thread mic??

[Dusty Stevens]

Could someone explain to me the science behind this HSS/carbide observation? I've heard this before and I'm open to input but I have not personally experienced this in my career. For me, setup rigidity and cutter geometry are the most important factors and cutting tool material only determines maximum surface speed and fracture/wear resistance. The only times I can recall higher speed improving cutting performance is with some high temp stainless materials where high chip heat improves chip flow and in cases where an RPM change breaks a harmonic cycle.

Could it be what you are really experiencing is a difference in cutting tool geometry? There are a lot of carbide inserts out there with less than desirable cutting edge geometry for an engine lathe with marginal rigidity.

The answer is yes. A very good geometry tool and bit as you know is very expensive. Most people buy phase 3 toolholders and inserts and just suffer thru blaming it on carbide inserts and never try a nice toolholder spec'd out by a tool man for their speeds and material

 

[skeetlee]

I really like my carbide tooling. I have little to no issues with it. Lee

 

[JerrySharrett]

A difference in cutting geometry, yes.

Some background first. When General Electric introduced us to "carbide" in the 1950's, a product they called Carboloy, we didn't have engine lathes with enough horsepower to use these tools.

The why. Carbides as we call then are made up of several components like Titanium carbide, talladium carbide and a few other "carbide" particles. The grades of carbides are determined by various mixtures of these components, C2, C5, C7, etc. All these components are "nodular", spherical, ball shaped. They are formulated, then this powder is put in molds. These are "poll molds" just like pills are made. Then they are pressed together, in a press, and "sintered" in an oven a high temperatures. This process bonds these various "balls" into the tooling we see.

Problem, visualize gluing a box of Ping-Pong balls together. Not much contact area, ball to ball. Whereas High Speed tooling is in crystal form components. Kind of like gluing random sticks of wood together, more contact area.

The carbide, while being very hard and wear resistant, is also very a fragile bond. i.e. It is not homogenous like HSS is. This his makes a tool with very fragile edges. So, the manufacturers make these with rounded edges and this makes the very cutting edge negative in nature. One can use a diamond impregnated grinding wheel and cure part of this problem, since the diamond can cut the carbide balls into sharp edges but this process is also very slow and very expensive. You an buy "diamond" sharpened inserts but they cost several times more than the regular molded product.

Simple illustration- glue a bunch of wooden balls together, then glue a bunch of wooden sticks together. Then, take a hammer and beat them apart. The glued balls will come apart much easier since they have such small surfaces being glued than the sticks.

Overkill explanation, I know but, hey!!


.

 

[Joe Woosman]

Not sure how good the attachment will be but here is a picture of some inserts. The two lighter colored inserts come polished to a mirror finish on top with the outer edges ground. The cutting edges are razor sharp. The threading inserts are some of the better ones I've used and all cutting surfaces are ground with sharp edges. The insert to the far left is an example of one with negative geometry that would probably challenge a less robust machine.

Current inserts with ground edges are not all that much more expensive than molded inserts. I'd guess maybe 20% more. The coatings actually make a bigger cost difference in a lot of cases.

 

[Zebra13]

A difference in cutting geometry, yes.

Some background first. When General Electric introduced us to "carbide" in the 1950's, a product they called Carboloy, we didn't have engine lathes with enough horsepower to use these tools.

The why. Carbides as we call then are made up of several components like Titanium carbide, talladium carbide and a few other "carbide" particles. The grades of carbides are determined by various mixtures of these components, C2, C5, C7, etc. All these components are "nodular", spherical, ball shaped. They are formulated, then this powder is put in molds. These are "poll molds" just like pills are made. Then they are pressed together, in a press, and "sintered" in an oven a high temperatures. This process bonds these various "balls" into the tooling we see.

Problem, visualize gluing a box of Ping-Pong balls together. Not much contact area, ball to ball. Whereas High Speed tooling is in crystal form components. Kind of like gluing random sticks of wood together, more contact area.

The carbide, while being very hard and wear resistant, is also very a fragile bond. i.e. It is not homogenous like HSS is. This his makes a tool with very fragile edges. So, the manufacturers make these with rounded edges and this makes the very cutting edge negative in nature. One can use a diamond impregnated grinding wheel and cure part of this problem, since the diamond can cut the carbide balls into sharp edges but this process is also very slow and very expensive. You an buy "diamond" sharpened inserts but they cost several times more than the regular molded product.

Simple illustration- glue a bunch of wooden balls together, then glue a bunch of wooden sticks together. Then, take a hammer and beat them apart. The glued balls will come apart much easier since they have such small surfaces being glued than the sticks.

Overkill explanation, I know but, hey!!


.

Jerry,

Thanks for that post...very interesting. Now I know the "why" behind the fragile nature of carbide.

You learn some cool stuff on this forum.

Justin

 

[Dave Tooley]

No disrespect to Jerry but in some circles there are individuals called gray beards. When they talk people should listen.

 

[SGS]

Could someone explain to me the science behind this HSS/carbide observation? I've heard this before and I'm open to input but I have not personally experienced this in my career. For me, setup rigidity and cutter geometry are the most important factors and cutting tool material only determines maximum surface speed and fracture/wear resistance. The only times I can recall higher speed improving cutting performance is with some high temp stainless materials where high chip heat improves chip flow and in cases where an RPM change breaks a harmonic cycle.

Could it be what you are really experiencing is a difference in cutting tool geometry? There are a lot of carbide inserts out there with less than desirable cutting edge geometry for an engine lathe with marginal rigidity.

No doubt that rigidity is a huge factor. The geometry of many inserts is such that it takes a lot of power to drive them and they just do not cut efficiently until they are running fast and pushing a good chip load.
I have come across a number of carbide inserts that do perform well on light machines and slower speeds. They usually have small radii and a slick finish, coated or not.

Although I have seen a lot of glowing reviews on the HSS inserts, I myself use carbide for nearly everything.