B
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I wish to thank the respondents on my previous post on this topic. What follows are the results.
The controllers, especially the Seco, have been checked and repaired where neeeded and are operating according to the manufacturers specifications. The Seco is used to control the Armature and the Baldor is used to control the field. I tried to reverse the hook ups on the controllers but the Seco could not be adjusted low enough for the field, so that option has been eliminated, and the original hook ups restored. Voltage readings with the motor hooked up are as follows; armature 36.5 @ 200 RPM, 250 @ 1650 RPM, 170 @ 1900 - 3700 RPM, field 123 0-1500, and 8 @ 3700 RPM. You will notice a discrepancy in the top end RPM from my previous post of a top end of 3700. This is because at the time of the last post the field trim pots had not been adjusted properly. What could not be explained last time was the voltage drop on the armature from to 250 to 170. When I disconnected the motor from the controllers and substituted light bulbs in its place, and the armature never went over 170. I can only conclude that the voltage differential is back EMF, as I understand it, and the most that could be obtained from the Seco is 170 in this application. Incidentally, I hooked the armature and field up to the Baldor controller and the most that could be obtained for the armature was 170, with a max RPM of about 1150. I also noticed a difference in the armature top end RPM's between the Seco(1650) and the Baldor(1150), the only explanation I can offer is that the Seco has torque and slope trim pots and the Baldor doesn't have the slope trim pot(I can't remember about the torque pot).
Considering the above facts, it was time for a reality check; actually take a cut, varying the depth of cut(DOC) the feed and the RPM's; @.125 DOC 1500 RPM setting .010" feed the RPM dropped to 900, @ .0064" feed the RPM dropped to 1150, @.0032" feed the RPM dropped to about 1350. When the DOC was reduced to .050" the RPM drop was much less, with a 1200 RPM @ .010" feed, 1425 @ .0064 and insignificant change at .0032" feed. With the RPM set at 800 @.125"DOC gained about 50 about to 850 for three feeds. I continued the tests increasing the RPM until I found the point where there was no change, either up or down, which turned out to be about 1150 RPM.
The material used was 1-1/4"D A-2 tool steel and 1"D 1018CRS, using a TNMG 321 insert. I did not notice any significant difference in the above tests using either material. I also ran tests at 2500 RPM with lighter DOC's not exceeding .050"@.0064" and lower feeds using the 1018 as the test piece. While there were RPM drops on the heavier DOC, the drops were in the 10% range, and as might be expected improved when the DOC was reduced.
I conclusion, while I am not entirely satisfied with the results of the tests, I must also admit that I don't ordinarily take cuts at the .010" feed rate on this size lathe, I can live the results for the present. The only way that the full potential of the machine can be obtained is to obtain a controller that has a 240VDC output for the armature. Harry Bloom
The controllers, especially the Seco, have been checked and repaired where neeeded and are operating according to the manufacturers specifications. The Seco is used to control the Armature and the Baldor is used to control the field. I tried to reverse the hook ups on the controllers but the Seco could not be adjusted low enough for the field, so that option has been eliminated, and the original hook ups restored. Voltage readings with the motor hooked up are as follows; armature 36.5 @ 200 RPM, 250 @ 1650 RPM, 170 @ 1900 - 3700 RPM, field 123 0-1500, and 8 @ 3700 RPM. You will notice a discrepancy in the top end RPM from my previous post of a top end of 3700. This is because at the time of the last post the field trim pots had not been adjusted properly. What could not be explained last time was the voltage drop on the armature from to 250 to 170. When I disconnected the motor from the controllers and substituted light bulbs in its place, and the armature never went over 170. I can only conclude that the voltage differential is back EMF, as I understand it, and the most that could be obtained from the Seco is 170 in this application. Incidentally, I hooked the armature and field up to the Baldor controller and the most that could be obtained for the armature was 170, with a max RPM of about 1150. I also noticed a difference in the armature top end RPM's between the Seco(1650) and the Baldor(1150), the only explanation I can offer is that the Seco has torque and slope trim pots and the Baldor doesn't have the slope trim pot(I can't remember about the torque pot).
Considering the above facts, it was time for a reality check; actually take a cut, varying the depth of cut(DOC) the feed and the RPM's; @.125 DOC 1500 RPM setting .010" feed the RPM dropped to 900, @ .0064" feed the RPM dropped to 1150, @.0032" feed the RPM dropped to about 1350. When the DOC was reduced to .050" the RPM drop was much less, with a 1200 RPM @ .010" feed, 1425 @ .0064 and insignificant change at .0032" feed. With the RPM set at 800 @.125"DOC gained about 50 about to 850 for three feeds. I continued the tests increasing the RPM until I found the point where there was no change, either up or down, which turned out to be about 1150 RPM.
The material used was 1-1/4"D A-2 tool steel and 1"D 1018CRS, using a TNMG 321 insert. I did not notice any significant difference in the above tests using either material. I also ran tests at 2500 RPM with lighter DOC's not exceeding .050"@.0064" and lower feeds using the 1018 as the test piece. While there were RPM drops on the heavier DOC, the drops were in the 10% range, and as might be expected improved when the DOC was reduced.
I conclusion, while I am not entirely satisfied with the results of the tests, I must also admit that I don't ordinarily take cuts at the .010" feed rate on this size lathe, I can live the results for the present. The only way that the full potential of the machine can be obtained is to obtain a controller that has a 240VDC output for the armature. Harry Bloom
