Carbide Inserts - Difference between MDF grade and General

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Terry Williams
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Carbide Inserts - Difference between MDF grade and General

Post by Terry Williams »

Hi,

I'm in the process of buying more carbide bits and v-bit inserts and had a question about the two different insert knife grades that are offered.

One is MDF - obviously for use with MDF and the other is General Purpose Use - used on chipboard, balsa, hardwood and plastics.

I asked the vendor what would happen if I used MDF for general purpose use or general purpose use for MDF and got the answer "The difference is carbide hardness. If you use it on general purpose knives on MDF you will not get the same results, but they will work" - with no details on what "results" they are talking about.

I'm assuming that the MDF knives are the harder of the two to help tool life in abrasive material, but the question I have is why not use the harder knives for all purposes?

Are harder grades of carbide incapable of keeping a keen edge in less abrasive materials (non-MDF) resulting in less detail?

Just trying to determine if it is a marketing ploy to get you to buy two sets of inserts when one would probably do for both uses.

Has anyone actually compared the results on using the MDF grade for general purpose use or using general purpose grade for MDF use in terms of cut quality and tool life?

Thanks,

Terry
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martin54
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Re: Carbide Inserts - Difference between MDF grade and Gener

Post by martin54 »

If the only difference is the carbide quality then yes you could use the MDF insetrs for all the general purpose stuff & they should last longer than the general purpose insetrs in the same way you could use the general purpose inserts for MDF & get the same results from a cutting perspective but they would'nt last as long.
Guessing the MDF inserts are more expensive as a higher grade carbide normally comes at a higher price.

The vendor may not be aware exactly what the differences are, often vendors just sell stuff & don't pay to much attention to what it does & why (just my on personal experiences) in various industries with suppliers.

It may be that as well as a different grade of carbide there are other differences like blade angle which can make a difference & the vendor is not aware of these other differences :lol: :lol:

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Re: Carbide Inserts - Difference between MDF grade and Gener

Post by Terry Williams »

I finally called Amana and asked them directly.

The only difference is the hardness - There are no geometry differences, so if you don't mind paying a slight premium, buy the MDF inserts over the general purpose and you'll get the same quality cut with longer tool life.

Thanks,

Terry
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Re: Carbide Inserts - Difference between MDF grade and Gener

Post by Leo »

Terry Williams wrote:I finally called Amana and asked them directly.

The only difference is the hardness - There are no geometry differences, so if you don't mind paying a slight premium, buy the MDF inserts over the general purpose and you'll get the same quality cut with longer tool life.

Thanks,

Terry
I am sorry for this conflicting view but they said the difference is in the hardness? Can they quantify that? I have been in the manufacturing industry cutting metals for MANY MANY years and have never heard of carbide refereed to in terms of "hardness". To me that is an empty answer just to get you off the doorstep.

Coatings can increase surface hardness, but the carbide substrate is made up of tungsten steel with a binder, generally cobalt. The tungsten steel is a powder that is mixed with the cobalt powder and formed by pressing the powders into shape (insert) under several TONS of pressure then processed through an over at near melting temperature. After that they may be precision ground. They they MAY be coated with any one or a multiple of coatings. There are coatings to serve different purposes.

As to the carbide substrate there ARE different "grades" of carbide. I could go further into explanation but suffice it to say there are top level grades that are called micro-grain and there are lower level grades. The better brands will be a good micro grain and I would suspect stuff with really low cost will be lower grades - think China. NOT to say all Chinese grades are junk. I have tested some that I would consider purchasing again.

Soo - when someone says that carbide is harder - ask what is the hardness as measured on a Rockwell C scale? A High speed steel end mill will be AROUND 60-62 Rc (same as HRC)

As searched on google --- how hard is carbide?
Hardness varies but all cemented carbides are harder than the hardest metals. Tungsten carbide with a Vickers number of 1700-2400 (85 HRC equivalent) is composed of 90% carbide particles by weight, 80% by volume.

In woods there is "some" difference but a good micro-grain carbide will be sufficient and if more tool life is needed then a good coating can be easily applied. The insert manufacturer will have a selection of coatings available.

Tin - coating is the gold color you commonly see. It is electrically applied and will be harder than the carbide substrate, typically Rc 85 and higher. Again there are quality issues with any coating. Some cheap applications are so thin that it is just coloring and adds very little to the quality of the tool. Good quality coatings have some thickness to them. There are plenty of HSS cutters out there that perform BETTER than carbide.

Coatings will add to cost and if you are only cutting a few parts the cost may not be worth while.

Sometimes when you call a company you will get a customer service person or a sales person. They may not know the answer to the question because it is often times far above their paygrade, so they tell you what they thing is the answer. If you get to talk to an engineer - like me - the answer can get deep, but it will at least be an answer.

Look up --- How is carbide inserts made.
Sandvik is a VERY VERY huge world wide organization and they have some awesome youtube videos on carbide

So as not to DOG Amana - They are an excellent outfit making high quality tools. I would not hesitate to buy from them.
It is my guess that they will sell the exact same cutter but with a coating on it.


Hope this helped at least a little bit.
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Re: Carbide Inserts - Difference between MDF grade and Gener

Post by martin54 »

Leo, I'm not so sure it is a conflicting view & you may be looking at it the wrong way, it's the engineer in you :lol: :lol:

I would probably say that the difference is one is harder if I were talking to most people, basically because it is something they can easily understand & if I went into different grades & compositions it s something that would send most of thm to sleep

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Re: Carbide Inserts - Difference between MDF grade and Gener

Post by TReischl »

I am with Leo on this one.

It has been many, many years since I took Strength of Materials and read engineering stuff. I seem to remember that different grades of carbide have different size "spheres" (thinking martensite here, but could easily be wrong). Which explains the term "micro grain" being used for higher quality carbide. I also seem to recall that the size of these "spheres" does not change the hardness of the carbide but rather how sharp it can be ground. The smaller the sphere the "sharper" the edge.

In actuality it is not possible to actually create a true sharp edge with carbide because these "spheres" cannot be ground, they come out intact.

All that said, I decided to try some really cheap (3 end mills, 1/4, 3/8 and 1/2 for $14 from HF). They are HSS. I was amazed at how smooth they cut. Of course that is because HSS can have a much sharper edge than carbide. Those HSS bits have become my go to bits for working with pine, walnut, maple and cherry. I have been digging around trying to find other shapes in HSS. Yup, they do dull faster. However they also get resharpened.

Anyway, that is my two cents worth.
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Re: Carbide Inserts - Difference between MDF grade and Gener

Post by ger21 »

Different grades of carbide are indeed "harder" than others. While I can't explain the technology, tools like the Vortex Xtreme Performance line last MUCH longer than standard carbide bits.
We use spiral bits from a local manufacturer, and they offer two grades of carbide. The "harder" grade lasts 2-3x longer cutting melamine particle board and MDF, and even longer with more abrasive materials like plastic laminate (Formica).
Gerry - http://www.thecncwoodworker.com

Terry Williams
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Re: Carbide Inserts - Difference between MDF grade and Gener

Post by Terry Williams »

Thanks everyone for all the great info - I really appreciate the feedback!
Terry
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