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

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.

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

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

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

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.

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

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.

So why is the back of the insert broken and the bottom of the toolholder damaged to what looks like the same depth as the slot being cut?

Depending upon the supplier I wouldn't be in the least bit surprised if the toolholder rubbed. You've only got to look at the grinding on some of the cheap milling cutters to realise that they'd never cut properly.

Andrew

The fracture could just have easily started from the front and propogated towards the rear of the insert, I'm sure I have a few chipped cutters that show similar fractures after catching the cutting edge rather than the back

Assuming the insert failed during a cut then the tool was still being fed as it failed so the holder would then have been run into the previously cut edge of the slot and produced the marks seen. Don't know how the holders can rub as the part that holds the cutter is smaller than the nominal size, if you look at this 12mm shank and 12mm cutting dia SECO one you will see the end is about 11mm dia so should not rub. You can also see this on Michaels enlargement wher the 12mm shank is just visible above the 11mm ish end

Yes that is why I asked where the holder and inserts came from, I'm sure one from SECO would be better than one from the likes of Bangood.

Edited By JasonB on 05/09/2018 07:52:11