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Author Topic: Newbie (not so dopey a question) Help with Feed Rates and Spindle Speeds.  (Read 2208 times)

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Well, current update is All Limits fitted and working, I have mastered the Soft Limits issues and I am now nearly ready to start making something (Weee!)  :)

 I have been following Mr Tweakies Project using an RC Model Aircraft 3 Phase Outrunner Motor as a Spindle Motor with great interest as I have one or two of these beasties knocking around looking for something to do. He makes it look so easy!!!

I have spent some time with CamBam and eventually got my head into it, produced a string of Gcode to make my parts and tested it on my Machine with a lump of expanded polystyrene and to my amazement it does exactly as the drawing - Wonderful!!

My question is that I want to machine some 9.5mm Aluminum Bar with a 3mm Long Shank End Mill and I am becoming confused with all the information about Spindle Speeds and Feed Rates around the web. I am not concerned about ripping it out at x rates of knots, time is no longer a bonus here, but what I don't want to do is snap bits and or destroy the metal.

What would the recommended Spindle Speed and Feed Rates be to give me a nice finish with this size of End Mill. I gather the feed rates are in feet per second Y/N

Thanks in advance  
God created Ale to make us all happy ..... 8)

Offline RICH

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BUGGALUGS,

Link to info on end mill speeds and feeds. You can calculate or consult the charts.

http://www.machsupport.com/forum/index.php/topic,20045.msg138970.html#msg138970

RICH
Hi Rich and thank you for your reply. I downloaded that sheet but in all honesty I'm still struggling. I think either I have forgot more than I remembered about imperial calculations, either that or my recreational chemistry habit is beginning to pickle my brain!  :(

Looking at that and reverse calculating it looks like my End Mill is about 1/8" and on the Chart it reads to me it reads as, Aluminum with 1/8" End Mill RPM 6112 and SFM 200 to 600. Wow.. is that right? 200 feet per minute is bloody fast??  ???
God created Ale to make us all happy ..... 8)

Offline Hood

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SFM is not feed per minute in case that was what you were thinking.
 If you think of a lathe then 200m/min surface speed will let you know the rpm for a given diameter of material, as the diameter increases the rpm will decrease and vice versa. It is similar with a milling cutter except it is the dia of the cutter that affects things.
So for example on a lathe if the SFM required is 200 then at a dia of 100mm the RPM would be 637, if the dia was 200 then the RPM would be 318, if it was 25mm dia then the rpm would be 2547.

I tend to look up the manufacturers data to get Vc (surface units per min) and Fz (Feed per tooth) for a given tool I can then work out whatever I  want from that

Attached is a xls spreadsheet that helps with that as it does the calcs for you.
Hood

Oh hey man, thats the Dogs DoDahs Thanks so much (once again) if it's a resistance, capacitance or inductance calculation or formula I can just about remember how to work it out mentally but as I have said before, this is one of a hell of a steep learning curve. 
God created Ale to make us all happy ..... 8)

Offline Hood

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Just to expand a bit as I dont think I was very clear above.
Vc (surface units per minute) will give you the RPM required for a given dia of material in the case of a lathe or cutter in the case of a mill
So say 200m/min Vc and a 10mm dia cutter, the RPM would be calculated as follows.
The cutters circumference is Pi x Dia so 31.4mm or 0.0314m, so  200/.0314 = 6367rpm

To get the feedrate you would need to know the amount of teeth on the cutter and the feed per tooth.

So say the feed per tooth was 0.2mm and the amount of flutes (teeth) was 3 then that would mean you can advance at  3 x 0.2 = 0.6mm per rev.
With the rpm given above that would mean the feedrate per minute would be 0.6mm per rev  x 6367rpm = 3820mm/min

Hood

Offline RICH

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There are lots of calculators out there, some free, some for a very resonable price, or on-line vendor calculators.
I would suggest you scan the internet to find something that suites you. A lot of the calculators out there take a lot
of factors into consideration and provode a lot of info to the user.

Cleveland actualy published a book on the experimentation they did. Sure wish the person i lent it to would give it back
as it was interesting reading. The reason i mention this is becuse a lot of what you see in calculators are based on the work of
Cleveland and some other associations.

RICH