how to harden a cutting edge

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I am making a press that will cut light plastic parts and I suspect that I will want to harden the cutting edge a but to help it hold an edge.  This part is 1/8" thick and about 30" long with a curve at each end (cutting edge forms an elongated C shape).I would like to use mild steel because that is what I have readily available and what I am comfortable working with.Can I just use my OA torch to add carbon to the cutting edge by heating it up and hitting it with a reducing flame?I don't think I need the hardness to go very deep since I am cutting plastic at low speed (manually pressed), I figured I could sharpen the edge and then harden it.Any pointers?Hobart LX235Victor 250 Oxy-Acetylene Rig (welding and cutting)Bobcat 773F-350, 1999, 4x4, 16' 10K# trailerOutdoor Wood Burner - 10 cords/year
Reply:Mild steel can't be hardened very much. Stainless can be easily hardened though. Just heat it up to a a nice orange glow and quench it in water as quick as you can.Ian TannerKawasaki KX450 and many other fine tools
Reply:Cutting blades are usually made of high carbon steel so they hold an edge better.MM350P/Python/Q300MM175/Q300DialarcHFHTP MIG200PowCon300SMHypertherm380ThermalArc185Purox oaF350CrewCab4x4LoadNGo utilitybedBobcat250XMT304/Optima/SpoolmaticSuitcase12RC/Q300Suitcase8RC/Q400Passport/Q300Smith op
Reply:Originally Posted by DesertRider33Cutting blades are usually made of high carbon steel so they hold an edge better.
Reply:What about hardfacing, and then grinding to shape and sharpen?  I'm no expert on hardfacing, but I've used it with really good effects on auger teeth.Dynasty200DX w/coolmate1MM210MM VintageESAB miniarc161ltsLincoln AC225Victor O/A, Smith AW1ACutmaster 81IR 2475N7.5FPRage3Jancy USA1019" SBAEAD-200LE
Reply:Obviously higher carbon steel is better, but mild steel can be case hardened, even localized areas. You need a carbon powder like this   http://www.midwayusa.com/viewProduct...tNumber=119479Taken from their site:Application instructions (from Kasenit) for Low Alloy or Low Carbon Steel:There are two methods of application.Method A: Heat the work uniformly to a bright red (1650 - 1700 degrees F), remove any scale with a wire brush, dip, roll or sprinkle the Kasenit powder on the component. The powder will melt and adhere to the surface, forming a shell around the work. Reheat to 1650 - 1700 degrees F, hold at this temperature for a few minutes and quench in to clean cold water. This will give the component a completely hard case of uniform character and depth.Method B: If a deeper case is required, then a container for the compound can be used. A discarded can, lid or tray is suitable for this purpose, but care must be taken to burn off the tin coating before use. Completely cover the component with compound and heat to a bright red (1650 degrees F) for five to thirty minutes, depending upon the depth of case required. Quench only the component in clean, cold water unsing dry tongs for handling. There are options, depends on your requirements.JasonXMT 350 MPA Dynasty 280DXSuitcase 8RC / OptimaSpoolmatic 30AThermco Ar / C02 mixerAssorted O/A gear
Reply:Originally Posted by fortyonethirtyMild steel can't be hardened very much. Stainless can be easily hardened though. Just heat it up to a a nice orange glow and quench it in water as quick as you can.
Reply:Sugar works for case hardening as well, but nowhere near as well.Still, if you case harden, you'll only get a very thin hardened layer that will be lost with the first sharpening, and the heating will hurt your edge that would need to be immediately sharpened.  That kind of nixes case hardening for parts that need a sharp edge.O1 steel would be your best bet.  Cheap, and easily hardenable, it also anneals when cooled in air, so its pretty forgiving.
Reply:Rlitman is correct, O1 would be the best choice. However, I also like AndyA's recommendation of using a hardfacing rod / wire. Which was expanded upon by Oldiron2 (milling a groove for the hard filler). I would like to throw out an idea (or 3) along similar lines:1) Rather than milling a groove, lap a sacrificial backing plate to the back side of the cutting edge to    lay the hardfacing material on. Grind it away or leave it in place if you can design around it.2) Would a copper backing plate work in the same manner, therefore not having to grind anything away (aside from sharpening)? I know this works for small areas, but long and thin? I haven't experimented with that. I don't see a stick welder in your sig, but maybe a hardwire exists that can be laid down with O/A? Or get a buddy to do it.I love throwing out ideas. I'm not saying they're the best. Choose what works for you.XMT 350 MPA Dynasty 280DXSuitcase 8RC / OptimaSpoolmatic 30AThermco Ar / C02 mixerAssorted O/A gear
Reply:The only process that I have is OA and I'd like to do the project myself so can anyone recommend a hard facing material suitable for OA?Hobart LX235Victor 250 Oxy-Acetylene Rig (welding and cutting)Bobcat 773F-350, 1999, 4x4, 16' 10K# trailerOutdoor Wood Burner - 10 cords/year
Reply:Well, a search shows they exist:http://www.stellite.com/ProductsServ...2/Default.aspxhttp://www.sulzermetco.com/desktopde...534_read-5399/Now it means a trip (or call) to the LWS to see what is actually available, and how much $$$. Hope it doesn't hurt too much...JasonXMT 350 MPA Dynasty 280DXSuitcase 8RC / OptimaSpoolmatic 30AThermco Ar / C02 mixerAssorted O/A gear
Reply:Originally Posted by BCRDWell, a search shows they exist:http://www.stellite.com/ProductsServ...2/Default.aspxhttp://www.sulzermetco.com/desktopde...534_read-5399/Now it means a trip (or call) to the LWS to see what is actually available, and how much $$$. Hope it doesn't hurt too much...Jason
Reply:Well, there is hard and then there is HARD.  See, the 'problem' with mild steel as a cutting edge/blade is that is not hard, so the edge doesn't last, and that it deforms under load and "yields", so the edge is no longer there.  Similar things but not quite the same.A 'real' cutting edge/blade is made with a steel alloy that can be hard and tough and durable and abrasive-resistant in varying degrees as needed for the task or job at hand.Usually that will mean a steel alloy that can at least be pretty hard at the actual cutting edge and then maybe a bit softer and thus 'tougher' back behind the actual thin edge.  That differential hardness can be achieved in a few different ways.But a plain mild steel edge is pretty much no good as a cutting edge, even on something as 'simple' as cutting paper.  (which by the way, is not all that 'simple' as cutting paper is actually pretty harsh on a cutting edge.)Hardfacing comes in all sorts of 'flavors', with varying degrees of hardness and abrasive resistance and toughness.  It isn't usually all that cheap.  And some of the more 'specialized' and highly-alloyed hardfacing fillers are $$$$$.For a 'blade', I'd suggest just getting a piece of alloy steel of an appropriate sort.  O1, D2, A2, W1, that sort of thing.  Than you have to get it hardened or harden it yourself.  And for a 'newbie', hardening a 1/8 inch thick 30 inch long piece of steel is not all that trivial of a task.  Depending on the exact alloy and the available equipment it is do-able, but not necessarily trivial.IMHO.    The best laid schemes ... Gang oft agley ...
Reply:Originally Posted by MoonRiseWell, there is hard and then there is HARD.  See, the 'problem' with mild steel as a cutting edge/blade is that is not hard, so the edge doesn't last, and that it deforms under load and "yields", so the edge is no longer there.  Similar things but not quite the same.A 'real' cutting edge/blade is made with a steel alloy that can be hard and tough and durable and abrasive-resistant in varying degrees as needed for the task or job at hand.Usually that will mean a steel alloy that can at least be pretty hard at the actual cutting edge and then maybe a bit softer and thus 'tougher' back behind the actual thin edge.  That differential hardness can be achieved in a few different ways.But a plain mild steel edge is pretty much no good as a cutting edge, even on something as 'simple' as cutting paper.  (which by the way, is not all that 'simple' as cutting paper is actually pretty harsh on a cutting edge.)Hardfacing comes in all sorts of 'flavors', with varying degrees of hardness and abrasive resistance and toughness.  It isn't usually all that cheap.  And some of the more 'specialized' and highly-alloyed hardfacing fillers are $$$$$.For a 'blade', I'd suggest just getting a piece of alloy steel of an appropriate sort.  O1, D2, A2, W1, that sort of thing.  Than you have to get it hardened or harden it yourself.  And for a 'newbie', hardening a 1/8 inch thick 30 inch long piece of steel is not all that trivial of a task.  Depending on the exact alloy and the available equipment it is do-able, but not necessarily trivial.IMHO.
Reply:Originally Posted by MoonRise) And for a 'newbie', hardening a 1/8 inch thick 30 inch long piece of steel is not all that trivial of a task.  IMHO.
Reply:Originally Posted by MoonRiseFor a 'blade', I'd suggest just getting a piece of alloy steel of an appropriate sort.  O1, D2, A2, W1, that sort of thing.  Than you have to get it hardened or harden it yourself.  And for a 'newbie', hardening a 1/8 inch thick 30 inch long piece of steel is not all that trivial of a task.  Depending on the exact alloy and the available equipment it is do-able, but not necessarily trivial.
Reply:Seeing we have established there are many metals, pros and cons of trying to harden, and it not being so simple as just heating and quenching and I for 1 don't think you would want to look down a piece of 1/8 material after you had just tried to hardface it with whatever, probably wouldn't stay very straight. Why don't you just pick up a blade for a paper cutter or maybe a 30" or 36 " stomp shear and adapt that for use.Would it be and option? I don't know the cost of such a blade but might save a lot of time or effort. Good Luck."Si Vis Pacem Para Bellum"Lincoln Idealarc 250 AC/DCMillermatic 251   Syncrowave 300   30A spoolgunLincoln MP210Hypertherm 45(2) LN 25(2) Lincoln Weldanpower 225 CV(4) SA200   1 short hood    SA250    SAM 400
Reply:Interesting point.  Maybe a cheap chinese sword from a novelty store?
Reply:Originally Posted by rlitmanInteresting point.  Maybe a cheap chinese sword from a novelty store?
Reply:Hi gwiley,If I have this pictured right in my head you could follow this link and scroll down to "steel rule dies" and then google study rule dies or steel rule dies for a bit. link here;http://en.wikipedia.org/wiki/Die_(manufacturing)With a backing plate, some jig-saw cut plywood, rubber pads for stripping and a bottom plate you're cutting away. The rule die material is very similar to a band saw blades with a knife edge and come in lots of sizes.Also we have a member here, "Monica" who is using clicker dies (very similar) to cut leather with.Good LuckMatt
Reply:If I understand the O/P correctly why not go to a wrecking yard and get an old leaf spring off a car or truck of suitable length and thickness.The spring is already very high carbon steel, heat up the spring red hot with your torch and shape it as required.  If you wish to cold work the steel you must "anneal" it.  Heat it up red hot then let it cool as slowly as possible by slowly applying less and less heat.  When the heat is totally withdrawn, bury it in some sand and let it cool slowly until cold.Pre-sharpen the edge with a grinder to shape desired, be careful not to burn the edge by overheating it..To harden the steel heat the entire piece up to red hot and quench in water until cool.  This makes the steel extremely hard and brittle, you now need to "temper" the steel so it is hard enough to hold an edge but tough enough to stand the use it will be put to.Polish several spots on the steel so you can see the steel temper colours. (or use temp stick).Heat slowly and evenly, watching the polished steel for tempering colours.  (use neutral flame) Probably a straw colour IIRC would work, look up "steel tempering colours" for a chart of the colours and pick the one most suitable. Depending on the tempering temperature the steel can be made anywhere from hard and brittle  (like a file) to softer but tough (like a chisel or an axe)  The edge will heat up faster than the rest of the spring because it is thinner, watch the edge doesn't get too hot.  The colours indicate the temperature, once the colour you want is present, quench the steel again in water.Result should be hard, tough and able to take an edge.  For more info, go to a blacksmithing site.  This is how high carbon steel knives and tools were made.I would look at attaching it to your press with set screws or bolts, if you weld it, especially with O/A the large HAZ will ruin the hardening/tempering you have done.You will probably need a rosebud tip for your O/A torch(es) to be able to get it hot enough.  If there is any experienced blacksmiths reading this they can probably explain this better than I have done here."The reason we are here is that we are not all there"SA 200Idealarc TM 300 300MM 200MM 25130a SpoolgunPrecision Tig 375Invertec V350 ProSC-32 CS 12 Wire FeederOxweld/Purox O/AArcAirHypertherm Powermax 85LN25
Reply:Wow - what an exciting possibility.  I have a few spare suspension springs laying around.  I think that I am going to play with shaping them.The best idea so far is to get a blade - I am thinking form a paper cutter or some other similar tool from the junkyard.  But I really like the idea of using scrap that I have laying around.The instructions above look easy enough to follow.Hobart LX235Victor 250 Oxy-Acetylene Rig (welding and cutting)Bobcat 773F-350, 1999, 4x4, 16' 10K# trailerOutdoor Wood Burner - 10 cords/year
Reply:As mentioned above, without a forge able to handle the dimensions of the blade it is darn near unlikely to be able to do even a half-a$$ed job of heat treating a long thin blade.Sure it is possible to make a hardened blade-like object from OCS (Old Chevy Spring).  If you have or can get a big enough supply of such springs all of the SAME alloy so that you have enough to experiment with and try and create a heat treatment profile.  And then expend the time and effort to -do- all that heat treating and try and come up with something that 'works'.  Oh, and you still have to make or buy a forge able to heat that long thin piece of steel.Or you can just go and buy a piece of alloy steel of known compostion and thus known heat treatment parameters.  You would still need the forge and such, but at least you would be -starting- with a known material.A 'scrap' cutter blade would probably be the 'best' bet IMHO.  And about cutting 'just some plastic'?  Plastic materials span a pretty big range of materials, with widely varying properties. Just cutting one or two?  Have at it.  Trying to cut 'lots' (you define what lots is) or more of a 'production/business' use, I'd say to make or buy a 'real' blade.  Real as in properly hardened and tempered steel.IMHO.    The best laid schemes ... Gang oft agley ...
Reply:Use material from http://www.wagnerdiesupply.com/steelrule.html
Reply:Originally Posted by fortyonethirtyMild steel can't be hardened very much. Stainless can be easily hardened though. Just heat it up to a a nice orange glow and quench it in water as quick as you can.Hi gwiley,1060 or 1090 are favorite materials for leaf springs (water hardened). It usually is hardened in the 45-50 rockwell "C" range making it very near file hard. and will begin to temper and lose hardness at 300°F.I don't have tempering charts near so I'll have to check the temper range for cutlery steels (about 42-46RC as I remember) which you can push around better if you need to warm up a leaf spring.Even fully annealed 1060 - 1090 is pretty strong and tough.I still like the rule die solution if I've got the picture right. Welding high carbon to keep in place is tricky and takes a duplex rod if your not going to heat treat it (very expensive rod).Matt
Reply:Originally Posted by gwileyI am making a press that will cut light plastic parts and I suspect that I will want to harden the cutting edge a but to help it hold an edge.  This part is 1/8" thick and about 30" long with a curve at each end (cutting edge forms an elongated C shape).I would like to use mild steel because that is what I have readily available and what I am comfortable working with.Can I just use my OA torch to add carbon to the cutting edge by heating it up and hitting it with a reducing flame?I don't think I need the hardness to go very deep since I am cutting plastic at low speed (manually pressed), I figured I could sharpen the edge and then harden it.Any pointers?