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Thread: Keys to Achieving Good Spot Welds

  1. #1
    Gunco Member John Smith's Avatar
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    Default Keys to Achieving Good Spot Welds

    Since I have yet to see a tutorial with acceptable spot welds, I started this thread to help builders achieve good spot welds. I will edit it and add pictures as I think of new things to add. When I first tried spot welding, my welds were terrible, so anyone who is having problems can do it. Keep in mind that this is the same cheap 115V Harbor Freight spot welder everyone else is using; however, a quality 110V or 220V Miller spot welder with a timer will achieve even better spot welds. With some reading, patients, and practice, everyone can have excellent spot welds. If anyone needs any help, post pictures of your welds and spot welder setup, and I will help you fix the problem(s). Also, if anyone else has pictures of good spot welds that they would like to contribute to this thread, please do so. Here are some excellent resources for spot welding: Miller Owner's Manual, Handbook for Resistance Spot Welding, Spot Welding Guidelines, http://www.gunco.net/forums/f43/spot...dimples-37801/.

    Keys to achieving good spot welds:
    • File upper tong tip to ~0.150-0.180" diameter; lower tong tip to ~0.180-0.210" diameter.
    • Adjust tong pressure so that lower tong flexes slightly even without any workpieces between tips. Be sure hex jam nuts are tight and hand lever stop is set.
    • Be sure tips are flat against workpieces when clamped together.
    • Be sure tips are properly aligned when clamped together.
    • If possible, plug spot welder directly into outlet.
    • Chamfer ends of lower rails where they meet trunnion. Use receiver stub as reference. This will allow for smoother operation of bolt and bolt carrier.
    • Be sure workpieces are free from dirt, grease, and oil.
    • Be sure workpieces are clamped properly. If spatter is expelled from between workpieces, they are not clamped properly.
    • Use correct number and placement of spot welds. Refer to the picture below and make reference marks on receiver. (There can be 2 or 3 spot welds above magazine well on right side.)
    • According to a professional I spoke with, weld time should be about 0.5 seconds to 1 second. I recommend about 0.7 seconds for 0.040" + 0.040" combinations and about 0.9 seconds for 0.040" + 0.0625" combinations; however, it may be easier to look at the size of the area of discoloration. Excessive weld time may warp your receiver.
    • Notice the area in the center of the spot weld is not discolored. If a portion of the area in the center is severely discolored, the tips were likely not flat against the workpiece, or there was not enough pressure.


    Last edited by John Smith; 07-07-2008 at 12:39 PM.

  2. #2
    Chief Administrator 7.62x39's Avatar
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    Nice job John.

    Some related threads.

    115VAC Spot Welder Update

    Spot welder lower tong mods
    .

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    Gunco Maniac sjohnson's Avatar
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    Thanks John Smith!

    I can agree with almost everything, the exception being:

    "Plug Spot Welder directly into outlet if possible."

    I'm just about guaranteed of burn-through if I plug directly into an outlet. I also go by color, and the threshold going from good weld to burn-through is a small fraction of a second if I plug directly.

    Going through 100 feet of 100/2 extension cord, my welds still take about 1 second, but I have an (estimated) quarter-second of slop time before burn-through, so I don't have to have to drink 4-5 cups of coffee before welding

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    Gunco Member John Smith's Avatar
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    Quote Originally Posted by sjohnson
    Thanks John Smith!

    I can agree with almost everything, the exception being:

    "Plug Spot Welder directly into outlet if possible."

    I'm just about guaranteed of burn-through if I plug directly into an outlet. I also go by color, and the threshold going from good weld to burn-through is a small fraction of a second if I plug directly.

    Going through 100 feet of 100/2 extension cord, my welds still take about 1 second, but I have an (estimated) quarter-second of slop time before burn-through, so I don't have to have to drink 4-5 cups of coffee before welding
    Since properly setting up my spot welder, I have done over 130 spot welds without having any spatter or holes burn through my welds. Although reducing the amperage and increasing the time will reduce the chance of burning holes through the welds, using higher amperage and less time reduces the chance of warping the receiver. If possible, it is better to use a shorter weld time, but I do agree that it may be more difficult. Notice that the NoDak Spud receivers have very little discoloration around the welds.

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    Gunco Maniac sjohnson's Avatar
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    Simply a tradeoff on proper electric use, spot-welder longevity, my (old!) reflexes, and a decent receiver weld.

    Warping might be an issue, but it sounds like we're both "on" the weld for about the same length of time. I just need more "slop time" to get off the weld.

    The NDS receivers, are they welded before or after heat-treating? From the relatively uniform surface appearance I was under the impression they were welded before.

  6. #6
    Gunco Member John Smith's Avatar
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    Quote Originally Posted by sjohnson
    The NDS receivers, are they welded before or after heat-treating? From the relatively uniform surface appearance I was under the impression they were welded before.
    Correct, they are welded before heat treating.

  7. #7
    Gunco Member dsniper's Avatar
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    I would like to see pics and know more about your tong setup.

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    Where's my lathe? ashhoe's Avatar
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    Just talkin straight up here, your welds are are like lil dimples compared to the factory ones. Factory has a nice uniform "dish": even depth and consistant from weld to weld. How can "we" duplicate that? I tried, so far I can't. Got some of my homies working on it tho, talking all about phase angle and percentages of frequency. I hear the old robotronic weld timers are good for this kinda stuff, series something or whatever. If you've read any of my posts from the past you should know I've been struggling with recreating "the perfect spot weld". I work with some freaks that really know way too much about resistance welding and I guess it's all about where in the cycle you start the current, for how long and where in the cycle you end it.
    Scratch free flat bends, perfect rivets and now on to the spot welds. Where is the rest for the wicked? Is it even worth it? Stupid BS keeps me up at night. What the hell is an SCR really? Yea, I know, silicon controlled relay, but what the hell does it do that's so fantanstic? Who's that guy in the wheelchair, I think I need his help.
    member # 575

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    Gunco Regular shoot-n-scoot's Avatar
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    Isn't SCR = Silicon Controlled Rectifier ?

    Anyway, this is great. I want more!

    John 3:16

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    Gunco Maniac sjohnson's Avatar
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    ashoe, your problem is too much nasty capitalist electric power.

    You need Soviet power, generator strong like bool, is gift from glorious proletariat to our comrades in Slobbovia, no?

    And some 92 year-old guy who knows how to make it run. No need to hurry, he only coughs up blood once in a while...

    Some GOOD power, that's what you need.

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