Annealed 4140

[stevec]

(01-15-2013, 10:07 AM)DaveH Wrote: like "ships passing in the night"DaveH

I enjoyed that Dave.
What I don't enjoy is "ships that pass on the right" particularly when I'm dodging the ones that pass on the left.

[f350ca]

Ed,
I may get shot out of the water for these comments (with all these armed ships passing ), the chips coming off your cutter are probably the ideal but when I'm turning 4140 the cuttings are long strings or curls. When I get them I get a good surface finish. A heavy cut often yields the bet surface finish, but on your long slender part you may be flexing the stock and getting the tearing action, usually this shows as a harmonic though. The specs for these inserts are often for industrial cnc machines cutting robust parts, not applicable to our lighter equipment and smaller parts. I'd try a lighter cut, lower feed rate and maybe a little faster, but I rarely turn much over 500 or 600 rpm.
My old Colchester slips the belt if taking much of a cut at 1000 rpm so the next speed down at 500 gets most of the use. The big lathe's four jaw is only rated for about 600 rpm, (would have to check)

[EdK]

(01-15-2013, 10:40 AM)PixMan Wrote: Dave is right, you need a LOT more speed to get the finish better.

How fast does your lathe spindle go? Even at 2400rpm with a 1" bar of stock you're just getting into the recommended cutting speed for grade WPP20 on annealed 4140, so let 'er rip! It's just a guess, but it looks like you're running about 400rpm. If you're afraid to try it, start by upping it one step up at a time without cutting, just to see how it runs. You need to get a lot more heat in the cut to get a good finish.

I suspected it might be related to RPMs. Good guess Ken. I think it was running at about 365 or 385. I'll do as you suggested and up it one step at a time to get used to it. I always turn things way too slow, I know. My lathe only goes up to 1500RPMs. The bar is .75" and I'm using the WPP10 insert. The portion I'm turning in the video needs to be turned down to .375".

Ed

[EdK]

(01-15-2013, 10:07 AM)DaveH Wrote: "Ships", why are we talking about 'ships' - I know "another pass" - like "ships passing in the night"
Well I thought it was good.

Ed, that finish is typical of 'shearing' 'ripping' you need to up the RPM and the depth of cut needs to be at least the radius of the insert tip.
That's my best guess
Sometimes in the home work shop emery cloth can be useful to smooth the rough
The video was good very clever - no utube

DaveH

Dave,

You caught me on the "ships". I know how to spell fairly well but my typing leaves a little to be desired at times.

The depth of cut was way deeper than the tip radius. The tip radius is only about .008" and I was taking a .020 - .030 DOC. The small tip radius might be part of the reason for the unspectacular finish. Maybe I need to go to a larger tip radius when I approach my target dimension to get a better finish.

Ed

[DaveH]

You weren't the only one Ed,
At least I do read the posts

DaveH

[EdK]

I had intended on trying the next speed up, which is 500+ RPMs, but didn't realize I had set the lever for double that. I ran a pass and it was slightly better but not much. Then I found part of my problem was I had one of the feed gear levers in the wrong position. I thought it was feeding much too fast from what I'm used to. Anyway, I was running out of diameter to turn so I had to abort. Galling is the major problem with turning the stuff now. I think I'll tackle another piece of 4140 for practice on another day.

Ed

[PixMan]

Try taking a light depth of cut, perhaps .008" per side, at .004" per rev and 1500rpm. That should leave a nice finish.

[EdK]

(01-15-2013, 07:46 PM)PixMan Wrote: Try taking a light depth of cut, perhaps .008" per side, at .004" per rev and 1500rpm. That should leave a nice finish.

Ken,

I'll give that a try.

I'm beginning to wonder if I really got 4140. It had a sticker on it that said it was hot rolled annealded 4140 but it could just as well be plain ordinary hot rolled A-36.

Ed

[PixMan]

I tend to agree that the material seems softer than most 4140 and galls more like a low-carbon steel. The finish shown in your photo is NOT something I'd normally see in 4140, that's for sure.

[EdK]

(01-16-2013, 07:35 AM)PixMan Wrote: I tend to agree that the material seems softer than most 4140 and galls more like a low-carbon steel. The finish shown in your photo is NOT something I'd normally see in 4140, that's for sure.

I think I'll order some 4140 from speedymetals.com in a larger diameter to play with. I think Enco sent me the wrong stuff, and the rod was bent so I couldn't use my cat eye to hold the 3' piece through the spindle like I wanted to.

Ed