Newbie looking for some help with CCMT21.5

[jpad]

Experience... virtually none other than metal shop a long long time ago.

I've got one of the 3 in1 shoptask eldorado machines and I can hardly make one cut without ruining the insert.

My setup

Glanze SCLCR holder with CCMT21.5 gold insert
Approximately 12" piece with 1" outside the chuck
3 jaw chuck
All dogs locked down pretty tight
Tool tip is aligned with dead center in tailstock and when facing leaves no tit on workpiece
1" steel piece, I think its cold rolled
RPM = 628
.010" facing cut
If I run the crossfeed fast or slow it doesn't seem matter (done by hand)
The tool holder is parallel to the face of the workpiece by eye

With a brand new insert the face is not machined nicely... if you look at the face you can see where metal has been dragged rather than cut, after a few cuts the insert is ruined and it starts to chatter and it's a mess.

I'm really pulling my hair (and wallet out) with this. Any help would be greatly appreciated.

Thanks,
Jim

[mechanicalmagic]

Jim,
First, welcome to the forum.

Next, my thoughts on your problem(s.

1. Cold rolled steel machines just like you are getting, change materials, 12L14 or 1144 would be nice. Add some cutting lube, brush on and take the cut.
2. Your rpm's give about 160 ft/min surface speed at the outside edge. Way too slow for a finish cut with carbide, how about 1500 rpm.
3. If you have a honed edge on that insert (doubtful) then it could be used for light finish cuts. Otherwise, you should take .030" or so. It depends on the radius of the cutting edge. (Not the nose, the edge.) Carbide is usually designed for heavy/medium cuts, and therefore has a slightly dull edge, to prevent chipping (of the sharp tip).
4. The burning you are getting on the tool tip leads me to believe you are rubbing the edge off, perhaps with too light a feed rate.

Just a few things to consider.

Dave J.

[PixMan]

That is awfully slow speed for a (TiN?) coated carbide insert, but it doesn't really matter so much because when you get down to the center of the part they're all cutting at ZERO surface feet per minute.

What you've not told us is just what grade of carbide you're using. Without that, I suggest you speed it up to at least 1000rpm. Then face it off down to perhaps a .100" diameter, back off the depth of cut to just .005" or .010", and face to center. take only very light cuts until you have the clean face. Too much load at a virtually no cutting speed is the death knell for carbide. Heck, if you were close to me, I'd come over and show you what to do to fix this.

[tommied]

Well for some reason my fingers outran my brain and now Ive givin up. Wish I had the metal here so I could play with it. good luck tommie

[PixMan]

Interesting. Where did the "7%" value come from and why is that number important? I've run carbide insert tooling for (far too many) years and just run on-center to perhaps a couple of thousandths of an inch above center, at most. I don't recall ever seeing or using a percentage value, and would like to know: 7% of what?

[tommied]

Man I need another drink. You picked up on that before I could read and figure out a brainfart.

[PixMan]

To the OP:

BTW, I don't recall seeing what tool nose radius that insert has. The nomenclature should read CCMT21.51 or 21.50.5, 21.52, etc.

For a stronger tip for facing, get a tougher, less wear resistant grade and a larger radius on the insert. If you can provide the full information about the insert you have, I can help determine the most economical corrective action for you to take. The "gold" tells me nothing but color, and we all know color means nothing.

[jpad]

Thanks all.

I'll try some of the recommendations tomorrow. My gut tells me if I take a .030" cut it's not going to go well... I've tried taking some deeper cuts... maybe .020 and it chattered terribly. Also, I think I've tried 1200 RPM too. It seems no matter what I do the result is the same... kinda leads me to believe I've got a problem other than feed/speed. The piece is not perfectly straight, there is a barely perceptible wobble to it, but I've had the problem with other pieces too.

The insert package says CCMT215.007 GP2000

[Harold_V]

The piece is not perfectly straight, there is a barely perceptible wobble to it, but I've had the problem with other pieces too.

It may pay to investigate your chuck. From your comments, I can't help but wonder if, maybe, it's sprung. If it's not new, especially if it's been in service for years, it may be gripping only at the rearward portion of the jaws. That's a very common ailment in three jaw chucks, especially if they've been used for chucking short items, where they're gripped only at the tips of the jaws. In time, they spread. The resulting oscillation of the material is death for carbide.

To determine if your chuck is contributing to the problem, chuck a length of (known) round material. A drill blank would work well, for it's round and straight. When the chuck is tightened, there should be no clearance between the blank and the jaws. If you find there is, that may be causing the short life of your inserts.

One more thing that you may wish to investigate. I have seen import carbide insert holders that are intended to run negative rake inserts that have no rake angle. That causes the insert to drag, and no amount of coaxing is going to permit proper performance. I am not familiar with that particular insert, but take a look at the holder to see if, when the insert is in place, there's clearance under the cutting edge and side that leads.

I have to wonder why you're using carbide in the first place. HSS will serve you perfectly well. If you've chosen to use carbide in an attempt to avoid the learning curve of grinding your own cutting tools, you are making a grave mistake.


Harold

[PixMan]

A big part of the problem may be that the insert is a .0078" nose radius, but without seeing the insert to evaluate the failure mode it's not possible to be accurate.

Just to be clear, are you turning or facing? Or both? If turning, what is the feed per rev? Is it in turning (rather than facing) that you get the terrible chatter. It really seems you may have a problem with looseness in the spindle side of things, and the fragility .0078" radius of the insert just adds to your problems.

[Richard_W]

If it were me I would run from1500 to 1900 RPM.

[jpad]

@Harold,

Can you please give a little more info on the mistake of using inserts vs. grinding my own tools. Yes, my thinking was use inserts to save the learning curve of grinding my own. My thoughts were just stick the insert in and go, looks like I might have been mistaken.

@Pix,

So, far I'm just talking about facing. I'm thinking I might try turning today with the auto feed to eliminate the jerkiness of my hand crossfeeding. To my eye the 0.0078 radius looks right, it's definitely a small tip.

If I extend the workpiece out 8" and try to wiggle it by hand I don't notice any looseness in the chuck or bearings but I haven't put an indicator on it. It is a new machine, but it is chinese too.