Maybe someone mentioned already but some guys set the compound at high angle & increment the DOC that way. Dimensionally this works but if your material and/or tooling doesn't like this 'creep up on it thou by thou' mode, then its of less value. Another option: I have my coated/steel inserts set up on different tool holders than my uncoated 'sharper' inserts for aluminum, so its easy to just plop on a that cutter with say 10 thou to go & do the finishing operation with that if it makes sense.
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4140 crankshaft modifications
- Thread starter phaxtris
- Start date
I have no doubt that this is an issue - especially with Carbide Inserts. They simply don't cut the same in both directions. Perhaps not the triangular inserts set on equal angles, or round inserts, but the rest do for sure. And I wouldn't trust triangular or round either unless the dimension doesn't matter.
I have been known to cut in both directions but NEVER on finish passes. I ALWAYS back off and rewind manually, then set the depth of my next cut based on what happened on the previous cut. Otherwise you have no idea what you will get. Especially with inserts on different angles, but also with HSS.
Yes, it was mentioned. But I think it's only of value if you are trying to creep up on a dimension instead of using the results of the previous cut. And quite frankly, I don't think creeping up on a dimension is as reliable as an experience based cut using the prior cut.
Hitting a precise dimension is not as simple as trusting the dials or even a DRO. Too many variables and too many factors. Experience based cuts are much much more reliable.
Creeping up on a dimension can work too, but it is also subject to many variables that are all conspiring to ruin your project. I only do that with honed sharp HSS that I trust in the material I'm cutting. Time might convince me to trust inserts for Aluminium or Stainless, but that time is still a ways off into the future.
In summary, for me there are really only two ways to hit a precise dimension cutting on a lathe. Experience based cuts with Carbide or HSS, and fine cuts with very sharp HSS.
Grinding is also an option, but we are discussing cutting here.
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Thanks to @RobinHood I have some more 4340!
It sure is soggy, Rudy and I put it in the drawer.....I surely couldn't get it out on my own ! Had to hook up a chain fall to get it out !
It sure is soggy, Rudy and I put it in the drawer.....I surely couldn't get it out on my own ! Had to hook up a chain fall to get it out !
152lbs, thing weighs more than I do
Anyhow, made a little bit of progress, took 25 min to cut a piece off with the 7x12 and whatever blade I have in there, and 1.5 hours of rough turning to get here
One thing, I cannot get the chips to break this time, tried all sorts of doc"s with different feed speeds, no luck on that front, just massive bird nests, I'll keep at it tomorrow if I have time, maybe I'll find a combination that works
Anyhow, made a little bit of progress, took 25 min to cut a piece off with the 7x12 and whatever blade I have in there, and 1.5 hours of rough turning to get here
One thing, I cannot get the chips to break this time, tried all sorts of doc"s with different feed speeds, no luck on that front, just massive bird nests, I'll keep at it tomorrow if I have time, maybe I'll find a combination that works
Looks like you are using a WNMG insert. It's my experience and opinion that WNMG TRIGON inserts usually break chips better than other insert styles except maybe square which is similar. However, it's important to use one designed for your material if you want good chip breaking. I think a big nose radius is also a factor because of the tendency to curl the chips a bit more. All that said, some materials just like to make bird nests. When I really need chip breaking on such a material, I grind my own HSS and I grind in a very aggressive chip breaker.
I wonder if you could make an aggressive chip breaker that might be held on by the insert clamp. Maybe even make a whole new clamp to do that in the clamp itself?
I turned some 4140 yesterday. 4340 should behave similarly.
TNMG (I think it’s a 432), 570 to 770 rpm, 0.050” DoC, 0.008 to 0.010 “/rev. The lathe has to work a bit, but nothing that’s going to hurt or break anything.
The large OD is 3.5”, the snout is 1.25”.
(Yes, the boss of my part is already scratched up because the fit was a bit too tight…)
TNMG (I think it’s a 432), 570 to 770 rpm, 0.050” DoC, 0.008 to 0.010 “/rev. The lathe has to work a bit, but nothing that’s going to hurt or break anything.
The large OD is 3.5”, the snout is 1.25”.
(Yes, the boss of my part is already scratched up because the fit was a bit too tight…)
I'm using the same insert from the other piece, tried new corners, it was breaking on that
I'm 560rpm, tried anything from .020-.040 doc, I'll check the chart, I think I was more like .oo48/rev, I'll check the chart again, i dont think i have the power for a .050 @ .010 cut
I have a few other inserts to try as well, I'll have to take a look at the machine tonight
I'm 560rpm, tried anything from .020-.040 doc, I'll check the chart, I think I was more like .oo48/rev, I'll check the chart again, i dont think i have the power for a .050 @ .010 cut
I have a few other inserts to try as well, I'll have to take a look at the machine tonight
I must have been running it much harder the first time around
Breaking chips now with .05 doc and .083 per rev at 560rpm, it does pretty well at that chip load. I don't think I will push it any harder, there is a pretty rough section of the rack I dont want to make any worse...one of these days I should take it off and braze/file that section, I don't imagine I can get a new one
Breaking chips now with .05 doc and .083 per rev at 560rpm, it does pretty well at that chip load. I don't think I will push it any harder, there is a pretty rough section of the rack I dont want to make any worse...one of these days I should take it off and braze/file that section, I don't imagine I can get a new one