milling insert damage

Hi All,

I've been playing with a 12mm TPUN single insert milling cutter in my Centec 2A. I ran it at 895 rpm The insert came with the cutter, used dry, the chips are 0.22mm thick.

The damage you can see to the tip pointing left was me stupidly stopping the cut in the slot before backing the cutter out.

Any idea what I did wrong to loose the edge on the working tip like that?

I tried 1400rpm but there's not enough power to sustain a cut and all I got were thinner chips and no increase in speed.

2A

8thou (0.22mm) chip load is more than I would tend to use, is that hub steel or CI? Looks like steel from the chips

Edited By JasonB on 03/09/2018 20:31:12

Hi. When I spoke to our engineering manager and told him I was going to buy a tipped cutter for my milling machine at home he told me not to bother. He said that home machines would not be ridged enough and that the tips would shatter due to vibration. I never tried so I do not know if he was right or not.

B

I use a 3 insert TPAN cutter quite alot and have never had an insert shatter or even chip like shon, it's my tool of choice for chilled cast iron that would take the edge straight off a HSS cutter.

Thanks for the replies.

It's a steel hub Jason, I didn't want to risk the only supplier of the cast ones.

It's possible the insert is a poor quality Far East copy, it has no markings at all on it

Brian,

I have quite a light Chester milling machine and the tungsten tipped cutters are fine. I rarely use HSS cutters.

Phil H

FWIW...1. Deflection to one side, as it is a single point so bouncing / loading off one side before cutting on t'other, Two & four tooth cutters will have tips cutting equally on ea. side so balancing cutting action equally, as opposing teeth will be under load at same time ..?. 2. Poor quality tips from far east.

George.

Yep, nowhere for the chip to go until half a revolution later, by which time the cut/tool would have advanced considerably. Needs two flutes to balance things up.

To answer the original question as to why the tip edge broke off I would say that carbide tips are hard and stand enormous compression loads, however when the tip is stationary and pressing into contact with the work surface any tensile strain will break off the edge. Keep the cutter revolving until it is out of contact with the work (does not help if the spindle stalls!)

I have lost a few tips just by facing very slightly past the job centreline.

Ian P

With no helix angle the chips are not cleared very well. It is possible that recutting of the chips in the work ares is putting excessive loads on the cutting edge.

Another thought I had is that with a single cutting edge the forces on the work piece act first one way and then the other. Any backlash in the table and loose gibs and you have the chance of uneven cutting forces as the work piece moves unpredictably.

Martin C

What are the scrape marks on the holder to the right of the carbide tip?

Might be just the photograph but it looks as if the cutter was rotated anticlockwise as you backed it out of the slot and that would certainly account for the tip breaking off.

Ian P

Rotated by friction

Edited By Ian P on 04/09/2018 19:41:03

Totally disagree, I use them all the time.

Tony

TPUN inserts are intended for turning, not milling. It would seem likely that the insert simply doesn't have enough clearance when trying to cut a slot not much wider than the insert width. That may explain why the back of the insert at the bottom is chipped and holder is scored.

Andrew

Iscar think differently as they do them for milling, though on larger dia holders where clearance is less of an issue

I use TPUN tips for milling because they are cheaper than TPKN milling inserts. I do however grind them on a diamond wheel to make more of a milling geometry. I get excellent performance and tool life and maybe four or five regrinds per tip edge. My favoured cutters are 40mm with three tips or 50mm with five tips.

All,

Today I went hunting for vibration causes and find I had 2 thou of out of center wobble on the cutter, I have managed to get this down to 1 thou on the cutter by tightening up the bearings . I have no idea if this is acceptable?

Andrew,

The whole clearance angle has flaked off. Are you saying don't go full width? But how else do you start a slot? The holders are sold as TPUN, obsolete I know as they are threaded.

Taking the JB Cutting tools idea that with a lot less power and speed you can use Alu inserts and still work on steel. I was wondering if I could get away with TMPR which has more of a proper cutting edge for my pathetic 1/2 hp + gearbox losses to drive.

Chris, we all like cheap, what changes do you make?

0.25mm DOC is quite high for a tool with no top rake and a low powered machine.

In practice it may be deflecting because of this, causing variation in the cut and chipping on the bigger. In contrast to Tubal Cain's advice I say DON'T keep up the feed rate, but try dropping it to about 0.1mm per rev, or less. As it's a single point tool it's effectively a small flycutter and a low feedrate is to be expected, one quarter of what you would use with a four-flute carbide endmill (which would probably have sharper edges too).

Neil

No, what I'm saying is that if the width of the slot you're trying to cut is too narrow compared to the width and thickness of the insert then the back edge of the insert will not clear the slot; leading to interference and a broken insert.

It's why boring bars for the standard CCMT inserts present the insert at a much steeper angle than the external holders so the bottom of the insert has clearance.

Andrew

The width of the slot won't make any difference to that bit of geometry. The relief angle of the insert and its position relative the centre of the tool will. Position of insert is fixed by the tool design, but it's possible that a higher relief angle insert could be found it that is the cause of the problem. I can't find any other than TPUN though.

There are several makers or at least sellers of these "12mm indexable end mills" that all use a similar TP$N inserts and as the third letter is only tolerence the actual geometry of the insert will be the same so I can't see that they would all be making holders that don't work due to the insert rubbing. I don't have a single insert one to comment on how they cut but the 1" dia 2 tip and 40mm dia 3 tip TPAN ones work well.

You do seem to be using an insert with quite a large tip radius which may be loading up the machine ( make sure you take the edges off the spokes so they sit down flush) and the tip and were you cutting full depth of slot or taking in in stages?. Where did the holder and the tips come from?