How much Bevel on Butt weld ?

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If butt welding two pieces of metal together, how much bevel should be ground on to both pieces ?1/4 ? 1/2 ? 3/4 ??Both sides ?If the pieces are only accessible from one side does the bevel have to be deeper ?If you can access both sides do you weld both sides, or just one really good penetrating weld on one side ?Through a previous post I found you don't butt them together tight, but rather leave a small gap. How big should this gap be ?I can hear the answer already (I think) ... "Depends on the thickness of the metal"Lets say the piece is 3/16" thick.If the piece was 1/2" thick, does the method change ?As you can tell, I am learning, or at least trying to.
Reply:Great question. You are right, the thickness of the metal will affect how much bevel you will need, as will how much penetration will you need. Also, it will matter if you are welding steel or aluminum. For most common welds where you can reach both sides of say a 3/16" thick plate, then a bevel of 1/3 the thickness on each side will be sufficient. You should be able to get a good bead with full penetration into the root, and when you weld the opposite side, you should get total fusion with little issue. For a weld that can only be done on one side, then I would suggest a bevel of at least 1/2 the thickness, maybe 2/3 thickness. So, on 3/16" with a one side bevel, I would say 1/8" solid for the bevel. On thin material, you can single pass. On thicker material, you will need to multi-pass to get full penetration. Of course, this will depend on weld process. You can get much better penetration with an arc weld rather than a mig weld, so the depth of bevel will vary on that note also. As for gap in the root, you figure 1/4 of the thickness for the gap. So, for say 1/4" steel, you can be reasonably sure that with a 1/16" gap to maybe a 3/32" gap you will be about right. Many welders will use a piece of filler rod to wedge into the gaps to be sure they will start with a proper open root.And then, after so much work...... you have it in your hand, and you look over to your side...... and the runner has run off. Leaving you holding the prize, wondering when the runner will return.
Reply:Excellent response, just the stuff I needed to know. Thanks heaps.
Reply:Is the principle the same with a fillet weld ?
Reply:No need to bevel a fillet weld, unless you want complete joint penetration, which is usually not required for a plate-to-plate fillet that will be welded on both sides, or pipe/tube-to-flange or pipe/tube-to-pipe/tube @ an angle, that will be welded all the way around.  If you do decide to bevel a fillet, grind the bevel at 45 degrees, leave a gap of at least 1/16" and leave a land of no more than 1/8". If beveling a plate butt joint and only beveling one side of one plate, prepare it as described for the fillet above.If beveling a plate butt joint and beveling both plates on one side, prepare each with a 22 to 30 degree bevel, leaving the same gap and land dimensions as described above.Typically, root gaps can be as little as zero, with a feathered edge bevel, or 1/16" to 1/4" with a land and lands can be as little as 1/16" up to 1/8".   A land is a flat edge at the tip of the bevel which forms a square root opening with the other plate, as opposed to a sharp-edged (feathered) bevel.MM350P/Python/Q300MM175/Q300DialarcHFHTP MIG200PowCon300SMHypertherm380ThermalArc185Purox oaF350CrewCab4x4LoadNGo utilitybedBobcat250XMT304/Optima/SpoolmaticSuitcase12RC/Q300Suitcase8RC/Q400Passport/Q300Smith op