The Home Machinist, Part 6

The Lathe, Levers and Levels
With the working environment taken care of, lets look at the lathe. Start by placing a level on the ways, first in the XY direction, then across the ways. If its not spot-on, you need to get it there by using the adjusters down on the floor.

Next, take a look at the various  hand wheels and levers. Are they tight on their shaft s? Set-screws can come loose in shipping, or maybe they werent even installed when you opened the box. Get a wrench or screwdriver on every bolt, nut and screw you can to make sure they are secure. My machine was a mess when it arrived, and I had to spend a lot of time tuning it up. Its annoying but necessary.

Take a look at the oil level. Most machines have a sight glass somewhere. The upper level of lubricant should be visible. If its not, drain it and refill it with the recommended material. In fact, even if its full, drain it and refill to the mark-if its a new machine, you’ll want to know what kind of lube is in there. If its a used machine, you may not know the last time it was changed. Take a look at what comes out, too.

The Brakes
Ill bet it hadn’t occurred to you that these machines have brakes. They do, and they are easily adjusted. Lets say you have the lathe head spinning at a couple of thousand rpm, and you hit the stop button. Imagine how long it would take to come to a halt if there were no brakes. Your machine is likely different from mine, but I would suppose they are similar in that something stationary is pushed against a spinning wheel. How hard it pushes is controlled by a setscrew. Youll figure it out.

Lubricating the Gears
My machine has an elaborate set of gears that are not submerged in the oil bath. As such, they make a racket. Go to the local motorcycle shop and buy a small can of chain lube. This stuff is great because it goes on as a low-viscosity foam that soaks into every crevice via capillary action. Turn on the machine to the lowest possible speed, and spray it into the point where the gear teeth engage. Be careful not to get the nozzle stuck in the gears. It wont hurt anything, at least it didn’t when I got too close, but if that had been my finger!

In just a few minutes the lube becomes an extremely sticky grease that wont fling off . LPS, ACF-50 and other spray lubes, while fine in many applications, just aren’t designed for centrifugal force. Chain lube is waterproof, too, and it works wonders on squeaky garage door mechanisms. Just don’t use it someplace where you’ll have to get it off later-and if you do, kerosene works wonders to remove it, or so says our motorcycle fanatic Editor in Chief.

Carefully using chain lube is especially important if your machine is like mine and has belts in proximity to the gears. You don’t want to have lubricant on the belts. Speaking of which, take a look at the belts and pulleys. They should be aligned; if they are not, you’ll have to get them that way. I leave it to you to figure out how simply because this is not something that is typically adjustable. Over-tension, and sometimes lousy design, can trash a belt. If a belt doesn’t track correctly, fix it or resign yourself to regularly replacing it.

Handy Gibs
In the first column in this series I wrote about keeping things that should move, moving smoothly. So far we’ve looked at the generic issues. Now lets go after those items that are unique to lathes.

The gibs (pronounced as in glib, minus the l) are there to accommodate manufacturing variance and tolerance stack-up during manufacture. Whats tolerance stack-up? Imagine that you work on an assembly line, and you put the last part on the widget. You find that it wont fit. You call QC, they come out with the print and measure your parts, finding that they are within tolerance. So they take the whatzit apart and start measuring all the other parts, only to find that they are all within tolerance  Whats going on here? The answer is simply that this device was assembled with parts all at the extreme end of their tolerance. The tolerances added up until your part, the last to be installed, would not fit on the gadget. You could take it apart, throw all the parts back in the bins, mix them around and not see the problem again.

A lot of energy was expended on calculating stack-up and adjusting tolerances to looser or tighter values. About 30 years ago one of the European car manufacturers bragged that its inspectors outnumbered its assemblers. That not only didn’t say much to the good for the assemblers, it didn’t catch all the goofs and only increased manufacturing costs.

The proper solution is to simply make every part exactly the same. I wont go into this at length, but greater precision is the result of a series of process changes, not simply tighter tolerances nd throwing away parts that don’t meet them. Thats what were trying to do here. I must also point out that extreme use will cause wear, and the gibs will compensate for that wear to some degree. However, were not in that category of use.

Moving Along
Now that you know what the gibs do and why they are there, lets adjust them. The first step is to make sure the mating parts are clean with no burrs or rough spots. Start by loosening the lock nuts and backing out the screws. These screws are of the set-screw species, that is, they are pointed on the end and can only push. That means you don’t have to remove them, just get them retracted to allow the long bar to be pushed out.

Tape a sheet of 320 wet-or-dry sandpaper onto a flat surface and add a few drops of oil. Any oil is fine, even 30 weight from the car or WD-40. Now just stroke the long bar around on the paper until you get a pattern for the whole length of the bar. Wipe it clean and slide it back into place. Turn the setscrews in until they stop, and then back off about 1/16 of a turn. Hold that position with an allen wrench or screwdriver and snug down the lock nut. If the component wont move smoothly, you might have the set-screw too tight. Keep at it until its nice and clean in its motion.

Dont fool yourself by loosening them too much; you’re trying to adjust these to eliminate all movement except in the intended direction. Use a magnetic base and a dial indicator to check for movement in the wrong directions. Just touch the indicator probe to the component, set the dial to zero, and then grab and push-pull in the direction it should not move. Youll find a place where the dial moves very little, perhaps only a couple of thousandths of an inch, but the entire assembly will move smoothly. This is a narrow window and might take quite a few tries, but its necessary if you’re going to eliminate the variables. If this doesn’t result in smooth motion of the component, you may have a burr on the ways. Look for rough spots and loose debris; some of the machines Ive seen were not cleaned well prior to assembly. Also try this in a couple of positions; its possible that the ways are not perfectly parallel.

Once you’ve done that for the left – right motions, do it again on all of the other gibs. The procedure is the same; be patient and recognize that you’ll have a lot more fun later when what you wanted to do is what actually happens. A digression: Buy a surface plate. Its a slab of  granite thats been ground to a very flat surface. They are amazingly inexpensive at about $15 for a 9×12 from Enco.

Routine Maintenance
When all of this is done, you will likely find that everything seems to move pretty nicely. To keep it that way you have to keep the ways clean, and there is no more destructive environment for precision fits than one with scattered metal shavings all over the place. Therefore, wipe the ways down and clean up the loose debris at the end of each work session. Notice that I did not say to oil the ways; that will only attract more of the really fine bits. A spray of WD-40 followed by a thorough wiping will be sufficient. If you can get to the lead screw (its the long one that goes left -right, located just below the ways), take a piece of twine and wrap a half-turn on the lead screw. Turn the machine on to extremely low speed and then let the twine clean the threads. Be extremely careful here. Dont take multiple wraps and don’t wrap the string around your finger. If the string catches, it could wind your hand into the screw.

The three-jaw chuck has a large spiral  screw that can get filled with junk or just wasn’t really clean to begin with. It will come apart by simply rotating the T handle to loosen the jaws until they release from the main body. Use a felt tip open to mark which groove each jaw came from, as you’ll have to put them back in the same slots and then pick up the thread in the proper order. If you dont, you’ll find that the jaws don’t all arrive at the center of rotation at the same time. Its not a disaster, just an easily fixed annoyance.

Tuning up the rest of the machine is pretty much a variation on these procedures. For instance, the milling head has to have the tapers clean, the sliding surfaces smooth and free without unneeded slack, and the various belts aligned. Its not hard; in fact its mostly a case of looking closely, being careful, understanding what each part does and then putting it back like you had it, but better.

Enjoy, and next month well make a small project with the milling head. If you have some sort of process or project youd like to see, let us know. No guarantees, but well sure try to find the answer.