It seems that every site I look at on-line there is someone is telling me how important it is to 'level' my lathe, heck, even John Bogstandard was telling us recently how frequently he levels his.
Now it is not that I do not appreciate the principles and the importance of having a straight lathe bed but really I am still to stumble upon an 'engineers' level'. Of course I could buy one, probably get a nice Chinese one for a hundred or two kiwi bux but I have instead had the word out at a couple of places that deal in used engineering equipment and instruments, no luck so far.
So what to do? Use the ole' noggin of course! So I sat down and thought about it for a while, about one cup of coffee really.
Now the lathe does not have to be level but if all the lathe is level we can be assured the bed is not twisted which is the imporant thing. If there is no way of accurately determining it is level then finding it is not twisted is really all that is required.
Old time astronomers such as Kepler needed accurate instruments which were impossible to make at the time so they got their accuracy by making their instruments big, for example he made a 30 foot high wooden sextant type device for measuring movement of the planets, so how to apply this principle?
I mounted a laser pointer on the top of the compound aimed at about right angles to the lathe to shine on the garage door about 20 feet away. I wound the carriage to one end of its travel and marked the position of the laser point on a bit of tape stuck to the door then wound the carriage to the other end and marked the new laser position.
If the lathe bed was not twisted the line between these two points would be parallel to the lathe bed. So if the lathe was level this line would be level too, unless the bed was twisted. The effect would be greater the further from the lathe.
I had two pencil marks on the door and a builders' level long enough to check for level between the two points, they were not exact. Then I took the level and laid it along the lathe ways and that was not exactly level either but it was about the same as the line on the door, which was a good answer showing that within the limits of the builders' level the line on the door was parallel to the top of the ways and hence the bed was not twisted.
A builders' level is not as accurate as an engineers' level but using the laser pointer and the length of the garage I had amplified the accuracy of the builders' level. The length of the line on the door is nearly 3 feet long and the distance from the lathe to the garage door is about 20 feet which multiplies the accuracy of the level by about 6.6 times.
I found it is possible with the builders' level to detect a .060" feeler gauge under one end so the accuracy of the level is .060" per 3 feet or .020" per foot. Using the laser pointer it is .060" over 20 feet or .003" per foot. By happy coincidence .003" per foot is the minimum accuracy specified in the South Bend Lathe book "How To Run A Lathe".
First picture, the handyman style Black and Decker laser device, you do not need one of these as a simple laser pointer in the tool post would be just as good.
Second picture, the red dot from the laser shown on the garage door about 20' from the lathe.
Third picture, two pieces of tape on the door marked with the position of the laser dot when the carriage is at either end of its travel.
Fourth picture, my builders' level across the two points marked on the garage door. The bubble is just touching the mark at one end.
Fifth picture, this time the builders' level is on the ways and again the bubble is just touching the mark at one end, because I have turned around to take this reading the end is 'the same' end as on the marks on the door.
It works!
But do not get too excited as it is almost impossible to put marks on the door to that degree of accuracy!
