Welding on a pickup frame

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Kenng
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Welding on a pickup frame

Post by Kenng » Wed Oct 25, 2017 3:05 pm

I am not a welder but have a Lincoln tombstone stick welder. I have a project facing me to mount a HF pickup crane to my F150. I want/need to mount it to the frame as cose to the tail gate as possible but all the stuff i.e. spare tire under carriage rack and towing brackets make it kind of awkward so I'm planing on coming in from the  top and cutting a hole in the bed, this is not a problem as the box is pretty well mangled and a hole is not much of a concern. I plan on making a flat bed out of it in the future (next spring). So my question is do you need to disconnect the battery - pole before welding because of all the computerized stuff? When I was a youngster I remember people said that welding on a frame could actually cause your transmission gears to weld together. I am thinking this may be related to where you place the ground.

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BadDog
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Re: Welding on apickup frame

Post by BadDog » Wed Oct 25, 2017 3:19 pm

You are correct about the ground. You want a clean stable ground using a good clamp as close to where you are welding as possible. I've heard both ways on the battery deal, but almost always disconnect just to be sure. The main thing that you want is to KNOW where the least resistance to current path will so it doesn't decide to travel through a bearing (or gear, etc) anywhere, including your computer components. Not that it is proof of safety, but my TBI buggy got welded on quite a few times without unhooking the battery with no problems.

All that said, I don't think I would weld a boom post to the frame for a variety of reasons. I would make an L bracket to bolt to the frame top and side, and weld the post base to that. I actually like to use frame pieces from sectioned frame left overs for such purposes. Good material, basically free, and has a shape that fits nicely. I've done that for bumpers, winch mounts, all sorts of stuff. But other than modifying the frame itself, I generally don't weld to the frame for most things.
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spro
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Re: Welding on apickup frame

Post by spro » Wed Oct 25, 2017 4:02 pm

Hello. I should know a little about this because I mounted those type crane/hoists in 3 different trucks. I tend to avoid welding in that area because of the gas lines and tank. Yes disconnect the battery. With heavy structural angle and thick plates, there was some drilling involved but they worked well.
There is another thing about support. The hoist pedestal was shorter than I wanted, so I copied the "floor jack shaft" design of heavier tube. So there is a tube inside the main pedestal tube, with a welded foot plate. There are holes which line up to the height of the bed in some load or the inner pedestal is retracted and pinned up, so the foot doesn't hang low.
The reason for this; When the hoist is extended all weight bears behind the rear axle springs. This causes the truck to sink lower while lifting. Sometimes you run out of cable or cylinder extension at that time. When the load is swung in, the suspension is more balanced and the truck rises. The extending foot is like an "out rigger".

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BigDumbDinosaur
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Re: Welding on apickup frame

Post by BigDumbDinosaur » Wed Oct 25, 2017 4:03 pm

Kenng wrote:...So my question is do you need to disconnect the battery - pole before welding because of all the computerized stuff? When I was a youngster I remember people said that welding on a frame could actually cause your transmission gears to weld together. I am thinking this may be related to where you place the ground.
As BadDog noted, place the welder's ground clamp as close to where you are welding as possible and on the frame member on which the arc will be struck. The goal is to guarantee that the welding current doesn't pass through any riveted joints in the frame structure. If you do this, the truck's electrical system will be safe, and there will be no need to isolate anything.

I have routinely welded on vehicle frames over the years without taking any special precautions to protect the electrical system. It's possible as long as the ground path is direct to the weld area and is not going from one structure in the vehicle to another.

Incidentally, disconnect the battery does not isolate the electrical system from ground.
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BigDumbDinosaur
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Re: Welding on apickup frame

Post by BigDumbDinosaur » Wed Oct 25, 2017 4:05 pm

spro wrote:Yes disconnect the battery.
Disconnecting the battery will not isolate the vehicle's electrical system from ground. Thinking otherwise is a common misconception.
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spro
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Re: Welding on apickup frame

Post by spro » Wed Oct 25, 2017 4:21 pm

True but its more isolation than having it connected. I'm quite wary of welding around these new cars of the 1990's.

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BadDog
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Re: Welding on apickup frame

Post by BadDog » Wed Oct 25, 2017 5:37 pm

As I noted earlier, I've heard both ways. I think the idea behind disconnecting the battery is that with the system "live" under power, it is more sensitive to transient currents which if additive exceeds the limits and blows diodes, or even caps that may not be so sturdy. I also have been told that if HF is used in TIG welding it amplifies the risk substantially. I never knew enough about the situation to be sure either camp was right, so when welding on someone else's vehicle I play it safe. But MIG welding on my buggy or my K5 expedition rig (both TBI) I was rarely bothered to do so unless welding near the ECM itself, and if I was that concerned I unplugged the ECM after the battery. Whether it saved my bacon or wasted my time I can't say, but that's what I've done and will likely continue to do.

But in the end the most important thing is what I said and others elaborated on, make sure you have a good clean ground nearby (and as I should have said, on the same structural piece too), and I don't think you will have any worries with MIG or SMAW welding on a frame. I would be more worried about compromising the frame depending on what was done, how well it was done, and where. Lots to be aware of on ladder frames, and one of the biggest problem I see is over zealous "reinforcement" causing localized stress concentration and eventual frame fractures. Along that line, with that long lever arm, and depending on how you plan to use it, that idea about a foot/out-rigger of some sort, and maybe a transfer bar to the far rail might be worth considering to avoid twisting the rail used for mounting. And I'll say again, bolted not welded. Particularly if you do cross from one rail to the other, bolted solution will likely outlast any reasonable effort at a welded solution (better able to manage the flexing).
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BigDumbDinosaur
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Re: Welding on apickup frame

Post by BigDumbDinosaur » Wed Oct 25, 2017 10:50 pm

spro wrote:True but its more isolation than having it connected.
I'll be blunt: that is not a true statement.
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Re: Welding on apickup frame

Post by spro » Thu Oct 26, 2017 2:00 am

I like you to be blunt. I don't like me to make an untrue statement. So, I wasn't advocating welding in certain areas for obvious reasons and I need to listen what you know. Pulling all the fuses out is useless. Ground wires everywhere. All ears Man.

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Re: Welding on apickup frame

Post by spro » Thu Oct 26, 2017 3:28 pm

Incidentally, not all frames are the same. I had the pleasure of owning a Hino type Isuzu for a while. Had to replace all the brake lines, brakes backing plates, battery holders etc and more than etc. The frame was shot. It was a 5 ton (max 7 ton) cool flat bed. I found out or should have known that it hauled caustic substances.
Lets put it this way. You are under the truck for hours, trying to find the frame integrity. Hammers chisels and layer after layer come away in your face. Needle scalers busting through another layer until it was hopeless to continue. I wouldn't find an actual "ground" except through the rusted laminations.
It is really too bad because those engines and transmissions were good stuff.

Diogenes on the hill
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Re: Welding on apickup frame

Post by Diogenes on the hill » Thu Apr 12, 2018 9:08 pm

Having welded custom exhaust for a few years, I can tell you with certainty, we never disconnected batteries or ECMs ever. And as for 'isolating the grounds' by disconnecting the battery, Hah! All you will do is force stray current into whatever is grounded to the frame instead of into that acid covered lead ballast resistor where it belongs. Leave the battery connected and ground your leads as close to where you are welding as is possible and you will have no issues. If in doubt of your ground, use a temporary one by welding a bolt close to where you are welding by holding it in the ground clamp and welding it in place. You can tack it there, do your weld, then bust it off and clean the spot up.
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John Hasler
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Re: Welding on apickup frame

Post by John Hasler » Fri Apr 13, 2018 3:29 pm

Diogenes on the hill wrote:
Thu Apr 12, 2018 9:08 pm
Having welded custom exhaust for a few years, I can tell you with certainty, we never disconnected batteries or ECMs ever. And as for 'isolating the grounds' by disconnecting the battery, Hah! All you will do is force stray current into whatever is grounded to the frame instead of into that acid covered lead ballast resistor where it belongs. Leave the battery connected and ground your leads as close to where you are welding as is possible and you will have no issues. If in doubt of your ground, use a temporary one by welding a bolt close to where you are welding by holding it in the ground clamp and welding it in place. You can tack it there, do your weld, then bust it off and clean the spot up.
This is correct. Even if your ground is flaky the current is going to flow directly between it and the arc if it can. Ground to something near where you are welding and connected to what you are welding to by solid melal. Leave the battery alone.

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