I’ve been looking for a “general” guide for feeds and speeds for various types of wood and bits. I understand the Carbide Create rates are very conservative so I want to make my CNC work more efficient. I know there are a few tools like G-Wizard but that seems to be more for industrial machines.
In general I cut soft wood like pine and various hard woods. This “guide” would cover 1/16", 1/18" and 1/4" end mills and 60 and 90 degree V-bits.
I will add that if your main priority is efficiency, you will want to look at @gmack’s worksheet that computes material removal rate, power requirement, and deflection as a function of your cutting parameters, so this should help a lot figuring out how far you can push things on your Shapeoko and/or compare sets of feeds and speeds. It might look a bit intimidating at first, but once you have filled in the static data for your setup (once), and figured out what the few critical cells are, it’s quite easy to use.
I have attached one version in the ebook (here) along with a few basic notes, but if you want to use the latest version it’s available in this thread.
I really like the calculators and use yours regularly but as discussed in other threads, I don’t know that we have nailed the V-bit optimal parameters including chipload. In particular, Carbide’s V bits have no optimal chipload identified so there is a bit of a guessing game.
True. My latest thought while we were trying to settle this matter of proper feeds and speeds for V-bits, was that we should consider them similarly to 1/4" square endmills, i.e. select the target chipload for a 1/4" endmill, pick a suitable RPM (likely at or below 18.000RPM, to be compatible with most V-bits’ rated max RPM), take the number of flutes into account (usually two, sometimes one), and determine feedrate from there.
Since a V-bit is essentially like a continuously-varying diameter endmill, that starts at diameter 0 at the tip and is often mostly used down to a diameter of 1/2", pretending that it’s a square endmill of the average diameter (1/4") could make sense. The smaller part (from 1/4" to tip) can probably take a much larger chipload than their equivalent small diameter square endmills, since there is no deflection and a small V shape is much more robust than a straight shape.
I dropped the ball on V-bits feeds and speeds guideline, but intended to add that to v3 of the ebook, so if anyone has a better suggestion than the one above, I’m all ears !
Yeah, the problem with averages is that it often does not apply in practice. If I have a foot in a bucket of boiling water and the other in freezing water, I should feel great… on average but in reality, it does not work like that.
Is the load constant from tip to top? Is chip evacuation also constant? Depending on the geometry, the flute depth is smaller at the tip than at the top. You say there is no deflection I’m not sure I understand. I larger bit will show less deflection at a given force applied than a smaller one but it is not 0.
Agreed, taking the average diameter is probably wrong, but my thinking was that 99% of people use Vbits in wood, not metal, so that is a forgiving situation and it should allow for a very rough rule of thumb to at least have a ballpark to start from, rather than pure guessing. I also imagined 1/4" being a good baseline just as a gut feeling from watching my vcarving jobs: shallow Vcuts in wood (where only the first 1/3rd of the Vbit is engaged) usually feel like cutting through butter, while when cutting deeper grooves (when e.g. 2/3rd of the Vbit is engaged in the stock) you can feel the machine working harder and the feeds and speeds should matter more then.
My comment on deflection was just considering that Vbit usually come with a 1/4" shaft, so when cutting a 1/8" wide V groove, deflection is much less than what one would have had when using a 1/8" square endmill and its 1/8" shaft.
Poor chip evacuation in deep V-cuts, now that’s an interesting effect to factor in the rule of thumb…
EDIT: and my apologies to @ctdodge for possibly hijacking this thread, but if we end up figuring out an agreed rule for Vbits, that will not have been in vain
@Julien - No apology necessary. People with far greater knowledge and experience than I have (which is currently not much) can hijack all they want. And in this case the hijacking was relevant to my question anyway, so it’s all good.
