When turning metal, I often find the finish quality is well less than desired. This can be worked around afterwards by polishing which can then get a very nice finish, but ideally I would like a better finish to start with. Here are some suggested causes of poor quality.
Poor quality is generally caused by one or more of these factors:
Generally, to get a good finishing cut, make sure you have good materials, sharp cutters (carbide or HSS), appropriate cutting fluid, appropriately fast speeds, appropriate tool height, heavy compound clamp, good quality tool holders, tight jibs, minimal overhang (both tools and work).
Note that this all applies to finishing cuts - general turning and roughing may be quite different.
| Cutting Speeds m/min | HSS Rough-Finish | Carbide Rough-Finish | HSS Drill |
|---|---|---|---|
| Aluminium | 75-105 | ||
| Brass | 45-60 | 45 | |
| Bronze | 24-45 | 150 | 35 |
| Mild Steel | 30-38 | 100-150 | 25 |
| Cast Iron | 18-24 | 60-100 | 18 |
| Steel | 15-18 | 60-75 | 15 |
Increase speed by 20% when using coolant.
Decrease speed by 20% for interrupted cuts.
To convert m/min to RPM, multiply by 320/diameter in mm or use this table.
| m/min | 10mm | 20mm | 30mm | 40mm |
|---|---|---|---|---|
| 10 | 320 | 160 | 107 | 80 |
| 20 | 640 | 320 | 213 | 160 |
| 45 | 1440 | 720 | 480 | 360 |
| 60 | 1920 | 960 | 640 | 480 |
| 75 | 2400 | 1200 | 800 | 600 |
| 100 | 3200 | 1600 | 1067 | 800 |
| 150 | 4800 | 2400 | 1600 | 1200 |