machining hard wood, examples of methods and feeds and speeds

I know there are lots of resources about this online I've been reading loads ever since we got the CNC in the shop but I'd love to talk about my specific situation.
I'm almost exclusively machining solid wood, which I struggle to find valuable information on, it's all metal out there!

What I'd mostly like to see is examples of feeds and speeds people are using in hard woods. I'm doing a lot of walnut right now, so that might be a good start, I'm guessing birch would be about the same speeds, I recently did white oak which was a whole other ball game so we can leave really hard stuff aside for the moment.

I have a 3hp liquid cooled spindle, I'm often cutting fairly thick parts, so my stick out length does often end up longer than the recommended 4x the tool diameter. Even when it is within the recommended tool stick out though what I often find is my cuts screech very loudly. I've read in a post somewhere someone saying they rarely needed to use ear protection when running their machine, that seems unfathomable to me.

My machine runs from 12 000 rpm to 24 000 rpm, I try to approach most of my cuts with an adaptive clearing method (fusion 360) to reduce the load on the machine.

So for instance with a 2 flute half inch end mill in walnut how would you approach a cut? I'm doing a 1/2" DOC using 25% of the end mill.

Using tool #46206k from this chart:
https://www.toolstoday.com/media/wys...-2-3-Flute.pdf

I'm using the recommended settings 18000 rpm, 200ipm, .0057" chipload. It works I do get a finished part at the end but the parts come out bumpy on the side walls and its quite loud. First off do these settings seem ok in general? Secondly, would the general approach to "loudness" be to simply reduce the ipm and rpm? In general I adjust feeds and speeds by calculating ipm based off a chosen rpm and the manufacturer recommended chipload. Does that seem correct? or should I fiddle with the chipload too?

So as well as just maybe reviewing this specific example, I'd love to see some other examples if you can tell me what type of wood you were cutting and your method and feeds and speeds, it would be really valuable to have a small bank of examples to run by. I don't have anyone in my entourage to discuss this stuff with!

I've been cutting walnut quite a bit myself lately. My spindle is bigger than yours, but I haven't been pushing it as hard - maybe that's why it's not screaming as loud (although it's more comfortable to wear ear protection around it than not to) . Roughing with a 1/2" diameter cutter, I've been restricting it to a 1/4" depth of cut, and only taking a tenth of an inch per pass (1/5 the diameter). I don't get a real RPM value from my VFD, but I run it about in the middle of its useful frequency range for a half-inch tool. I've been running the feedrate at about 4 inches per second, or 240 ipm, but it doesn't actually go that fast unless it hits a straightaway. The chips it makes seem about right to me, and the cut quality is good. But it's probably taking me a longer time to rough out a piece than you. If your gouges aren't showing up in the finish passes, and you (and your neighbors) can tolerate the noise, it's probably okay for you to keep going like you are; otherwise I'd say reduce the DOC.

As a general rule, if the bit is screaming, it's because you aren't cutting fast enough, or the rpm is too high.
It can be hard to give recommendations, because machine rigidity comes into play.

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I'm using the recommended settings 18000 rpm, 200ipm, .0057" chipload. It works I do get a finished part at the end but the parts come out bumpy on the side walls and its quite loud

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I suspect the bumpiness is due to machine flex, due to the constant movements of the adaptive tool path.
I've never used Fusion generated, or any Adaptive Toolpaths. But with a 1/2" bit, in walnut, you should have no trouble at 15,000 rpm and 400ipm. Walnut is actually a pretty soft wood. Birch would be harder.
I'm not sure you can actually get the machine to move that fast with Adaptive toolpaths, wiothout it shaking a lot.

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Secondly, would the general approach to "loudness" be to simply reduce the ipm and rpm?

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The opposite. Lower the RPM, but increase the feedrate. With a 1/2" bit, you should never need to spin it faster than 15,000-16,000 rpm.

Thanks for the response, i've been a bit mia here but this is some great info.
So let's forget about the bumpy sidewalls for now, I'm interested what you said about lowering rpm and increasing feedrate.

To make sure I understand, chipload or feed per tooth is a product of the rpm, ipm, and flute number, so lowering rpm or increasing ipm will increase the chipload, correct? If so, is it generally acceptable to stray away from the recommended chipload? Let's say I have a bit that sounds a bit loud at the recommended chipload but increasing that chipload improves the sound can I conclude that if it sounds good then there is no problem?

I'm somewhat under the impression that the higher the chipload the harder the machine will work, since its taking larger bites per rotation, that's why I figured I had to decrease ipm and increase rpm. I assume though that it is something I still need to consider, I should be careful not to overload it?

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But with a 1/2" bit, in walnut, you should have no trouble at 15,000 rpm and 400ipm

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When running a bit at that speed in black walnut how deep are you cutting, and if you say you don't use adaptive toolpaths, would you generally be slot cutting using the entire width of the cutter in one pass?

I'm also wondering about climb vs conventional. I've taken to generally cutting climb because conventional rips out big chunks along the wood grain, that said it hasn't really bothered the final result if I do a finishing pass afterwards, so sometimes I run it both ways to save time on repositioning moves, is that ok? Also are their times where you'd want to use conventional over climb or vice versa.

I'm just going to add to my previous post. In terms of the example you gave @ger21

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But with a 1/2" bit, in walnut, you should have no trouble at 15,000 rpm and 400ipm

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Using the info given with the mill I was specifically referring too, it's telling me 200 ipm with .0057" chipload at 18000rpm, if I reduce the rpm to 15000 and increase the feedrate to 400ipm I end up with a chipload almost twice as big as the recommendation. Would this be wise to attempt?

@awerby I hadn't seen your post at first, that is interesting, I'm trying to push the machine mainly for production speed reasons, of course that may be the problem as well! That is interesting that you go so much lighter, might be worth backing down that doc.

I find this page helpful when a job in an unfamiliar material comes along https://www.cutter-shop.com/informat...oad-chart.html

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Using the info given with the mill I was specifically referring too, it's telling me 200 ipm with .0057" chipload at 18000rpm, if I reduce the rpm to 15000 and increase the feedrate to 400ipm I end up with a chipload almost twice as big as the recommendation. Would this be wise to attempt?

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It depends on how rigid your machine is. Try reducing the RPM, and keeping the feedrate the same to start. Then, if your machine is capable, try increasing the feedrate as well. You could try reducing depth of cut with the higher chipload. But I'd definitely reduce RPM. There's no reason on a hobby machine to ever spin a 1/2" bit more than 15,000 rpm.


I find Amana chip loads to be extremely conservative.

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When running a bit at that speed in black walnut how deep are you cutting, and if you say you don't use adaptive toolpaths, would you generally be slot cutting using the entire width of the cutter in one pass?

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Depends on the specific application. For pocketing, probably 60-75% stepover.

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I'm also wondering about climb vs conventional. I've taken to generally cutting climb because conventional rips out big chunks along the wood grain, that said it hasn't really bothered the final result if I do a finishing pass afterwards, so sometimes I run it both ways to save time on repositioning moves, is that ok? Also are their times where you'd want to use conventional over climb or vice versa.

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I always use conventional cutting, unless tearout is an issue. In that case, climb cut. Conventional will almost always give a better finish in wood.