[How do I?] Use the shars 8” machinists level

[chiroone]

I have one of the PM 1340 lathes. I have finally gotten around to installing the three phase conversion and I’m getting ready to level the machine. I have an 8 inch Shars machinist level. Unfortunately, the instructions are in we could best be described as Changlish and I can’t figure them out. The only video on YouTube is narrated in Chinese.

It seems that the bubble is not In the middle of the level. I understand this is not important as long as it’s in consistent position. Is this true? Can anybody give me some advice on how to use this thing?

 

[ErichKeane]

Do you mean this one? https://www.shars.com/products/measuring/levels/8-master-precisions-level

If it is like mine, under that red rubber 'button' is a set screw for calibrating it. In order to calibrate it, find a very clean, flat surface (machine ways, surface plate, etc). Place the level on the surface and let the bubble 'settle'. Then, flip it 180 degrees, and let the bubble 'settle' again. The bubble should be in the same location (relative to the surface) each time. If it isn't, turn the calibrating screw until the bubble moves 1/2 way to where it was in the other direction. Then, repeat.

 

[mikey]

It seems that the bubble is not In the middle of the level. I understand this is not important as long as it’s in consistent position. Is this true? Can anybody give me some advice on how to use this thing?

A precision level works better if the bubble is in the middle when the level is actually level. I am going to assume that you're asking how to confirm that the level is accurately calibrated, which is different from doing the actual calibration.

Find a known flat surface, like a surface plate or a machined table, and put two things that are also square to orient the level. 123 blocks or something that is heavy enough to stay put. One of these objects should orient the long side of the level and the other should orient the end. The reason for these two things is so when you flip the level 180 degrees, it goes back to the same exact position. If the level is level, the bubble will be in the same position either way. This is what people mean when they say the bubble position is not important. If the bubble is not in the exact same position then you have to calibrate the level and that is another thing.

To do a calibration correctly, it is best to use a leveling table instead of some random surface. Rather than going through the procedure here, I'll just attach a document to read and it will make it clear. The leveling table need not be complicated. A flat piece of MDF or Melamine ply with three adjustable feet will work just fine. Rather than two heavy objects to orient the level, I use a small aluminum framing square clamped to the table. I also use a round bubble level to get the table roughly level before use.

A precision level is extremely sensitive. Trying to calibrate one without a leveling table is an exercise in frustration so give this a read. Also remember that the bubble can take up to a minute to fully settle so don't move too quickly. Try to work in a quiet space; running machines nearby can actually affect your bubble!

 

[SLK001]

The top of your way's pyramid is a precision surface, so the first question is will the 8" level span the distance? If so, then proceed to level the machine. "But it is a huge chunk of cast iron!", you say. You'll be surprised at how much out-of-level you can get just by putting your hand on one end.

Find two spots on your ways with no dings (one at the head and one at the tail) and place the level across one of the spans. Notice the position of the bubble (you will just survey the lathe with the first couple of measurements). Repeat that at the other end. If the bubble position is the same, then you might not want to do anything else. Contrary to popular belief, a lathe doesn't have to be level, but it does have to be planar. With the bubble in the same place for both measurements, your lathe is planar.

If the bubbles aren't the same, then start at one end and adjust the feet so that the bubble appears in the middle (since we have to adjust the lathe, we might as well make it level and planar). Repeat at the other end. Now, find a place in the middle of the lathe and place the level perpendicular to the other two measurements and see how we're doing in level on the longitudinal axis. If significantly off, adjust the tail end to make it level. Now repeat all these steps until the bubble is in the center for all. Now, hold any cheering, as we have to let the lathe settle for a day or so, then repeat all this again. Hopefully, the next day's adjustment will be very, very fine, then voilà, your lathe is leveled!

 

[ErichKeane]

Of interest, this video just popped up on my youtube. Check out this:

He does the calibration of his as we've described.

 

[chiroone]

So it’s not really necessary then to center the bubble, is that correct?

 

[ErichKeane]

So it’s not really necessary then to center the bubble, is that correct?

I guess you could do without and just make sure it shows the same when flipped, but that sort of doubles the amount of work you have to do...

 

[chiroone]

I guess my question is how do I know that I have a completely level true surface as a reference point so when the bubble goes to the center I have a true horizontal surface? I was just trying to get my head around this I’m sorry if it appears to be a stupid question

 

[ErichKeane]

I guess my question is how do I know that I have a completely level true surface as a reference point so when the bubble goes to the center I have a true horizontal surface? I was just trying to get my head around this I’m sorry if it appears to be a stupid question

The cool part is you don't actually NEED a level surface to calibrate it, just a flat surface (that doesn't move!) that you can put the level down in the same place. By flipping the level long ways, you will get 2 readings. The 'average' reading between the two is 'true level', so if you simply make sure that they measure the same as eachother (in reference to the surface), you will have calibrated your level to be 'perfectly level'.

 

[chiroone]

So even though the bubble is not in the direct center of the level, all I have to do is have it in the same position when I zeroed it and then I will know that my lathe bed is a true horizontal?