Yes it is common especially on very small machines.

The cutting forces tend to push the workpiece and cutting tool in oppsite directions to each other .

Provided the tool is not digging in on the reverse pass i would not worry too much about it .

There are other factors to consider such as how much the work piece is sticking out of the chuck , the more stick out the less ridgid the more flex & what material you are cutting etc

The easy way is to not worry about the return or spring cut on roughing cuts but only machine in one direction on finishing cuts then retract the cross slide (after noting or zeroing the setting on the dial or dro) and return the carriage to the start position ready for the next pass .

When i get to around .005 in or 0.1 mm above finish size i usually take a spring cut or two ,after zeroing the cross feed dial or dro ( digital readout ) i retract the cross slide 1 turn of the feed handle , return to the start of the cut , return the dial or dro to zero by feeding back in the 1 turn i wound out and run a pass this gets rid if any flex or springing of the workpiece and machine and usually gets me very close to finish size.

You will learn with experience where to stop your roughing cuts an it may be as much as .010 inch above finish size as the ridgidity of the workpiece will vary with diameter and how far it is sticking out of the chuck.

The compact lathe by Stan Bray & lathe work a complete course by Harold Hall are two books i would recommend and you could try youtube there may be some stuff on there about the Sherline but you may only find people showing off their modifications. Most of the stuff on youtube is with much larger more ridgid machines so the return cut is less of an issue .

Hope this helps !

Ian

I have small lathe and it always does that. Do not worry about it until you get down to your finishing cuts.

Edited By Brian John on 25/11/2015 07:41:55

Edited By Brian John on 25/11/2015 07:42:20

Correct

To set the gibs remove the lead screw and slide and apply some slide way oil. Put the slide back on and adjust the gibs for slight resistance to movement pushed by hand then refit the lead screw. On lathes like the shereline the same should be done to the saddle as it can and will tilt when it's moved back and forth. It's a problem with dovetail beds. Sometimes it helps as the tool may move away from the work when it's wound back – rare.

Usually if the bearings are severely loose the same cut setting will remove metal rather than just scrape on several passes. It will remove more metal right up to the end of the cut but more at the end of the work. Any looseness causes the same problem. Generally if some wear and they are only slightly loose running the same cut again can spoil the finish. Many lathes have a minimum cut which will produce the best finish. It will change with diameter of the work. That aspect makes hand feeding more difficult as each time the rate changes marks will be produced on the work. Usually rings. The same thing can happen when using power feed especially when too light a cut is taken or when the feed rate is too low.

If say 2" of 1/2" bar is turned the metal may bend while it's being cut. If the same cut is run again more metal will be removed at the end but it will turn into something more like scraping as the tool gets nearer the chuck.

If no bending and decent bearing settings running the same cut again will be more like a very light scraping. The finish might look worse in some respects but the actual depth of the defects will be improved.

Another problem with tiny lathes is the the lathe itself may distort. If everything is basically ok then running the same cut again is likely to give a good finish.

My only experience of using lathes of this size is with a Taig / Peatol. Nothing bends on these as there is a strip of concrete under the bed. I'd assume that area isn't a problem on Sherelines. Set up correctly as new and with a suitable tool they can produce a finish like glass on materials like free cutting mild steel. Some materials such as silver steel tend to tear what ever lathe they are on but in terms of um depth of defects the finish can still be pretty good for a lathe. Some cast iron can have the same problem.

Really any serious book on turning should go through all of this so that people can sort things out to suite the lathe they happen to have.

John

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Unless I'm going blind, I'm surprised that nobody has asked (and you haven't said) if you are using the tailstock support, nor how long your workpiece is.

Roger

I use 10mm tooling or down to 1/4 hss on my boxford and don't get problems with the tool flexing. I do get a bit of a bearing problem due to the front one wearing a little oval so it can't be tightened to correct that and like everybody on any lathe the work can bend.

I spent a couple of months one a dsg once using 5/16" hss in a holder. No problems from flexure at all and a finish like glass. Material supplied would generally allow 3 cuts to finish to size circa 0.1" off the diameter or more each time. The trick to finishing exactly on size to a few 1/10 thou or better is to note how much the 2nd cut actually took off and aim to make both the 2nd and last cuts the same size. Or improve further given the sufficient material increase the number of cuts.

Only problem with that is that the lathe wasn't very old and only a couple of people a year used it for a month. I did 2 due to being picked to do international turning test. The other aspect is that the lathe was in such good condition and quality on this particular model that it was perfectly capable of taking miniscule cuts down to a few thou even to the extent of finishing things off that had an 0.015" grinding allowance left on them bang on size without any problems at all. Some lathes due to wear and headstock design just wont sensibly do this sort of thing hence the cut sizes we were told to think about. Some need it but it's a shame about the taper even as little as it is. More wear and even this wont work.

On the other hand take a lathe that 20 odd people used for a week every year and had been around for some time and nothing could be done about the rings that appeared in the work as it was all small stuff circa 1/2" dia and less and the fact that the headstock bearings were not adjustable so out comes the emery cloth.

John

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good afternoon to all,

i was doing internal threading (soft turning)in lathe machine.After this the components will be heat treated and descaled.After this am doing hard turning (internal threading)on same profile i have done before. but my components after hard tuning ,getting ovality(outer diameter and inner diameter ) issues an particularly thread depth is varying. Because of this somany components getting rejected everyday .Give me suggestion how to fix the same axis of turning before and after (soft and hard)turning to get exact thread depth and thread flat.but both hard an soft turning done in different machines.

If you remove an item from the lathe for heat treatment then put it back in the lathe then unless you use an independent 4 jaw chuck to set the part running true you will have concentricity problems. Also heat treatment may cause distortion.

Martin C