# How to calculate "Z Axis feedrate" on Mill for CAM software setup?



## countryguy (May 15, 2014)

Hi everyone, 
I am a bit stymied on this one.  The newb about 30days into Milling CAM software.  I am cutting, but in Styrofoam.  I am working thru the formulas and getting the parms all set for optimum cutter life and such.  $180 is expensive for a Mill cutter! Wow.  worth getting the math right!

 I am not sure what the value should be for 'Z-Axis feedrate' on the Dolphin V12 CAM tool setup screen. It's near the bottom. (DARN-  I keep getting a Quota exceeded on the image?????   so no image on the post here). Anyone have an idea on what they are asking me to calculate? 

I have searched all over for formulas and cannot find much. Is this the depth of cut? Does not seem like it. Having a hard time finding a definite answer in the help files and manuals as well. Going to the boards!


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## Don B (May 15, 2014)

I am new to CNC myself, sorry I can't give you a definitive answer but my advice would be start at 1 ipm and slowly work up from that, starting at a high feed rate and working down is not financially beneficial as I have sadly found out.


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## Ray C (May 15, 2014)

countryguy said:


> Hi everyone,
> I am a bit stymied on this one.  The newb about 30days into Milling CAM software.  I am cutting, but in Styrofoam.  I am working thru the formulas and getting the parms all set for optimum cutter life and such.  $180 is expensive for a Mill cutter! Wow.  worth getting the math right!
> 
> I am not sure what the value should be for 'Z-Axis feedrate' on the Dolphin V12 CAM tool setup screen. It's near the bottom. (DARN-  I keep getting a Quota exceeded on the image?????   so no image on the post here). Anyone have an idea on what they are asking me to calculate?
> ...



The Z feed rate is the same concept as an X or Y feed rate.  I'm not familiar with your CAM program but, the one I use and others I tested have a clearance plane and feed plane.  When the bit is being moved to a different location or region, it raises to the clearance plane (usually 1" above the highest region of the part) and moves at the max table velocity to the new location.  When it reaches it's new location, it lowers at maximum speed to the feed plane.  When it reaches the feed plane (usually about 0.1" above where it touches the metal) it slows down and enters the metal at a rate specified by the Z feed rate.  A rule of thumb is that for straight in plunging, the Z feed rate should be about 1/3 of your normal X or Y cutting rate.  Somewhere along the line, I saw formulas for it based on chip load but, I typically tweak the values suggested by my CAM program.  The amount of tweaking is something you learn by trial and error.  Also, there are many feed-rate calculators out there.  Here's one that is popular but, I'm not familiar with it.  http://hsmadvisor.com/index.php?page=buy

Anyhow, whenever possible, I avoid straight plunges and try to spiral or ramp into the material.  

Ray


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## Ray C (May 15, 2014)

Oh, one thing to mention...  About that calculator that I mentioned in the previous post, I know it is very popular but, I'm not familiar with it and have no first-hand experience using that program.  I know of a few people that use it and like it a lot.  It's pretty powerful so I'm told and has the ability to take available horsepower into consideration to calculate DoC and feeds/speeds.  There are other programs similar to that one.  I tried many of the free programs and didn't like them.  My gut feeling is that the ones that cost money might actually be useful.

For those in the market for a CAM program, auto-calculation of feeds & speeds should be high on your list of criteria along with a good simulation package. 

Ray

EDIT:  Add word to make sentence correct.


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## Ray C (May 15, 2014)

I just happen to be setting up a CNC job and looked at the Z feed rates more closely.  Depending on the material and cutter, it seems to vary between 25% and 33% of the X-Y feed rates.  To be on the safe side, a conservative starting value would be about 20% of the X-Y feed rate and then work your way up from there...  You can speed things up quite a bit if you ramp or spiral into your cuts.  You can also shave a lot of time off a job by doing a good job of calculating your clearance planes carefully and radically decreasing the clearance and rapid plane values.  -Be careful not to crash anything though and ALWAYS simulate your cuts before going live.

Oh boy, I'm about to get into trouble... I set my table rapid speed from 30 to 45 ipm.  FWIW, my max spindle is 3000 RPM and I usually over-ride it to a max of 2800 RPM just to be conservative.  Most calculated X-Y cutting feed rates fall in a range of 15-30 ipm for most of the materials and cutters I work with.  


Ray


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## DaveSohlstrom (May 16, 2014)

When I generate a Gcode file using CamBam as my CAM program I use Gwizard to figure all my feeds and speeds. If you like you can take a look at it here.  http://www.cnccookbook.com/CCGWizard.html
It is a very good program and will save you from running your end mills to fast or to slow.

Dave


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## countryguy (May 17, 2014)

Awesome stuff Everyone!  Thanks a ton!         I'm going to try and actually cut metal today!   No more Styrofoam!  This will be the machines first ever metal cuts!   I sort of just want to run the Simulator and toss some paper chips around (as Ray C. say's it is just as much Fun! lol    Firs time Milling jitters for sure.  

  Wish me luck.


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## Don B (May 17, 2014)

countryguy said:


> Awesome stuff Everyone!  Thanks a ton!         I'm going to try and actually cut metal today!   No more Styrofoam!  This will be the machines first ever metal cuts!   I sort of just want to run the Simulator and toss some paper chips around (as Ray C. say's it is just as much Fun! lol    Firs time Milling jitters for sure.
> 
> Wish me luck.



Yes good luck..!)


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