- Joined
- Dec 25, 2017
- Messages
- 20
Hello,
I am trying to machine a 6" round cast steel part on my little Grizzly G4000 lathe. Due to the smallness of my lathe I have to take very small depths of cut (that's okay, I've got time). Overall I need to remove about 0.25" from the diameter of a 0.5" wide section of the casting to make it fit in an assembly.
I'm using carbide tooling [1]. I'm currently in the process of running compressed air to my machine so I can cool the part. Feed rate is approx 0.005"/rev.
I have found that at 120 RPM I get no sparks, but the torque is too much (at only 0.002" DOC) and causes the 1/8" wide drive belt to slip. At 300 RPM I get some sparks and no slip. At 600 RPM I get lots of sparks; no slippage either. I think I could have gone deeper and used faster feed, but I was afraid of overheating my tools without coolant.
First question is, are sparks okay? As best as I can tell they are okay so long as I keep the tooling cool.
The second question is what should the speed and feed be for my flimsy little lathe? I have done a calculation below, let me know if it is sane for my setup.
I am trying to machine a 6" round cast steel part on my little Grizzly G4000 lathe. Due to the smallness of my lathe I have to take very small depths of cut (that's okay, I've got time). Overall I need to remove about 0.25" from the diameter of a 0.5" wide section of the casting to make it fit in an assembly.
I'm using carbide tooling [1]. I'm currently in the process of running compressed air to my machine so I can cool the part. Feed rate is approx 0.005"/rev.
I have found that at 120 RPM I get no sparks, but the torque is too much (at only 0.002" DOC) and causes the 1/8" wide drive belt to slip. At 300 RPM I get some sparks and no slip. At 600 RPM I get lots of sparks; no slippage either. I think I could have gone deeper and used faster feed, but I was afraid of overheating my tools without coolant.
First question is, are sparks okay? As best as I can tell they are okay so long as I keep the tooling cool.
The second question is what should the speed and feed be for my flimsy little lathe? I have done a calculation below, let me know if it is sane for my setup.
Code:
According to [2] for cast iron with carbide 400 SFM would be my (rather optimistic) goal.
This yields a target RPM of 255 which is roughly 300 RPM. With 0.005"/rev that gives a feedrate of 1.5 IPM.
Using turning horsepower the calculator on [3] with 300 RPM, 1.5 IPM, 6" diameter, 0.005" DOC, 1.4 HP/in^3 [4], gives 0.2 HP of spindle HP required.
My lathe is 0.75HP. Assuming I don't run into the drive belt torque limitation [5], I should be able to cut 0.005" DOC or maybe even 0.010" with coolant.
[1] Grizzly G5640 Lathe Bit Set
[2] https://littlemachineshop.com/reference/cuttingspeeds.php
[3] http://www.custompartnet.com/calculator/turning-horsepower
[4] Manufacturing Processes Reference Guide. Page 157. Table of unit horsepowers for turning.
[5] There is also mention of a clutch in the G4000 parts diagram; this also could be cause of my slippage. I need to investigate further.