Contouring advice

[lfdgonzalez]

Hello forum

I need to contour a part but it's taking me ages with a 3/8" 4-fluted flat endmill (carbide). The total length of the contour is 22.5", with a depth of cut of about 0.004", and the total depth should be 2". Speed is at 1000rpm and feed is 4.68IPM (0.004685" IPR, 0.001171" IPT), so this takes about 4:49 per pass. I'm not retracting with each pass, so I drilled a 7/16 hole to use as relief, so I won't dull the endmill (although it's become so due to the high feed I'm working with). Needless to say, I'm doing this on the VMC I have at work.

Now, I'm thinking about cutting the part with the flank of the endmill so I can get it done in, say, four passes of 0.5" each. What I plan to do in order to get this done as quick as possible is keep the RPM as it is (1000), slow down the feed (maybe at 1 IPM so the endmill will eat about 0.001" per revolution, I infer it'll break otherwise), and to avoid chatter and unnecessary vibration, while leaving a decent finish (I think).

Would anyone advise in favor of, or against this technique? One of the machinists at work told me it could work as long as I kept a slow feed, but I wanted to make sure just because, before I sit down and code the whole thing. And break an endmill.

By the way, I'm machining AISI 9840T. Between 250 and 300BHN.

Thanks in advance,

Francisco.

[little bubba]

Sorry for sounding like a jerk, but a 4 thou stepdown?????? You must be getting paid by the hour to watch this thing.

First, I couldn't find an AISI spec that had more than 3 #s, so I have no idea what it is, but its not that hard. I don't care much how crappy the material is(Ti, inconel, unobtanium), but, with a carbide endmill, you should be running at an absolute min, 100sfm, which you are doing, barely.

At the suggested 1ipm, you will only be pushing .00025 per rev, at 1/2D that is really bad, but at anything less, its even worse, you didn't say. You'll just push material, and eat up the endmill, without actually cutting anything.

Please supply some more info, what is the actual material, the actual endmill, width of cut, coating, wet/dry, the machine.

[lfdgonzalez]

I know. 4 thousands is a royal pain. As you've put it, it's just pushing material and the edges go dull in no time.

Alright. Here are some specs:

Material: AISI 9840
AKA: ASTM A274, ASTM A322, ASTM A519, SAE J778, AMS 6342C
Hardness: 280 (Brinell), 99 (Rockwell B), 35 (Rockwell C)
Condition: Quenched, 540°C temper, 525°C nitride for 40 hours with 20-30% ammonia dissociation
Machinability: 70%
Composition (typical values):
Carbon - between 0.38% - 0.43%
Chromium - 0.800%
Iron - 96%
Manganese - 0.800%
Molybdenum - 0.25%
Nickel - 1.00%
Phosphorus - less than 0.035%
Silicon - 0.23%
Sulphur - 0.04%
Stock shape: Billet, 13 3/8" x 9 7/16" x 2 7/8"

Endmill: Solid WC 3/8", 4 flutes, flat, about 4" height, shoulder is 1 5/8". New.
Coating: None
Speed: 1000 rpm

Machine:
Mazak VTC-41 w/Mazatrol EIA controller (eww)
HP: 7.0
Max RPM: 7000

Cutting fluid: Soluble oil, flooded at all times.

Thanks a lot for the reply.

FGB.