Wanted to do some testing of my bed ways on my south bend 16" Not sure where the best point to measure from along the ways with a dial indicator. Would I put the indicator on the very crest of the V or on the sides perpendicular to the V. I would mount the indicator base on the carriage and move from the unworn part of the ways near the head stock to the unworn part closest to the tail stock. When I have seen pictures of bed wear it looks like the side of the ways is where the wear takes place and not so much at the top of the V?
Inspecting the Machine:
Now that you've taken 30 seconds or so to evaluate the seller and the machine's surroundings, it's time to move on to actually inspecting the machine. Inspecting a lathe This section includes general advice on lathe inspection. Brand specific advice will be discussed in a later section.
Tip: You should spend some time familiarizing yourself with Lathe nomenclature and basic operations. The book "How To Run A Lathe" by Southbend is an excellent source of information.
The bed ways:
The heart and soul of any lathe is its bed ways. The condition of the bed ways will determine the accuracy that the lathe is capable of. In my opinion, the condition of the bed has the greatest effect on the overall value of the lathe.This axiom holds true for other types of machines as well. Ideally, the ways should be perfectly parallel and even so the carriage travels parallel to the axis of the spindle, and the tailstock center is perfectly on center with the headstock spindle.
A large percentage of lathe work takes place close to the headstock. This leads to uneven wear of the bed ways. Uneven bed wear, in turn, causes the carriage (and therefore the cutting tool) to travel in a plane that is no longer parallel to the work piece (and no longer at the same height as the starting point.) The result will be a workpiece that tapers in proportion to the bed wear. All used machines have some degree of bed wear, your goal should be to determine the severity of the wear.
Tips for inspecting the condition of the Lathe bed:
Under ideal circumstances, cutting a test bar between centers would be the best way to test the accuracy of a lathe. Unfortunately, circumstances seldom permit such a test.
You should first determine the method employed by the manufacturer for finishing the bed ways. Grinding or hand scraping are the two general means. Hand scraping is generally followed up with decorative flaking which produces characteristic marks (usually crescent shaped marks in a uniform pattern), whereas grinding produces a uniform, brightly finished surface. Since the carriage is unable to travel in the area directly under the headstock (and cause wear), check this area to determine what the bed looked like originally. If you determine that the bed was originally hand scraped, the presence or lack of hand scrape marks over the length of the bed will give some indication of the degree of bed wear. View the original handscraping on a Southbend Lathe bed under the headstock
Tip: Since the bearing surfaces of the carriage do not ride on the full width of the bed ways, a ridge will generally form at the top or bottom (depending on the machine) of the ways (the same holds true for the tailstock.) The absence or presence of such a ridge can give an indication of the severity of bed wear.
Trap: Many unscrupulous sellers will file away any ridges on the bed and touch up the surface with a honing stone. To the casual observer, the bed will appear to be in excellent condition even though it is actually quite worn.
Countermeasure: With the carriage as close to the headstock as it will go, tighten the carriage binding screw until the carriage can no longer be moved. Loosen the binding screw slightly until the carriage just begins to move smoothly again. Now crank the carriage all the way toward the tailstock. If the bed is in real good shape, the carriage will make it all the way to the other end without binding.
You can also try to lift the carriage off the bed. You should not be able to see much movement if the machine is in good shape.
Note: You should now have some idea of the condition of the bed ways. If there is excessive wear, you may want to avoid the machine entirely, or you may choose to live with it. I generally consider that a worn bed is one of the few things I can't fix myself. Figure that it will cost between $1200 and $2000 to have an average lathe reconditioned (ie bed reground and components hand scraped to fit.)
Advanced Reading: The book "Machine Tool Reconditioning" by Edward F. Connelly (Machine Tool Publications St. Paul, Minn.) Is an excellent source of information on the art of hand scraping in particular and machine reconditioning in general.
The headstock: A)The spindle:
The condition of the spindle bearings and the spindle itself is the next most important thing to check. If either is damaged beyond repair, you will be looking at a costly replacement. I happen to have spare headstocks for certain lathes in stock, so I don't sweat this part of the inspection as much as you should.
Ideally, running the spindle would be a big help in determining bearing condition. Unfortunately, this is not always possible. If you are able to run the machine, run the spindle at one of the higher speed settings for a while. Listen for unusual noises. After the spindle has been running for a while, feel the bearings. They should not be too hot to touch.
Assuming that it is not possible to run the spindle, you will have to rely on your sense of how the bearings feel, how much slop or play is in the spindle etc. It is a good idea to take a look at the oil cups (if fitted.) You will want to see that they are full of clean looking oil. On lathes with wick lubrication such as southbend, you should be able to fill the oil cups to a certain level and have that level remain fairly constant. If the oil cups lose there level quickly and often, it is an indication that something is wrong with the wicks. The resultant lack of proper lubrication of the bearings will in turn lead to costly damage.
The condition of the spindle nose is also important as it will determine how true the chuck or centers will spin. The first time lathe buyer will generally encounter one of three spindle types. These include L-type, D-type, or threaded.
The L-type spindle (or long tapered spindle) features an external spindle taper with a key way. A threaded ring draws the chuck tightly against the spindle taper. The taper centers the chuck on the spindle. The threaded ring can be backed off to push the chuck forward and unseat it from the taper.
The D-type spindle also has an external taper, but it is much shorter than the L-taper. The D-type spindle uses cam pins to pull the chuck onto and off of the spindle taper. A common misconception about D-type spindles is that the associated number designation has something to do with how many cam pins are present on the chuck. Following this rule, you might wrongly think that a chuck with three cam pins is a d1-3, a chuck with 6 cam pins is a d1-6 and so on. This is not always the case. For simplicity sake, just remember that a D1-4 has a larger taper (in terms of the opening) than a D1-3. The larger the number, the larger in turn will be the opening.
On either of these tapered type spindles, it is important to check the condition of the tapered section of the spindle as well as devices for pulling the chuck onto the taper (ie the threaded ring or camlock as applicable)
On a threaded spindle, as the name implies, the chuck is threaded onto the spindle. There is a shoulder at the rear of the threads that serves to center the chuck on the spindle. It is important to check the condition of the threads as well as the shoulder.
On all of the above spindle types, the spindle should also feature an internal taper. This taper will be used for driving the headstock center and collet adapter sleeve. The condition of this taper is also important. B)The back gears: (if equipped) The back gears are essentially a set of reduction gears which serve to provide low RPM and high torque to the spindle. On some lathes (Southbend, Logan, Sheldon, Atlas and others) the back gears are easy to inspect. On other machines (particularly geared head machines) it is not possible to view the back gears without minor disassembly of the headstock. If the gears are readilly visible, they should be inspected for chipped, broken, or worn teeth. If they can't be visually inspected, the next best thing to do is listen to them run.
I believe you cannot judge the ways using the carriage as a reference point because the carriage will rise and fall in concert with the bed wear. I think the reference point must be from an unworn area of the ways, for example the surfaces the tailstock runs on but never touches like the area near the headstock. Even so, using the bed to measure itself is a compromise method.
Mark
On September 20, I gave a very detailed account on how to measure the approximate wear. It relies on the fact that there are 2 surfaces on almost every lathe that get no wear. how approximate? - within a few 10ths of a thou...
682bear, You are right - dings will raise material that will give false readings - My instructions include a check for and a stoning of the high spots that are raised from dings...
Thanks everyone for your responses. I am going to try to get readings on the side of the ways. I saw a video on youtube with Keith Rucker using 123 blocks and sliding them along the unworn flats of the bed that the tail stock would slide on. It looked like a good way for setting up the indicator. I will report back my results. I did put the indicator mount on the saddle with the tip on the bed and then lifted up by hand. needle on indicator went to 40 thou. Soooooo...looks like half nuts and other issues?? Lead screw has some wear as expected not sharp threads but probably half of original.
Wait- the leadscrew and halfnuts shouldn't have any influence on the fit of the carriage to the ways. The 40 thou you saw is probably not an issue, for most work the carriage normally does not lift off of the ways unless you are rear cutting with an upside down tool
Mark
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