View Full Version : Turning aluminium with carbide, testing and chipbreaking...

16-12-2012, 02:17 AM
Previously I have always used HSS tools than I hand grind to a likely looking shape for general turning and carbide for parting / boring. Recently I've been turning some aluminium shafts from 70mm bar which required removing a significant amount of material and kept getting the 'rats nest' problem with long stringy chips:


I briefly tried grinding a chipbreaker on to the HSS tool, but that didn't work. Looking back I think I wasn't using a high enough feedrate, but anyway I decided to buy this carbide tool which accepts CCMT09 inserts:

ISO Klemmdrehhalter SCLCR 2020 K09 + WSP NEU 004 | eBay (http://www.ebay.co.uk/itm/110980389626?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649)

After I bit of reading and experimenting I've found that at a feed of greater than abou 0.009ipr or above (I tried up to 0.015ipr), the chip breaks nicely leaving a sensible pile of swarf. I used 2.5-3mm depth of cut, so 5-6mm from the diameter per pass:


Much tidier:

Considering this is just a roughing pass, the finish isn't bad:

The reason I'm posting this is I'm not sure if it's going to cause excessive wear to my lathe using it at this sort of speed, since it's so much greater than I'm used to using with HSS. Clearly I want to use this tool efficiently, but not at the expense of the spindle bearings. The power used for the last cut was about 1.8kW (based on chance in current from no load to when cutting) and using a fraction under 2.2kW, which is the spindle motor rating.

The spindle speed I used is probably a bit fast, so if necessary I can reduce the power by decreasing that. Every website I look at seems to quote a different feed/rev for aluminium - anything from 0.005ipr to 0.05 ipr. I suspect the insert manufacture is the best place to find out, so the datasheet for an insert similar to the one I'm using (CCMT09T308) suggests 0.3mm/rev and up to 4.5mm DOC, which is not far off what I used, except I think those figures are for steel and this insert is intended for steel. Using a greater feed/rev should reduce the spindle power required for a given material removal rate, but it looks like I'm close to the limit of the insert I'm using.

Has anyone here used these inserts (http://www.shop-apt.co.uk/pcd-diamond-turning-inserts/ccmt-09t304-pcd-1300-diamond-turning-insert-for-aluminium-alloys-with-less-than-12-si-content.html), I've read good things about them but at 5-10 times the price of the normal inserts I should hope so? I've used the polished aluminium ones from APT in a boring bar and they work very well in aluminium.

16-12-2012, 03:24 AM
Now days I only ever use carbide insert tooling has the removal rates are so much better than HSS. When first started using them I wasn't too impressed until someone far more experienced using lathes told me I was cutting far too slow and shallow.
For Aluminium I have CCGT tooling using HA or AR inserts and Couldn't believe the difference and time savings when I eventually plucked the courage to try deeper than steel. Seemed the more I pushed the better it got( up to a point obviously)
I rough cut Alu at 0.3mm/rev but slightly lower DOC @ 3.5 and It certainly hasn't hurt my little Boxford.

16-12-2012, 08:06 PM
The biggest issue with taking such big cuts with aluminium, is more speed than the amount of force required, so just keep an eye that things aren't heating up too much, and the headstock oil is clean and topped up.

PCD is for tough materials and/or where long term tolerance needs to be held i.e. on CNC machines that are expected to churn out thousands of parts while unattended. On anything else, it's pretty much a waste of money with minimal benefits.

Peter Griffin
16-12-2012, 08:20 PM
I find polished inserts the best ( I get them from where I work) also the faster the spindle speed the better. The "birds nest" could also be down to the grade of Aluminium that you use.Again I get bar ends from work, we use FC1 and it chips beautifully. I also find a light spray of WD40 helps with cutting and finish.