As a follow up to my previous post on Camshaft Breakage I am now considering making my own billet cam blanks and have a Cam Grinding Co. do the heat treatment and grinding. Does anyone have any ideas as to what material I should be looking for? I see that Crane is using 8620. Information that I find says that 4140 or 4340 would be a better choice as far as strength and hardness go. By looking at the description of the process on Crane's website it would apear that they are putting carbon into the lobes when doing the heat treat, hence the need for the copper coating. This would give them a softer core with a hard surface. Maybe better to resist breakage?
My plan would be to simply turn the cam with round lobes on the lathe and send it off to be finished. Has anyone had any experience with turing their own blanks and if so do you have any tips?
Thanks for your input.
RMS Performance
Billet Camshaft Material
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Looks like you got some good response to the first post on this...
IF there is a billet core available even if you do the work you are not going to get it done cheaper and CORRECTLY for less. I would say the learning curve in getting the cam blank correct is going to cost more than the $1000 billet core.
For example a round lobe billet core for a SBC (the most common V8 motor for aftermarket cams) at my cost as a dealer is close to $600. This is a cam that still needs to be rough ground then heat treated then finish ground, and they have a few of these cores in stock... Now go to a John Dere like your application and $1000 for a finished cam sounds about right to me.
Reinventing the wheel is expensive and very hard to do without a ME and a metalugist working hand in hand with you.
I'm sure someone on here will give you a way to do this, but I would guess the heavy hitters would suggest otherwise.
Bret
Looks like you got some good response to the first post on this...
IF there is a billet core available even if you do the work you are not going to get it done cheaper and CORRECTLY for less. I would say the learning curve in getting the cam blank correct is going to cost more than the $1000 billet core.
For example a round lobe billet core for a SBC (the most common V8 motor for aftermarket cams) at my cost as a dealer is close to $600. This is a cam that still needs to be rough ground then heat treated then finish ground, and they have a few of these cores in stock... Now go to a John Dere like your application and $1000 for a finished cam sounds about right to me.
Reinventing the wheel is expensive and very hard to do without a ME and a metalugist working hand in hand with you.
I'm sure someone on here will give you a way to do this, but I would guess the heavy hitters would suggest otherwise.
Bret
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OldSStroker
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Steel camshafts are usually made from 8620 (a carbuizing grade of Nickel-Chrome-Molybdenum alloy steel). The "20" indicates only .2% Carbon which isn't enough to achieve the hardness needed for wear resistance. Only the wear surfaces are carburized, or heated in a high-carbon atmosphere until carbon diffuses into the surface a given amount, perhaps .050 in. In order to prevent all the surfaces from being carburized, the core is copper plated. This prevents diffusion of the carbon into the steel in the areas where it is not desired.
Obviously the surfaces requiring carburization have to be free from copper. This would usually be done by grinding the journals and cam lobes slightly oversize after plating and before carburizing. The lobes, especially have to be close to finished size, because there is only a limited "case depth" or hardness layer for finish grinding.
After carburizing the camshaft is hardened by heating to the correct temperature and quenching, or rapid cooling. The case gets above Rc60, and the "core" or uncarburized portion may get into the high Rc30s. The entire part is them tempered to reduce brittleness and achieve the final surface hardness desired.
The beauty of 8620 is that when carburized and hardened, it has a very hard wear resistant case or surface because the extra carbon has formed Chromium carbides. Think of them as little hard balls in somewhat softer, but still very hard matrix. The core, or everything not casehardened, is extremely strong, tough and not at all brittle. If you were to use 4340 or 4140, the .4% carbon would get to about Rc 50 which isn't quite hard enough for the lobes and too hard for the toughness you need in the rest of the cam.
Many cam companies do NOT make their own cores; they buy cores ready to finish grind the lobes. If your chosen cam company DOES make/heat treat their own cores, they MIGHT entertain finishing your blank, but at a high cost. Remember they make money on the machining of the core also.
As a contract manufacturer, we are always hesitant to take someone else's blank and finish it. It may not be machined exactly as it should be, and sometimes the material is not what is claimed. If anything goes wrong in heat treatment the contract shop (cam company in this case) really has no liability, and you will be charged for the work even if the processing doesn't work. This happens. Been there, done that. It is really a can of worms, and convinces most shops not to do this kind of thing.
As for advice: I wouldn't make my own core blanks. I would pay the pros.
Good luck...you might need it.
My $.02
Obviously the surfaces requiring carburization have to be free from copper. This would usually be done by grinding the journals and cam lobes slightly oversize after plating and before carburizing. The lobes, especially have to be close to finished size, because there is only a limited "case depth" or hardness layer for finish grinding.
After carburizing the camshaft is hardened by heating to the correct temperature and quenching, or rapid cooling. The case gets above Rc60, and the "core" or uncarburized portion may get into the high Rc30s. The entire part is them tempered to reduce brittleness and achieve the final surface hardness desired.
The beauty of 8620 is that when carburized and hardened, it has a very hard wear resistant case or surface because the extra carbon has formed Chromium carbides. Think of them as little hard balls in somewhat softer, but still very hard matrix. The core, or everything not casehardened, is extremely strong, tough and not at all brittle. If you were to use 4340 or 4140, the .4% carbon would get to about Rc 50 which isn't quite hard enough for the lobes and too hard for the toughness you need in the rest of the cam.
Many cam companies do NOT make their own cores; they buy cores ready to finish grind the lobes. If your chosen cam company DOES make/heat treat their own cores, they MIGHT entertain finishing your blank, but at a high cost. Remember they make money on the machining of the core also.
As a contract manufacturer, we are always hesitant to take someone else's blank and finish it. It may not be machined exactly as it should be, and sometimes the material is not what is claimed. If anything goes wrong in heat treatment the contract shop (cam company in this case) really has no liability, and you will be charged for the work even if the processing doesn't work. This happens. Been there, done that. It is really a can of worms, and convinces most shops not to do this kind of thing.
As for advice: I wouldn't make my own core blanks. I would pay the pros.
Good luck...you might need it.
My $.02