Fillet Weld Question

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This is a question I can't seem to find the answer to.  If a fillet weld is not specified, what value is used to calculate the size of the fillet weld.  Any input would be helpful.
Reply:I am not sure if I am correct here, but I thought the height of the filet weld should equal the thickness of the metal you are welding..
Reply:Let's talk T fillets just for fun. And we'll stay real basic. Here we won't take the amount of penetration into consideration. Altho penetration is a large factor it won't apply to the following for profile purposes. And keep in mind no joint can be made any stronger than it's thinnest member. Imagine looking at eye level at the end section T fillet you've just done. Put the T upside down as you view it and place an imaginary trangle within the bounds of the bead. As large a triangle that will just barely fit inside all of the bead. You'll have two legs, one along each member of the T and what will be called the throat which is an imaginary line at a 45 from the apex or meeting point of the T to the center of the triangle (bead) cross section. The throat should be as deep as the thickness of the thinnest member and each leg should be at least as long as the thickness of the thinnest member. Beyond that you are just filling for fun. Less than that and you are sacrificing strength. Most of us will error on the side of the overdoing it. That's fine. Have I made it confusing enough ???? Dang, looks confusing to me. Hopefully someone else can give a better graphic description.Last edited by Sandy; 03-29-2005 at 11:19 PM.
Reply:hmmm.. I'am confused...  Got a video?
Reply:Yeh, I thought I had it figured till I read my own post. Maybe I can scan something and post it a little later.
Reply:Okay, I'm not any better at this image conversion than welding, but maybe this will help some.Depending on joint prep and penetration there are formulas that help reduce the volume of bead but in the world we are in we don't need to worry about that. Looking at the pic, figure the thickness of the thinner piece and make each leg (w) and the throat equal to that thickness. Attached ImagesLast edited by Sandy; 03-30-2005 at 12:34 AM.
Reply:Thank you,The last reply was my answer as well, however I beleive they are looking for a standard value or number to use in the calculation.  I was unable to locate any standard calc's in the CWI information I have.
Reply:I've always gone by using the "legs" of the weld being equal to the thickness of the thinner of the two pieces being welded.  Which I think is what Sandy was saying...
Reply:Originally Posted by PAToyotaI've always gone by using the "legs" of the weld being equal to the thickness of the thinner of the two pieces being welded..................
Reply:Rule of thumb is the leg of the fillet should be 2/3 of the thickness of the material in a tee joint.  With a similar fillet on the other side you have full strength.  Using trig. the number is .707 but 2/3 is close enough.  If you were doing a 1/4 inch plate you would need 3/16 leg fillets on both sides.  If you were welding half inch plate the print would call for a 3/8 inch fillet on both sides.  The weld metal is in most cases far superior in strength to the parent metal.  If you were to weld on one side only of a half inch plate tee joint you would need a massive fillet around 5/8 to 3/4.  A bevel prep is a better choice to increase penetration.
Reply:Originally Posted by lotechmanRule of thumb is the leg of the fillet should be 2/3 of the thickness of the material in a tee joint.  With a similar fillet on the other side you have full strength.  Using trig. the number is .707 but 2/3 is close enough.  If you were doing a 1/4 inch plate you would need 3/16 leg fillets on both sides.  If you were welding half inch plate the print would call for a 3/8 inch fillet on both sides.  The weld metal is in most cases far superior in strength to the parent metal.  If you were to weld on one side only of a half inch plate tee joint you would need a massive fillet around 5/8 to 3/4.  A bevel prep is a better choice to increase penetration.
Reply:I would think most of the time the answaer is provided by engineering working on stress strain and required strength. When not given running a good quality single pass fillet weld with proper transition to base metal would do most simple applications. for example 1 pass 7018 on 1/4 or 3/8 plate would yield a 1/4 fillet (meaure of legs of previously mentioned inscibed triangle). If working with heavier stock 3/4 or 1 inch use three pass weld is about 3/8 fillet.
Reply:One "old" Lincoln text Metals and How to Weld Them, gives some good examples of adequate weld size.  Also it shows a Tee joint with properly sized fillets but a full 1/16 undercut on both sides of the Tee.  When pulled in tension the joint still did not fail at the weld.  Most people overweld.