, welds are extremely hard to grind ( dont confuse hardness with penetration).
The best is TIG and would be the only thing I would use if you are planning suspension work.

 

I shortened a 1975 F100 almost 3 feet to fit under my '50. I used stick.

Make sure the cuts are strait (obviously) and grind the leading edges to a broad "point". This will give the weld a notch to fill and gives a little more surface to penetrate.

Once everything was done and cleaned up, I made plates from 3/8" steel to fit inside the frame rails on either side and bolted them on over the join, about 10" out on either side. I worked with BIG trucks for several years, and this was a requirement when modifying those frames. The safety inspector will apreciate the attention to detail if you do it on your pickup, as well as it being a good idea in case the weld ever does decide to crack.

Hope that helps!
/Kris

 

Copeina,

Did you grind down the welds to flush. It seems that a weld usually doesn't fail but the material on either side will. Is this because of metallurgical changes with the heat or what? Is this why you install the plate? How many and what size bolts did you use? Why couldn't you weld the plate in? Wouldn't that be stronger?

Thanks charles

 

https://www.ford-trucks.com/dcforum/User_files/franklin2/3be9efd76bf42a3a.jpg

 

Thanks for the information. Here is the frame before I cut it.
Attachments:

 

I would weld it up with the low hydrogen 7018 I would add a plate as other have said but I would attach it by putting 1/2 or 5/8 holes maybe 4 for each side of the frame connection and use these to weld the frame to the plate. I would put some 2 in welds with spaces along the top and bottom. Good luck Ed ke6bnl





>Copeina,
>
> Did you grind down the welds to flush. It seems that a
>weld usually doesn't fail but the material on either side
>will. Is this because of metallurgical changes with the heat
>or what? Is this why you install the plate? How many and
>what size bolts did you use? Why couldn't you weld the plate
>in? Wouldn't that be stronger?
>
>Thanks charles

 

We welded the notched seam, then ground it smooth, but not totally flush. I beleive we used 7018 rods as everyone else has mentioned.

The decision to use bolts instead of welds on the plate was simply because we figured if the weld were to fail, the stresses would probably be enough to crack the weld on the plate (leverage of a twisting/bending frame). We used 3x 3/4" bolts on each end of a square plate.

As far as why a weld would ever fail, the only time I've seen it, it appeared that the bead did not "stick" to the old metal. Probably a matter of improperly prepped surface and poor (no) penetration.

Hope that answers some questions.

/Kris

 

When I worked as a certified welder at a power plant construction site, I did lots of fishplating on truck frames. Look at the post above that shows the diagrams. Use the rectangular pattern as shown and weld the plates on top and bottom only, not on the ends. Use 1/2 inch or heavier plate. Use 7018 rod and make sure to use plenty of heat. Most MIG welders do not give enough penetration for this kind of work. Make a root pass and then a lower and upper pass on top of the root pass. Hope this helps. Good luck. Let me know if you need more info.
Stretch

 

kciv,
I don't have anything to add, but out of curiosity, how big a truck did this frame come from? From the cab I'd say F6 to F2, but I'm stuck there. Good luck with your project - tim

 

 

It is a F5. It has a 158" wheel base. I am taking 36" out of it. Then I will make a pickup bed for it.