welding on frame (grain structure?)

[lofly'a]

this question is for "jiggs" or anybody who'd care to enlighten me. in a previous post about making a lwb into a swb jiggs states that you should never weld vertically on the frame cuz it will mess up the grain structure. i think i understand the part about grain structure from my schooling in metallurgy, but what do you mean about welding vertically specifically? i have no plans to weld on mine, i just want to understand the do's and don'ts for future reference.

[Huck]

No expert here but---me thinks that this goes along with the idea that any weld can weaken the metal around it a bit and that a verticle weld would probably have the most pressure on it to pull apart. Kind of goes along with what you see in woodworking. Wood trim is cut and pieced on a diaginal plane / verses vertical one I . It is especially critical in areas of stress like in the middle of the frame when you cut down a long bed to a short bed. Ever hear about these scrap title cars being put together - retitled - only to have some poor dude find it break in half in an accident! I believe the best weld on a frame would be a Z weld with some backing. Good luck----Huck

[Erl]

First, horizonal welds are always stronger than vertical. A horizonal weld would be on a flat surface like a table top, and a vertical weld would be like a wall. Welding on a horizontal surface allows greater penetration, because you do not have the molten metal puddle trying to run-off. As far as grain structure goes this is not a problem here. Steel is a homogeneous material, which means that strength properies are the same in all directions, unlike wood. The direction of the grain structure is most important in fatigue loading (i.e., engine connecting rod). The grain of the metal will be aligned along the length of the frame. this is because the original stock was rolled along the length. Then formed into a C shape. Since the frame material is a mild steel the grain structure will not change when you weld it, but it will realign. This applies only if you allow the weld and surrouding metal to air cool. If you quench the metal then you will change the grain structure of the effected area. Do not quench the frame, because it will become very brittle.

[CraigS]

Later model trucks than ours can have tempered frames and should not be welded without proper heat treating. You should be fine welding on yours.

[lofly'a]

i understand now, thanks a lot guys

[palallin]

BTT

[jiggs]

Sorry I haven't posted sooner. As said before the grain structure runs the length of the frame. Welding vertical will alter the grain structure to also run vertically. How strong would a 2x4 be if the structure ran across the board instead of with the board. Obviously you can't weld horizontally or with the frame or it will never get welded up, so the best of both worlds is to cut and weld it at a 45 degree angle. Another bad thing of welding vertically is "notching" This is at the beginning and end of a weld. it is where cracks start. If the weld is vertical there is more stress on the top and bottom of the weld. If welded diagnal it will lessen the stress. Also the beginning and end of the weld will be at different points on the frame. I don't know if this makes sense or not.

[Hotrodhenryj]

First a horizontal weld is not a flat weld; it is a weld from left to right or right to left on a surface in the upright position. Flat welds are not stronger than vertical welds. Any weld(s) regardless of position are only as strong as the base metal. Welding does not weaken the parts being welded unless it is done wrong, (to hot or cold). Welding on a flat surface does not give it more strength, only allows for more metal to be deposited. Vertical welds allow all impurities to flow out and down out of the weld fillet. Flat welding has a tendency to trap slag and have porosity because of welding speed (going to slow). If your metal is running out your vertical welds your also going to slow and not doing it correctly. Any weld that is made in any position done correctly is as strong as any other is, and 100% as strong as the material being welded. To do a frame graft correctly (because of its thickness) you would have to do an open root pass with a backing plate. This would allow full penetration and knitting of both pieces. Then do a full weld completely around the backing plate. Vertical or on 45 the strength would be the same. This information can be found in any AWS code book.

[lofly'a]

i'm glad i asked this question, opened up some very good discussion and i learn a little more with each post. thanks again guys. anyone else got anything to add???

[chewed 71'er]

Same here, learn something every time I read this board. Have some deep frame rust above rear spring supports, didn't have a clue on how to fix it. At least now I know a repair is possible.