Wreck,
I'm not sure I follow? I was looking for recommendations for a general purpose carbide tool holder, and possibly one for threading as well. I've seen the Kennametal holders, and I guess they must be quite good, as they're 2x the others I've found. I'm ok with spending the money, but I'd like to get 1 tool that will work for most general lathe operations. If that's not practical, that's ok too, it's just that New Old Tony said he uses one cutter for the lion's share of his lathe work.
Thanks,
Evan
What Wreck is saying is that you need different tools for different tasks (jobs), i.e., many different tool holders if you want to use insert tooling for all those tasks.
The closest to a general purpose tool holder is something like the SCLCR toolholder used with the CCMT/CCGT inserts (e.g.,
http://www.ctctools.biz/sclcr-l-indexable-turning-tool-holder-i28/), since as Mikey mentioned, this type of toolholder+insert allows you to both turn outside diameters and face without adjusting the toolholder orientation (as depicted by the arrows in the diagram in the ctctools link). SCLCR + CCMT/CCGT is just one example; there are of course other combinations that also give you this flexibility. From my understanding, though, many of the other insert types that give you this turning+facing geometry tend to be neutral or negative rake, i.e., the insert designation has an "N" in the second postion (e.g. WNMG); see
http://www.carbidedepot.com/formulas-insert-d.htm.
At any rate, take some time to consider what Mikey said above regarding the 816 lathe and carbide insert tooling. It is possible that the "sweet spot" for the carbide insert tooling is a bit close to the maximum capability of the machine. To put this in perspective: I started out with hand-ground HSS tooling, and eventually took a leap of faith and bought an SCLCR holder (I got the SCLCR/L2020K09 from ctctools) with a mixed party-pack of inserts. With the "general steel" grade CCMT insert, I have turned 4140 (both annealed and hardened) under following conditions: diameter ~ 40 mm [1.5 "], spindle speed 1150 RPM, depth of cut 0.5 mm [~20 thou] (i.e., 1 mm off the diameter), feed 0.2 mm (~8 thou). This is a little below the typical cutting speed for carbide on 4140 steel, but this cut already requires about 0.64 kW according to the Sandvik TurnCalc Android app. Note that 0.64 kW is about 0.85 hp; I saw that some of the other 10" Logan lathes came with a 1/2 hp motor.
Just dropping the feed rate to 0.1 mm/rev [~4 thou] might make this cut work on a 1/2 hp motor, but that is probably pushing the machine quite hard. So what can you try to reduce the power requirements?
We can try to drop the cutting speed, but I know (because I started slower) that the surface finish was rather poor (teared, smeared surface finish on the 4140) at about 750 RPM and lower. So you will hear people saying that "carbide likes speed"; I think This Old Tony mentions that. The practical meaning of this is that you will not obtain that nice, shiny finish if your cutting speed is too low, so we cannot really drop the RPM (for this diameter).
We can try to reduce the depth of cut, but you will see that the chipbreaker on this CCMT style insert requires a minimum depth-of-cut to actually break chips. According to the ISCAR specs, my CCMT09 inserts want a minimum depth of cut of 0.5 mm (
https://www.iscar.com/eCatalog/Item.aspx?cat=5502778&fnum=738&mapp=IS&GFSTYP=M&srch=1). If you take a more conservative cut (say, 0.1 mm [~4 thou]) then you have blue-hot razor strips spinning around your part (those "stringy bastards" as doubleboost calls them). The manufacturer's minimum depth of cut may be a little overstated, so the chipbreaker might still work down to, say, 0.3 mm [~12 thou] off the radius, but I cannot recall the exact numbers that still worked in this example. You might be able to find a smaller CCMT insert (say, the CCMT06) with a small nose radius and a chipbreaker designed for a more manageable depth of cut, but I cannot say whether such an insert even exists.
Anyhow, my initial cutting parameters resulted in the chipbreaker working as expected, but I can tell you that it was a little scary. Those chips are blue-hot, and every now and then one would make it past the chip guard. If this was an enclosed CNC lathe, this would probably be fine for everyday operations, but I only use such aggressive parameters (well, aggressive for me) when I have a lot of material to remove.
I hope I have managed to convey in practical terms what carbide insert tooling means in practice. I suspect that this is what Mikey was alluding to as well. Given that you can buy an SCLCR toolholder and a mixed 10-pack of inserts off ctctools for about $70, it is probably not that expensive to give the insert tooling a try, but I defer to the judgement of people more familiar with your lathe.
