Myford ML7: Chuck Runout.

[ParCan]

Hi Guys.
Been away doing other things for a while.

My Myford ML7 has been givin me a bit of general gip lately.
It had a good clean over the weekend in readiness for my next Engine project.

I just chucked a 4" Steel slab in the 3 Jaw. Fired it up and I could see it wasn't anywhere near central in the chuck.

Dial gague tells me .15 mm out - A country mile......

The big Jaws had never been used when I got the lathe and this is the 2nd time I have used em.

Suggestions welcome.

[tekfab]

You've tried all the usual things, turning it in the jaws, turning it end for end etc etc ?

Mike

[Miner]

Best guess? You've got the jaws in the wrong order, or you've got at least one jaw out by at least one tooth on the scroll. If you've got a good chuck, the scroll should be numbered and each jaw also numbered. If it's a cheap no name chuck? Then all bets are off.

Pete

[ParCan]

Turning it in the jaws produces a very similar result, as does end over end.
The steel is square and sitting flat on the Jaws.
Spindle Outside has zero runout. certainly less than .01mm
Chuck backplate has .02mm run out but the chuck has .01mm.

If the Jaws are incorrectly inserted then it's mm out, not 0.15 mm.
Jaws checked 1 - 1, 2 - 2 , 3 -3 and scroll in in the correct order.
The chuck is Myford, No idea on date or how much abuse it's suffered in the past.
I Stripped and cleaned it a year ago, it was seriously full of C**P and the factory lube was somewhat not....
I do know it was certainly within .05mm after that.

[tekfab]

I'm totally biased but can i suggest the dreaded 4 Jaw ?

Mike

[ParCan]

I think that's where I'll end up for this job. It needs to become a flywheel.
I have the Myford 6" 4 jaw so it'll also fit better in the jaws.

Workshop is far to warm to work in now, will have another look tomorrow I think....

[andyf]

This is the sort of thing that independent 4-jaw chucks were designed to do. There is a way to pack one jaw of a 3-jaw scroll chuck to turn an eccentric to a particular offset, so I suppose it coiuld be used in reverse to get something which is eccentric to run true. Looks far more complicated than just clocking the job in a 4-jaw, though:
< http://www.steves-workshop.co.uk/tips/lathetech/eccentrics/eccentricindex.htm >

Andy

[Miner]

Parcan,
Not  100% for sure on being MM's out since if you were indexed one slot out on your chuck jaw slots then you could be out that almost .006". But to be honest, we all have a fixation with 3 jaw lathe chucks and expect them to repeate better than the average chuck is designed to do. To state the obvious, a 3 jaw chuck isn't designed to partially turn work, remove, flip 180 degrees and then re-tighten in the chuck. Yes for lower tolerance work they will do it. But a 3 jaw should be thought of more as a convience than a precision holding method. Ideally you turn the work completely without re-chucking it. If you do have to rotate the work to finish it? Then that independent 4 jaw already mentioned is a far better holding method.

The self closing 3 jaw chuck was invented a long time after the face plate, face plate adjustable dogs, and then the 4 jaw independent chuck. Depending on your work, and your accuracy requirements, you might find a 3 jaw has very little use in your shop. Most of us probably don't use a 3 jaw for or how there designed to be used. You could also have a single piece of swarf inside your chuck that would give you the exact results your saying your chuck has.

Pete

[DavidA]

It may be a silly question,  but is the slab actually round ?

If not you will never get it centred even with a four jaw chuck.

Dave

[vtsteam]

Also scrolls can vary in accuracy depending on where on the scroll the jaws are when tested. So an earlier test that showed .05mm for a round held in the jaws might have been at a different and more favorable scroll position.

[Trebor]

I'm continplating buying a second hand 3 jaw chuck but after reading this I won't bother, I'll save up for a while.

[tekfab]

I'm continplating buying a second hand 3 jaw chuck but after reading this I won't bother, I'll save up for a while.

Don't you dare desert your 4 jaw !  stick with it, it's much more fun and more accurate !

           " 4 JAWS RULE ! ! ! "

Mike

[Anzaniste]

Could it be that the face of the slab is not perfectly square to the axis?
Registering the sawn face against the jaws will produce a wobble that would also show up as eccentricity.

[DavidA]

Parcan,

Just had another look at your pictures.

It's a relatively thick block.  Why not skim it until it is cleaned up all round, Getting as close as you can to the chuck jaws. Face it then reverse the block in the chuck.  You should still be able to re-clock on the newly skimmed surface; avoiding the un-skimmed part.

If the original error was in the chuck then it will probably still be there when the block is re-mounted on it's newly machined surfaces.

Dave.

[ParCan]

4 Jaw came out and got dusted off.

The steel was round. Clocked it to within .02 mm, More than good enough.

Both sides faced really nicely. Center is spotted as well.
That'll do tonight. Now I need make it into a flywheel.....
 

[tom osselton]

Before making a flywheel try some smaller dia like 1/2 or 3/4 " and see if that makes a difference a piece that size wouldn't take much to throw it out.

[ParCan]

OK - Flywheel blank all Chucked up in the 4 jaw.

I'm using a 4mm dia Shaping tool to hollow out the middle to a depth of around 9mm.
As I started to work to the outside the bottom of the lathe tool starts catching on the work.

Brain in over ride mode thinks Angle the tool. Nope !

So I decide to have a square corner on the outside and put a std tool in. Nope !

I guess I need a Boring tool / Bar / Doofah thing yes ?
 

[vtsteam]

Not exactly sure what you mean by hollowing out the center of a flywheel -- could mean several different things  -- but it does sound like you are doing a boring operation -- meaning enlarging a bore of some sort outwards, and you are getting interference from the bottom corner of the tool.

Depending on what you're doing, you may not need a boring bar, and even if you did you'd need adequate clearance at the bottom of the tool.

Just grind enough clearance. Also a smaller square tool will help.

One other thing.....the cutting edge should be set slightly above dead center.

[NickG]

Yep, you just need a rad on bottom
Corner of tool smaller than that of the recess you are trying to turn. I put a sketch on here somewhere as the question came up before. With the 3 jaw though, sure it should be smaller run out than that. Someone said one of the jaws could be 1 scroll out but as you said I'd think it would be further out than that. Do they meet properly in the middle? I've always Done my flywheels in the 3 jaw.

[ParCan]

I'll move the tool up a tad. It's on centre at the moment.
I'm using an insert type tool so won't be hard to trim down a bit.

That should give me more than enough clearance.

Thank you.

[Fergus OMore]

Now here's an interesting thought. It's a ML7. That's a machine with split Glacier bearings, isn't it?
So it dates back to - well, any time to when they were £25.- the lathe- not the chuck.
Perhaps making a back plate using a 4" SC chuck- to hold it for machining.

I'd have to be pretty desperate to go along those lines. I haven't done the calculation but it's quite a load for  a ML7 spindle to hold - virtually unsupported.

Nope- I hae me share of doots.

[ParCan]

Yup. It's a fairly early ML7. The bearings are split white metal shells with a soft spindle.
Lube is by drip feed oilers.

The Machine has some wear all over but the bearings are good with no play in any direction.

I have the option on Bronze Bushes and hard spindle as an upgrade. For an already worn machine it's hard to justify the costs.
If I did do the spindle I'd prolly do a complete overhaul and bed regrind and still have a machine worth about the same.

[Fergus OMore]

My memory is somewhat shaky now but you can take up play in the spindle by removing part of the laminated shims- prior to going along the replacement of the old spindle and bearings.  Again, you CAN remove a lot of bed wear(?) by having the bed 'Blancharded' as a cheap alternative. I wrote it up in ME years ago about my antics on a friend's machine. Cost was perhaps £30 and involved a bit of scraping and using the new bed surface as a datum.  Actually, it is not too difficult with a bit of 'blue', an old file as a scraper and a bit of flat bar.
We got it down to a sensible 3-6 thous rather than a lathe which would only turn banana shapes.

As for the heavy chunk of metal to be held in a set of reverse jaws in a somewhat wonky chuck, I'd have done a bit more to hold it more firmly. I'd have probably drilled the blank and screwed it firmly to the faceplate or the 4 jaw and I would have attempted to take up 'slogger' with a rotating centre. If you MUST use carbides, lack of rigidity is a great way to break them.

As an aside, I would probably 'improve ' your three jaw by removing 'bell mouthing' but it is not a way to get a near new chuck again but merely something a touch better.

Meantime, my best regards on what could be an interesting task or three.

Norm

[ParCan]

The White Metal shells and the Saddle are adjusted with Shims on the ML7.
I have totally rebuilt the spindle and re shimmed it. The biggest change was the oil consumption (and subsequent mess from it) dropped BIG TIME.

In the bottom of the tobacco tin I found a Boring tool
Thankyou for the tip on running above centre for this job. Worked much betterer....
Side 1 is done well enough until I get some real dimensions.

1st pic shows the tools I'm using to hollow this all out.
The others are what I have done.

[Fergus OMore]

Glad to pass on a few wrinkles. I'm 83 and have lots to spare

Seriously, you have a PM which may be more useful.

N