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Virtual Machine Shop Forum  |  Machine Tool Technology  |  Questions, answers, ideas  |  Topic: How To Calculate Mill Spindle RPM? « previous next »
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Author Topic: How To Calculate Mill Spindle RPM?  (Read 4329 times)
Zero Cool
Guest
« on: December 25, 2006, 06:31:50 AM »

Hello,

 Newbie here. I am looking for basic information on milling. I recently purchased an old but very hefty Mill/Drill and i need some basics to get started. I am interested in making aluminum parts for audio projects i build.

 I found information on cutting speed. but how do i calculate spindle rpm for a given bit diameter and material?

For example, if i am milling 1/4" thick aluminum with a 1/2" 4 flute end mill. what RPM should i set the machine up for?

 I will be milling slowly by hand at first and adding PC Based CNC later. Quality of work is more important then speed. etc.


Thanks


Zc
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Ron
Admin
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Posts: 730

« Reply #1 on: December 25, 2006, 06:52:51 AM »

Hello,

 Newbie here. I am looking for basic information on milling. I recently purchased an old but very hefty Mill/Drill and i need some basics to get started. I am interested in making aluminum parts for audio projects i build.

 I found information on cutting speed. but how do i calculate spindle rpm for a given bit diameter and material?

For example, if i am milling 1/4" thick aluminum with a 1/2" 4 flute end mill. what RPM should i set the machine up for?

 I will be milling slowly by hand at first and adding PC Based CNC later. Quality of work is more important then speed. etc.


Thanks


Zc
Every material has a "cutting speed"
Its up to you to know what that is for the material you are machining.
Cutting speed is not RPM... cutting speed is the speed in linear feet per minute that a given tooth on the cutter will be moving when it slices through the material
Cutting speed is feet per minute or "FPM" for short
All materials have a documented cutting speed or "CS" for short
As a general rule the CS for Aluminum is close to 200 FPM
For mild steel, about 100 FPM
To find RPM then you need to follow this formula: RPM=(CSx4)/D
Where CS is the cutting speed in feet per minute, 4 is a constant, and D is the diameter of the cutter
Saying it a different way, multiply the cs by 4 and then divide the result by D

Ron
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Zero Cool
Guest
« Reply #2 on: December 25, 2006, 04:33:17 PM »

Ahhh i see, so, if i am understanding correctly and using your formula RPM=(CSx4)/D  and this is for example only.

 If the aluminum cutting speed is 200fpm, (again example only, not actual). then we multiply 200 by 4 = 800 then divide by the bit diameter, lets say .5" for example, so then the spindle speed should be set to 1600rpm or as close as the machine will go....correct?? and a .25" bit 3200 RPM.


 Got it. that is easy enough.

 Thank you very much!


Zc 8-)

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nic8559
Guest
« Reply #3 on: January 08, 2007, 01:16:37 PM »

Take the cutting speed off the chart multiply it times 4 then divide by the diameter of the cutter.
Jim.
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