Newbie question: what's causing this finish?

[Involute]

I'm new to milling and the SX3, but I've got my machine set up and it works fine w/ Mach3. I was testing out the wizard for circular pockets with a piece of aluminum, a .5" TiN end mill at 1500 RPM, .005" feed rate, and coolant. Everything was going fine, so I bumped the feed rate to .010". Things started OK, but then the machine started to shudder so I stopped and went back to a .005" feed rate, but the shuddering continued, so I quit. Attached is the photo of the lousy finish that resulted. The finish before I went to the .010" feed rate was good.

I assume I just learned that .010" is too fast under these conditions and I dulled my cutter, but I wanted to check here first for other interpretations. Thanks.

Involute

[under-dog]

how deep are you cutting with each pass? I found it is better to make multiple shallow fast cuts to get to depth than going for broke on the first pass.

[under-dog]

Is your mill square and trammed up properly?

From the one directional swirl pattern looks like it might not be square as well so the cutter is cutting on one edge instead of across the whole cutter which would also make a scalloped effect to the base of the cut

[Involute]

Regarding depth of pass, I shouldn't have used the term "feed rate" as I meant depth of each pass. I.e., initially I was taking off .005 with each pass and increased it to .010, which is when the trouble started.

As for tramming etc., I did go through the whole procedure and just remember thatI got it within spec; I don't remember the actual numbers.

Involute

[P Riedie]

Ten thou depth of cut with a 1/2" end mill in Aluminium ? That's a joke. You should be able to go 1/8" at least in one pass if the machine is capable.
I have seen the X3's cutting this but don't know about the SX3 as our importer doesn't carry them.

Query's.
You say 1/2" end mill but does it have one tooth going over centre to allow centre cutting or is it the type that has a clearance hole in the centre ?

If it's the latter then that's your problem. These can't plunge as they leave a pip on the work which snaps off and then stays in the end of the cutter and smears the work.
At 5 thou the pip is probably not big enough to cause problems.

It pays to buy cutters that can centre cut and then they can be used for all operations.

PR.

[Mitsui Seiki]

It seems to me that something is either lose or your end mill is sticking out too far.Is everything properly clamped???

[InspirationTool]

As PR said, is it a center cutting end mill? Post a close up picture of the tip of the end mill if you don't know.

What are your speeds, feeds, and inches-per-tooth?

The problem isn't your depth of cut.

-Jeff

[SyilAmerica]

With 1/2" 2 flute Tin Coated HSS, in aluminum, I run .125" deep, 3200rpm and 9 ipm.

Make sure your head is trammed and you are using a center cutting end mill.


I have gone as deep as .175" and 13 ipm but I start getting the finish you are getting.

[keen]

Something may be loose - if you mount a dial indicator (between the cutter and work) and push the cutter with say wood - quite hard. (try the cutter holder first) you will get flex - but the indicator should return to position when the load is relaxed. If it does not, you have something loose or out of adjustment - it could be cutter mounting, cutter holder mounting, head not secure, or a gib not adjusted properly - or something else loose.

[Involute]

Thanks for all the helpful comments. I think the problem was feed rate. The bad results were achieved with 30 ipm (I warned you I was a newbie). Those in the attached photo with 9 ipm (and .020 depth increment, twice the highest I tried before); both with a center-cutting endmill. The finish looks pretty good to me, but what do I know? Would a slower feed rate and less/more overlap improve them?

On an unrelated note, when I try to set the spindle speed with M03 S1500, I get an error in Mach3: Error on line 2 - Unspecified failure, and it presents a VB debug screen. I'm pretty sure I have the machine set properly (CNC mode switch is down and the Start button on the keypad has been pressed to remove the Stop annunciator). What might be causing this?

Thanks.

Involute

[MichaelHenry]

Is the end mill sharp? Maybe I missed it, but if you aren't using lubricant try spritzing the cutter/part with WD-40 once in a while or using a shop vac to suck up the chips as you cut.

Mike

[Involute]

Yup.

Involute.