Re: Grinding weld on patch panel
[Re: Red383]
#2787205
06/19/20 06:54 PM
06/19/20 06:54 PM
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Joined: Feb 2003
Posts: 1,637 Florida
GMP440
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I would grind just a little more or else you'll need to use a lot of filler to level the whole area. It wouldn't hurt to weld up those large gaps. Then grind down and it will look good. Are you using one those flap disks? Those are very good for knocking down and smoothing the welds.
Last edited by GMP440; 06/19/20 06:56 PM.
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Re: Grinding weld on patch panel
[Re: Red383]
#2787262
06/19/20 09:44 PM
06/19/20 09:44 PM
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Joined: Jan 2003
Posts: 4,287 Morrow, OH
markz528
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You really should be using sanding discs like the ones below either 24 or 36 grit. As stated, you have to be careful not to take off the parent metal. These discs allow you good control and work great. Right angle grinder/sander and you vary rpm as necessary and always keep it moving. You use backing pads like the ones shown below. As the disc wears, you go to a smaller backing disc and trim the edges of the disc with a pair of tin snips - does not need to be perfect. https://www.autobodytoolmart.com/product/3-pc-phenolic-backing-plate-setSanding DiscsThat is the technique I used in this guard on the edges - there is no plastic in that corner.
Last edited by markz528; 06/19/20 09:48 PM.
67 Coronet 500 9.610 @ 139.20 mph 67 Coronet 500 (street car) 14.82 @ 94 mph 69 GTX (clone) - build in progress......
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Re: Grinding weld on patch panel
[Re: Red383]
#2787263
06/19/20 09:46 PM
06/19/20 09:46 PM
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Joined: Jan 2003
Posts: 4,287 Morrow, OH
markz528
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Do the welds all need to be smooth and blended in before filler, or are small imperfects ok? Any weld high spots will stick out like a sore thumb. Once you get all the welds pretty much even with the parent material, you do just a touch grind/sand on the whole surface.
67 Coronet 500 9.610 @ 139.20 mph 67 Coronet 500 (street car) 14.82 @ 94 mph 69 GTX (clone) - build in progress......
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Re: Grinding weld on patch panel
[Re: Red383]
#2787280
06/19/20 10:53 PM
06/19/20 10:53 PM
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Joined: May 2006
Posts: 1,757 Phila
PhillyRag
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After welding in a patch panel, at what point am I doing more damage than good when grinding the weld down? Does it have to be completely smooth before applying filler? Thanks What panel is that? Looks like a trunk drop-down. If that weld area is "hidden", more important to fill gaps then to flat welds.
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Re: Grinding weld on patch panel
[Re: Red383]
#2787324
06/20/20 08:38 AM
06/20/20 08:38 AM
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Joined: Mar 2006
Posts: 9,882 MI, usa
dvw
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How far to grind? Depends on how good your repair is after welding. If there is some warpage and the weld isn't higher than the rest of the area by more than .060" your probably very close. Grinding to thin just for sake of appearance now could cause issues later. Use a straightedge and check for high spots. If it's low leave it.Make sure there are no pin holes or seal it from behind. Personally a cut off wheel with good hand movement will knock the weld down quicker with less surrounding damage to the sheet metal than a disc. then finish with a hard backed disc. We are hobbyist here. That means as we learn our patches will not be like someone who has done it for years every day. The longer you do it, the better you will get. I did these awhile back. I've also done some when learning that weren't as nice as the ones you pictured. You're off to a good start. Doug
Last edited by dvw; 06/20/20 08:42 AM.
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Re: Grinding weld on patch panel
[Re: Stanton]
#2787859
06/21/20 06:40 PM
06/21/20 06:40 PM
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Flap disk ... NO, NO,NO. The weld is usually harder than the surrounding metal. The flap disk has too much flex and will remove the softer surrounding metal more than the weld - so you end up with thinner base metal and thicker weld. To grind welds you want to use a solid composite disk OR if you're using an air angle grinder you can use the small 2" or 3" disks on the appropriate mandrel.
There is nothing wrong with using a flap disk. If you angle the flap disk just on the welds that will work fine and then finish as someone stated with an 90 degree angle tool with the the disks that were pictured.
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Re: Grinding weld on patch panel
[Re: GMP440]
#2787915
06/21/20 09:43 PM
06/21/20 09:43 PM
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Joined: Oct 2005
Posts: 8,911 Ontario, Canada
Stanton
Don't question me!
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Don't question me!
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Ontario, Canada
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Flap disk ... NO, NO,NO. The weld is usually harder than the surrounding metal. The flap disk has too much flex and will remove the softer surrounding metal more than the weld - so you end up with thinner base metal and thicker weld. To grind welds you want to use a solid composite disk OR if you're using an air angle grinder you can use the small 2" or 3" disks on the appropriate mandrel.
There is nothing wrong with using a flap disk. If you angle the flap disk just on the welds that will work fine and then finish as someone stated with an 90 degree angle tool with the the disks that were pictured. Knock yourself out bud - but I can pretty much guaranty you won't find flap disks in a professional body shop. And it isn't because they can't afford them.
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Re: Grinding weld on patch panel
[Re: Stanton]
#2787920
06/21/20 09:59 PM
06/21/20 09:59 PM
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Joined: Feb 2003
Posts: 1,637 Florida
GMP440
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Florida
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Flap disk ... NO, NO,NO. The weld is usually harder than the surrounding metal. The flap disk has too much flex and will remove the softer surrounding metal more than the weld - so you end up with thinner base metal and thicker weld. To grind welds you want to use a solid composite disk OR if you're using an air angle grinder you can use the small 2" or 3" disks on the appropriate mandrel.
There is nothing wrong with using a flap disk. If you angle the flap disk just on the welds that will work fine and then finish as someone stated with an 90 degree angle tool with the the disks that were pictured. Knock yourself out bud - but I can pretty much guaranty you won't find flap disks in a professional body shop. And it isn't because they can't afford them. Thanks for your input. Didn't want to get into a debate here. Just giving a suggestion on this topic as others have.
Last edited by GMP440; 06/21/20 10:20 PM.
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Re: Grinding weld on patch panel
[Re: GMP440]
#2787952
06/22/20 01:37 AM
06/22/20 01:37 AM
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Joined: May 2006
Posts: 1,757 Phila
PhillyRag
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Flap disk ... NO, NO,NO. The weld is usually harder than the surrounding metal. The flap disk has too much flex and will remove the softer surrounding metal more than the weld - so you end up with thinner base metal and thicker weld. To grind welds you want to use a solid composite disk OR if you're using an air angle grinder you can use the small 2" or 3" disks on the appropriate mandrel.
There is nothing wrong with using a flap disk. If you angle the flap disk just on the welds that will work fine and then finish as someone stated with an 90 degree angle tool with the the disks that were pictured. Knock yourself out bud - but I can pretty much guaranty you won't find flap disks in a professional body shop. And it isn't because they can't afford them. Thanks for your input. Didn't want to get into a debate here. Just giving a suggestion on this topic as others have. They do serve a purpose. Nice to use for a smoother finish. Takes off some grinding marks a cutoff wheel may leave. And they do come in various grits.
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