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+--- Thread: Machining 4140 (/thread-4203.html)
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RE: Machining 4140 - Cross Slide - 07-04-2020
(07-04-2020, 11:01 PM)EdK Wrote: You're getting a good finish.
Ed
Thanks Ed
RE: Machining 4140 - Pete O - 07-05-2020
(07-04-2020, 06:24 PM)f350ca Wrote: Even prehardened isn't that tough to machine with carbide. You have to take reasonable heavy cuts to get a good finish. If you come up shy and have to remove 1 or 2 thou the finish sucks.
That makes a lot of sense, I use this stuff for a lot of my projects and I've been frustrated so many times that I'll be getting a good finish through the whole roughing process then stuff it up in the last couple of cuts. Also I was encouraged a while ago to push it harder to make chips rather than ribbons; I was surprised how hard I had to go, i.e. in SFM, DOC and feed. Previously I'd always had one chip per cut.
RE: Machining 4140 - Cross Slide - 07-05-2020
(07-05-2020, 05:53 AM)Pete O Wrote:(07-04-2020, 06:24 PM)f350ca Wrote: Even prehardened isn't that tough to machine with carbide. You have to take reasonable heavy cuts to get a good finish. If you come up shy and have to remove 1 or 2 thou the finish sucks.
That makes a lot of sense, I use this stuff for a lot of my projects and I've been frustrated so many times that I'll be getting a good finish through the whole roughing process then stuff it up in the last couple of cuts. Also I was encouraged a while ago to push it harder to make chips rather than ribbons; I was surprised how hard I had to go, i.e. in SFM, DOC and feed. Previously I'd always had one chip per cut.
I was getting the same. I wasn’t getting 6s & 9s. My machine just isn’t big enough to pull that off. On my facing cut I was getting short ribbons. Maybe 1” long with a nice straw and light blue color. Once I started boring out the ID I was constantly taking .030 DOC and getting a really nice finish. Not like the finish I got on the face. But it was still really nice. For the boring I was getting long ribbons. And luckily the ribbons where automatically going into the spindle and would fall out of the headstock. So nothing was getting tangled up around the chuck or tool post.
I did however find out the limitations of my machine. It has a emergency cut off switch that tripped while doing the boring. It reset right away and I continued. I should not have done that. A couple cuts later and the spindle was slowing down on its own and the switch kicked out again. I thought I fried something. Luckily it was just a thermal cut out. Once it cooled right down it allowed me to reset and finish the boring. I was still doing .030 DOC and it was doing great. But at least I learned more about the capabilities of my machine.
Once I was to my dimension on the bore I had to take .001 more. My gauge was just to tight. The finish is still nice on the bore. But it’s not the nice shinny finish I was getting with the bigger cuts. I’m still very happy with it!!!
Trevor