Dear Canerodscom,
From what you have described, your lathe ways are worn, but this is not the end of the world. Before you start tearing the machine down for a bed regrind and or a rescrape of the ways, to restore them beack to factory or better specs, you need to assess the degree of wear and out of tollerance. I would go on to say that a clunker lathe may only need some TLC to get her running within acceptable parameters and be accurate enough for the home workshop.
When I did my aprentiship final exams, I was allocated the worst lathe in the workshop and only had a weeks turning experience on the machine before producing my trade masterpiece, so to say. That was many years ago and the journeymen in the shop helped me out a bit, by giving me the following advice;
Take a piece of scrap round bar about 1 to 2 inches in diameter by about 8 inches long and tighten it into your 3 or 4 jaw chuck, holding about 2 inches in the chuck for rigidity. Then take a rough and then a finishing cut over the 6 inch long bar. By doing this, you have made a home made reference test bar to see how much the lathe is worn or out, where most turning jobs get done.
Now measure the diameters at the end of the bar and at the closest end to the chuck. This will tell you the amount of off true that the headstock spindle is to the lathe bed. The ideal will of course be 0.0 inch difference between the two measurements, but even on a new lathe, this is not always a given. Next, have a close look at the finish that you have obtained on your home made test piece. A rather rough finish as a final cut may indicate to you a problem with headstock spindle bearings, vibrations induced by belt drives, rough spindle drive gears, loose compound slide, loose cross slide jibs or compound slide jibs, worn or loose cross slide thread nuts, dings with burrs on the lathe bed, a poorly sharpened tool bit and a host of other things that I may not even be aware of.
Then, using a dial test indicator and magnetic base mounted on the cross slide, measure the underside (or overside) along the centreline of the lathe spindle axis. This will indicate amount of drop (or rise) in the lathe bed, in relation to the test piece. You will have to correct the measurements obtained using the DTI, from what you have previously measured, with regards to the taper of your home made test piece. While you have the DTI setup, place it at the end of the test piece (furthest away from the chuck) and pull the test piece up and see if there is slack in the headstock bearings. You may be able to adjust the headstock bearings a little to reduce an up or down deflection of the lathe spindle, which should be 0.0 slack on a taper roller bearing headstock or 0.001" per inch of spindle diameter on a bushed headstock bearing.
As you can see, what I'm trying to say is that you may be able to eliminate some of the lathes problems by a process of elimination, which has worked well for me in the past.
Once you have corrected some of the faults that you have found by doing the process above, you can continue as follows;
Using the same piece of material that you have used to make your home made test piece, centre drill both ends. Then, using another piece of scrap bar, turn up a dead centre in the chuck, using the compound slide. Set up your test piece in the lathe, between centres, using a dog to drive the home made test bar, take a roughing and finishing cut over the length of the bar and measure the diameters of each end of the bar. Any differences in diameter can now be adjusted by adjusting the tailstock off-set. (Tailstocks can be used for taper turning, therefore have a means of adjustment from side to side. Again take another cut, after adjustment of the tailstock and compare the measurements obtained. You should be able to remove all taper from your home made test piece, by repeating this operation until the taper is zero.
Again, when you have eliminated the home made test piece taper, using a magnetic base mounted on the cross slide and DTI, run the DTI under (or above) the home made test bar, as done before and compare the difference between the chuck side and the tailstock side readings. This will indicate to you the amount that the tailstock is out, in a vertical direction, in relation to the headstock centreline. Of course, using home made test pieces of different lengths, you will start to be able to plot onto a graph the amount of wear that has taken place on the bed, where the tailstock bears down onto the bed. It's normal that the tailstock will wear in a way that the tailstock centreline is below that of the headstock centreline.
You can go on by looking for a round piece of 1/2 inch thick round plate, as big a diameter as what will fit into the lathe and take a roughing and finishing facing cut, using the cross slide. By placing a straight edge on the finish cut surface, you will be able to observe if the cross slide is indeed 90 degrees to the lathe spindle axis. If a feeler gauge blade can fit between the straight edge and the workpiece at the centre of the workpiece, then the cross slide is worn. (ie Look for a dish faced surface - concave or convex.) A simple adjustment of the cross slide jibs may greatly improve your lathes accuracy.
There are other ways of checking a lathe for accuracy, such as ground test bars, etc. but I prefer the price of a piece of scrap to that of a factory made ground test bar with a certificate of accuracy in a nice wooden box that will most probable end up going to the auctioners when you shuffle off.
While I'm no expert on lathes, I did manage to pass my trade test on the klunker lathe. Even the shop stewart was impressed as to what I did to the klunker lathe in the short period that I worked on it. They even started using the klunker lathe for production work, in the shop after I left for greener pastures.
I hope that my thoughts on your lathe problems are helpful to you and others and ask any other members to add to my writings just in case I have not got the message over clearly enough or if there is anything that can be added to help you fix your machine.
To all, a Happy Christmas and a Prosperous New Year from Geoffrey Owen, Walvis Bay, Namibia.
