I have a board I made from Ash and Curupay (“Patagonia Rosewood”). The Curupay has a Janka hardbess of 3840 - obscene versus the 1300 hardbess of the Ash. I was trying to flatten the baord with the cnc at 15mm/s x/y rate and a mere .75mm depth of cut on a 1/8" shaft, 1/8" endmill. Not sure entirely what happened but there was a small spot where the bit ran into it and the cnc jhst stopped moving. You could see / hear it struggling to move, but it wasn’t going anywhere. Any tips / tricks I should try to get it going on a 2nd attempt? Thanks.
Try to half down the speed!
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^ what he said. You’ll need to design your cut for the hardwood.
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CNCing very hardwoods need a very slow feed rate, and very shallow step down. I’ve done quite a bit of hard maple/ash, slow and light cuts are better, but exponentially effect speed of cut.
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I went down to 7mm x/y feedrate and only .5mm depth of cut. It successfully cut out 8 x 1-2" diameter circles 4mm deep into the Carupay but it got stopped again on the first pass of cutting out the entire board. I ended uo cutting it by hand with a jigsaw instead (which was still difficult, and I tried a scrollsaw first which was basically impossible). It had no problem with the ash in the board which is 1/3 the hardness of Curupay so I’m still pretty hopeful that I can do guitar bodies on this haha.
Next up though is testing purpleheart which is 2/3 as hard as Curupay.
Try halving those numbers, 3.5mm x/y feed, and .25mm depth. Still a bit thicker than a card paper stock per cut
I appreciate it but at that point I think it’s a better use of my time to cut it out with a jigsaw. Those speeeds would give me ~10 hours to cut outa ~9.8" x 19" shape .7" deep.
In the future I’ll make sure to check the hardness of the wood before I buy it.
I’m wondering what spindle you are using? It’s strange that it’ll take so long. I guess some wood can be harder than metal even, and the size of the piece matters of course as well…
I have used mine to flatten walnut and oak, both with about 1.5mm doc and a speed of 25mm/min and that worked just fine with the makita around 3-4 with a 16mm bit. What I rrealized thought is that it’s important to take the z-zero at the highest spot 
Now I actually realized what’s going on in this question hahaha for that kind of hardness you probably have to go very slow, yes 
No more answering on tired evenings.