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  #1  
Old 01-14-2009, 03:33 PM
monkeyboy monkeyboy is offline
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Default SMAW electrode size/ amp selection

I'm trying to teach myself how to stick weld and need help with a very basic question. Everything I can find relates rod size to amperage, but how do you select your amps for a given metal thickness? I realize thicker metal needs more amps, but I don't think the 1 amp per .001" rule applies here. I guess I could use some examples for different metal sizes. I've searched all the welding forums for an explanation and have come up empty. I don't mind trial and error, but my shop time is pretty limited and would at least like to be in the ballpark to start.
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Old 01-14-2009, 03:44 PM
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Amperage not only depends on the metal thickness, it also depends on what rod you are using and other variables. To keep it simple, get some metal around 1/4" thick to practice on and some 1/8" 6011 or 6013 rods. Set your welder to about 100 amps and have at it. After some practice you will be able to tell whether you need to go hotter, cooler, move faster, or move slower. lol I'm not trying to confuse you, but just get what I said and burn them. After that, post pics and more questions and we'll help you.
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Old 01-14-2009, 06:06 PM
David R David R is offline
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Try using the # of amps by the diameter of the rod. 1/8" start at 125 and go from there. 3/32 = 93 amps. It depends on the rod type and size of the plate, but this is another good rule to start with.

If you go to the miller website, there is a welding calculator that recommends rod size and amps for a plate thickness and rod type.

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Old 01-14-2009, 09:33 PM
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It's more important to understand the feel and look and sound of the correct heat. And when you look at it, has it the proper profile, no undercut, and does the slag fall of without hardly a brush? Go for the finished result, not the technical spec. It's only a engineers wet dream.
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Old 01-15-2009, 08:22 AM
monkeyboy monkeyboy is offline
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Thanks for the help. I've looked at the Miller calculator, but it still just gives the amp range for a given rod size and type, not material size. I know you can't learn without doing it, but I still don't get what the basis for amp selection based on material thickness is. 125 amps would be good for 1/8" steel in MIG or TIG, but what would that be used for in this case. My welder is good for 160 amps dc, what is the upper end of what that can weld (without taking duty cycles and multiple passes into consideration). Thanks again for the help and patience.
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Old 01-15-2009, 11:23 AM
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Monkeyboy

Not that I'm a pro, but... IMHO, after about 1/8" - 3/16" material, the amperage (and also weld heat) becomes less variable. As long as the weld bead has no undercut (too fast/too hot) and no cold laps (too cold/too slow) and has a nice slightly convex profile the heat required to make nice beads on thicker material changes by a few amps. The parent material's bulk becomes a big heat sink and that effect tends to overwhelm the localized heating of the weld pool.

Multiple pass welds on very thick material can benefit from amperage adjustments if the work is not allowed to cool between passes. With 1/8" rod and following the "leg thickness = material thickness" rule I can make an acceptable single pass weld on up to 3/8" material using a weave, but full strength welds on thicker should be done with 3 or more passes.

FWIW, I use 1/8" 7018 dc reverse for 80% of the work I do at 115 - 125 amps on my Century 250 AC/DC machine. It is not uncommon for me to weld material from 3/16" to 1/2" and not touch the amperage adjustment. The improvement in weld quality from tweaking the amps is too small to be significant when compared to rod manipulation, travel speed, weld position, weave pattern, etc. Check out the image on my Avatar. That machine was stuck together in the manner just described. I don't think I adjusted the amperage for days at a time... The welds aren't Xray quality, but they don't absolutely have to be...

My $0.02 cdn. YMMV

Cam
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Last edited by camdigger; 01-15-2009 at 11:29 AM. Reason: Adding asorted images of welds
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  #7  
Old 01-15-2009, 12:00 PM
monkeyboy monkeyboy is offline
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This all helps a lot. I weld as a hobby, mostly on automotive and racing type chassis with tube or sheet in the .065" - 120" thick range, up to .250" inch or so for some suspension brackets. SMAW is something I thought I should know how to do, a rite of passage to becoming a real man , I guess?
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Old 01-15-2009, 12:45 PM
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For the thinner section material you've spec'd, personally, I'd shy away from 7018 and move toward a higher deposition/shallower penetration rod like 6013 or one of the sheet metal rods like 6012/7024, or small diameter (1/16") fast freeze rods like 6011/6010. I don't do much thinner than about 14 Gau, but the last of that I did I used 3/32" 6011.

Again, my $.02, YMMV.
Cam

Check out the application vs rod type chart here
http://www.mylincolnelectric.com/Catalog/consumableseries.aspx?browse=104|2030|
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Old 01-15-2009, 01:21 PM
monkeyboy monkeyboy is offline
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Sorry Cam, I should have been clearer in my last post. For the stuff I mentioned I use my MIG and am getting better with the TIG. I just figured since the TIG welder can do both, I should learn how to use the stick as well. Parts of the stick process seem foreign to me compared to the other processes. For example, trying to keep a constant arc length as the rod gets shorter is harder for me after trying to do the same with a TIG torch or MIG gun. I just like to know how to do as much as I can. How does it go, Jack of all trades, master of none?
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Old 01-15-2009, 06:00 PM
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FWIW, I find feeding the rod to keep a constant arc length is almost automatic if I watch the end of the rod and the weld pool.

Typically I concentrate on the weld pool shape (looking for correct fill and placement) and the glossy molten filler material just behind the pool as well as monitoring the arc length. Sounds harder than it is because all three of these things are within a 1/2" diameter hemisphere. Usually that hemisphere is all I can see after striking the arc anyway

Cam
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