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Best CNC Router Speeds and Feeds Calculator

May 15, 2017   //   by Bob Warfield   //   Blog, CNC Router, FeedsSpeeds, Software, Techniques  //  2 Comments

I had a customer contact me recently to talk about Speeds and Feeds for CNC Routers.  It was an interesting conversation because he really wanted to understand what it takes to have the Best CNC Router Speeds and Feeds Calculator.  In explaining it to him, I felt the best approach was to consider a combination of things.

cnc wood router

Image courtesy of AXYZ

First, I wanted to cover the questions that CNC Router users ask me most often, particularly questions relating to CNC wood router work.  Second, I want to cover the areas I’m most proud of that set our G-Wizard CNC Router Speeds and Feeds Calculator apart.

Question #1 – Is G-Wizard for CNC Wood Routers or CNC Metal Mills?

By far the most common question I get from the CNC Router crowd is, “Is G-Wizard meant for routers or CNC mills working on metal?”
My answer is that the Material Database has a giant database of wood species as well as tons of plastics and other soft materials such as foam that CNC Router users commonly cut.  I ask them to take a look at the “More” button next to the material selector and to experiment with the Search function on that panel.  It doesn’t take long for most to see that G-Wizard has a very extensive library that’s well suited to their needs.
There are over 150 species of hardwood alone:
wood cnc machine
There are over 150 species of hardwood alone in the Material Database…
You can’t very well create the Best CNC Router Speeds and Feeds Calculator without having an extensive database of woods, plastics, and other materials that CNC Router owners typically cut.

Question #2 – Does G-Wizard Handle Downcut Spirals and Other CNC Router Bits for Wood?

Something the metal-cutting community probably doesn’t know is that there are many specialized CNC Router bits (cutters) intended to overcome difficulties in wood, laminates, plywood, and other materials.  The difficulty is splintering.  You want to cut to size and leave a nice clean edge.

The tendency to splinter is due to upward forces from the cutter’s flutes tearing the wood up from below.  The CNC Wood Router world has developed several cutter geometries that minimize this tendency.  For example, there are Downcut Spirals.  With these cutters, the direction of the helix is reversed, which directs the forces down rather than up.

Downcut Spirals have much less tendency to splinter because of that downward force.  It certainly protects the top surface, but even the bottom surface has less tendency because it is supported by the spoilboard below.  Nevertheless, there are CNC Router Bits for Wood called “Compression Cutters” that are designed to produce forces towards the center of the bit.  This prevents splintering and tear out from happening to either the top or bottom surface and can lead to nice clean edges.

G-Wizard handles both of these special CNC Router Bits for Wood, and more.  Here’s the Geometry selector for Endmills (these cutters are all just specialized sub-species of endmill):

cnc router bits for wood

CNC Router Bits for Wood marked in red on the Geometry popup…

G-Wizard handles Downcuts, Compression Cutters, and Straight Flutes.  It also handles V-Bits, which are commonly used for engraving, sign making, and wood carving applications.

Let’s talk about Straight Flutes for just a second, because this is a very handy cutter type for CNC Routers.

Many CNC Router Bits are what are called “Form Cutters”.  They have no spiral, but they do describe a shape of some kind.  Typically they’re used for creating decorative edges and cutouts in panels for cabinetry, moldings, or doors.  Here’s a typical example from Amana:

cnc router panel cutter bit

With G-Wizard, just select the Straight Flute cutter and use the largest diameter of the cutter that is in the cut and you’ve got feeds and speeds for your panel cutter.

Being able to handle all the special CNC Router Wood Bits is important for the Best CNC Router Speeds and Feeds Calculator.

 

Question #3 – Will G-Wizard Work For My Small Hobby CNC Router?

Okay, last really common question, “Will G-Wizard work for my small (insert Shapeoko, Chinese, Inventables, DIY, etc.) hobby CNC Router or is it just good for industrial routers?
These folks have a valid concern as a lot of packages don’t consider that small machines can perform very differently.  They give unreasonably high feeds and speeds that are a problem on smaller machines due to their lack of rigidity.
We offer a couple of ways to help with small machines.
First, there is the Tortoise-Hare slider.  Most people really love it, and it helps tremendously.  I do find that a lot of folks are a little over-zealous about going to the Tortoise side.  I always tell them to go with what they’re comfortable with, but to experiment with going a little faster over time.  There will be a sweet spot that is typically quite a bit faster than their first instinct.
Second, we will adjust based on our estimate of machine rigidity.  This feature has made a lot of folks with particularly flexible machines or small machines very happy.  If your machine will go slow enough, you can cut just about anything.  There are a lot of ways to interpret “slow enough.”
In this case, when talking rigidity, slow enough is all about how much power is pumped into the work by the spindle.  It is that power that generates cutting forces that can cause the machine to deflect and cause trouble.
G-Wizard can adjust to accommodate small machines like this Shapeoko…
So G-Wizard has this notion of an “ideal machine rigidity” based on how much the machine weighs and how big the envelope of its travels are.  A light machine with huge travels is very flexible.  A machine with tiny travels (say 2″ x 2″ x 2″) that weighs 200 lbs is very rigid.  So we look at both variables and adjust the spindle power limit based on rigidity benchmarks from industrial machines known to be solid performers.
This works really well when you need high precision or to find a very conservative starting point.  G-Wizard will even adjust it for Routers, since Industrial Routers are typically less rigid than Industrial CNC Mills aimed primarily at high precision metal work.
I tell folks to set up two machine profiles–one with the weight adjustment and one without.  Then I suggest they start working with the adjusted on, and head towards the values from the non-adjusted one.  Go maybe 20% of the way each test.  They will again find a sweet spot that works for them.
I don’t know if handling small machines well is a requirement to be the Best CNC Router Speeds and Feeds Calculator, but I do know it’s a feature that makes our customers very happy.
Phew!
Those are customer motivated.  Now, let’s talk about things they discover after using G-Wizard for a while.  These are features I’ve put in at customer urging that most who discover them are really pleased with.

Feature #1 – CNC Router Vacuum Table Support

Vacuum Fixture Mini-Calc limits cutting forces so parts stay locked down…

Vacuum tables are super convenient for CNC Router users.  Plop down a sheet of material, turn on the vacuum, and start cutting.  No muss, no fuss, and the parts are held down.  Just one little problem–sometimes, the CNC Router will knock the parts loose.  When that happens, you often wind up scrapping one or more parts.

This was one of those Aha! moments you get talking to customers.  My brother works with CNC Routers all day long and we talk a lot about his problems.  He mentioned small parts popping off vacuum tables and it didn’t dawn on me that G-Wizard could help.
Then, I was talking to someone who was deciding not to buy G-Wizard.  He was worried that since G-Wizard seemed so aggressive, he would get little use from it.  Most of his work was with small parts that easily pop off vacuum tables.  For some reason when he implied G-Wizard should be solving his problem, a light bulb lit up.
So I created the Vacuum Table Mini-Calc.  It considers part surface area and vacuum strength and from that it figures out how to limit spindle power (just like with machine rigidity) so forces are not strong enough to pop the part off.  I gave a free copy to this customer as well as my brother already had G-Wizard and they both loved the feature.  Many others have commented that it really helps them get things right the first time on vacuum tables.

Feature #2 – The Cheat Sheet

speeds and feeds cheat sheet
The Speeds and Feeds “Cheat Sheet”…
Have you ever noticed the “Cheat Sheet” button below the Tips area on G-Wizard?
This was motivated by I problem I used to hear about constantly, but hardly do any more since I added that button.  This problem can affect any beginner, but happened particularly often to CNC Router users.
The problem comes from discovering that the machine is physically incapable of feeds and speeds that are required for some scenario.  Most often it happens because a spindle can’t spin slowly enough (minimum rpms are common on CNC Routers because they have high-speed spindles) or a feedrate can’t feed fast enough (common on DIY CNC Routers because they combine relatively slow feedrates from DIY architectures with very high spindle speeds that want to drive up feedrates together with cutting soft materials that also want high feedrates).
I used to hear this so often I did a blog post:  What To Do If Your CNC Won’t Go Slow Enough or Fast Enough.
I answers a wealth of “Can’t get there from here” questions.  Over time I had to learn that my original mind-set that G-Wizard’s job was to find the BEST answer was really more like:
Find the BEST answer for THIS particular user based on their capabilities and preferences.
The article helped, but eventually I realized people would get some feeds and speeds out of G-Wizard and then they’d want to nudge them in some direction or other:
–  My machine can’t run the spindle that slowly.  How do I get higher rpms?
–  My machine won’t feed that fast.  How do I get slower feedrates?
–  I want better tool life, not faster cycle times, how do I get that?
–  etc.
So the Cheat Sheet tells you how to use G-Wizard to solve for all of these common problems.  Use it to help you understand which things you should change to achieve various end results.  It even lists the changes in order from most to least desirable.
Since I added the Cheat Sheet, I just don’t hear these questions much any more.

Feature #3 – CADCAM Wizards:  Feeds and Speeds from the CAM Software’s Perspective

I could actually go on with features for CNC Router users for a long time, but shouldn’t, LOL.  Just this one more, but it’s a doozy!
CADCAM Wizards are a radically different approach to Feeds and Speeds.  The traditional Feeds and Speed Calculator (of which I think GW is the finest example, natch!), starts from the perspective of a manual machinist and how they were taught in vocational schools and apprentice programs.
Yet we are in a CNC world.  Is there some way to reinvent conventional Speeds and Feeds to make them better?  Why do we need Feeds and Speeds?
There are lots of lofty answers, but really here is the bottom line:
–  We just need Feeds and Speeds that work so we can tell our CAM software what they are.
Side note:  Yes, a lot of CAM has built-in Feeds and Speeds, but it’s really lousy with only one exception I’ve ever seen (Solidcam).   People complain about this regularly on our CAM Surveys, so I know most of you agree.
Back to our story:
We are serving the needs of CAM Software!  
Well what if we approach Feeds and Speeds from the CAM perspective.  Let’s quit asking all these weird questions and thinking about surface speed, chipload and other arcane things.  How would CAM think about it?
Well, it would start with Machine and Material.  Then it would ask what kind of toolpath (Pocket, 2D Profile, Hole, etc.)?  It would ask a couple of other simple questions, then it would expect Feeds and Speeds.
Whoa!  That is radically different.
If you try to create something that gives feeds and speeds starting with that information and asking the absolute MINIMUM other questions, some really cool things happen:
1.  It can be much easier for beginners.  After all, CADCAM Wizards even tell them what kind of tool to use.  They give a complete recipe.
2.  It can give a BETTER answer.  So many will give a Cut Depth and Cut Width without thinking about it much.  They use a rule of thumb, guess, or what always worked.  Yet, the vast majority of freedom to do the job more efficiently is gone once you know Cut Width and Cut Depth.  And the interaction of those two is complex–simple rules of thumb don’t give good answers.
CADCAM Wizards use powerful AI technology to figure out an optimum cut recipe…
One of my biggest disappointments is I haven’t yet succeeded in getting every G-Wizard user to even try them, let alone to use them regularly.  But those that do rave about it.

Conclusion:  Best CNC Router Speeds and Feeds Calculator?

So, is G-Wizard the Best CNC Router Speeds and Feeds Calculator?

Gee, I don’t know.  I sure haven’t seen a better one, and I’d love to hear about it if there is one.  Are there more features that might make for a better CNC Router Speeds and Feeds Calculator?  Probably.  In fact, almost certainly.  I don’t know exactly what they are yet, but I suspect one or more of you will tell me before too long.  Sing out any time, because I’m very eager to hear!

 

 

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Best CNC Router Speeds and Feeds Calculator
5 (100%) 3 votes

2 Comments

  • I can totally concur that G-Wizard is awesome on a CNC router. I have one, a $3K one where half the gantry, and nearly ALL the z-axis carriage and frame are made from HDPE…yes, plastic. As in milk-jug plastic! There is flex, and there is “nose dive” and a lot of other things.

    Getting GWizard turned my machine from an almost-capable wood working machine, into a fully-capable milling machine. I cut aluminum daily, and am happy to report I get no edge buildup anymore, the carbide bits last about forever, the chips that come off show no signs of excessive heat, and all because I am always able to both create and verify my “cut catalog” of verified and approved cutting parameters.

    My machine might take longer…okay, a LOT longer…to finish than one of the big-boys, but the surface quality I’m getting is essentially the same, because deflection in the bit has the same math on my machine as it does on the large ones. An 1/8″ extended-length bit won’t take much push on their machines, nor on mine.

    In the forums I frequent, I’m often asked by new users whether some F&S is “okay”. And, like Bob says, the numbers they were told by machinist friends, or online F&S calculators are way too fast. It seems the reasons are more down to that those F&S calculators don’t give **all** the information about a cut, and instead go simply from SFM, hardness, flutes and bit/stock material.

    And indeed, you can tell from their before-and-after photos showing stringy uncut pieces of wood, what we’d call “burrs” in the metal-cutting, that completely go away when the proper F&S are used.

    I could not have achieved any of the things I do on my cheap machine if it wasn’t for G-Wizard. I’ll also throw in an endorsement for the Editor portion. Being able to visually verify things like safe heights, clearances and cut depths outside the CAD/CAM software’s simulators has saved my bacon and machine more than once. Errors when going through a new toolpath that say things like “there’s no spindle-on command before movement starts”, or “No feedrate specified” yet in the file, are HUGE. You won’t get that in the CAD/CAM software, not now, not ever. These days, I verify every toolpath in the GWizard editor, because I know if there’s something bad in there, it will reveal it.

    Cheers!

  • Thom, that’s very kind of you, thanks so much!

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