So, I had a project and used a chunk of 2-3/4" hydraulic cylinder made from 1045 medium-carbon steel. This material is not free-machining like resulpherated steels such as 12L14, but it's strong and relatively cheaply available as scrap. And it can be hardened if that is important.
I turned it in a South Bend 14-1/2" lathe. My first cuts were at 600 RPM (434 SFM), which is the next-to-fastest speed on the lathe. (And my lathe operates somewhat faster than in factory trim--a 1410 RPM motor was replaced with a 1780 RPM motor when the original purchaser sold it back in the deeps of time. The pulley was not changed, however, so the spindle speed benefitted from the faster motor speed.)
I was using a CNMG 432 insert designed for turning steel with a chip-breaker design. I was turning with a .050 to .100 depth of cut and a .005 feed rate. I used Tap-Magic cutting oil. The chips came off the steel blue-hot, and straight as an arrow, quickly wrapping around everything and becoming a strong, sharp, and hot birds nest. This is the issue using a negative-rake tool like a CNMG with a slower and less powerful machine. With a heavier feed rate and maybe a higher speed, perhaps the tool would have broken the chips. I've read that a carbide insert needs to be "slammed" into material like 1045 to provide good chip management. My lathe lacks the power to pull that off.
I switched to a CCMT 431 insert, which is similar (including the chip-breaker design) but has a positive rake. That insert also would not break chips, but did curl the chips into tight worms about an eighth in diameter. Again, the chips came off the cut blue-hot. The curled worms were a big improvement over the birds nest, but they still went everywhere. The CCMT insert also was not as picky about surface speed, and made the same chips at 450 RPM.
This was my first experience with steel that doesn't machine well, and I explored the matter. Maybe this post will save someone the search. The trick that I learned was "peck-feeding". Just as we break chips in when drilling by pecking at the hole using the quill, we can do the same with the power feed on the lathe. All I had to do was momentarily release the apron clutch every few seconds. The slight pause in the feed would break the chip. I ended up with a chip tray full of 4-inch tightly curled worms, which was safe and manageable.
There are plenty of other options I might have tried, but that one worked in this situation.
Finished part:
During turning--but the pic was not when the machine was actually feeding, but rather was posed for the picture before engaging the power feed clutch. For this picture, the depth of cut was 0.100 (actual, not diameter), feed rate was .0048, tool was CCMT 431 insert with coating and chip-breaker for cutting steel:
Rick "still on the steep part of the learning curve" Denney
I turned it in a South Bend 14-1/2" lathe. My first cuts were at 600 RPM (434 SFM), which is the next-to-fastest speed on the lathe. (And my lathe operates somewhat faster than in factory trim--a 1410 RPM motor was replaced with a 1780 RPM motor when the original purchaser sold it back in the deeps of time. The pulley was not changed, however, so the spindle speed benefitted from the faster motor speed.)
I was using a CNMG 432 insert designed for turning steel with a chip-breaker design. I was turning with a .050 to .100 depth of cut and a .005 feed rate. I used Tap-Magic cutting oil. The chips came off the steel blue-hot, and straight as an arrow, quickly wrapping around everything and becoming a strong, sharp, and hot birds nest. This is the issue using a negative-rake tool like a CNMG with a slower and less powerful machine. With a heavier feed rate and maybe a higher speed, perhaps the tool would have broken the chips. I've read that a carbide insert needs to be "slammed" into material like 1045 to provide good chip management. My lathe lacks the power to pull that off.
I switched to a CCMT 431 insert, which is similar (including the chip-breaker design) but has a positive rake. That insert also would not break chips, but did curl the chips into tight worms about an eighth in diameter. Again, the chips came off the cut blue-hot. The curled worms were a big improvement over the birds nest, but they still went everywhere. The CCMT insert also was not as picky about surface speed, and made the same chips at 450 RPM.
This was my first experience with steel that doesn't machine well, and I explored the matter. Maybe this post will save someone the search. The trick that I learned was "peck-feeding". Just as we break chips in when drilling by pecking at the hole using the quill, we can do the same with the power feed on the lathe. All I had to do was momentarily release the apron clutch every few seconds. The slight pause in the feed would break the chip. I ended up with a chip tray full of 4-inch tightly curled worms, which was safe and manageable.
There are plenty of other options I might have tried, but that one worked in this situation.
Finished part:
During turning--but the pic was not when the machine was actually feeding, but rather was posed for the picture before engaging the power feed clutch. For this picture, the depth of cut was 0.100 (actual, not diameter), feed rate was .0048, tool was CCMT 431 insert with coating and chip-breaker for cutting steel:
Rick "still on the steep part of the learning curve" Denney
