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  #1  
Old 01-02-2019, 12:33 PM
Terry Williams Terry Williams is offline
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Default Carbide insert grades - MDF versus General purpose

Hi,

I posted this over in the Vectric forum and thought I would see if anyone here could help enlighten me.

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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  #2  
Old 01-02-2019, 01:25 PM
Jim Becker Jim Becker is offline
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If I'm not mistaken, the "harder" knives are "harder" to get as sharp as with "softer" edge material.
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Old 01-02-2019, 02:11 PM
Terry Williams Terry Williams is offline
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I finally called Amana and asked them directly.

The only difference is the hardness - There is 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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Old 01-02-2019, 05:45 PM
Jim Becker Jim Becker is offline
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Thanks for the follow-up on that Terry. Good to know...as I need to buy more inserts for my 90ļ V-bit soon.
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Old 01-26-2019, 04:45 AM
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Joey Jarrard Joey Jarrard is offline
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If the knifes are the same geometry then they would produce the same cut quality. The difference between them is carbide quality. The better carbide will last longer due to its molecular structure. If you could look at the two under a microscope the cheaper carbide will look like pot metal, no uniformity. A high quality carbide will look much like a block wall. The cells would be uniform in size and layers. Just like cast steel pot metal breaks under far less stress than a quality piece.

The reason for having both is to run the cheap stuff when you can and save money. But if you are going from one material to another the savings donít make up for the time to change tooling.

Hope this helps
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Old 01-29-2019, 08:12 AM
Terry Williams Terry Williams is offline
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Yep - you are right on that one - time is money.

I had a couple of projects when I first got my Cobra back in 2012 that used Ipe (Janka hardness 3510 versus red oak at 1290) - I bet I would have saved some money if I had understood this back then. As I recall, Ipe dulled my bits very fast.
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Old 01-29-2019, 10:22 AM
John B John B is offline
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Quote:
Originally Posted by Terry Williams View Post
Yep - you are right on that one - time is money.

I had a couple of projects when I first got my Cobra back in 2012 that used Ipe (Janka hardness 3510 versus red oak at 1290) - I bet I would have saved some money if I had understood this back then. As I recall, Ipe dulled my bits very fast.
Here's a handy little chart to use in making your choices:
http://tinytimbers.com/pdf/chart_janka.pdf

and more on Janka hardness:
http://tinytimbers.com/janka.htm

Last edited by John B; 01-29-2019 at 10:27 AM.
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