Confused with SFP

[zerodegreec]

I have spent the last 2 hours looking for the answer, but I am still confused.

Surface Feet Per Min... Okay what EXACTLY is the surface feet per min? I timed myself and I can move the table at exactly 1' per Min. But obviously thats not what we are looking for. Are we actually looking for the area removed per min? Example a 1" wide by 12" long piece of material that we will remove 1" of material. thats 12 cubic inches. If I can move at 12" per min thats 12 cubic inch per min.... thats obviously not the right number.



I need RPM to figure out SFM but what is a SFM?

[juergenwt]

Zero- sfpm is the speed a cutter, drill or other cutting tool should have on it's outside dia..
So if you have a 1" drill the circumference would be 1 x 3.14 (Pi) = 3.14". So if you are given a certain sfpm as cutting speed for a certain material than convert the feet into inches and divide by the circumference of your cutting tool to get your rpm.
In metric it is given in m/min. Same formula. Dia. x Pi = Circumference in mm. Convert m (from m/min) into mm by moving the decimal point three places to the right and divide by the circumference of your cutter (in mm) to get rpm.
If you are using a lathe the dia you are turning x Pi = circumference.

In other words: sfpm is the recommended speed in feet/min or m/min that the outer edge of the cutting tool has when cutting thru the certain material.
All of this depends on your material, cutting tool, cutting depth, rigidity of machine tool etc. . Take it as a guide only
Do not confuse this with the feed rate given. That is a different ball game all together.

[zerodegreec]

Thank you very much. Exactly what I was looking for. I appreciate you taking the time to clarify this for me.

I am also confused on the feed rate and depth of cut. Any "rules of thumb"? I have James Harvey's Machine Shop Trade Secrets and he talked about the tan chip rule. I am not running a CNC (want to learn how to run the machine by hand first).

[Algirdas]

also confused on the feed rate and depth of cut
feed rate is tool movement (following the shape) speed. The same, as axis movement speed. Presumably, the edge of the tool is cutting, that's why the name "feed" is. If You draw a line by pencil, the feed rate is speed of pencil nose in regards of paper.
Depth of cut is how deep the tool edge goes into material. If You draw the line on a paper, there is almost no depth of cut at all
want to learn how to run the machine by hand first
do You ride the bicycle? do You swim?

[zerodegreec]

Originally Posted by Algirdas also confused on the feed rate and depth of cut feed rate is tool movement (following the shape) speed. The same, as axis movement speed. Presumably, the edge of the tool is cutting, that's why the name "feed" is. If You draw a line by pencil, the feed rate is speed of pencil nose in regards of paper. Depth of cut is how deep the tool edge goes into material. If You draw the line on a paper, there is almost no depth of cut at all want to learn how to run the machine by hand first do You ride the bicycle? do You swim?

I know WHAT they are, I am not stupid. I am asking how to know WHAT feed rates and depth of cut should be used.

and I ride A bicycle not THE bicycle....and what does that have to do with learning how to run a mill by hand before I convert it into a CNC?

[hpowell]

Originally Posted by zerodegreec I know WHAT they are, I am not stupid. I am asking how to know WHAT feed rates and depth of cut should be used. ...

Feed rate and depth of cut depend on so may variables that a rule of thumb must be VERY general.
A generic, good quality endmill in mild steel would cut half its diameter deep at about .002" per tooth per rev. That's if you're cutting a keyway, for instance. Drilling into the groove should be at half the lineal feed.
Using just the side if the cutter, you can double the depth of cut and the feed.

More things to take into consideration when deciding on Cutting speeds and feeds and depths of cut:
Material of the cutter. Eg: HSS, solid carbide, inserts, etc.
Rigidity of the machine and workpiece.
Type of material being cut.

I suggest you speak to your tool salesperson about specific jobs, or even post your question on this forum for specific jobs until you feel comfortable deciding yourself.
A short night course in machining at your local technical school would be a great help to you.

Machinist's Calculator from http://www.machinist-calculator.com/can help you make these calculations. Disclosure: Machinist's Calculator is produced by my company.

[Algirdas]

what does that have to do with learning how to run a mill by hand
just a general education question. Do You imagine bicycle run training without bicycle and learning how to swim without swimming?
WHAT feed rates and depth of cut should be used
tool (insert) supplier provides detailed information. It is balance between insert life time and production time consumption. You can use Iscar, Sandvik, Granlund provided information for other inserts and tools also.
In addition what Mr.hpowell said, I will add a little.
There is possibility to cut without cooling. You can use maximum depth of cut and feederate then. It ensures best productivity. The machine must be ready for hot chips and powerfull enough.

[beege]

SFM is the relative speed of one object's surface to another object's surface in feet per minute. If you dragged a rod along the street while driving at 40 MPH, the surface speed of the rod against the pavement would be 3520. The surface speed of the tires relative to the pavement would be zero, unless you slam on the brakes and the tire skids. If you spun a 1" rod in one direction, and contacted a 1" rod spinning at the same RPM in the other direction, the SFM would be zero, because the two surfaces would not be sliding against each other. Drilling a hole at say, 30 SFM, means you calculate the speed of the drill at its largest diameter as it passes rubs against the hole walls. The SFM of the same drill at its center is zero:

((pi X diameter (circumference)) X RPM) /12 (to convert inches to feet); you see that if diameter goes to zero, then so does SFM.

SFM will dictate the heat generated at the cutting edge of your tool. The feedrate will determine the thickness of the chip. Hope it's not too confusing...