- Joined
- Jan 10, 2016
- Messages
- 29
hello folks, I need to machine an SKS bolt (a fellow who did a Rockwell test on it claims that hardness varies depending on the specific area - from ~ 40 to ~ 5o ) It may also vary depending on where / when the gun was manufactured. But for all practical purposes I think it is reasonable to assume the hardness between 40 and 50. So I have a hitorque mini mill from LMS (about 1/2 HP and spindle speed range from zero to 2500).
Also got a 3/8" carbide end mill (two flute). The question is the optimal speeds, feeds and the depth of cut. I have read about carbide bits to be usable at much greater speeds. I have experimented on a broken bolt with different settings. The cuts are possible up to 1 mm in depth using the maxium speed of 2500. The 0.4 mm (0.016") depth at 2500 rpm are seem to be reasonably possible, even though the vibrations are much stronger than when I cut aluminum. I was able to go as deep as 1 mm (0.04") with the same RPM but much lower feed. At this extreme settings the mill vibrated like crazy but with very low feed level it still did remove the metalg. I was impressed, but not for long. When I closely examined the carbide end mill I have noticed that it its cutting edge got some damage. Tiny pieces of carbide got broken off (not much just in a couple of place but still - paying the price for my foolish experimenting) So what are some basic rules when cutting hardened steel on a mini mill using carbide tools? And what must be done differently (if anything) if using HSS?
Oh, also I almost forgot to mention using TapMagic cutting fluid which created some smoke but also reduced the vibrations. After that I read some warnings against using cutting fluids with carbide tools allegedly because they get too hot and uneven cooling because of the cutting fluid can produce micro-cracks in the tool. Not sure if this is the reason for the chipping of the tool's edge or is it because I had a couple of "hard" startings - that is not sure how to properly start the cut without the tool being slammed into the work peace the hard way. I hope I express my self clearly here.
Also got a 3/8" carbide end mill (two flute). The question is the optimal speeds, feeds and the depth of cut. I have read about carbide bits to be usable at much greater speeds. I have experimented on a broken bolt with different settings. The cuts are possible up to 1 mm in depth using the maxium speed of 2500. The 0.4 mm (0.016") depth at 2500 rpm are seem to be reasonably possible, even though the vibrations are much stronger than when I cut aluminum. I was able to go as deep as 1 mm (0.04") with the same RPM but much lower feed. At this extreme settings the mill vibrated like crazy but with very low feed level it still did remove the metalg. I was impressed, but not for long. When I closely examined the carbide end mill I have noticed that it its cutting edge got some damage. Tiny pieces of carbide got broken off (not much just in a couple of place but still - paying the price for my foolish experimenting) So what are some basic rules when cutting hardened steel on a mini mill using carbide tools? And what must be done differently (if anything) if using HSS?
Oh, also I almost forgot to mention using TapMagic cutting fluid which created some smoke but also reduced the vibrations. After that I read some warnings against using cutting fluids with carbide tools allegedly because they get too hot and uneven cooling because of the cutting fluid can produce micro-cracks in the tool. Not sure if this is the reason for the chipping of the tool's edge or is it because I had a couple of "hard" startings - that is not sure how to properly start the cut without the tool being slammed into the work peace the hard way. I hope I express my self clearly here.
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