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Turning problems

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Andrew Kershaw24/11/2015 23:57:21
8 forum posts

I have a Sherline lathe and have started learning to use it, but I'm having problems with basic turning and I don't know why.

When using the lathe, feeding the tool from right to left, it cuts material off the work-piece no problem. However, when moving the tool back to the start position (left to right) ready for the next pass, it also cuts material off the work-piece. Should it do this?

It makes no difference if I use a sharp steel tool or a carbide insert tool, it still happens. I'm taking shallow cuts of about 10 thou, and In wonder if I'm not taking a deep enough cut or not feeding fast enough. I've tried deeper cuts and faster feeds but am still having problems. Since this is only a small lathe I don't want to go too heavy handed with it.

It doesn't appear to affect the finish, and It ends up at the required dimension, but I would like to know why it does this. Watching videos on YouTube, others don't seem to have this problem.

Any help appreciated. Thanks.

Hopper25/11/2015 04:24:34
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2799 forum posts
44 photos

Common cause of this is worn or sloppily adjusted headstock bearings.

It could also be cross slide gibs need adjusting.

XD 35125/11/2015 04:51:52
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961 forum posts
38 photos

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

Phil P25/11/2015 07:39:50
409 forum posts
113 photos

I agree with the reply above, and always retract the cross slide when returning to start a new cut.

It is not just your lathe that does this, I think most will to some degree. It usually leaves a spiral on the work which is not what you want. It also does not do the tip of the tool any good by letting it rub on the work.

Just take a mental note of the dial reading before you move it, and only back it off "less than a full turn", that way it is easy to return it to the previous position and add your new cut depth. Always add the cut by turning the dial in a clockwise direction, (assuming you are cutting on the outside diameter) if you go too far back it off again and reset it, that makes sure you have no backlash in the feed screw.

If you are cutting an internal diameter just do the opposite to this re the direction of turning the dial.

Phil

Brian John25/11/2015 07:41:19
1435 forum posts
579 photos

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

Bodgit Fixit and Run25/11/2015 08:50:02
90 forum posts
2 photos

Make sure your tool overhang is not too big either. This can cause small cross section tools to flex.

Ajohnw25/11/2015 10:04:20
3631 forum posts
160 photos
Posted by Hopper on 25/11/2015 04:24:34:

Common cause of this is worn or sloppily adjusted headstock bearings.

It could also be cross slide gibs need adjusting.

yes 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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Andrew Kershaw25/11/2015 10:49:05
8 forum posts

Thanks for all the replies. I appreciate the information.

The Sherline I have is fairly new. It has sealed-for-life headstock bearings and the headstock itself is keyed onto the lathe bed, so I'm going to rule that out as a problem.

The cross-slide seems fairly tight on the lathe, but I'll check the gibs and see if that makes a difference. I keep the tool overhang to a minimum but I am cutting some small diameters (1 inch and below) so it may be flex in the work-piece.

I'll play around with it and see what happens.

Roger Head25/11/2015 11:05:56
209 forum posts
7 photos

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

Andrew Johnston25/11/2015 11:10:39
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3969 forum posts
487 photos

It happens on all lathes, irrespective of size. I get the same effect with my Harrison M300, which is rather bigger than a Sherline. smile o It's all to do with tool and work deflections; albeit I'm taking rather deeper cuts than 10 thou on the Harrison. I don't bother retracting the cross slide after each cut, unless it is the final cut.

Andrew

Andrew Kershaw25/11/2015 12:12:59
8 forum posts

I'm not using the tailstock, but the work piece is only projecting from the chuck by just over one inch and is one inch in diameter. Aluminium this time.

jason udall25/11/2015 12:18:12
1989 forum posts
41 photos
As has been said.
ALL machines "flex"..as does work and tools

200k cncs too

The question is how much

Anyway in your setup this would be called a springing cut...
Acut taken at same setting to allow for this flex.
Ajohnw25/11/2015 16:36:22
3631 forum posts
160 photos
Posted by Andrew Johnston on 25/11/2015 11:10:39:

It happens on all lathes, irrespective of size. I get the same effect with my Harrison M300, which is rather bigger than a Sherline. smile o It's all to do with tool and work deflections; albeit I'm taking rather deeper cuts than 10 thou on the Harrison. I don't bother retracting the cross slide after each cut, unless it is the final cut.

Andrew

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.

laughOnly 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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John Reese28/12/2015 18:28:42
530 forum posts

When turning a diameter to a specific size leave the part a little oversize. Take one or more passes with no infeed until you no longer make chips. Then mike it and adjust the cross feed to get to final size. If you fail to take those extra passes before measuring, it is likely the finished diameter will be undersized. The purpose of those extra passes is to allow spring back of the machine. Deflection under load is more of a problem on the light hobby lathes than on larger industrial machines.

gorli vasu11/02/2018 07:43:16
1 forum posts

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.

larry Phelan12/02/2018 13:27:15
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544 forum posts
17 photos

I get that effect too, on my Craftsman lathe, so I get around it by simply retracting the tool at the end of the cut and winding back to the start before making a new cut. Just make a note of the dial reading each time. Result--no marks!.

As another Member said,most if not all lathes do it,so it,s no big deal and nothing to worry about.

Martin Connelly12/02/2018 14:49:28
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682 forum posts
71 photos

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

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