Diamond v. Carbide : Weighing the Costs and Benefits

Diamond v. Carbide : Weighing the Costs and Benefits

Under the right conditions and with proper maintenance and handling, significant cost savings can be achieved by running polycrystalline diamond (PCD) tooling.   Understanding the basics of diamond tooling is important when contemplating its use in your own production line.  First and foremost, think of it as the marathon runner, as it will yield the best results in continuous and steady cutting of homogeneous materials. Diamond tooling is not advisable as an all-round tool that will be required to meet demands of a wide range of cutting applications on a day to day basis.  So, if you are machining different materials and want one tool to do it all, the diamond tool will not be able to excel as well as it will if you are machining, for instance, 3/4″ MDF all day long.

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Polycrystalline diamond is manufactured in a high-pressure, high-temperature laboratory process that fuses diamond particles onto a carbide substrate, which, in turn, allows the diamond to be brazed onto a tool body.  PCD has an exceptionally high wear resistance factor, in particular with abrasive composite materials that are often difficult to machine with carbide.  Examples are:  particleboard, MDF, OSB, high pressure laminate, phenolic, fibre glass etc.  Depending on what material is being machined, it is not unheard of for a diamond tool to outrun carbide by a ratio of 300 : 1!  Nevertheless, when deciding whether to switch, be conservative in your cost analysis and base your decision on the diamond bit lasting 25x longer than carbide.  You won’t be disappointed!

The original developers of synthetic diamond were GE (Specialty Materials Division) and DeBeers  (Element 6) who pioneered this process and mastered the know-how of synthesizing diamond for industrial cutting applications.  Meanwhile, there are a number of synthetic diamond tool blank manufacturers, and the quality, durability and wear resistance is not always equal.

When shopping for a PCD tool, it is important to discuss your proposed use and expectations in detail with the tool manufacturer as this allows for selection of the proper PCD grade (grain size), and optimum tool design.  In particular,  you want to be certain that there is no more PCD on the tool than actually needed (i.e. don’t order a tool with 1.1/4″ cut length when you only cut 3/4″ material because that needlessly increases the tool cost.

To understand the complete picture and compare “apples to apples” when shopping, it is important to ask the following questions:
How many times will I be able to sharpen this tool under normal wear conditions?
What will it cost to sharpen this tool?
How long will it take to turnaround a tool when sharpening?

If you neglect to get answers to these questions,  you might be in for a surprise to find you were sold a “disposable” tool that cannot be sharpened at all, or can only be sharpened once.  Or, you might think you are getting a bargain when you buy the tool, only to find you are going to be expected to pay 50% of the new tool cost to get it sharpened.

These factors significantly affect the cost per linear foot machined so are important to know when doing a cost comparison or justification for PCD tooling.  Below is an example of a cost comparison using a diamond saw blade versus a carbide tipped blade:

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$.0028/$.0143 = PCD costs 19.6% of carbide when comparing $/Linear Foot (80.4% cost reduction) 

Another advantage of PCD tooling, apart from the longer tool life,  includes the quality of finish which is often significantly improved and therefore requires less sanding.  With carbide tools, the finish starts to deteriorate from the very first cut onward, whereas the diamond tool maintains a nice clean finish right up until it becomes dull…..at which time it plummets and should be pulled for sharpening.  Pushing a diamond tool to run a little longer once it shows signs of becoming dull  (a good indicator is when the machine amps increase), can result in a substantially larger sharpening cost as the diamond face can shatter and require re-tipping/replacing of the cutting edge.

At first glance PCD tooling seems expensive when compared to carbide however when we compute the cost per linear foot machined, in the right application, PCD will be revealed as the only choice for discerning shops that are cost conscious.  As you can see from the cost calculation above, the investment in PCD tools pays off rather quickly. Some of the top PCD applications are machining abrasive materials, composites and workflows that do high volume of the same cut and material type.

With PCD router bits, maintaining correct chip load is very important as heat buildup during the cut will damage the diamond and can lead to tool failure.  Accurate tool clamping systems with close tolerances are also essential as is firm material hold down to avoid any vibration during the cut.   For specific questions about PCD tooling, please contact us or give us a call at 1-800-544-8436

Post by PixMan » Wed Jun 23, 2010 8:36 am

There have been some amazing advances in carbide insert tooling in the last few years. While it's true that in general carbide doesn't take well to interrupted cuts, there are grades available now that might really surprise you in just how tough they are.

For example, I was reading a post on another HSM forum who was having trouble turning the face of a crankshaft blank. He had tried a number of different carbide inserts, and good HSS. The material was a forged 4130 or 4150 steel. The HSS didn't fracture as readily, but running at less then 100 rpm and light passes was taking too long. I had some inserts made specifically for interrupted cuts in steels, and sent him a couple. Problem solved. He is now getting "number of passes per insert" instead of "number of inserts per pass."

The processes used in coating most inserts just a few short years ago were a high-temp chemical vapor deposition operation that resulted in erosion of the very sharp edges. Physical Vapor Deposition (PVD) coated inserts came onto the market also, though at higher cost. Newer medium-temperature CVD and PVD processes are such that a coated insert can have a nearly dead sharp edge. Uncoated inserts that have been peripherally ground after molding can be dangerously sharp. Those are used in machining non-ferrous metals, aluminum and plastics. With the newer coating processes, most manufacturers of inserts have some coated ones that are still extremely sharp. I've used some from Mitsubishi, Kyocera and NTK on Swiss-style machines.

As others have pointed out, the most commonly-found characteristic of lathe and mill inserts is that honed edge. Sometimes it's actually honed, more often it's just a result of the molding process and dies. When molded to a theoretical sharp edge, the coating process can often erode the edge by a tiny bit. These edge preparations, in conjunction with the molded-in chipbreaker designs are what determines the feed rates at which an insert will exhibit good chip control and to some degree, tool life in a given material. Primary consideration for tool life is matching the cutting speed (surface feet per minute), insert coating and substrate grade to the material being cut. Match the depth of cut and feed rate to the chipbreaker.

Inserts aside because of the high cost to a home shop machinist, brazed carbide tools can be a very cost-effective upgrade from HSS. The key to success, just as in HSS, is to start by using quality tools and grinding them right. Carbide can be so hard that it's not unlike a ceramic in the way it grinds. The reason that an Agathon grinder comes mounted with two different grit size diamond wheels is that you're supposed to rough it out with one and finish with the other. More than just a polish, the fine wheel removes the "grinding damage" done by the rougher. Minute fractures propagate from the surface created by the rougher wheel, you remove them with the finisher. That results in a stronger edge and longer-lasting tool.

This "damage level" done by the rough grinding process is, IMHO, the reason why brazed carbide tools just ground with a rough silicon carbide wheel don't seem to last as long as one carefully roughed out and then finish ground with a resinoid-bonded diamond wheel. My experience with HSS tools seems to parallel my carbide experience. When I had only a 36 grit aluminum oxide wheel to grind a lathe tool, it didn't seem to last nearly as long as they do after I got the 80 grit wheel.

I think a lot of HSM'ers who try carbide for the first time get discouraged. It happens by getting something at a flea market/yard sale and try it without knowing just what the grade is for, how to grind it or how to run it. The same thing happens when we buy a $5 "this weeks' special" 1/2" carbide end mill of suspicious origin and it doesn't last 1/2 as long as the Niagra HSS-Co end mill. We have no idea how the carbide powder was purified, mixed with it's alloying elements, fired or ground, yet we'll expect it to perform magic over HSS. It's setting ourselves up for disappointment.

What difference it is between, for example, buying a new Valenite brazed carbide AR-6 tool bit and a made in who-knows-where one. Part (though not all) of the reason the name brand stuff costs 2x or more is they know there's more steps to processing the tool, and do it. The same holds true in carbide end mills, inserts, and drills.

With no documented qualifications to be spewing the above rant, take anything I write with a grain of salt. That's what I do and why I've posted it to the "Junk Drawer".

The debate over HSS vs. carbide tooling for home shops will go on forever. What I write here is just my own view based upon my experience. It is worth NOTHING to many because I have no engineering degree, and have never worked directly at making, coating or grinding carbide insert tooling. The closest I'd been was when Norton Company started making their own PCD (PolyCrystalline Diamond) inserts back around 1990. I didn't work on it, but was "near it". Take what I write here for what it's worth....to you.There have been some amazing advances in carbide insert tooling in the last few years. While it's true that in general carbide doesn't take well to interrupted cuts, there are grades available now that might really surprise you in just how tough they are.For example, I was reading a post on another HSM forum who was having trouble turning the face of a crankshaft blank. He had tried a number of different carbide inserts, and good HSS. The material was a forged 4130 or 4150 steel. The HSS didn't fracture as readily, but running at less then 100 rpm and light passes was taking too long. I had some inserts made specifically for interrupted cuts in steels, and sent him a couple. Problem solved. He is now getting "number of passes per insert" instead of "number of inserts per pass."The processes used in coating most inserts just a few short years ago were a high-temp chemical vapor deposition operation that resulted in erosion of the very sharp edges. Physical Vapor Deposition (PVD) coated inserts came onto the market also, though at higher cost. Newer medium-temperature CVD and PVD processes are such that a coated insert can have a nearly dead sharp edge. Uncoated inserts that have been peripherally ground after molding can be dangerously sharp. Those are used in machining non-ferrous metals, aluminum and plastics. With the newer coating processes, most manufacturers of inserts have some coated ones that are still extremely sharp. I've used some from Mitsubishi, Kyocera and NTK on Swiss-style machines.As others have pointed out, the most commonly-found characteristic of lathe and mill inserts is that honed edge. Sometimes it's actually honed, more often it's just a result of the molding process and dies. When molded to a theoretical sharp edge, the coating process can often erode the edge by a tiny bit. These edge preparations, in conjunction with the molded-in chipbreaker designs are what determines the feed rates at which an insert will exhibit good chip control and to some degree, tool life in a given material. Primary consideration for tool life is matching the cutting speed (surface feet per minute), insert coating and substrate grade to the material being cut. Match the depth of cut and feed rate to the chipbreaker.Inserts aside because of the high cost to a home shop machinist, brazed carbide tools can be a very cost-effective upgrade from HSS. The key to success, just as in HSS, is to start by using quality tools and grinding them right. Carbide can be so hard that it's not unlike a ceramic in the way it grinds. The reason that an Agathon grinder comes mounted with two different grit size diamond wheels is that you're supposed to rough it out with one and finish with the other. More than just a polish, the fine wheel removes the "grinding damage" done by the rougher. Minute fractures propagate from the surface created by the rougher wheel, you remove them with the finisher. That results in a stronger edge and longer-lasting tool.This "damage level" done by the rough grinding process is, IMHO, the reason why brazed carbide tools just ground with a rough silicon carbide wheel don't seem to last as long as one carefully roughed out and then finish ground with a resinoid-bonded diamond wheel. My experience with HSS tools seems to parallel my carbide experience. When I had only a 36 grit aluminum oxide wheel to grind a lathe tool, it didn't seem to last nearly as long as they do after I got the 80 grit wheel.I think a lot of HSM'ers who try carbide for the first time get discouraged. It happens by getting something at a flea market/yard sale and try it without knowing just what the grade is for, how to grind it or how to run it. The same thing happens when we buy a $5 "this weeks' special" 1/2" carbide end mill of suspicious origin and it doesn't last 1/2 as long as the Niagra HSS-Co end mill. We have no idea how the carbide powder was purified, mixed with it's alloying elements, fired or ground, yet we'll expect it to perform magic over HSS. It's setting ourselves up for disappointment.What difference it is between, for example, buying a new Valenite brazed carbide AR-6 tool bit and a made in who-knows-where one. Part (though not all) of the reason the name brand stuff costs 2x or more is they know there's more steps to processing the tool, and do it. The same holds true in carbide end mills, inserts, and drills.With no documented qualifications to be spewing the above rant, take anything I write with a grain of salt. That's what I do and why I've posted it to the "Junk Drawer".

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