Lathe MN-80. Lead screw fix
It is shown how I eliminated the unevenness of the rotation force of the cross feed handle of the MN-80 lathe when adjusting the gap in the lead screw-nut connection.
It turned out that the uneven force of rotation of the handle was caused by uneven wear of the thread of the lead screw along its length.
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Lathe MN-80. Modernization":
• Токарный станок МН-80. Модернизация
“Machine tools. Repair and improvements. Modernization ": • Станки. Ремонт и доработки. Модернизация
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• Токарный станок МН-80. Исправление ХО...
In the place where the caliper is most often located, the thread has worn out the most. The difference in mean diameters along the length of the screw was 0.18 mm.
Side wear 0.09 mm. For metric threads with an angle of 60 °, the wear of the screw thread in the axial direction will be 0.05 mm.
The split nut is probably worn out too. And most likely even more than a screw. And if you adjust the clearance in the area of the screw with minimum wear, then in the area of maximum wear of the screw there will be an axial clearance - backlash - in the screw-nut connection. And this backlash will be at least twice as large. 0.05 + 0.05 = 0.1 mm.
Another reason for uneven crank rotation could be uneven wear in the dovetail. This is easy to verify with the lead screw removed.
With the help of adjusting screws, I reduced the clearance in the dovetail. The force increased evenly along the entire length. That is, the dovetail on my machine is worn evenly along its entire length and does not affect the uneven rotation of the handle.
I checked the axial clearance (backlash) on the indicator. In the place where the screw is least worn, the play is 0.005 mm. And in the place where the wear is the most, the backlash is 0.10 mm, as according to the preliminary calculation.
Axial clearance is manifested in the appearance of a backlash on the handle. In my case, according to the calculation, this is 24 °, and visually it is clear that this is approximately the case.
There are three ways to eliminate uneven crank rotation.
1. You can adjust the gap in the split nut in the position of the caliper when the nut is on the screw in the place of its minimum wear. This is the position of the maximum retraction of the caliper.
But then, when the nut is in the position where the screw is most worn out, there will be an axial clearance - a backlash in the screw-nut connection. In my case, this backlash will be at least 0.1 mm.
2. If you have to work with either large or smaller diameters, the gap in the split nut can be adjusted each time depending on the position of the caliper. But this, it seems to me, is inconvenient.
3. Uneven wear on the lead screw thread can be corrected.
We can only reduce the thread diameter - make it the same along the entire length of the lead screw, equal to the minimum diameter - in the most worn part of the lead screw.
You can fix the thread with a die. M10x1.5 thread. Left.
Of course, the die must be squeezed. For this, I cut the die.
The die was fixed in the tool holder. Gradually squeezed and calibrated the threads.
Achieved that the difference in average thread diameters became equal to 0.01 mm.
Put the lead screw in place and adjusted the axial clearance. The force of the handle has become uniform in any position of the caliper. According to the indicator, the backlash is 0.01 mm, the angular backlash of the handle is a couple of degrees.
This is how I eliminated the uneven rotation of the cross feed handle of the MH-80 lathe when adjusting the gap in the lead screw-nut connection.