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- Jun 12, 2014
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I often get questions on thread cutting using a proximity stop system, recently I had to make several threaded micrometer shafts out of O1 steel, all with the same dimensions and thread tolerances. I do not have any fancy camera holders or editing software, so just propped the camera on the head stock and hoped it didn't fall off. More just showing how I do most threading with this system, typically on a heavier lathe you can take deeper cuts on the first few passes, but I take 0.01" depth passes until I am close to target (or very deep thread), then a 0.005" or too target depth if step is less than 0.01", and then a spring pass. Use of a center is advised for longer stock stick out or thin stock. There is always some degree of flex when turning so finished dimensions do not always correlate with dial or DRO readings. There are also some variances based on the material, speeds and feeds. I use lay down carbide inserts, usually by Carmex or Mitsubishi, I have been using the same insert for over 2 years and only rotated it because I banged/broke one of the tips. Previously with vertical threading insert holders, the inserts broke frequently. I use standard thread cutting oil applied with an oil can, and only about half makes it onto the thread.
With an electronic stop system with a VFD, it can turn the motor off at a designated position and then apply quick braking. When using a VFD for threading, I recommend turning down the Hz to the 20-30 range as this will result in quicker braking then a higher Hz range. The repeatability of an electronic sensor system varies based on many factors such as the sense range, refresh rate, and repeatability characteristics of the sensor. There are also mechanical slop in the gear train and feed system, the threading speed and pitch or feed rate. I typically thread steel in the 250-450 RPM range depending on the diameter, aluminum and softer materials up to 600 RPM with the carbide lay down inserts. The limiting factor as to RPM is more about the sense/trigger range of the sensor, the rate of travel (velocity) of the carriage and the braking rate speed. There is a point where the carriage travel will exceed the travel distance once the system is triggered. This is also a significant problem when using a mechanical switch, as they will be damaged in an over travel scenario.
In the attached video I am using 1/2" O1 steel threading at ~400 RPM, the thread length is 1.4" with a pitch of 20 TPI. I only use the cross slide to advance the thread cutter, and leave the half-nut engaged throughout the threading process, so the threading dial is not used and it doesn't matter if it is an imperial or metric thread. I use the threading insert to cut the relief grove which is usually the target thread depth +0.005". The nice feature of the ERL-1340 and also the larger 1440TL (RML, TRL lathes) is the universal gearboxes, so no change gears are required unless one is doing a DP/MOD type thread.
With an electronic stop system with a VFD, it can turn the motor off at a designated position and then apply quick braking. When using a VFD for threading, I recommend turning down the Hz to the 20-30 range as this will result in quicker braking then a higher Hz range. The repeatability of an electronic sensor system varies based on many factors such as the sense range, refresh rate, and repeatability characteristics of the sensor. There are also mechanical slop in the gear train and feed system, the threading speed and pitch or feed rate. I typically thread steel in the 250-450 RPM range depending on the diameter, aluminum and softer materials up to 600 RPM with the carbide lay down inserts. The limiting factor as to RPM is more about the sense/trigger range of the sensor, the rate of travel (velocity) of the carriage and the braking rate speed. There is a point where the carriage travel will exceed the travel distance once the system is triggered. This is also a significant problem when using a mechanical switch, as they will be damaged in an over travel scenario.
In the attached video I am using 1/2" O1 steel threading at ~400 RPM, the thread length is 1.4" with a pitch of 20 TPI. I only use the cross slide to advance the thread cutter, and leave the half-nut engaged throughout the threading process, so the threading dial is not used and it doesn't matter if it is an imperial or metric thread. I use the threading insert to cut the relief grove which is usually the target thread depth +0.005". The nice feature of the ERL-1340 and also the larger 1440TL (RML, TRL lathes) is the universal gearboxes, so no change gears are required unless one is doing a DP/MOD type thread.
