When is it OK to remove clamps.
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  1. #1

    When is it OK to remove clamps.

    I'm a hobby welder and I've mostly welded inconsequential stuff.
    Now I'm MIG welding a mild steel frame and adding some fish plates so some of the runs can be long.
    I'm using various techniques to minimize distortion including multiple clamps to keep things in line.

    Just wondering how soon after I finish a welding run is it safe to remove the clamps?

    Thanks.

  2. #2
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    Re: When is it OK to remove clamps.

    I’ am a hobby welder too!
    Weld sequence is the trick. On long welds, back step the welds to help control the amount of heat you put into the steel.
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  3. #3
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    Re: When is it OK to remove clamps.

    I remove my clamps when the heat build up in the joint dissipates beyond the heat affected zone. That could be anywhere from a minute for alum, to an hour for steel. Depends on your weld-ment and when pee break is.
    Weld like a "WELDOR", not a wel-"DERR"
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  4. #4

    Re: When is it OK to remove clamps.

    This is 3/16 to 1/8" mild steel. Without any external help, the weld seems to be cool enough to touch after about 15 minutes or so. Is it safe to assume if I can touch it I can remove the clamps?

    I never thought of peeing on it though...is that some sort of uric acid tempering technique?

  5. #5
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    Re: When is it OK to remove clamps.

    Quote Originally Posted by steveu812 View Post
    This is 3/16 to 1/8" mild steel. Without any external help, the weld seems to be cool enough to touch after about 15 minutes or so. Is it safe to assume if I can touch it I can remove the clamps?

    I never thought of peeing on it though...is that some sort of uric acid tempering technique?
    Absolutely you can remove the clamps if you can touch it. Really of it gets below 600 degrees you are good to go by a long shot because puddle temp has flowed out. Steel melts above 2000 degrees F.

    Peeing on it definitely would cool it down faster.
    Weld like a "WELDOR", not a wel-"DERR"
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  6. #6
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    Re: When is it OK to remove clamps.

    I say the answer to when it's safe is "never."

    If you want it to stay straight like it is in the clamps, taking them off will only lead to heartache and a threat titled "how does heat shrinking work?"
    Dave J.

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  7. #7

    Re: When is it OK to remove clamps.

    Quote Originally Posted by MinnesotaDave View Post
    I say the answer to when it's safe is "never."

    If you want it to stay straight like it is in the clamps, taking them off will only lead to heartache and a threat titled "how does heat shrinking work?"
    I guess I should weld the clamps to the work?

  8. #8

    Re: When is it OK to remove clamps.

    Quote Originally Posted by shovelon View Post
    Absolutely you can remove the clamps if you can touch it. Really of it gets below 600 degrees you are good to go by a long shot because puddle temp has flowed out. Steel melts above 2000 degrees F.

    My gut said this was the case, but this isn't a patch on a burn barrel so I figured I'd ask.

    Thanks

  9. #9
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    Re: When is it OK to remove clamps.

    Quote Originally Posted by steveu812 View Post
    I guess I should weld the clamps to the work?
    There you go - that's work

    Really though, metal pulling after the clamps are released does still happen.

    It can make you crazy...
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  10. #10
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    Re: When is it OK to remove clamps.

    12 to 36 hours after the vibrator shuts off depending on the coffee supply and engineer's mood.

  11. #11

    Re: When is it OK to remove clamps.

    I would say generally a few seconds after the color has gone out of the weld the clamps have done about all they will do.
    The weld metal is soft when red hot. Thats why blacksmiths heat metal up and pound on it when it is red hot, not when it cools.

    Think about a hot tack. That where you make a small weld and time a hammer blow just as the red disappears to close up a gap in the fit.
    If you wait too long the hammer blow doesn't do much. To quick while metal is red hot and it just springs back.

    So very soon after the weld metal has no red color, it has taken a set and leaving the clamps on longer will not help.

    Welding almost always is going to pull or distort in some way. It expands when hot but is soft while red hot, and shrinks as it cools and gets stronger. The net results is that the weld metal pulls.

    Experience and a good guess as to how much to tack out of square or plumb so after all is said and done the welded pieces are where they should be.
    For instance tacking a column. Find the corner that the column is leaning away from both directions. Tack it.
    Then lean column away form the other adjacent corner till the bubble on the level is ALMOST touching the line (on the vial).
    Tack it and watch it pull back to plumb.

    You can clamp something square, weld it and wait till hell freezes over, take the clamps off, and it will spring out of square.
    Last edited by Paladin; 10-09-2018 at 10:49 PM.

  12. #12
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    Re: When is it OK to remove clamps.

    My experience is generally the same as above. Once you flip the hood up, it’s all over but the cryin’....leave the clamps on to avoid facing the inevitable if you want.


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  13. #13
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    Re: When is it OK to remove clamps.

    Sometimes after welding the clamps fall off on their own as it cools then it’s “oh crap the stuff shrunk now what?” But seriously heres a video all about welding caused distortion:

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  14. #14
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    Re: When is it OK to remove clamps.

    I used to weld alot of 4130 .065 wall in fixtures that weighed 1000k the weight of the final part welded in it and were machined and ground within .0005 some parts would still twist upon removal you just had to figure which ones and adjust your fixtures or cut s to compensate for it, if you need 30 degree cuts bent and welded you would machine to 28 or 29 degree and the weld would pull shrink it to 30

  15. #15
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    Re: When is it OK to remove clamps.

    I only leave the clamps on long enough to tack it, after that you just check the critical angles/gaps as you weld and adjust your welding pattern/heat/fill accordingly... takes a bit of practice but things usually come out pretty decent anymore every once in a while got to break out the 12 pounder or do a bit of fit-to-cut heh heh.

  16. #16
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    Re: When is it OK to remove clamps.

    Yes, there is just one really important rule to remember, the surface you’re clamping too must be heavier and stiffer than the item being clamped. Otherwise the distortion will very much still happen, but it will also distort whatever it’s clamped to! Cooling steel can move some weight, I’ll tell ya!

    I used this to my advantage on my recent table build. By the time I got done welding all joints I had two corners pulling up(or two opposing pushing down). So what I did was took the plate that had a little bow in it, ran it opposite the direction of the lifting frame corner, afixed table top to frame, flame straightened(controlled distortion done on purpose) the top plate straightened and straightened the frame with it!

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  17. #17
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    Re: When is it OK to remove clamps.

    Also, if you’re clamping something straight in an effort to keep it straight, you’ll often be disappointed with the results. You may have better luck clamping it with some preload (slight bend) in the opposite direction it’s going to pull, then let your weld pull it straight. Takes some experimentation to figure out where/how much to preload it.


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  18. #18

    Re: When is it OK to remove clamps.

    Awesome - thanks for all the info and "real-world" experience examples.

    Sounds like with something like this - basically a one off project - take precautions, anticipate imperfection, find a good strategy to make it right

    Wow - sounds a lot like LIFE. Takeaway: "Welding is life"

    Great forum!

  19. #19
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    Re: When is it OK to remove clamps.

    Quote Originally Posted by djd775 View Post
    Also, if you’re clamping something straight in an effort to keep it straight, you’ll often be disappointed with the results. You may have better luck clamping it with some preload (slight bend) in the opposite direction it’s going to pull, then let your weld pull it straight. Takes some experimentation to figure out where/how much to preload it.


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    This works excellent in my experience.
    It's going to pull, so pre-stress the other way an appropriate amount (learned through having too much, or not enough, many times.....)
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  20. #20
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    Re: When is it OK to remove clamps.

    Quote Originally Posted by MinnesotaDave View Post
    It's going to pull, so pre-stress the other way an appropriate amount (learned through having too much, or not enough, many times.....)
    +1

    If you pre-stress/pre-strain it too much, when you weld it and your yield strength drops (due to the steel reaching critical temperature around the weld) it may go too far the wrong way...then you'll WISH it had shrunk MORE! If "a little" is good, "a lot" isn't always better!

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  21. #21
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    Re: When is it OK to remove clamps.

    Newbie here again. I've been working on a cart I built the three shelves first that went as well as expected for someone doing there first "job" mostly after first class but they were straight. I added the cross beams to one shelf no issues, added cross beams to second shelf well with the 6 inch warp I now have pratice steel. Lesson learned.

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