How to remove the backlash of the MN-80 lathe support
It is shown how to eliminate the backlash of the caliper of the MN-80 lathe by adjusting the gap between the caliper and the bed.
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Recently, I began to notice that it became difficult for me to provide the required accuracy when turning some parts.
I decided to check the clearance in the transverse direction.
I installed a measuring stand with an indicator on the bed. The indicator tip rests against the tool holder. When applying a transverse force back and forth, I found a gap of 0.04 mm. I tried to select this gap with a wedge, but it turned out that the supply of the wedge was exhausted. The wedge was short. I dismantled the wedge and extended it from the wider side with this piece of metal.
He began to adjust the gap and achieved a gap of 0.01 mm.
But when I wanted to move the caliper to the left side of the bed, I failed. Caliper wedge. This means that the wear on the bed is uneven.
The support touches the bed in six places. This is shown in the figure.
In the vertical direction, the caliper touches and rubs in four places. The wear of these surfaces does not affect the longitudinal play.
And the wear of the other two surfaces - the outer side of the bed facing us, and the other, far, side of the guide, leads to lateral play of the caliper.
If the wear is uneven along the length of the bed, then the gap will be different.
Due to the fact that the cutting force squeezes the cutter from the part, that is, on us, the surface far from us wears out more.
Began to check both surfaces for wear. An external examination of the outer side shows that in the place where the caliper most often moves, longitudinal risks have formed from contact with the moving caliper. With the help of a mirror, I examine the far surface. Wear is visible there.
Wear is assessed using a straight edge and feeler gauge. The ruler is long, and in order to use it, you need to remove the caliper. I will not do this yet. I will use a shorter, curved, first class ruler.
The ruler cannot be applied to the far surface. I apply a ruler to the front surface of the guide. The 0.02 mm probe does not fit. There is no smaller probe.
I take food foil 9 microns. The ruler clamps the foil along the entire length. This means that the wear on the outer surface is less than 9 microns. And the backlash of the caliper is 0.04.
This means that the wear is mainly on the far surface, as expected. It is impossible to measure it with a ruler.
In this case, my goal was not to establish the size, but to measure the deviation from the size. And I want to achieve a deviation of the guide width of no more than 0.01 mm.
And therefore, in order to estimate the amount of wear, I decided to use the principle of calibers: it climbs - it doesn't.
For a long time I used a homemade device for working with gauge blocks. I used old tiles as sponges, in this case - 10 mm each.
Between them I installed different sets of gauge blocks and used these sets as a pass-through bracket.
With the help of such a bracket, I will control the completion of the bed according to the principle of climbing - not climbing.
Usually the cast-iron beds of the machine tools are scraped. But this surface is inconvenient to scrape. And I decided to file it with a file.
When the surface was finalized, he moved the caliper to the left and checked the right side of the guide bed. I also modified it to a size of 22.07 mm.
Installed the adjusting screw and adjusted the clearance. The adjustment is made with two screws. To reduce the gap, it is necessary to unscrew the left screw, and tighten the right one, that is, it is necessary to move the screw to the left.
I checked the backlash. It is now 0.005 mm at all points on the bed guide.
This is how it was possible to fairly easily reduce the gap between the caliper and the bed guide, moreover, without dismantling the caliper.