Lathe MN-80. Cutting off during spindle reverse rotation
The well-known method of cutting on a lathe is shown - the reverse rotation of the spindle and with an inverted cutting tool.
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As you know, cutting on a lathe is one of the most difficult operations.
The work of the cut-off tool occurs in difficult conditions due to the fact that it is difficult for the chips to exit the groove.
It shows schematically what forces are generated during normal cutting, when cutting back with a cock tool and when cutting back with a raised tool post.
An animation of the cutting process is shown here:
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The same effect of pushing the cutter out of the groove is possible with direct rotation of the part, if you put the cutter in an additional tool holder. This is shown in my video “Lathe MN-80. Additional TOOL HOLDER":
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Cutting off with the spindle reverse requires either a cockerel cutter or some modification of the cutter post.
When the cutter is turned over, its cutting edge becomes located below the axis of rotation of the part. This can be compensated by raising the entire tool holder to the height of the tool.
In this case, the length of the fixing bolt is no longer sufficient to secure the tool holder.
In one of my videos, I showed the processing on a small MN-80 machine of a large diameter part - 240 mm.
“Lathe MN-80. Machining a large diameter part":
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To do this, I raised both the headstock and the tool holder. At the same time, I made special elongated bolts.
Therefore, I now have the opportunity to lift and fix the tool holder in order to install the cut-off tool in it in an inverted position.
To test this method, I took a steel billet.
The cutting process went well. The machine did not strain, the chips came off easily, evenly, softly.
For comparison, put the cutter in the usual position. To do this, the tool holder lowered.
During the cutting process, it was felt that the chips did not come off evenly, not smoothly. The cutter and the machine are loaded more.
Thus, when comparing two cutting options, it was confirmed that with an inverted cutter, cutting is more favorable, more reliable, with less load.
I used this method 50 years ago when I cut cores in the blanks of turbine disks for aircraft engines. It turned out to be the only acceptable way in that case.
I used the core cutting on both sides in the manufacture of the bronze bushing:
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I advise turners to make long bolts for the tool post for their machines, so that they can raise it if necessary to work with an inverted tool when cutting off with a reverse rotation of the spindle.
In this simple way, the cutting process can be significantly improved.