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Old 04-01-2020, 09:16 AM
tjratz tjratz is offline
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Default patch help

This is probably a no brainer for all of you in here. But when making a patch panel, do I make the patch fit the hole or the hole fit the patch?



Thank you all in advance
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Old 04-01-2020, 09:26 AM
StingRay StingRay is offline
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I'd say a bit of both.
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Old 04-01-2020, 10:14 AM
blue62 blue62 is offline
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And no square corners.
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Old 04-01-2020, 12:47 PM
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Steve Hamilton Steve Hamilton is offline
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Which ever is easier to do.

The patch is able too be worked on at a bench or in a vice, or claimed to the bench. Good light and a comfortable working position makes trimming accurately much easier.
If the patch is small or hard to hold, then place it over the panel, scribe a line tight to the patch edge. Snip, grind, sand or file, to get the best fit possible.

Time spent on good fit up will make the welding go much better and quicker.

Also less welding heat will cause less warpage, which means less panel finishing.

Steve
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Old 04-01-2020, 04:56 PM
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sometimes the panel is in a darkened location making it hard to see or awkward location, etc where I prefer initial cut there and final cut on the patch where you can move to better lighting, rotate the smaller patch around for an easier cut to get a more precise fit. Here’s a sample of what we did on the hood in the shop now, shows a bit of the marking and trimming.


Quote:
The affected area was cut out using an air body saw, use what you have available. Note we have no corners in the cut to help improve consistency in weld shrinkage on either side.





The flange bend line is traced from our profile template/body sweep, and bent using tipping wheel on the bead roller (since it's not a straight bend). Here test fitted to the hood..





An Ice Pick (something everyone should have if doing this type of work) is used to mark the area of the cut and more importantly, the cuts for the flanges.





Next we trim the panel on the band saw leaving 1/4" extra around our marks. Next, we use offset snips and trim the flanges to the lines scribed. And ONLY the flanges.. Then the panel is re-fitted with the flanges flush with the original, and RE-scribe the round line, this time with more force to see the mark better.

Note the scribe line has moved closer toward the flange as we located the panel correctly with flanges flush..





Fitted... panel should be as tight as you can get it to minimize any shrinking/pulling.





Flanges and outer surface are both aligned to the original first and I use TIG to tack on the exact corner on both ends to maintain this alignment.. Side note.... tacking only one end and working around to the other may shrink as you go, pulling other end down where it no longer aligns. So in this case, align both ends, tack both ends, and then progressively work your tacks side to side toward the bottom of the circle.





Note here the flange was left long on our replacement. Trying to weld it in place already trimmed to fit will invariably cause the edge to burn back, making it more difficult to weld this seam all the way to the edge. Leaving the flange on our patch long makes the outer part serve as a heat sink where this burn back effect is less of an issue. Once the welds are dressed, trim the excess using offset snips..


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Old 04-01-2020, 06:35 PM
foamcar foamcar is offline
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Very good explanation Robert.
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Old 04-02-2020, 06:54 AM
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If the hole is somewhere that will not allow access to the back side of the weld, and enlarging the patch by an inch will allow access, adjust hole then make patch to fit.

One other way I have found to get precise fit is to lay patch behind hole and hit it lightly with spray paint. That eliminates line width of a marking tool but the patch must fit contours well.
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Old 04-02-2020, 07:44 AM
tjratz tjratz is offline
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Thank you all for the great info. Much appreciated.
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Old 04-02-2020, 08:04 AM
foamcar foamcar is offline
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Another tip I read if no access behind is to raise HAZ area up some before welding. Antone doing this?
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Old 04-02-2020, 03:35 PM
crystallographic crystallographic is offline
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Ditto in other shops - tack all - then hammer HAZ, skip weld, hammer that, skip weld, hammer, weld, hammer... done. Keeps it flat and in control all the way.



P1120267 copy.jpg
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straightedge used to check flatness
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