Skip to Content.
Sympa Menu

machinist - [machinist] Leveling a Lathe - Practical Machinist Thread

machinist@lists.ibiblio.org

Subject: Machinist

List archive

Chronological Thread  
  • From: "Lawrence F. London, Jr." <venaurafarm@bellsouth.net>
  • To: machinist@lists.ibiblio.org
  • Subject: [machinist] Leveling a Lathe - Practical Machinist Thread
  • Date: Sat, 24 Oct 2009 21:29:13 -0400


Leveling a Lathe - Practical Machinist Thread
http://www.practicalmachinist.com/vb/showthread.php/leveling-lathe-190984.html
The real Leigh

The purpose of leveling a lathe is to return it to the exact position in which it was trued at the factory, thus duplicating the location of all stresses and pressure points. This can be done most easily by using the Earth's center as a reference point.

The best possible configuration is a three-point suspension, with two points under the headstock and a single one under the far end. If your machines are set up this way you're way ahead of the game.

You'll need a very precise level such as the Starrett 199Z, with sensitivity of .0005" per foot (0,04mm/meter). The Starrett catalog sheet in PDF format is here http://www.starrett.com/download/338_p439_444.pdf

This 15" level is considered the standard of the industry. Comparable models from other manufacturers are available in different lengths, with 15" being most common. Length doesn't matter. The important spec is sensitivity. Lesser products (Starrett 98 et al at 0.005"/ft) are not sensitive enough for precision work.

Levels are self-calibrating. Check yours for accuracy before you start. I've included a test and calibration procedure at the end of this post.

The following general procedure is applicable to most lathes with three or four leveling feet. Longer beds with six or more feet present a different problem.

Run all of the leveling feet out the same number of turns. This gives you working range and roughly squares the machine. You can also preset the working height at this time.

Start with two co-planar reference surfaces as close to the spindle nose as possible, one behind the other (i.e. across the bed from front to back). Be sure that the surfaces you select are finished (either ground or scraped) and that they are supposed to be on the same plane. (Obviously, all surfaces used must be absolutely clean and free of debris.)

Adjust the rear foot under the headstock to bring that end level. Duplicate that adjustment on the rear foot under the tailstock, to keep the machine roughly square. Repeat as needed to get the headstock dead level.

Put the level (running left-to-right) on a flat bed surface (toward the front if possible), and adjust the front foot under the tailstock to bring the bed level side to side. If there's only one foot under the tailstock, you're done.

If there are two feet... Put the level front-to-rear at the tail end of the bed (move the tailstock out of the way), duplicating the position used at the head end using the same reference surfaces. Adjust the rear foot at that end to set the bed level front to back.

This sequence is repeated (in its entirety) until the results are as close as desired. At least two passes would be expected, with no adjustments on the final pass which just checks that everything is correct.

I believe the theory behind the procedure is obvious.

The final test of any lathe installation is to turn some stock and check that it's straight, i.e. that it does not turn a taper as will happen if the bed is twisted.

The classic test is called the "two collar" test, as discussed in "How to Run a Lathe" from South Bend Lathe Co. This book has a wealth of information. I suggest you buy a reprint from Lindsay Books if you don't already have a copy.

There's a huge fallacy with the "two collar" test. Depending on the exact nature of the bed twist, you could actually turn a Coke-bottle profile, but not realize it because you're only measuring two points on the piece.

A better test is to turn a piece of heavy stock perhaps 12" long and thick enough that it won't deflect under cutting tool pressure. Mount it in a solid chuck and center the axis of rotation at the far end as accurately as possible. Don't use a rest or center to support the stock.

Do a couple of skim cuts the full length of the piece, then measure the diameter at several points. All should be identical. If not the bed is twisted (or possibly quite worn) and corrective action is warranted.

Anyhow, apologies for the long-winded response. The actual effort will probably take less time than reading this post.

Not a huge challenge. Good luck with it.

- Leigh

NB. Level checking and adjustment

Any precision level will have an adjustment for setting the vial true. This setting can be checked (and adjusted if need be) using a reference square and a flat surface.

The reference square is just to provide a positional reference so you can turn the level around 180° and put it back in exactly the same positon. Any small carpenter square or similar will work.

Tape the square on the surface plate, which should be approximately level but precision is not required. Position the level in the inside corner of the square. Note the bubble position in the vial, which should have several graduation marks.

Rotate the level 180° and put it back in the same position in the square. Note this reading and compare it to the previous one.

If they're exactly the same (need not be "dead center"), then the level is reading accurately and no further action is required.

If the readings differ, turn the adjusting screw to remove HALF of the error. Note the new reading.

Turn the level around and compare it with the previous after-adjustment reading. They should be identical. Iterate if needed.


peterve

Leigh
you only took the easy ones with 3 or 4 leveling feet

Actually a lathe with 3 leveling feed needs no leveling because it is impossible to bend it square with the aid of gravity
That is the big advantige of 3 leveling feet
But any serieus lathe has at least 6 leveling feet making all much more complex You bend the ways lenghtwise like a wave very easy
And a used lathe is even more complex Because of the wear you have in the ways it is impossible to have it level everywere So you have to compromise
I first get the bubble free floating Then I correct it 1 stripe at a time checking at different places If it is a long lathe say 3mtr you have to check
the vertical plane also That can be done with a wire and a microscope
I use a spirit 0,02mm/mtr And sorry I never check it I always place it orientated the same way Also in exactly the same place and those places I stone down before placing a spiritlevel I also clean the level and the place I put it every time Yes every time And I do it again if a reading is not what I suspected it to be

Peter from holland


The Real Leigh
When dealing with a machine having more than four feet, you must follow the manufacturer's instructions for trueing the bed. The taught line and microscope that you mentioned are pretty standard for that type of work.

- Leigh


misterT

The way I have always leveled lathes up is to run four of the feet down, set the level on the bed running length wise to get it somewhat close end to end. Next set it on the crossslide running crossways at the headstock end and I set it with the bubble one mark forward of center. this will set the front higher and help prevent coolant from running under the cross slide into the apron and rusting the gears up. Next run the saddle down to the tailstock end and set it the same and keep repeating this unitll it reads the same at both ends. Then I take a light cut on brass or aluminum to check it, if the end by the chuck is larger than drop the front screw at the tailstock end a light bit ( only 1 degree at a time). If the other end is larger than raise the frone tailstock crew a bit untill it is straight. The I run the remaining screws down watching the level to see when they start to change it. Lock down your jam nuts and you are good to go, you can buy a King way tool to do it by the book. But I have set up too many lathes to count and got them all less than .0003" in 8" using this method.



  • [machinist] Leveling a Lathe - Practical Machinist Thread, Lawrence F. London, Jr., 10/24/2009

Archive powered by MHonArc 2.6.24.

Top of Page