Lathe levelling

[Gary WoodingParticipant @garywooding25363]

Bill,

The term 'lathe levelling' refers to removing the effects of bed twisting. It's actual level is not important.

[Howard LewisParticipant @howardlewis46836]

If you read the various articles on updating Myford ML7s from narrow to wide shear location, you will see pictures showing that in many cases, of used machines, the saddle does not make overall contact with the bed. In which case, it could be liable to wobble in a vertical plane.

Also, to enable the saddle to move along the bed, it must have clearance.

So if there is any clearance between saddle and bed, there is the chance that it it may change (very likely if the bed is twisted ) and so introduce inaccuracy.

Laying the level so that it rests on the bed minimises the number of parts involved and sources of error.

The more directly that the measurement can be taken reduces possible errors.

Not applicable in this case, but think in terms of drilling ten holes in a strip of steel, with Centre distance 1.000.

If you dimension every hole from one datum point, then every hole will be within 0.005" of the nominal position.

Dimension to a +/- 0.005" tolerance on the individual centres, and the last hole one could be as much as 0.045" more or less than the nominal 10 inches.

The moral is: minimise the number of dimensions involved. So work direct off the bed, because that is what you wish to measure, not in terms of thous or microns, but graduations on the level..

You would not try to measure the backlash in your cars transmission by measuring an angular movement between the road wheel and the flywheel

If you did, there will be clearances in both ends of the drive shaft, gears in the differential, gears and their splined shafts, gear to gear clearances, and between the splines between first motion shaft and clutch centre plate.

But you would not know if there was an excessive clearance at any one point..

As the amateur radio fraternity say, KISS "Keep It Simple Stupid"

As an Engineer in a Quality Department, I was trained to think logically, and to measure as directly as possible.

Howard.

[Swarf, Mostly!Participant @swarfmostly]

Hi there, all,

I hope that I will not be censured for an off-topic post but this post isn't about 'lathe levelling' – it seemed like a good place to interject an observation about engineers' precision levels and their calibration.

Half of my offering is from Stan Zinkovsky's channel on YouTube (He of the Bar-Z Bash fame). The rest is my idea but probably not original.

An engineer's level is accurate if it reads level both ways round when on a level surface. How do we determine if a surface is level with a 'wonky' level? Not all of us have more than one level! But many of us do have a surface plate.

Stan pointed out that somewhere on a non-level plane surface, there is a line that is absolutely level – it is at right angles to the line of maximum slope. It obviously helps if the plane surface (e.g. surface plate ) is fairly close to level. So, how might we find this level line? If we can find the line of maximum slope, we're only a single step away.

One way to find it is to use an ordinary ball bearing. Put it gently in the middle of the plane surface, it will roll down the line of maximum slope. If the ball doesn't know which way to roll, that's useful information. We're nearly there but we'll get a better result if we repeat, placing the ball at the top edge of the plate. We know where that is now. Mark the path of the ball with a Sharpie and repeat a few times to get an average. Then use a square to draw a second line at right angles to the first.

The level to be calibrated can then be aligned with our level line and adjusted until it reads level both ways round.

Have I confused everyone? If not, let me know and I'll try again!!

Best regards,

Swarf, Mostly!

[Howard LewisParticipant @howardlewis46836]

If the surface is off level, an accurate level will show the same deviation when rotated through 180 degrees.

i.e. if the surface is 1 degree off horizontal, the accurate level will show a deviation from horizontal. Roating the level through 180 degrees should show the same reading, but in the opposite direction.

If the level is out, it should be adjusted until it shows the same which ever direction it faces.

Think of a DTI on a base where it can swivel. Set Zero, on a line normal to the slope.

Swing DTI through 90 degrees so that it is now up the slope. Say it reads +1.

Swivel through 180 degrees so that the DTI is now down the slope. The reading will now be -1

So having the surface absolutely horizontal is not absolutely needed. The objective is that the level reads the same whether one end is up the slope, or the same, but opposite, reading when that end down the slope.

Howard

[Swarf, Mostly!Participant @swarfmostly]

Hi there, Howard,

Thank you for your response to my post.

What you wrote is fine UNLESS the slope is so great that the level goes into saturation, i.e. it's so far beyond its range that its reading is meaningless.

If the position of the level line is known to be close to level, one can proceed as you wrote without having to iterate through many off-scale steps.

Best regards,

Swarf, Mostly!

[old martParticipant @oldmart]

One reason for actually checking and truing using turned diameters is that very few people will be in the possession of a sufficiently sensitive spirit level.

[Author]

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