Thanks, I appreciate the comment. I’m glad that it’s useful.
If not it should be.
Please don’t take the following the wrong way. I’m primarily addressing this as I don’t want others to be mislead.
There are no easy answer to your question without more data (need specific material and basic tool geometry at a minimum). You might find something similar that will work for you but that again depends on the variables not listed here being similar to the ones you find elsewhere.
Normally you have a big enough range that you can run with a conservative estimate/example. When you get into micro tools that range is so much smaller that it becomes an issue. It’s also why everyone starts to jump at the runout numbers as you no longer have as much room for them to be absorbed. I’ll give some examples below but they are by no means a comprehensive list. In the following when I say “changes chipload” that means potentially both the minimum and maximum chipload before breaking the tool.
Tool geometry:
Number of flutes
Obviously a 3 flute cutter vs a 1 flute cutter is going to cut at very different feed. Additional to this all things being equal there will be a large change in flute volume and core potentially changing the chipload of the tool.
Aspect ratio
This is the ratio of the length of cut to the diameter of the tool. The greater the ratio the more fragile the tool. So someone using something like a stub endmill where the length of cut is 1.5x the diameter will have a different experience then someone using a deep reach that is 10x.
Upcut, downcut, 0°
A upcut tool will have the least load and the 0° will have arguably the greatest. A downcut tends to pack the flutes and has more force issues due chip flow and tip geometry. These can all change the chipload.
Helix
As previously stated this can change the direction of force and strength of the cutter. This again will change your chiploads.
Rake
Rake is basically the angle of attack of the flute. The more positive rake you have the less force to make a cut but the thinner and weaker the edge gets. So if you are using a more generic cutter the rake will probably be causing more load and again change your chipload. This doesn’t address neutral or negative rake which change things even more.
Material:
Hardness
To give some quick references wood hardness is usually measured by the Janka scale. Silver maple is 700 lbf, birdseye maple is 1,450 lbf, brazilian rosewood is 2,790. These can’t be cut the same, you will break a cutter at too low of a chipload in the silver maple due to rubbing while maybe getting away with that in the birdseye, and being the true minimum for the rosewood. Alternatively the chipload that will work for the silver maple may break in the rosewood.
Expansion, binding
For lack a another simple explanation this is how much room the cut material takes in the flute before packing and if there are additional components in it that make it “gummy”. Not just chipload in this case but also required changes in geometry.
Material strength
For this purpose this is how much the material is bound to itself. It’s ability to resist the cut and stay together basically. This can greatly change the chipload numbers. This is different from hardness as the grain structure can change it (hard but brittle depending on grain direction and size).
Now lets apply this to the first example in that post. they say they are using a 0.024" cutter at 24KRPM and 40IPM and 0.010" pass depth. So lets go down the list. How many flutes is it? That isn’t in the first post but further down they say they are using a 2 flute and their friend is using a 3 flute. That’s all fine as long as it’s at least stated and you change it by a ratio or chipload per flute.
So let’s calculate the chipload. Chipload = Feed/RPM/Flutes so 40/24000/2 gives us a chipload of 0.00083" (0.021mm). We’ll assume for the time being that this is actually cutting although that’s impossible to tell without the material and runout.
The next thing to look at is the aspect ratio. They list it as 0.12" so 5:1. If ours is the same or shorter then we can maybe use this data. If it’s longer might just snap it right off.
We don’t know what this tool is but most likely an upcut. So again we can assume that if we have the same it should work. However if we have a 0° tool we are engaging the entire flute at once and causing more load that can again break the tool.
Don’t know their helix angle either. Maybe they are using a 20° and we have a 35°. Like for like we again might be breaking the tool.
Rake is also not know. Could be that they have a soft media tool with high rake and we have a lower rake general use tool. That will equal more load and again we are potentially breaking the tool.
Material is a whole mess too. Since they are cutting fingerboards, and looking at their small chipload the are probably cutting rosewood or ebony. This is a very hard wood, that acts almost more like a composite due to the integrated silica in the grain structure. Most of them require little flute volume and don’t bind up like more oily woods. This will work the opposite of most of the above. Using these numbers in too soft of a material will cause so much extra load and heat from rubbing that you will break the tool from too small a chipload. The other possibility is they are cutting a softer wood but have a decent amount of runout effectively moving all the cut to one flute at a much higher chipload.
Some of the above are minor changes and might not have a great effect on their own. However, most likely a few features will be different from any other example and that could change things significantly. The material changes can also be so great that they alone determine a great deal in terms of minimum and breaking chiploads/feeds.
Again, this is isn’t to attack your post. I’m just trying to point out that there is no easy answer here with this number of undefined variables. Even if this one worked for you it wouldn’t for the next person with a different enough tool or material. There are potentially good starting points with more data but not universal ones.