This is the rear foot of the lathe bed and not the cabinet, I take it?

The principle is that the bed is supposed to be bolted down and a twist is introduced to it by jacking up/down one corner. The twist is very, very slight and is applied until no error in parallel remains in the test piece.

The lathe should turn close to parallel when unbolted from it's cabinet base and if it doesn't, then there could be a problem as highlighted by Michael Williams.

Martin.

"free end"? are you using a tailstock?

Work can "push off" without support from a tail stock…it can even with one if cutting force high enough

this pushoff leads to part being larger at the furthest point from support….

symptomatically part isn't constant taper.

if head,bed ,tailstock/center or slide misallignment taper tends to be constant.

btw is compound slide in use?

Hi Chris,

David said in his original post (my italics):-

"followed the manufacturers instructions, turning a one inch bar over a length of five inches, without using the tailstock"

seems clear to me ,

Hi David,

You could try the same test using the tailstock (checking first that the tailstock is in accurate alignment with the headstock) and see if you get the same result. Rememer that the downward force on the cutting tool will have an equal and opposite force on the material, lifting it upwards, even with light cuts (Newton was correct about that law) – causing the free end to turn to a larger diameter. This will cause a taper. You need to take repeated cuts several times so that the forces are reduced with each pass.

Best regards

Terry

Hi Terry,

So he does, must clean the specs before reading posts.

chriStephens

David levelling a lathe is one of lifes great challenges as you have found out. A couple of thoughts on the subject: –

(1) Have you had the level calibrated? This is important………don't ask how I know but it was a long time ago.

(2) What is the base mounted on? A wooden floor is fraught with problems.

(3) Did you turn a "dumb bell" shaped test piece, and then apply a .002 – ,oo4 uninterrupted cut along its entire legth including the relived central section?

(4) Your realisation and others notes about not levelling the stand but levelling the machine itself are also key to success.

(5) As somebody else has observed…….what condition is the lathe in? Is there, for instance movement in the slides that will allow the tool to move out during the cutting process?

(6) How accurate are you expecting it to cut along a 6 inch length, bearing in mind its age and condition?

(7) On a positive note your cutting a test piece without using the tailstock is absolutely correct at this stage.

Sorry no simple answers even at this late stage of the postings but you will have to work methodically through each element to get it absolutely spot on.

Ady the test piece refered to has nothing to do with good custom and prctice when using the lathe. It is Myfords test procedure to test the level condition of the lathe. In normal use I am sure that none of us would consider machining a 4" or 6" long dumb bell shaped part without a centre and/or a steady. However if the machine is not set up correctly then a taper may still result.

Your observation about using a clock to check the movement in the test piece is correct but in this instance is not really relevant. It may be useful to use a clock to establish the amount of movement in the slides, and also to run it with the cutting tool to see if it is in fact the tool being "repositioned" during its travel along the work piece.

Nothing, unfortunately, is simple when setting up an old lathe, there are just so many variables to come along and bite you in the bum (can I say that on here?) at the same time.

Helpfull hints for beginners or how to suck eggs for most of you experienced machinists.

The process is mostly only called levelling because a level is used in the process and it is very occasionally helpfull if it is level though that is mostly on milling machines. It is really "untwisting" the bed. A tilt is ok but it needs to be a consistent tilt. Therefore the level does not need to be calibrated, just repeatable which you can check by lifting and replacing it in the same place a dozen times and observing the variation in result. Then set the bed with the same tilt at each end and if that is also dead level then fine but don't sweat over it. If your lathe bed has Vs or other non flat shapes place parallels or eg tool bits on a flat bit to produce a higher reference points.

Rather than taking cuts use a new bar that you have checked for straightness by rolling on a surface plate or milling table, and checked for roundness at the measuring points only with a micrometer.

Mount it in the 3 jaw fairly straight . Mount a dial indicator for horizontal reading at center height.on the saddle or if on cross/top slide pull up all slack and lock them. Rotate the chuck to find the peak reading and mark position with felt pen. Record reading, rotate 180 and read again. It doesn't matter that the chuck/bar is not true – the difference in the readings tells you where the center is. You can cross check by testing at 90 & 270.

Return to mark, run saddle along to far end of bar, take reading, rotate 180, and again the difference tells you where the center is. I don't think it actually matters if the bar is a bannana or your second set of readings is taken at a different rotation of the chuck. The key is you have found the center each time without taking cuts.

You obviously assume the saddle travells down the bed with a consistent relationship to the center line (though not true if it is worn, or long and stressed into a camel). The two centers measured above are the true line of the mandrel in its hopefully true tight bearings so should be the same unless the head is scewed. Costs nothing to adjust and repeat.

When you have got the horizontal sorted repeat on the vertical line using the indicator above the bar.

The tailstock alignment also does not need a cutting operation. Set up a bar between centers and measure where the centerline is in the same way provided your drilled centers are true. If not you can turn just the ends but bot the body which will relieve stresses and create a banana.

A better way is to take the trouble to drill the centers on a better lathe or set up on the steady so you have an unmachined bar with true centers that can be used for setting the topslide inline.