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Run Out on unwell made Chinese Metal Lathe

cobbadog

Registered
As you may remember some time back I bought a 2nd hand unwell made Chinese metal lathe to learn on. In the time I have had this I have learnt a few things and much of it with help from you guys here.
I am now starting a small project to make some new valve guides using cast iron. I mounted the solid rod into the chuck, tightened it up and played around to get it to run true and then used the centre drill to make a small hole at one end so I can use the 'live end" (I think it is called so I can then machine most of the length of the rod. Out of curiosity once I was happy with the set up being one end locked tightly in the chuck and the opposite end being supported by the live end I made a few very light cuts along the rod to make the rod nice and round. The rod is 250mm or about 6" in over all length.
Once I had a nice smooth surface along the rod I started to check measure and found that the diameter of the rod that has just been machined is larger near the chuck and reduces at the other end by 0.14mm.
Is this normal, I think not. Is there an adjustment to fix this issue?
Thanks in advance for any and all help.
 

Rob Charles

Sponsor
Last Subscription Date
04/05/2017
You need to adjust the tailstock setover so the lathe will turn straight while using the tailstock. How well the lathe is leveled also affects how straight it will turn both just using the Chuck and tailstock. There should be a setscrew just above where the tailstock splits. Might be one on either side. You need to move the tailstock 1/2 the error. Rob
 

Pete Spaco

Registered
"Live Center".
What is the diameter of the rod that you are turning?
I wonder if the headstock is out of alignment with the bed.
I'd try testing a bar of about 1 inch diameter or more, with about 3 or 4 inches sticking out of the chuck, but no live center.
Take light cuts with a sharp tool and then check for diameter differences. If zero difference, then headstock alignment is okay.
The reason I mention this is that, if indeed, it's a tailstock misalignment issue, that means you are BENDING the workpiece as it turns.

Experts, please correct me if I am wrong with this thinking,
Pete Stanaitis
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I like oldstuff

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Last Subscription Date
11/09/2015
Yeah, seems your tail stock is way out of alignment so you're cutting a taper. We could write for hours on the subject but there are tons of you tube vids on adjusting this. Grab a cold one and watch some and pickup tips and methods on correcting it. Once adjusted and on a small China lathe I imagine you can get the taper down to .02- .04mm over your 250mm length. As these machines don't have a lot of rigidity you'll find that making very fine cuts you'll reduce the errors.

*Make a cut on a 200mm long piece without it being held by the tailstock centre. Only a couple hundredths deep... Same dial setting at the end and at the chuck end. I bet you'll see very little taper. You can try it with plastic as this won't stress and deflect the machine like metal will.
 

cobbadog

Registered
Thank you very much gents, this gives e something to look for, adjust and get it as close to being right as I can.
Being a learner driver on this I am not sure of where "tailstock splits". So when I start watching the YouTube clips this may well become apparent.
The question was asked about the diamter of the rod I was machining and the final very light cut made the diameter to be 27mm. At a guess at converting it to imperial it is around 1 1/8" od.
Thank you once again and I will have a play again soon if not on the weekend as work is going to get in the way of learning.
 

Rob Charles

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Last Subscription Date
04/05/2017
Lathes need to be accurately leveled to turn straight.the beds are very flexible. Leveling long ways is not as fussy unless the lathe is very long but cross ways needs to be very close. I use a .0005 per foot level. You level it right ahead of the tailstock and at the far tailstock end. If there's a slight twist in the bed it won't turn straight with the work mounted in the chuck. You can cheat some if you are using the tailstock as it will pull the work over an turn straight. If the bed has a twist the carriage doesn't bear evenly on the ways. Lathes that have been used a long time while the bed is twisted wear the carriage to that twist. Then if you level it properly the carraige will rock on the ways . I had a lathe that was used that way. Could never get it to turn straight so it went down the road. Being it's an unwell made import lathe it's also possible that the headstock isn't aligned straight and also will turn tapered. Some if the lower quality machines have adjustment screws to align the head stock. High quality lathes use the tailstock ways to line the headstock and no adjustment
Anyway you need to start with a good leveled bed then proceed to line up the headstock if it's adjustable. Then adjust the tailstock.
 

Steve Kunz

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Last Subscription Date
06/23/2020
I used to mess with the old time machinist at the plant I worked at. I would tell him that I needed a taper cut on something and he could just offset the tail stock. He would throw a fit, saying that he would not move the tail stock because he had it set perfect and it was to much work to get it back.
 

OTTO-Sawyer

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Age
58
Last Subscription Date
07/15/2019
Another possibility, depending on how badly abused it was before you got it, is the tailstock center itself could be Bent, throwing the tip off center.

If it has a 'knock-out' ram or pops out when you retract the tailstock all the way it "Should" be OK, but if it is one that's been popped out with a "Pickle-Fork" chance are it's Bent and every time you remove it and put it back in it will line up differently.

Or, a small chip or speck of grit may have gotten under the tailstock itself throwing it out of alignment. If there's a lot of wear, or it's just poorly machined, there could be some 'wiggle-room' in the ways which you can check by loosening the nut holding it down and seeing if you can twist it one way or the other as you tighten it down. . . You Might be able to eliminate your taper just by doing that.

:salute:
 

cobbadog

Registered
Thank you so much for all the very helpful tips. I do have an adjustment on the tailstock so that is a step in the right direction. I also picked up some solid steel rod today and it is 28mm OD and fits into the chuck but only goes through the chuck about 50mm then stops so this means I really need a piece of 25mm stock which I will pick in order to carry out the adjustments as described.
Next is that I have just now ordered a magnetic base dial indicator to accurately measure the run out. This won't be here until late next week or early the one after. So while I am waiting I will do some basic leveling and then do a final one with the indicator on the cross slide running across the level across the bed.
As you will see in the pictures, especially the bottom one I certainly won't take any notice of that indicator marks. (very upmarket these are). But the screws are there so I will ,make the attempt as soon as I have what I need to go forward.
We are heading on a much needed holiday on the 4th July for a week so if I make no comment on this before then it is becasue we are out having fun, yeh!.
 

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I like oldstuff

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Last Subscription Date
11/09/2015
Once you get your indicator and base you'll have it setup perfectly.

There are many ways to check centreing. For a quick method I made two checking shafts for mine from cheap Morse taper adapters for drill chucks. http://rover.ebay.com/rover/1/705-5...2&toolid=10001&campid=&icep_item=222019013201
This makes checking the machine very easy and fast.

Your tail stock looks like a MT2 but I don't know what the headstock is. (possibly a mt3 as you can't pass a 25mm part through the headstock) At any rate, take these shanks with the jacobs chuck taper and machine both chuck ends to an exact dimension say,, 20.00mm. To check the lathe, put both of them in the machine. Set your nifty new dial indicator to 0 on the headstock end. Then run the carriage all the way down and pass the indicator over the one in the tailstock. It also should read 0. Your check is completed within 30 seconds.
 
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cobbadog

Registered
Thanks once again for the very helpful tips.
I am sorry for not posting a picture of the chuck (head stock). With the jaws open I can fit a 30mm diameter rod into the chuck passed the the jaws then it stops. I am guessing it stops when it get to the hollow part further inside. At hat point I can put 27mm a bit further in but then it stops so now I am guessing that at least a 25mm rod will fit all the way through and out the end of the lathe. while waiting for the dial indicator I will also buy a piece of 25mm bright steel to do an initial set up to true up my toy lathe.
today I had a moment to play around with leveling and found that it ran down hill from the head stock to the tail stock but now is level. I must have known something but when it was initially set up here I did actuall make it level from from to back and is all the way along the bed.
With the Morse taper how do you machine them accurately as both ends have a taper or do I also need something to hold it when machining? Sorry for the newbie beginner questions.
 

I like oldstuff

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Last Subscription Date
11/09/2015
If you want to go the morse drill chuck adapter route as the leveling tools you can get an adapter that takes a 3 or 4 down to a 2. Assuming your head stock is a 3 or if it has a taper at all. Take the chuck off to find out.
Slip the number 2 into the headstock morse adapter then turn the drill chuck end (which also is a short taper) not the long precision morse taper end straight. Then do the other one. No need to support these morse drill chuck adapters as the end you're machining straight is only about 20-25mm long. Be sure to get them both absolutely identical in diameter.

First you'll do the get the centre centred operation. If you want to take it farther look into doing the bed leveling.

Leveling the lathe is sorta a misnomer. It actually refers to taking the twist out of the bed. The lathe doesn't care if one end is higher than the other or if it's tilted towards or away from you. It's called leveling as an ultra precision level is put across the bed at the headstock and the whole machine is then leveled. Then the level is moved to the far end. Any discrepancy is removed with leveling screws on the far end or the floor mounts or with shims under the end mount to tweak the bed to dead flat. Lots of vids on this routine also.
 

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OTTO-Sawyer

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Age
58
Last Subscription Date
07/15/2019
Leveling the lathe is sorta a misnomer. It actually refers to taking the twist out of the bed. The lathe doesn't care if one end is higher than the other or if it's tilted towards or away from you. It's called leveling as an ultra precision level is put across the bed at the headstock and the machine is then leveled. Then the level is moved to the far end. Any discrepancy is removed with leveling screws on the far end or the floor mounts or with shims under the end mount to tweak the bed to dead flat. Lots of vids on this routine also.
Exactly. . .

Think About It. . . They had Lathes (complete machine shops) on Ships that were Far From "Level" as they tossed about.

You could bolt a lathe to a wall Horizontally Or Vertical if you so desired, and it would function perfectly fine as long as the bed is Straight.

:salute:
 

Fred Van Hook

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Age
71
Last Subscription Date
11/05/2019
Squarillel is what I used to call it.. When I ran the laser on our equipment we made sure that the machine was square and parallel to itself.. What your issue is not run out but taper.. That being said what I used to do was sweep the tail center with a indicator and moved tail stock to compensate. Like Otto said and long as the lathe is square and parallel you could hang it on the wall and get good parts. Most of the time we just made sure the coolant ran back to the sump...
 

cobbadog

Registered
This is all very helpful and all I need now is the delivery which should be late next week. I certainly will let you know how I get on once I have finished playing.
Thanks again for posting the picture of those Morse tapers used for alignment.
 

I like oldstuff

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Last Subscription Date
11/09/2015
Figured a piccy would work. For the number 2 I used an old broken drill bit as opposed to buying a new one for ten bucks.
 

cobbadog

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I like oldstuff, you would like a pic of what please so I can put it up for you.

The idea of using drill bits, would that work using 2 drill bits the same size and fit one in the chuck and the other in the tailstock chuck? Or is that too inaccurate?
 

I like oldstuff

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Last Subscription Date
11/09/2015
Drill bits won't work as you need the tapers and machined straight areas for location accuracy.
Don't want to use the taper measurement method due to cost of making these dedicated parts? Watch the vid for method number 1.
Make your test piece as long as you can fit in the machine.



Method 2 with the test bar is good but a test bar is $$$.
 
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