Correct welding rod advice

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I have a circular blade I use to cut thick rubber. The blade cracked from the arbor hole to the outer edge of the blade. I ordered another but it takes over a month to get because it has to be custom made. I need to keep running the machine. The blade is hardened steel, I dont know what kind or how it was hardened. 1/8" thick.  I have an arc welder, acetalene and a small 90 amp Mig.  I figure the arc welder would be the best to use? What would be the best welding rod to use? And how should I prepare the crack. I was thinking using a small diamond grinding stone on a dremel tool and grinding a groove along the crack.
Reply:Hardened steel requires specialized procedures. Just welding away on it is a good recipe to simply having it crack even worse, especially under load and centrifugal force. Also spinning blades are balanced. Adding weld material will signifigently change this balance causing severe vibration when spun at high RPMs, adding to the stresses involved.My guess is that this probably shouldn't be done unless it's welded by someone who knows exactly what the metal composition is, and is familiar with the techniques involved. I can almost garante stick is not the right process. Possibly tig, or maybe brazing/silver solder, but my guess is that people who really would know how to fix this would run away like mad knowing the dangers and difficulty involved, if it's even possible.This is not a DIY project from where I sit..No government ever voluntarily reduces itself in size. Government programs, once launched, never disappear. Actually, a government bureau is the nearest thing to eternal life we'll ever see on this earth! Ronald Reagan
Reply:How fast is that spinning and what happens if (when) it flies apart?You might squeak by with silver soldering or brazing.  Any significant heat is going to screw up the hardness.  Arc or MIG is going to produce hard and soft zones and presents the possibility of cracking.  Read up about welding on hardened (tool) steel, pre- and post-heat, etc."USMCPOP" First-born son: KIA  Iraq 1/26/05Syncrowave 250 w/ Coolmate 3Dialarc 250, Idealarc 250SP-175 +Firepower TIG 160S (gave the TA 161 STL to the son)Lincwelder AC180C (1952)Victor & Smith O/A torchesMiller spot welder
Reply:Originally Posted by raye321I have a circular blade I use to cut thick rubber. The blade cracked from the arbor hole to the outer edge of the blade. I ordered another but it takes over a month to get because it has to be custom made. I need to keep running the machine. The blade is hardened steel, I dont know what kind or how it was hardened. 1/8" thick.  I have an arc welder, acetalene and a small 90 amp Mig.  I figure the arc welder would be the best to use? What would be the best welding rod to use? And how should I prepare the crack. I was thinking using a small diamond grinding stone on a dremel tool and grinding a groove along the crack.
Reply:Can you install "fender washers"? Put the washers on each side of the blade and install it in your saw. Spin it by hand to check for running true. Install short "tacks" around the outside of the washers. I'd start out trying to use something similar to 309 stainless steel rods. Make sure and clamp your ground to the saw blade.Just my humble opinion.Thanks,HoboLincoln SA200's... at least 15 - 20. They come and go. Growing partial to the "Short Hoods" in my old age. Last count on Short Hoods was 13 in possession.
Reply:I wouldn't run a circular saw with a cracked blade in a million years.The same goes for a REPAIRED cracked blade.When a circular saw blade breaks (and a cracked one will, it's just a matter of time) it's like a bomb going off.Good way to bleed.
Reply:hand grenade, accident waiting to happen.
Reply:It's not a circular saw blade. It's a circular blade about 4.5" dia. with a knife beveled edge. At no load top rpm is about 300rpm but it is much less than that when cuttng.
Reply:The blade is still working, if it did break it would just stay where it is.What type brazing rod would you use? I'm just looking to squeak by until I get the new ones.
Reply:I read about a guy that was grinding with a 5 inch grinder and the wrong style disc, the disc splintered, shattered, and impaled him in several areas.  Needless to say, these types of parts must be in good shape and used on the right machine or things can go horribly wrong.  I would never use a cracked blade under any circumstance.  Please don't end up being another statistic.Matthew MortonTexas A&M '06Logsdon Seminary '13"Who Dares Wins""AFTF""WH2PH"SA 200 (Code: 5337)TB 302CP 302 w/22A Wire FeederMillerMatic 200Miller Syncrowave 200MillerMatic 252BurnTables 4x4 CNC MachineHypertherm 65
Reply:A grinder goes at about a couple thousand rmps. this machine when cutting through 3" rubber is going about 75rpm's  I have had blades that cracked and shattered while cutting and it cant go anywhere but simply drops to the floor. A machine shop welder once told me that a weld is much stronger than the metal of the part itself, thats not true?
Reply:Yes the weld is usually stronger than the base metal. However, the problem is that hardened steel frequently cracks next to the weld in the area affected by the heat of welding. It's not the weld that fails, it's the base material that fails because it was welded. Simply cooling down, the base material can start to crack like glass, with hundreds of tiny minute cracks that can quickly grow under stress. Hard steels are usually brittle to begin with even if they are strong. Cracks due to welding and the changes in the material due to the heat involved simply compounds issues that already exist..No government ever voluntarily reduces itself in size. Government programs, once launched, never disappear. Actually, a government bureau is the nearest thing to eternal life we'll ever see on this earth! Ronald Reagan
Reply:Originally Posted by DSWYes the weld is usually stronger than the base metal. However, the problem is that hardened steel frequently cracks next to the weld in the area affected by the heat of welding. It's not the weld that fails, it's the base material that fails because it was welded. Simply cooling down, the base material can start to crack like glass, with hundreds of tiny minute cracks that can quickly grow under stress. Hard steels are usually brittle to begin with even if they are strong. Cracks due to welding and the changes in the material due to the heat involved simply compounds issues that already exist.
Reply:raye321I have worked on large, turn-key projects in very remote locations.  The welder is called to fix anything metal, regardless of the degree of repairability.Your repair is one that I would be called to attempt regardless of metallurgical, or safety considerations, because it was 9000 miles to the store.  Consider this, 'a bush only repair'.Take it to the best TIG welder you can find.Use nickel filler.  Nickel is ductile and high carbon friendly.Weld short beads from the outside-in, alternating sides, to control the thermal gradient.Weld over a back-purged [round] reservoir so the blade can be easily flipped for alternating short beads.The back-purging is so you can run a back-bead on clean metal.Calibrate the bead penetration/fill, to the gauge of the blade, so the back will accept a bead without grinding a groove.Take your time.Guarantee is off! Opus
Reply:Drill a hole at the end of the crack to nip it in the bud. Only use if you absolutely have to, wait for new and good blade.Disclaimer; "I am just an a$$hole welder, don't take it personally ."
Reply:I'd rather go to the hardware store and pick up a construction blade, grind the teeth off and sharpen it, than to fix a cracked blade.My name's not Jim....