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Thread: Buillding a body jig, couuld use a little help

  1. #1
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    Buillding a body jig, couuld use a little help

    Hello everyone,

    I would consider myself a intermediate DIY home welder, but I have a project that is probably going to push my limits in a few ways, Welding, Design, Fabricating. I am attempting to build a body jig to aid in the restoration of 65 Mustang. I will be doing a significant amount of uni-body replacement and the jig will keep everything in its place, at least that is the plan.

    The design is 16' long main tubes with 4 - 3' cross members. All tubing is 4"x2"x3/16". (see attachment)

    I have everything set up on 2 saw horses, the main tubes were leveled first with a bubble level, then started using a laser level
    Each main tube has about 6 small drilled holes 3/32" that I am using a tram gauge to take cross measurements.
    I started at cross member 2, set the main tubes 36" apart , on the inside, and proceed to take cross measurements to ensure I was square. The first cross member went in fairly easily, and it was square to each main tube, AND my cross measurements were still ok.

    At this point ALL welds are only tacks

    I them moved to cross member 3, squared it to the main rails, them tacked it in. Cross measurements still looked good. But here is where it goes strange. The cross member appears to be in slightly not square. They are only tack welded in so I figure I could break the tack and straighten it out once I tacked in #1 and #4

    I tacked in #1 and #4 much like #2 and #3, and here is where the disappointment comes in. Cross measurements are all out of whack! One rail is about 3/16" - 1/4" shifted forward compared to the other. AND if I run a string line along the verticalside of one of the long rails, there is about a 1/4" horizontal bow in the rail.

    So.... Where did I go wrong?

    One place I think I went wrong is to not weld in temporary diagonal bracing. I had planned to do this, but somehow it got missed.

    The other place, and this is where I need some help, is the order of welding in the cross members. I had planned on 2, 3, 1, 4. BUT I think I should have started at one end and went straight done the line 1, 2, 3, 4 . Making sure I was square at each step.

    So.... what does everyone think? Any suggestions to help keep this square?

    Thanks!

    Rusty




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  2. #2
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    Re: Buillding a body jig, couuld use a little help

    I DOUBT that it is possible to take ` L` O `N `G ` thin members like that,, hang them out on a saw horse, and try to get them square.

    Consider welding the parts to a piece of sheet,, or something to help hold squareness,, to get you started,,

  3. #3
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    Re: Buillding a body jig, couuld use a little help

    Quote Originally Posted by SweetMK View Post
    I DOUBT that it is possible to take ` L` O `N `G ` thin members like that,, hang them out on a saw horse, and try to get them square.

    Consider welding the parts to a piece of sheet,, or something to help hold squareness,, to get you started,,
    Unfortunately, what you see is it. I do have some angle iron I can use for bracing, but no sheets anywhere near that size.

    Rusty

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    Re: Buillding a body jig, couuld use a little help

    Quote Originally Posted by rusty105 View Post
    Unfortunately, what you see is it. I do have some angle iron I can use for bracing, but no sheets anywhere near that size.

    Rusty
    In 1979, we had a machine built that was designed to apply epoxy to carbon fiber.
    It was the size of a large Snap-On tool box, and weighed over 6,000 pounds.

    Well we were assembling rollers to the frame, and trying to align the rollers with shims.
    The specs called for the rollers to be aligned within 0.002 inches.

    We had optical equipment, and several other types of measuring tools set up, and we could not get it in alignment.

    We took a break on the third day,, I leaned against the machine,, and someone noticed that the alignment of the machine shifted 0.006 inches!!

    Well, right then, we realized that even though the machine was massive, and stiffened,, there was no chance that the 0.002 number could be achieved.
    We quit, tightened the bolts as it sat,, and started the machine
    It ran the carbon fiber perfectly,, the 0.002 dimension was someone's dream,, not a necessity.

    Weld the frame as you have it now, and shim the body as you bolt the body to the frame,,
    It will work, you will be happy,,,

  5. #5
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    Re: Buillding a body jig, couuld use a little help

    I built a similar Rotisserie to work on mine and a buddies street rods, I will need to look for the images for that. I also build a body hoist for removing and installing the bodies on frames or moving them around. Here is an image of the hoist. The rotisserie was great for other projects I build a few CNC Plasma table using it for welding the frames up too. We made some attachments that held a 78 firebird body on the rotisserie so we could spin the body to work on all parts of it. I use 3" square tube with 1/4" wall and large casters.
    Attached Images Attached Images      
    DIY CNC Plasma table USB BOB Price THC
    Hypertherm 65
    Everlast PowerTig 255 EXT
    Miler 180 Mig
    13" metal lathe
    Mill/ Drill
    ECT, ECT,

  6. #6
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    Re: Buillding a body jig, couuld use a little help

    I'm afraid you've reached the point where you need to learn how to use a rosebud. Nothing ever welded, since the first lava flow happened to touch a piece of iron, has ever been square after welded. It just doesn't happen. All the keyboard warriors will try to tell you that THEY did it, but ain't so. You need to flame straighten everything that's been welded, if tight tolerances are required.

    This is the reason that precision machines are mostly made of pieces mechanically joined with fasteners. Heat warps..........period.

    I believe you'll find it's less of a headache to make the jig square, then shim anything attached to that jig. You can fight this till the cows come home,, and not have a satisfactory outcome if you're truly chasing precision.

    Square is possible within about 1/32 on something like you're building, maybe even down lower. But that's only after it's been straightened after welding. Do your setup based on measurements, tack it up, weld it, then repair it.

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    Re: Buillding a body jig, couuld use a little help

    Quote Originally Posted by SweetMK View Post
    ..............Weld the frame as you have it now, and shim the body as you bolt the body to the frame,,
    It will work, you will be happy,,,
    This is about where I am . The car (1965 Mustang) had tolerances from the factory that I believe were something like 1/16" (0.06"), 1/8" (0.12") if the measurement was over 100" That is not to say I don't want to start with the best possible starting point, within reason.

    Along with the jig 'table' I have a few attachments that will get clamped to the rails of the table (see below), so I will have some leeway when mounting the car body.



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    Which brings me to another question. Is there a trick to scribe a line all the way around a square tube, and not have it move one way or another?

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    Re: Buillding a body jig, couuld use a little help

    Quote Originally Posted by rusty105 View Post
    This is about where I am . The car (1965 Mustang) had tolerances from the factory that I believe were something like 1/16" (0.06"), 1/8" (0.12") if the measurement was over 100" That is not to say I don't want to start with the best possible starting point, within reason.

    Along with the jig 'table' I have a few attachments that will get clamped to the rails of the table (see below), so I will have some leeway when mounting the car body.



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    Which brings me to another question. Is there a trick to scribe a line all the way around a square tube, and not have it move one way or another?
    I use a legasse " lesquare". It's a wide base combination square. I bought mine on " welding tips and tricks" online store. Harry J Epstein's also sells them. Not cheap but a real quality tool. The other way is to get a 6"x12" carpenter square and cut a piece of 1.5"x1.5" x1/8" angle on one blade. That works but the wide blade combination square is much handier.

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    Re: Buillding a body jig, couuld use a little help

    I use a wider piece of masking type usually or pipe wrap.

    I've also leveled the square tube, scribed a line across one face with a square then and laid a double weighted line (double plumb bob basically).

  10. #10
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    Re: Buillding a body jig, couuld use a little help

    This guy built a body jig for his 66 mustang. Maybe you can glean some details from his build
    https://www.garagejournal.com/forum/...ustang.362241/

  11. #11
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    Re: Buillding a body jig, couuld use a little help

    the main thing is to clamp or support the rocker panels at the 4 corners and square your jig. make sure the car won't move from this point, that is how they build a car. if its not perfectly square and level, the built and replacement panel won't fit right, including doors, windshields, etc. you will be fighting it the whole way.

    uf you move the jig, fixture, on the uneven concrete, then the jig has to be REALLY,REALLY SOLID. cheat on this jig and rest of build won't go right. did body work in new car dealerships and especially frame work. also buy a cheep mountable laser to level and square this jig. have someone help you, should be able to get gif within 1mm.of level and square.
    lincoln 125sp
    dayton 250 ac/dc
    miller 211 w/spool gun
    ahp 200 sx tig
    lotos ltp5000d
    kubota b3200 FEL BH
    of course duramax diesel

  12. #12
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    Re: Buillding a body jig, couuld use a little help

    Some can build easy frames like that square the first time, and very easily keep it square. What most people dont understabd is that they screwed up, just like the OP, at least a dozen times. We learn to do it right because the price of metal costs a lot when you cut it all apart and rebuild it.

    This is the aftermath of the issue, but you should have put diagonal bracing on the bottom of it. Welded the bracing in place, rechecked all dimensions, then weld the main frame. Leaving the diagonal braces on it forever, that's why they would be on the bottom.

    Welding frames squarely takes a lot of tedious requirements to remember every time. Like which joints to weld for strength, which joints will cause the lost warping, which joints cause the lost racking and either not welding certain spots, or counter acting it with other welds.

    Since you have 2 parralell members and 4 cross members, I'm assuming you welded from 1 corner all the way around to the other. This is very wrong. You should weld 1 weld from inside to outside of frame, then weld the same weld on the other parallel member from inside to outside. Then do the same 1 weld on another cross member and then the opposite side of that one. This will keep the least amount of heat into the metal before you lock the whole frame in. I would only have done 16 welds max on that whole frame, besides any diagonal bracing.

    If you think that frame is bad, if that was stainless, it would look like a pretzel if the steel moved 1/4"

    Sent from my SM-G960U using Tapatalk

  13. #13
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    Re: Buillding a body jig, couuld use a little help

    Quote Originally Posted by Country Metals View Post
    Some can build easy frames like that square the first time, and very easily keep it square. What most people dont understabd is that they screwed up, just like the OP, at least a dozen times. We learn to do it right because the price of metal costs a lot when you cut it all apart and rebuild it.

    This is the aftermath of the issue, but you should have put diagonal bracing on the bottom of it. Welded the bracing in place, rechecked all dimensions, then weld the main frame. Leaving the diagonal braces on it forever, that's why they would be on the bottom.

    Welding frames squarely takes a lot of tedious requirements to remember every time. Like which joints to weld for strength, which joints will cause the lost warping, which joints cause the lost racking and either not welding certain spots, or counter acting it with other welds.

    Since you have 2 parralell members and 4 cross members, I'm assuming you welded from 1 corner all the way around to the other. This is very wrong. You should weld 1 weld from inside to outside of frame, then weld the same weld on the other parallel member from inside to outside. Then do the same 1 weld on another cross member and then the opposite side of that one. This will keep the least amount of heat into the metal before you lock the whole frame in. I would only have done 16 welds max on that whole frame, besides any diagonal bracing.

    If you think that frame is bad, if that was stainless, it would look like a pretzel if the steel moved 1/4"

    Sent from my SM-G960U using Tapatalk

    you could have that jig looking like a pretzel as long as the jig you made was rock solid and cant twist and bend more that one maybe 2 millimeters. as long as you have this solid jig and the 4 attachment points to the rocker are on the same plane, square and not trapezoid shaped, you will be fine. the auto's unibody was designed and built around the rockers.

    with that said, u should get your jig as as square, level and rigid as possible because YOU can measure off you jig. DO NOT GO CHEAP ON THAT JIG!! PERIOD!!!!! THATS WHAT YOU WILL BE BUILDING AND REPLACING QUARTER PANEL PARTS WHICH ARE PART OF THE UNIBODY!!!
    Last edited by duramax-rob; 08-28-2021 at 03:42 PM. Reason: typing errors
    lincoln 125sp
    dayton 250 ac/dc
    miller 211 w/spool gun
    ahp 200 sx tig
    lotos ltp5000d
    kubota b3200 FEL BH
    of course duramax diesel

  14. #14
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    Re: Buillding a body jig, couuld use a little help

    I know it has been a while since I updated this thread, but I do have an update.

    First off, I cut all the tack welds and cleaned up all the remaining weld material, I realigned the two main rails (2x4 tubing) so that the reference points for cross members 2 & 3 were square. (see first post to see what theses reference points look like).

    I clamped in some temporary cross members, 1x1 angle iron cut exactly at 36", to ensure the main rails were 36" apart, I also welded in a temporary diagonal bracing in this area (see attached photo)
    I then tack welded in cross members #2 & #3. The reference points at these locations still showed the jig as being square from #2 to #3

    At this point I was fairly sure that the main rails and #2 & #3 cross members were square with each other

    Using string lines & laser lines I noticed each main rail was bowed . I pushed each back into a straight line and welded in more diagonal bracing to hold them in place. I rechecked 'squareness' along the rails at several points, and all seemed good. I could shoot a laser line along the tops of the main rails, and the line goes right over the alignment points (small 3/32" holes).

    I then tacked in the #1 & #4 cross member. I also tacked some permanent diagonal bracing from the #1 & #4 cross members. (the ones with some yellow paint on top of them)

    At this point ALL cross members and the permanent diagonal bracing are only tacked in place.

    What are your recommendations as to the order of permanent welding? I was going to weld in #1 & #4 cross members and their diagonal bracing, then weld in #2 & #3 cross members?






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    I also have a question regarding these legs.

    I have 2x2 tubing, 4 1/2" tall, with another 6" or so of threaded rod for legs. I was originally not going to weld in any diagonal support for these, but I am rethinking that, maybe some 1" x 1" x 1/8" diagionally back tothe main rails and cross members.

    Opinions?

    and as always, THANKS!!

    Rusty


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    Last edited by rusty105; 10-07-2021 at 03:20 PM.

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  16. #15
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    Re: Buillding a body jig, couuld use a little help

    Wire or ratchet straps help holding/pulling squarness, too.

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    Re: Buillding a body jig, couuld use a little help

    Good job spending the time squaring your fixture. Time well spent on the front end of the project

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