Speeds and feeds question

i would like to know from those experienced in cnc on the speeds and feeds. just recently i have ordered brand new collets and bits and i would like to know is it better to run at a smaller depth per pass at a higher feed rate or a higher depth per pass at a slower feed rate. i ask because as i was working on a project, with a 1/4 inch bit, at 2mm depth per pass and 15 inchs a min on pine, i was getting alot of chatter especially going in the x (+) direction or the x axis moving to the right. i wasnt sure if i shouldve gone at a lower depth per pass with much higher feed rate vs a higher depth per pass at a lower feed rate.
Please let me know what you guys think, thanks in advanced

Generally a higher feed rate at a shallower depth is better. That is an EXTREMELY slow and shallow pass, if I’m picturing it correctly.

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Assuming you have the standard 24v 300w spindle, be careful with 1/4 bits. They will put more stress on the spindle.

That aside, smaller depth but faster feed seems to be the rule of thumb and that seems to be holding up in my limited experience too. (I’m also a newb).

Pine of course has grain. The chatter might simply be where you are cutting along/across the grain.

What I’ve been doing is running L shaped jobs repeatably in a new material at different depths per pass and feed rates to find the sweet spot. Doesn’t take long to do and can seriously improve the speed and/or quality of cuts. Just remember to document those numbers :smile:




Sorry for the newbie question but… In trying to understand feeds and speeds I copied this from the Shapeoko Wiki:

Milling Formula

RPM = SFM x 3.82 / Tool Diameter
IPM = RPM x # of Flutes x Chip Load
Chip Load = IPM / RPM x # of Flutes
SFM = .262 x Tool Diameter x RPM
Revolutions per Minute (RPM): Number of revolutions the endmill makes in a minute
Inches per Minute (IPM): Number of inches the endmill passes through the workpiece in one minute
Chip Load: The amount that each flute cuts during a single revolution of an endmill
Surface Feet per Minute (SFM): This is the cutting speed of the endmill. It is the number of feet per minute that a given point on the circumference of a cutter travels per minute

My question is which of these do I calculate first since I need answers to any one of the calculations to answer any of them!

Does that make sense? I can’t complete one equation because I need the answer from anothe requation to answer the first one!!

My head hurts! :\

I usually look first at the recommended chip load for a give bit and material, then find a feedrate that matches a spindle speed my Dewalt 611 router can accommodate.

For example: in hardwood with a .125 inch bit I like a chip load of .003 to .005 so that means i need a feedrate of 120 ipm and a spindle speed of 20,000 rpm (about a 3 setting on the Dewalt).

Since I am conservative I would reduce that feed rate to 100 ipm (and I have done many cuts at that speed and it seems to work well)

So I guess the main takeaway is to use feed and speed calculations as a rough guide to the range you should be using, but you need to get a feel for your machine to understand what feedrates it functions best with.

Since we are generally not cutting hundreds of parts in a production environment not having the exact rates is not a huge problem.

Here is a copy of my excel sheet for calculating speeds and feeds, I created it for the Dewalt, but it may answer some of your questions CNC Speed Calculator.xlsx (14.6 KB) .


Now THAT’s a nice little chart!
Thanks so much, Allen. sockin’ that puppy away!

Russ from Coral Springs, FL, USA

Can you use the spreadsheet? It will allow you to change the feed rate and see what spindle speeds are required.

it comes up here as a picture. i don’t believe i can copy it down as a spreadsheet to show any formulas you may have.


You should be able to click on the blue words “CNC Speed Calculator.xlsx” in the original post to download it.

geeze, sometimes I swear I cannot see the forest for the trees!!!
Sweet -
I’m pretty fluent in Excel. where are you getting the 13553/2072.9 numbers from. (I love being educated!)
VERY nice. I’ve been plugging in numbers into D4.
is it possible that you could create coefficients (like the 13553/2027.9) that would interact so that you could enter the material, too? Or does it not work that way?

Thanks so much for this! I WILL be using this once my “mock-carves” start becoming real.


The (30,000 - 13553/2072.9) is the linear equation that fits the Dewalt speeds (1 to 6) to actual RPM

All the other formulas are pretty straight forward.

The chip load is determined by the material and bit size and is a recommendation from the bit manufacturer. In a perfect world each bit would have it’s own custom chip load data, but since they don’t I am just using these recommendations that seem to work pretty well.

I have much to learn, so Chip Load (the number) is what you want to strive for?
Or is Chip Load what happens when you use such & such bit at such & such speed on such & such medium?

Both. The speed rate, the spindle RPM and the bit size and number of flutes determine the chip load. (How big the bites out of the material are)

I think I get it, to the point that it makes sense to me. I will do some reading up on this - It sounds like a good area of knowledge to have under your belt.

I understand that feed rate is tied into rpm, bit type and the power of your spindle, but all that aside, do we know how fast the X-Carve COULD go (in/min)?
I’m sure that may depend on the type of stepper motors, but are there ballpark figures out there?


I started a thread asking just that question and the answer is in excess of 300 ipm. Way faster than any reasonable cutting speed.

Good to know.
Little tidbits like this I should store away in a document, somewhere. <-- I hope i get to that.

Yet, your sheet does come up valid numbers for speeds in excess of 300. I guess that would be for more “professional” setups than the X-Carve?


Very true, I have not added any limits to the feedrates in the spreadsheet.

I really like your spreadsheet.

is the chip count where you would get your depth of cut?

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I use:

Federate = RPM x # of flutes * chip load

I’ll start with a shallow depth of pass and increase it until the result become poor.

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