As a new owner of a logan 1820 10 in lathe and a newby to machining in general i have had fun with some minor turning projects with aluminum, brass and tool steel. One question i have is when to run higher RPMs and when to use back gear and go slow. Are there any generalizations I can apply that will help me know when to use each? Thanks!
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when to go fast, when to go slow?
- Thread starter Eliotmay
- Start date
backgear is generally used for extreme slow turning like when threading, or rimming.
high spindle speeds are used for general turning. the actual RPM you want your spindle to turn at depends on the part you are turning - it's size, and material. there is a chart in the Machinist handbook (and online references if you do a quick search) that lists the suggested sufrace feet per minute for each material, and there are formulas to convert that SFM to RPM based on the diameter of the part you are turning which should give you the suggested speed you'd want the spindle to turn at.
do a search for SFM, and RPM, and turning
high spindle speeds are used for general turning. the actual RPM you want your spindle to turn at depends on the part you are turning - it's size, and material. there is a chart in the Machinist handbook (and online references if you do a quick search) that lists the suggested sufrace feet per minute for each material, and there are formulas to convert that SFM to RPM based on the diameter of the part you are turning which should give you the suggested speed you'd want the spindle to turn at.
do a search for SFM, and RPM, and turning
In general, the smaller diameter pieces need to spin faster and aluminum needs faster speeds than steel.
Like Sharon mentioned, it's all about Feeds & Speeds. Here's a good reference based on material and diameter of workpiece. http://www.southbaymachine.com/setups/cuttingspeeds.htm
The section called " Quick RPM/Spindle Rate Calculations: Lathe, Mill, Drill (HSS Cutter) " is most relavent to your question. If you're using carbide on manual equipment, increase RPMs by 2-3 times and leave feed rates the same.
Ray
Like Sharon mentioned, it's all about Feeds & Speeds. Here's a good reference based on material and diameter of workpiece. http://www.southbaymachine.com/setups/cuttingspeeds.htm
The section called " Quick RPM/Spindle Rate Calculations: Lathe, Mill, Drill (HSS Cutter) " is most relavent to your question. If you're using carbide on manual equipment, increase RPMs by 2-3 times and leave feed rates the same.
Ray
An easy RPM calc is
RPM = SFM*4/DIAMETER
RPM is obvious, SFM is the recommended surface feet per minute for your material/cutter (there are tables of this all over the place, just look for "speeds and feeds"). Diameter is the diameter in inches. For a milling cutter this is the diameter of the cutter. For turning, this is the diameter of the part.
HSS works much better at lower speeds than carbide. Stay below this value to keep from burning up cutters. For off the cuff calcs, figure 70 SFM for steel and 200 SFM for aluminum using high speed steel cutters. So, if you have a 1/2" end mill, in aluminum, figure
200*4/0.5=1600RPM
Those numbers are conservative. They go up or down depending on cutter coating, coolant, etc. They are meant as a starting point, so start there, and play with things to get something that feels/sounds right.
RPM = SFM*4/DIAMETER
RPM is obvious, SFM is the recommended surface feet per minute for your material/cutter (there are tables of this all over the place, just look for "speeds and feeds"). Diameter is the diameter in inches. For a milling cutter this is the diameter of the cutter. For turning, this is the diameter of the part.
HSS works much better at lower speeds than carbide. Stay below this value to keep from burning up cutters. For off the cuff calcs, figure 70 SFM for steel and 200 SFM for aluminum using high speed steel cutters. So, if you have a 1/2" end mill, in aluminum, figure
200*4/0.5=1600RPM
Those numbers are conservative. They go up or down depending on cutter coating, coolant, etc. They are meant as a starting point, so start there, and play with things to get something that feels/sounds right.