Author Topic: Lathe help needed (Read 10563 times)

Hellogoodbye · « **on:** August 19, 2011, 01:15:27 PM »

Hi my first post so be gentle.
After visiting the Harrogate show in may i took the plunge and got myself a mini lathe, nice day out it was too.
Two weeks later my lathe arrived in one very big heavy crate (110kg) oh the joy of unpacking the thing.
I'd worked in an engineering shop but not actually worked on a lathe so i knew there were lots to learn.

Im now regretting buying the damn thing having problem after problem with it.
Everytime i put round bar in the damn thing i get this happening, its only part cutting

Chuck or jaw problem i really dont know but you can see somethings nit quite right.
Anyone help here please.

Jasonb · « **Reply #1 on:** August 19, 2011, 01:32:17 PM »

By the looks of the tool marks you only have a thou or two run out which is about par for the coarse with a 3 jaw chuck.

Best thing to do is get a dial test indicator and then you can measure the TIR (total indicated runout)

One of the chuck key holes should be marked, use that one to tighten the jaws, you may also be aqble to reduce the runout by adjusting the chuck on its backplate.

Have a search for "TIR" and "chuck runout" its been covered plenty of times.

This is why you should do all critical machinging that has to be concentric without moving the work in the chuck or use a 4 jaw to clock the work true if its a really critical part

J

Arnak · « **Reply #2 on:** August 19, 2011, 01:34:41 PM »

Hi,

That could be normal behaviour if the bar is not truly round or the chuck is not true, most likely the former.

Have you got a dial test indicator to check the chucks run out with a test bar?

If not just turn the bar down until you have it cut all the way around then put the turned in back into the chuck and see if it now runs true.

If it does then the bar was out of round.

Martin

andyf · « **Reply #3 on:** August 19, 2011, 01:42:10 PM »

Three-jaw chucks are usually a little inaccurate, holding the stock slightly off the lathe's spindle axis. So an initial light cut will only shave one side of the work. However, as you go in deeper so that the tool is cutting all round, the result will be circular in cross-section, and concentric with the spindle axis. That is fine if you are making a part which can be finished without reversing it in the chuck, and will simply be cut off from the parent stock once it is finished. If you do reverse it as you have done in your video and then try (for example) to turn the other end to the same diameter, the two ends won't match up.

It may well be that you will end up buying a 4-jaw chuck with jaws which can be independently adjusted to get the work dead on centre, with the aid of a dial indicator or "clock" bearing on one side of the work. Another technique is to turn the work "between centres", so you can turn it along its whole length.

Andy

Davo J · « **Reply #4 on:** August 19, 2011, 02:12:21 PM »

Just like the others have said it's just because it's a cheap 3 jaw, even an expensive one will have some run out.
If you machine something in a 3 jaw you do all operations without re moving and your fine. Once you remove it no matter what you wont get it to run true again.

The fix for this is 2 things, one has been mentioned is to buy a 4 jaw so you can adjust it to run true after taking it out or machining something that needs to be true like the end of a motor shaft.

The other way is if this is a bolt on chuck, is to machine down the chuck register on the back plate a little (0.5mm) and then the chuck can move a little and you can adjust the 3 jaw. The way adjust it, is to finger tighten the bolts, place a dial indicator on the job and turn it around and tap the chuck with a soft face hammer until it runs true, then do up the bolts tight.
If your doing a few the same size and the chuck is not to bad, it should stay true at that diameter.

I have done this to my 3 jaw on my 12 x 36 lathe and the chuck stays pretty true at all sizes. I have a few 4 jaws so I use them for anything precision.

Dave

Hellogoodbye · « **Reply #5 on:** August 19, 2011, 02:31:18 PM »

I actually got a 4 jaw with the lathe.
In time i hope to do a lot with the lathe, an expensive tool upgrade is definately on the cards (QCTP for starters)
In the meantime im trying to sort out my other problems.
Warco havent been very helpfull with me,
Alarm bells were ringing after i opened the crate,

And then i found this,

And then this,

The Email responses were laughable, basically 'fix it yourself'

Hellogoodbye · « **Reply #6 on:** August 19, 2011, 02:38:35 PM »

And more gear oil here,

And another i plugged with a fibre washer,

Ah well, serves me right i suppose.

jgroom · « **Reply #7 on:** August 19, 2011, 03:12:18 PM »

It's like an old Jag, as long as it's leaking oil it's OK. It's when it quits leaking oil you know you're in trouble.

Cheers

Jeff

Jasonb · « **Reply #8 on:** August 19, 2011, 03:13:07 PM »

You will find all the imported lathes tend to weep a bit, some more than others, at least it keeps the rust at bay

Jason

Davo J · « **Reply #9 on:** August 19, 2011, 04:03:00 PM »

You can do what I said with the 3 jaw to get it running better, but use your 4 jaws for anything that needs to be spot on.

As for the leaks I cant help much as I have never owned one. If you have no luck with warranty supplying new seals, there are a few groups around for that size lathe, and they maybe able to help by giving you part numbers, etc.

Dave

jim · « **Reply #10 on:** August 19, 2011, 04:19:41 PM »

don't lose faith, post your problems on here

Jonny · « **Reply #11 on:** August 19, 2011, 04:19:59 PM »

Looks a lot more than a few thou to me.
Cant believe no one has told him to check the index bolted to spindle 0 and whether the jaws are in the right place, unforgiveable.

If 0 lines up on backing plate check the jaws, anticlockwise until 3 drops in, keep pressure on all three jaws whilst clockwise turning until into scroll with key. If jaws meet when fully screwed in its reasonably safe to assume jaws are in right. Known a few chucks where jaws put in wrong will meet ie jaw 3 in 2 etc.

snoopdog · « **Reply #12 on:** August 19, 2011, 05:09:42 PM »

Just use a small brass hammer as you tighten the chuck as you spin it by hand. it happens every day in shops all over the world, slowly tighten the chuck till its good and get on with it.

John Hill · « **Reply #13 on:** August 19, 2011, 06:55:25 PM »

My advice, dont shorten your life by worrying about it! Just think, if it were not for this class of machine mere mortals would never be able to afford a capable lathe for our home shops.

My 12x36 leaks oil, there are even places where they drilled right through the casting to bolt a bracket on or some such, oil drips from the places I have to manually oil. They were very considerate too and painted my lathe white so that I can easily see these reassuring oil slicks!

Pete. · « **Reply #14 on:** August 20, 2011, 01:23:00 AM »

Have you used a dial gauge to measure the runout? Hard to tell from the video exactly what it is - 2 or 3 thou would be normal.

Jasonb · « **Reply #15 on:** August 20, 2011, 02:33:43 AM »

Quote from: Jonny on August 19, 2011, 04:19:59 PM

Looks a lot more than a few thou to me.

What part are you looking at, I'm looking at the slight tool mark about 1/8" in from the end of the bar. The tool can only just have touched the bar and its leaving a mark about 1/2 way round the bar so runout can only be a couple of thou. which is usual for a cheap chuck.

What does the test report that came with your machine say the permissible and actual runout is? My WM280VF is within tollerance and gives 0.05mm or 0.002 at 100mm from the chuck. If its within the stated tollerances you can't really complain to Warco. First thing to do is get yourself a DTI and test the TIR.

As For the oil its par for the course on thes emachines, look at mine

Still running fine after 3 years just neded a new set of brushes in that time and the oil leaks and chuck runout have not stopped me making this on it

J

loply · « **Reply #16 on:** August 21, 2011, 11:18:32 AM »

There's absolutely no reason to think that stock is round to begin with, unless you know it is.

Generally round bars aren't round until you make them so.

Until then you will cut only on one side if you make a small pass like that.

Turn a bar round then chuck it up and try again. Note that I said bar, if you use a tube the act of chucking it will probably egg it up a bit.

dickda1 · « **Reply #17 on:** August 21, 2011, 01:54:23 PM »

I'd buy a cheap dial indicator so that you can quantify the amount of runnout that you think you have.

We all have to live with some misalignment (tail stock to head stock centers, gibs that are bent or rough, three jaw chucks and drill chucks with appreciable runnout). I would expect a high degree of finish and alignment on a Hardinge or Myford as delivered, but most of us can produce good work with a whole lot less. A good chunk of satisfaction in this hobby comes from understanding the peculiarities of our individual machines, making fixes and additions.

Welcome.

-Dick

Jonny · « **Reply #18 on:** August 27, 2011, 05:18:26 PM »

Looks no more 1/3 of a rev Jason, look at the jaws.

The three stud fixing to back plate, try revolving 120 degrees, if no good try the next 120 degrees, can leave that round in saves removing. Once found, hard mark back plate and chuck.
True the jaws have inbuilt errors.

andyf · « **Reply #19 on:** August 27, 2011, 07:30:20 PM »

One point which I don't think has been mentioned yet is that you may find that one of the three square sockets for your chuck key has a mark of some sort stamped beside it. On my 3-jaw, its an "0".

In theory, that's the one you tighten up last, to get the minimal runout. However, I suspect the Chinese makers of chucks like yours and mine don't go to the bother of testing each one, but simply bang a mark in at random so it looks as though it has been tested.

Andy

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Author Topic: Lathe help needed (Read 10563 times)