Machining 4140 Chrome Moly

epanzella

epanzella

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I'll be cutting a Savage breech plug into a McGowen barrel that they advertise as "4140 Chrome Moly" steel. Can I use HSS steel tool bits on that or do I need carbide? I regularly turn & bore with both but my threading bits are all HSS.
Thx
Ed P
 
epanzella said:
I'll be cutting a Savage breech plug into a McGowen barrel that they advertise as "4140 Chrome Moly" steel. Can I use HSS steel tool bits on that or do I need carbide? I regularly turn & bore with both but my threading bits are all HSS.
Thx
Ed P
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If you happen to know the hardness that would be very helpful to calculate the speeds. Also, are you doing surface work and threading or, just threading? If you're doing surface work, how long are the cuts. Also, what's the diameter of the piece?



Ray
 
I installed a 4140 muzzle brake a couple months ago on a M70 chromoly barrel and used regular HSS that i ground. Threads and finish came out very nice. Oh, used a AR warner threading insert, which is a grade of HSS.
 
Ray C said:
If you happen to know the hardness that would be very helpful to calculate the speeds. Also, are you doing surface work and threading or, just threading? If you're doing surface work, how long are the cuts. Also, what's the diameter of the piece?



Ray
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The barrel is 1.25" dia which will be turned to 1.1", barrel lug tigged on, and then the breech end will be be bored from.458 to whatever I need for the breech plug, which I don't have yet. It's prolly something to the tune of 11/16 x 20, judging from other plugs. I'm good with the turning as I have both carbide & HSS but was wondering if I should be acquiring a carbide threading capability while waiting for my barrel & plug to arrive. I believe the barrel hardness is in the low 30's (typical barrel steel) but I've as yet been unable to verify that.
 
benmychree said:
Be advised that carbide threading inserts are expensive, and OH! so easy to chip.
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Oh, I know, that's why I don't already have them. Clumsy gorilla that I am, It took me a while to get the hang of using carbide turning & boring tools without chipping them every 5 minutes. I think internal threading with carbide will have an expensive learning curve. Half the chips will be 4140 and the other half carbide.
 
I just got done making a shaft from 4140 at work, and I can say that the finish that I got from HSS was far better than the finish I got from carbide inserts.
 
Why is everyone such carbide devotees for the HOME SHOP? HSS gets sharper than carbide and makes cleaner cuts. It can do interrupted cuts. You can easily grind custom shapes. I even make W1 cutters where I need a complex shape that can't be ground with what I have. (just slow the speeds down!)

You guys don't need to use carbide for much except long facing jobs like taking a cut across your cast iron face plate. Cast iron eats up HSS pretty fast. I also use carbide on HARDENED steel sometimes(though that is not its intended purpose). Pre hard 4140 is not all that hard. I use HSS on it all the time.

We are not operating factories here. I think many waste a lot of money they don't have to on carbide and inserts. Most of your home shop machines don't run fast enough to even make the proper use of carbide.
 
george wilson said:
Why is everyone such carbide devotees for the HOME SHOP? HSS gets sharper than carbide and makes cleaner cuts. It can do interrupted cuts. You can easily grind custom shapes. I even make W1 cutters where I need a complex shape that can't be ground with what I have. (just slow the speeds down!)

You guys don't need to use carbide for much except long facing jobs like taking a cut across your cast iron face plate. Cast iron eats up HSS pretty fast. I also use carbide on HARDENED steel sometimes(though that is not its intended purpose). Pre hard 4140 is not all that hard. I use HSS on it all the time.

We are not operating factories here. I think many waste a lot of money they don't have to on carbide and inserts. Most of your home shop machines don't run fast enough to even make the proper use of carbide.
Click to expand...

Ready-made disposable HSS inserts? Yes, that's a joke. I think.
 
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