Feed and Speeds

[jcnewbie]

This my sound a stupid question, so please bare with me..


How does one calculate feeds and speeds. I know there are calculators on the net which will give you the results, how ever I would like to calculate it myself.

Please let me know if I am doing it correctly.

For all roughing operations I am assuming 240 SFM with 4 flute length , 240*4 = 960. ( should I always multiply the flute length)?Then to calculate the spindle speed I am going to round that value to 1000 and / it by the tool diameter (0.5). which equals 2000.

To calculate the feed rate I am going to multiply 2000 * 0.005(diameter of tool / 100) = 10 in/min

So for a 0.5 diameter flat endmill my spindle speed I would enter in Mastercam for the roughing operation = 2000 rpm and feed rate = 10 in/min

Am I doing this correct ?

[tobyaxis]

Originally Posted by jcnewbie This my sound a stupid question, so please bare with me.. How does one calculate feeds and speeds. I know there are calculators on the net which will give you the results, how ever I would like to calculate it myself. Please let me know if I am doing it correctly. For all roughing operations I am assuming 240 SFM with 4 flute length , 240*4 = 960. ( should I always multiply the flute length)?Then to calculate the spindle speed I am going to round that value to 1000 and / it by the tool diameter (0.5). which equals 2000. To calculate the feed rate I am going to multiply 2000 * 0.005(diameter of tool / 100) = 10 in/min So for a 0.5 diameter flat endmill my spindle speed I would enter in Mastercam for the roughing operation = 2000 rpm and feed rate = 10 in/min Am I doing this correct ?

I do not know how MC calculates F&S but what are you cutting???
Whenever I use MC I use the overrides based on Set-Up, Tool, Operation, and Machine Capability. MC F&S are usually way too slow for me.

[brandou10l]

to calculate rpm for a given tool dia

sfm*3.82/cutter dia

ex.

.5 inch tool 200sfm

200*3.82=764

764/.500=1528

1528 is the rpm

to find feed rate

rpm*chip load*flutes

1528rpm .0025 chip load and 4flutes


1528*.0025*4=15.28

the feed rate is 15.28 ipm

[jcnewbie]

tobyaxis : cutting steel

brandou10l: where are you getting 3.82 from ? sfm*3.82/tool diameter
Is that a default value, i'm using 4...

As for the feedrate rpm*chip load* flutes, could the "chip load" vary from tool to toll ?

[brandou10l]

3.82 is a constant used in all calculations with that formula, there are other methods of getting the rpm but this one is the easiest

yes the chip load will vary from tool to tool

generally the larger diameter of the tool the bigger the chip load, but keep in mind the setup, bieng rigid or not and or finish requirements, matl bieng cut,
if you are unsure of cutting parameters, usually the catalog you get your tools from will have a guide for speeds and feeds

maybe you should look into getting a book on basics of machine shops or something like that,
when i started out i got one and they have a tremendous amount of useful information

[Andre' B]

Originally Posted by jcnewbie brandou10l: where are you getting 3.82 from ?

3.82 = 12 / Pi = 12 / 3.1416

It is a combination of constants needed because cutter diameters are measured in inches, the 12 gets that to feet which you need for SFM (surface feet per minute). Pi gets you from diameter to circumference.

[BobWarfield]

jcnewbie, there are quite a few calculators out on the net you can try. Mine is called G-Wizard:

http://www.cnccookbook.com/CCGWizard.html

Cheers,

BW

[Fegenbush]

jcnewbie,

I am going to recommend you get the book Machinery's Handbook (

Amazon.com: Machinery's Handbook, 27th Edition (Toolbox Edition) (9780831127008): Franklin D Jones, Henry H Ryffel, Erik Oberg, Christopher J McCauley, Ricardo M Heald: Books

Amazon.com: Machinery's Handbook, 27th Edition (Toolbox Edition) (9780831127008): Franklin D Jones, Henry H Ryffel, Erik Oberg, Christopher J McCauley, Ricardo M Heald: Books

). It has the answer to your question, which is also above, and also the answer to just about every other machining related question. In addition to the charts for gears, belts, screws, feeds and speeds, etc. the text explaining everything is very easy to read and informative.