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A lot of things must be considered when determining speeds/feeds for a particular job. These are some of them:
I made the above table for my personal use about fifteen years ago so I can't recall exactly how I came up with some of the numbers except that most of the information was extracted from the 17th edition of "Machinery's Handbook".
There are SO MANY variables that influence the cutting RPM that any table is useful only as a starting point. My own procedure is to calculate the cutting speed using the table and then adjust the machine tool to the next lower standard speed for the first trial. After a cut or two, you should have a pretty good idea whether the speed can be increased or have to be decreased.
Most of my work is with steel and steel isn't that hard to "read" if you're cutting too fast. With HSS tools, run the speed up until the chips are just starting to discolor - very, very light yellow, then back off the RPM to the next lower speed. This assumes a SHARP cutting tool and a tool life between sharpenings of about two hours. (A dull cutting tool will heat much more quickly, wear much faster and require lower cutting speed, as well as not producing as good a finish as a sharp tool.)
For carbide tooling, if the tool is brazed carbide, I increase the speed until the chips are coming off yellowish-brown. For solid carbide tools and carbide inserts, I usually increase speed until the chips are light purple. These are generalizations and better results may be obtained by increasing/decreasing RPM. It's well-known that best surface finishes with carbide tooling usually occur with very high RPM.
Again, the above presumes fairly sharp tooling - if the cut is an interrupted one then a slower speed and very fine feed would be wise.
When cutting aluminum, a sure sign that the speed is too high is chip welding on the cutter. This may also occur when the cutting oil isn't optimum for the job, the cutting tool is dull or the DOC is too great. Chip welding, whether on lathe cutting tool or end mill, is very visible and if the cutter is intended to be used again, the welded chips must be carefully removed. One method is to remove the tool from the machine then using a sharp scribe with some optical magnification to carefully pry the chips away from the cutting edge of the tool.
It's been over forty years since I machined non-ferrous alloys with any regularity so my personal opinions just aren't reliable when it comes to "reading" the operation and adjusting the speed accordingly for these types of materials. In general, I use the table the determine the RPM when roughing the work then increasing the RPM for the finish cut.
Another important note is that the table above is based on dated information. The book was published in the early 1960's and the information included in the book was collected much earlier than that. Many HSS and carbide alloys are much better performers than they were in the 1950's, when the data was likely collected. The implication is that the speeds in the table may be a bit conservative.
If you have access to a more current copy of MH then you should use it. A comment regarding how speed is usually characterized. 99% of the time, a particular operation will note a speed in surface feet per minute (sfpm). That started a long time ago and frankly I don't find it at all useful these days unless one is operating a big planer or planer-mill or maybe turning a 20 foot butterfly valve for a hydroelectric dam.
The information needs to be converted to RPM by first multiplying by 12 (number of inches in one foot) then dividing by Pi (3.1416, approximately). This gives a normalized figure of RPM/inch of cutter or workpiece. The actual RPM is the normalized figure divided by the cutter diameter (if milling or drilling) or the workpiece diameter (if turning) in inches.
The table gives the normalized speeds and RPM is determined by dividing by the cutter or work diameter in inches.
- Material
- Heat treatment/hardness of material
- Depth of cut
- Cutting tool material
- Geometry of cutting tool - appropriate for material
- Rough or finish machining
- Type of cutting oil
- Time between tool sharpening
- Condition and rigidity or machine tool
I made the above table for my personal use about fifteen years ago so I can't recall exactly how I came up with some of the numbers except that most of the information was extracted from the 17th edition of "Machinery's Handbook".
There are SO MANY variables that influence the cutting RPM that any table is useful only as a starting point. My own procedure is to calculate the cutting speed using the table and then adjust the machine tool to the next lower standard speed for the first trial. After a cut or two, you should have a pretty good idea whether the speed can be increased or have to be decreased.
Most of my work is with steel and steel isn't that hard to "read" if you're cutting too fast. With HSS tools, run the speed up until the chips are just starting to discolor - very, very light yellow, then back off the RPM to the next lower speed. This assumes a SHARP cutting tool and a tool life between sharpenings of about two hours. (A dull cutting tool will heat much more quickly, wear much faster and require lower cutting speed, as well as not producing as good a finish as a sharp tool.)
For carbide tooling, if the tool is brazed carbide, I increase the speed until the chips are coming off yellowish-brown. For solid carbide tools and carbide inserts, I usually increase speed until the chips are light purple. These are generalizations and better results may be obtained by increasing/decreasing RPM. It's well-known that best surface finishes with carbide tooling usually occur with very high RPM.
Again, the above presumes fairly sharp tooling - if the cut is an interrupted one then a slower speed and very fine feed would be wise.
When cutting aluminum, a sure sign that the speed is too high is chip welding on the cutter. This may also occur when the cutting oil isn't optimum for the job, the cutting tool is dull or the DOC is too great. Chip welding, whether on lathe cutting tool or end mill, is very visible and if the cutter is intended to be used again, the welded chips must be carefully removed. One method is to remove the tool from the machine then using a sharp scribe with some optical magnification to carefully pry the chips away from the cutting edge of the tool.
It's been over forty years since I machined non-ferrous alloys with any regularity so my personal opinions just aren't reliable when it comes to "reading" the operation and adjusting the speed accordingly for these types of materials. In general, I use the table the determine the RPM when roughing the work then increasing the RPM for the finish cut.
Another important note is that the table above is based on dated information. The book was published in the early 1960's and the information included in the book was collected much earlier than that. Many HSS and carbide alloys are much better performers than they were in the 1950's, when the data was likely collected. The implication is that the speeds in the table may be a bit conservative.
If you have access to a more current copy of MH then you should use it. A comment regarding how speed is usually characterized. 99% of the time, a particular operation will note a speed in surface feet per minute (sfpm). That started a long time ago and frankly I don't find it at all useful these days unless one is operating a big planer or planer-mill or maybe turning a 20 foot butterfly valve for a hydroelectric dam.
The information needs to be converted to RPM by first multiplying by 12 (number of inches in one foot) then dividing by Pi (3.1416, approximately). This gives a normalized figure of RPM/inch of cutter or workpiece. The actual RPM is the normalized figure divided by the cutter diameter (if milling or drilling) or the workpiece diameter (if turning) in inches.
The table gives the normalized speeds and RPM is determined by dividing by the cutter or work diameter in inches.