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Old 12-15-2016, 03:39 PM
ojh ojh is offline
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Default Secrets to no undercutting?

I'm working on an old grille to send for chrome plating and I'm filling the little dings etc silicon bronze but I'm getting this undercut at the edge of the weld, how do I avoid it?
I'm Tig'g.
Thanks, Oj
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Old 12-15-2016, 08:38 PM
BTromblay BTromblay is offline
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Hi,

It is a little hard to explain. Run the current level high enough for your first pass to get enough penatration/adhesion. Make a second pass at a much lower current setting to make a cold weld to fill in the under cut.

I define a cold weld as a bloppy, tall bead. The current level is just high enough to melt the welding rod.


Hope it helps.

Bill
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Old 12-15-2016, 09:19 PM
SWT Racing SWT Racing is offline
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Sounds like a little too much heat. Or, the metal is some sort of cast or leaded steel.

You'll aslo want to keep your arc length very short.
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Old 12-16-2016, 09:22 AM
ojh ojh is offline
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I manuevered and manipulated enough to get it finished, I'm thinking the undercutting might have been into the original brass under the chrome! Isn't that what the chrome shop does as part of the plating, a layer of brass or copper?
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Old 12-16-2016, 11:02 AM
crystallographic crystallographic is offline
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Quote:
Originally Posted by ojh View Post
I manuevered and manipulated enough to get it finished, I'm thinking the undercutting might have been into the original brass under the chrome! Isn't that what the chrome shop does as part of the plating, a layer of brass or copper?
OJ, Are you tigging SiBr onto a brass grille? HAs the chrome been stripped off already? You might be digging a hole when you could be sanding your fill smooth ....?
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Old 12-16-2016, 12:20 PM
Ron Naida Ron Naida is offline
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Good chrome over base metal is usually copper nickle, chrome
polished after each layer.

I usually have the chrome people strip to base metal since they will be doing anyway.
Then I make the repairs ( no soft solder as the buffer can pull that out and
you'll have dips)

If the chrome shop has good buffers the copper can be moved around a bit
and level slight divets.

For cheapie replating brass If I recall the chrome layer is right over the polished brass.

Ron
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Old 12-18-2016, 06:47 PM
SWT Racing SWT Racing is offline
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Quote:
Originally Posted by ojh View Post
I manuevered and manipulated enough to get it finished, I'm thinking the undercutting might have been into the original brass under the chrome! Isn't that what the chrome shop does as part of the plating, a layer of brass or copper?
That is/was likely your problem. Low melting alloying elements will do things like that. If you encounter a chunk of "steel" doing the same thing, it is usually a free machining leaded steel like 12L14.
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