Creating a formula for feeds/speeds based on janka hardness?

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WillAdams
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Creating a formula for feeds/speeds based on janka hardness?

Post by WillAdams » Mon Apr 07, 2014 11:16 am

I've theorised about this in the past. Am I missing something? Or is there not a reason to do this?

For those not familiar w/ it: http://tinytimbers.com/janka.htm

I'm asking 'cause my next project involves cutting Ipé.

I'm also thinking we should just bite the bullet and put everything into tables on the materials page --- then, copy only the materials for a stock Shapeoko 2 into the introductory/overview table at the top....
Shapeoko 3XL #0006 w/ Carbide Compact Router w/0.125″ and ¼″ Carbide 3D precision collets

RobCee
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Re: Creating a formula for feeds/speeds based on janka hardn

Post by RobCee » Mon Apr 07, 2014 12:50 pm

I believe that it would certainly give you a guide to the correct range, but there are other aspects that would alter the calculation, such as the 'oilyness' or 'sappyness' of the wood.
As long as you stuck to woods, you should be ok, as most will be pretty free-cutting compared to plastics and metals
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TDA
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Re: Creating a formula for feeds/speeds based on janka hardn

Post by TDA » Wed Apr 09, 2014 7:19 pm

While Janka tables are a good guide for the general hardness of the woods you can't use it for a feed guide. There are many other things that have to be considered grain structure, and mineral content are two huge ones. To give you an example Ipe is actually much easier to cut then ebony. Despite the fact that they are very close on the Janka table (depending on specific wood type) they are very different in grain structure and mineral content. While Ipe is fairly uniform ebony is not. Ebony integrates silica into the gain but not uniformly across the grain. This is why in some ebony you can see light striations though the wood. That is where a lot of silica has collected. These light areas are much harder to cut as you are basically cutting glass.

Hope that helps.
John Torrez
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Nigel K Tolley
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Re: Creating a formula for feeds/speeds based on janka hardn

Post by Nigel K Tolley » Thu Apr 10, 2014 9:17 am

I had no idea. Fascinating.

I should have, of course - forge slag (klinker) is basically glass, & for the same reason.

As for cutting wood, the direction of cut to the grain is probably as important as anything else.

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WillAdams
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Re: Creating a formula for feeds/speeds based on janka hardn

Post by WillAdams » Mon Jun 02, 2014 4:10 pm

Turns out the Precise Bits folks feel that this is a reasonable guesstimation technique:

http://www.precisebits.com/tutorials/Gu ... _Rates.htm
Shapeoko 3XL #0006 w/ Carbide Compact Router w/0.125″ and ¼″ Carbide 3D precision collets

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