Carbide vs high speed steel part 2, efficiency 

I am afraid I can't comment much re HSS as I don't use it. Carbide inserts are all I use in my benchtop cnc lathes. 100 diameter chucks and 1/2 hp and 3000rpm. Aluminium inserts from most makers have 20 degrees of rake, use them in a manual lathe and they can actually pull in to the cut or pull the work piece out of the chuck, I have had that happen using a boring bar. I often use aluminium inserts to turn free cutting steel, they don't last as long as the others but they are easy on the lathe. Inserts come in a huge variety, some of which are "finishing" made for light cuts and with high rake angles through to "roughing" that usually have much less rake and are made for deep cuts and high feed rates. I use finishing inserts, as my general purpose inserts these have ground edges and 15 degrees of rake and work well with 1/2hp. Inserts can be "moulded" or "ground" with the ground edges being very sharp, but the moulded edges can be stronger particularly for heavier cuts. I have just discovered some "finishing" inserts that are moulded and as these are 2/3 the price of the ground edge inserts I can't wait to give them a try. I use the 35 degree inserts a lot and I think they are easier on the lathe than the 80 degree inserts but this may not be true. They do allow swarf to clear well which can be a problem with the 55 and 80 degree tools. I think the greatest problem most folks have with carbide inserts is using the wrong type and secondly not using high enough rpm. I would run mild steel at 2000rpm for one inch. Buying cheap inserts off the web is really only a good idea if you know exactly what you are buying and know it will do what you require. Apologies for the long winded comment, just hope it helps

Nice test. Good to see the amp draw vary with the different cutters. Thank you for the video.

The tool geometry makes most of the power difference you see, the real difference is tool life and as you said, light cuts are generally better with HSS. With the same geometry, the same amount of material removal should roughly need about the same power, but you can hog a lot more material off with a carbide tool, providing you got enough power and the right speed My old 14.5" South Bend does quite well with carbide on larger diameters, obviously until i reach the power limit. On smaller diameters it just cannot produce enough surface speed to get the tool anywhere near the recommended parameters. The result is usually too much tool pressure at too little speed, which results in excessive heat and therefore short tool life.

Interesting. Thanks!

Interesting....I'm wondering if you change the geometry of the hss bit like you mentioned, and maybe taking the honing a little bit further what results you would get. I totally expected something different out of this test, like you did. great vid, learned something here...keep 'em coming!

I find that the positive rake inserts and holders for carbide work better on my 12" Grizzly. I have only experimented with the cheap inserts from Banggood for the most part. I like it because it saves a lot of time on the grinder and I have a huge variety of cutter shapes in the toolholder sitting ready to go. I have found some of the negative rake profiles to push rather than cut although I haven't tried really high speed rpm yet. I also have found the sharper tip profile on the inserts work better for me. I assume by lightening the cutting load. Very good topic for the home hobbyist. Thanks for the videos. Take care. Doug

the feed pressure you noticed is most probably due to the geometry of the carbide inserts. Not only is yours a negative rake insert, but the edges can not be as sharp as the HSS, due to the coating of the carbide

Video and comments helpful... "Gonna need a bigger lathe..." not really, making due with the one I have...