Great Saunders Youtube on aluminum feeds and speeds ref. lathe inserts

[mikey]

@mikey, you referred to the insert in the video as being an "AK". Is that a manufacturer specific code or is it a standard?

As far as I know, AK is a style of insert with a very positive rake and a parallel pattern chip breaker. Most have a radius just before the insert screw hole to direct chips upward, presumably to curl and break the chip. All AK inserts are for non-ferrous turning, are polished and ground and the ones I am familiar with are uncoated. They come in different grades but H-01 is the one I use. The grade designation varies with the maker but the AK style is pretty standard.

 

[mikey]

Alan, I should clarify that there are all sorts of AK insert. There are diamond AK's in 80 degree and 55 degree, round and maybe even other shapes. The CCGT that I and many others use, including the one in the video, looks like this:



You can see that it has only two usable points when using the SCLCR tool holder and the entire upper edge of this thing is sharp enough to slice flesh. You cannot see it but it has a very positive rake and a raised ring near the hole - this gets the chips moving in a hurry, carrying heat out of the cut with the chips - but you have to get past the nose radius before cutting takes place. Given that the nose radius of an insert has a significant impact on all your cutting conditions, choose wisely.

 

[jbolt]

I think Mike might have mentioned it but when using inserts you need to take a bigger cut. I had the same issues you are having when I first got started (I'm still a beginner) and found that you can "hit the number" by measuring when you are close and then "going for it" on the last finish cut. After awhile you will find that you can get very close even when taking .015" to .020" final cuts.

Just to expand on this a bit.

When I am turning to a precise dimension all I am really concerned about is the final finish pass. I find the RPM, depth of cut and feed rate that achieves the desired finish and then set my tool zero to that.

Lets say 700 RPM, .015" DOC and .005" feed rate, for the tool used, gets me the results I'm looking for. I will take a couple of finish passes at this setting and measure. If I'm hitting the number I'm expecting. based on my zero. then I'm confident that when I take that cut as my finish pass I will hit my number. If I am removing a lot of material I may wait until I am close to the finished diameter before fine tuning my tool zero but I always fine tune with the cutting parameters that get me the finish I need.

For roughing, depending on the tool geometry, DOC and feed rate, the roughing cut may be slightly larger or smaller than the input value due to spring, rigidity, lash, tool grab etc. As long as I know how the tool will behave at the finishing cut, I can rough to within a few thou of the finish cut depth and then take my finish cut without having to sneak up on it.

 

[Alan H.]

. . . . . . . .

I'm waiting to see your HSS tools, Alan!

Okay Mike, finally got 'round to it. So here's one with geometry that you may recognize. I ground this bad boy to see if it will peel .002" off some aluminum. It is a 1/2" Rex 95 bit in a BXA holder. If it works well I will grind a left handed one to match.

 

[mikey]

Nice! Bet that tool will cut aluminum nicely - let us know how it works. For someone who is new to tool grinding, that is a great job, Alan!!