Problem with hardened steel

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Hi Guys I'm new here and I am just looking for some help with a project I'm working on. I'm putting a chainsaw engine on my bike and I just need the sprocket welded onto the centrifigul clutch. I went to a welding shop to get the bike sprocket welded onto the outer drum of a centrifigul clutch I have at a welding shop the other day. Anyways the guy said that he couldn't weld the sprocket to the clucth because the sprocket was hardened steel and he couldn't weld hardened steel. He said it would weld fine but once there was any tension on it it would break off. Then I talked to a friend of mine who said that a welding shop should be able to weld hardened steel they just have to heat it up hotter. Or he said I could temper the sprocket to try and soften it and see if they will weld it. So what do you guys think? I'm trying to find out an answer to what I should do. I can't really get a non hardened steel sprocket because all the sprockets they make are hardened. So do you have any ideas or will what he said work? Thanks a bunch!
Reply:If its tempered steel, you can heat it cherry red and let it cool slowly.  No drafts.... Weld it, then heat the whole thing up to a low cherry red again and drop it in a bucket of oil.  DO THIS OUTSIDE.  The white smoke that comes out of the bucket IS flammable.  It can self ignite.  This should re temper the sprocket and clutch.  You would have to remove any bearing from inside the clutch before you start.  How big is this sprocket?Whereyafrom?DavidReal world weldin.  When I grow up I want to be a tig weldor.
Reply:I already had my friends dad press out the needle bearing. The sprocket is only 13 teeth since it is a drive sprocket and it fits perfectly on the clutch. The sprocket isn't tempered steel it is hardened steel which is why they said they couldn't weld it. What my friend said is that they should be able to weld it and have it hold as long as they heat it up before they weld it. Or he said I should take the hardened steel sprocket and temper it to soften it so that they can weld it. Would either of those work? If not then do you have any other ideas?
Reply:Originally Posted by MisterSteve124I already had my friends dad press out the needle bearing. The sprocket is only 13 teeth since it is a drive sprocket and it fits perfectly on the clutch. The sprocket isn't tempered steel it is hardened steel which is why they said they couldn't weld it. What my friend said is that they should be able to weld it and have it hold as long as they heat it up before they weld it. Or he said I should take the hardened steel sprocket and temper it to soften it so that they can weld it. Would either of those work? If not then do you have any other ideas?
Reply:Ok thanks I don't know why they said they wouldn't be able to do it. Then again the guy that was there was atleast 75 so maybe he was loosing his mind. Oh and just incase this might matter all of the stuff is really small. Maybe I'll just post some pics. Good idea brb.
Reply:Ok here are the pictures: Think it will work?   Thanks for you help again guys.
Reply:I think if you ever got it going, it would be WAYYY to fast.  This guy you want to weld it may be thinking the same thing.  The new sprocket has to be centered exactly on the clutch.  How many RPM does this motor turn you are putting on a bicycle?  Can you figure out how fast its going to go?Real world weldin.  When I grow up I want to be a tig weldor.
Reply:I imagine the guy at the shop just didn't want to do it. Some guys don't want their name and work associated with a cobble job. If you paid the price all the heat treatment and effort was worth you could fab or buy a set-up. You have to understand that part. That clutch drum won't be the most compatible thing to weld that sprocket to. In theory you'd be ruining that drum too. Sounds like the saw is history anyway and the motor is going to be donated to your new invention so it's not like it'll be a catastrophe if it doesn't last long. It's doable, just not guarantee-able.  Not for a few bucks anyway.
Reply:Chainsaws max out at 10,000 + rpm unloaded (new ones up to 13,500) and 8000+ under load of cutting.  Hard to pedal that fast.
Reply:Dave Is correct about the sprocket being to BIG for the application. The engine may have th balls for the job but that clutch wont. You need the sprocket on the engine as small as possible.Me!
Reply:Are you saying that the clutch won't work because the sprocket is too big? What does that have to do with anything? I know people have done this same thing almost exactly and it works. And I know it needs to be centered. As long as it can be welded on there I have everything else figured out so it will work. Oh and Sandy I bought the chainsaw specifically for this and it was only 55 bucks so it's not a big deal I don't ever intend to cut down a tree with this again, I have another one for that.Last edited by MisterSteve124; 09-25-2007 at 11:00 PM.
Reply:Others have commented on the welding, so I won't. My concern is for the gear reduction ratio. I  assume you have another series of chains and sprokets before you are going to transfer the power to the rear wheels right? Your final reduction needs to be in the range of 100:1 or so compared to the pedal RPM to have much driveability with a high RPM engine like a chainsaw. Assume your cruising speed to be 60 RPM with the pedals, so if you are going ot lug the saw engine to 6000 rpm, - then you need the reduction gearing. A 10:1 setup feeding another another 10:1 would work. Above all, have fun! sounds like you already are.-Ryan McEachern
Reply:And I hope you're planning to cover everything with a chain-guard . . .  at least then if something breaks it won't take your foot or leg off.
Reply:you might try matching the clutch to something belt drivin there is a lot of heat and area there or maybe a machinist with to much time and a briliant mind ?
Reply:most clutch companys have some sort of cross reference
Reply:As long as it can be welded on there I have everything else figured out so it will work. Oh and Sandy I bought the chainsaw specifically for this and it was only 55 bucks so it's not a big deal I don't ever intend to cut down a tree with this again, I have another one for that.
Reply:The next question is what size tires and what size rear gear (Teeth) for a ratio. I played with the pic and it looks like you could grind that clutch 6 tooth into a gear, the teeth spacing is really close, it would only be a 6 toothed gear but it would get you going. some time spent measuring and marking, then an angle grinder and some patience may lead you to a 6 toothed gear that would work for your application. you have a sprocket to design your tooth pattern, only costs are time and maybe a cutting disk and grind.
Reply:You will need to do a lot of math for that question Everything you mentioned will change the final number and may or may not effect if it will work at all.Smaller tires will be easier to drive but do not role over objects as well   What you will need to do is determine you gearing ratio from having a max speed you want to attend (for a $55 chain saw I would say 25MPH would be a respectable top end  )You will also need to know the max RPM of the motor...To determine how fast this thing will move do this:Tires = 10"Circumference = 31.415926" (how far the wheel will travel in one turn)Now we have distance so lets add time...100:1 gearing (just using it since it was mentioned) = 800 RPM31.415926" x 800 RPM = 25,132.7408 inches/min.Now convert it to MPH...25,132.7408 inches/min. x 60 (munger of min in hour) = 1,507,964.45 inches/hour(1 mile = 63,360 inches)1,507,964.45 inches/hour  /  63,360 inches = 23.8 MPH !You can get the answer by doing it a few other ways also....Me!
Reply:ME!Thanks for doing all the math, but if  he has  maybe 10 to one ratio?  Does that mean it will go 238 mph? Just bustin.  DavidReal world weldin.  When I grow up I want to be a tig weldor.
Reply:the chainsaw engine will never pull a bike and rider to 23.8 mph. A factory made, much lower geared mini-bike will do about 30 to 35 with a 5hp engine.
Reply:Send it to me up in Washington.  I weld hardened steel to mild steel all day long.  It can be done, and easily too.  That shop is lazy, or doesn't have skilled hands to do it the right way.
Reply:Originally Posted by WelderBoySend it to me up in Washington.  I weld hardened steel to mild steel all day long.  It can be done, and easily too.  That shop is lazy, or doesn't have skilled hands to do it the right way.