Myford Super 7 Spindle Runout

[Mike DonnerstagParticipant @mikedonnerstag]

I have a Myford Super 7 and have found a half thou runout that only occurs every two revolutions. Am I right to assume this is the rear bearing that is at fault?

Cheers,

Mike

Edited By Mike Donnerstag on 20/06/2022 18:51:26

[Mike DonnerstagParticipant @mikedonnerstag]

[Tony Pratt 1Participant @tonypratt1]

Is it axial or radial run out?

Tony

[Chris CrewParticipant @chriscrew66644]

I am probably going to get lynched for stating this by those who apparently work to NASA and NPL standards, but to me 0.0005" run-out on a Myford is neither here nor there on such a 'flimsy' lathe. I would bet that the tension of the drive belts or normal cutting forces pull and push the spindle out further than this in normal operation. I am now taking cover!

(BTW, no amount of money could tempt me to part with my cherished ML7-R, but you have to accept it for what it is)

[Tony Pratt 1Participant @tonypratt1]

Chris you are quite right .0005" is neither here nor there but the guy asked a question. BTW even NASA & NPL should only use tight tolerances where appropriate.

Tony

[bernard towersParticipant @bernardtowers37738]

I really am fed up with people calling super 7s flimsy I regularly part off 2 inch 304, maybe its the blunt tools !!!

[martin haysomParticipant @martinhaysom48469]

Posted by Tony Pratt 1 on 20/06/2022 20:49:03:

Chris you are quite right .0005" is neither here nor there but the guy asked a question. BTW even NASA & NPL should only use tight tolerances where appropriate.

Tony

and when they do its with very expensive equipment that's regularly calibrated

[blowlampParticipant @blowlamp]

What's its runout when being driven at slow speed?

The oil film needs to build up and stabilize in the front bearing, before taking a reading.

Martin.

[HopperParticipant @hopper]

Could be a hardened old V belt with a tight spot in it. Try testing with belt off the pulley.

[Neil LickfoldParticipant @neillickfold44316]

I would look at replacing the rear bearing, and at the same time replace the belts. From motor to the clutch or Primary drive as I see it, I went for a link belt without the metal parts. Then on the secondary drive, clutch to spindle, I went for the gates type belt, that has the cut outs on the inside and smaller depth cut outs on the outside. Like what is used on some older cars. I have al ink belt for the secondary drive, but the gates belt has not worn yet.

Being that the runout is not on every rotation, it can come from anywhere, except the very front taper spindle bearing. The amount you are talking about can come from the spindle moving back and forwards , depending on the amount of end play there is. It can also come from a worn belt if the lathe spindle has been stalled at some point etc It will be from something that has an error in itself. Having the tension too tight on the secondary belt can also cause spindle running conditions to alter a very small amount.

With great care, the S7 and the ML7 lathes can be very good in deed. It just takes a lot of time to get them correctly adjusted and in place.

[Chris CrewParticipant @chriscrew66644]

"I really am fed up with people calling super 7s flimsy I regularly part off 2 inch 304, maybe its the blunt tools !!!"

Bernard, my remark was not meant as a criticism of the Myford 7 series of lathes. They are wonderful machines and I cherish and value my much modified ML7-R (now a S7 less gear-box in all but name). I too have performed some heavy work, parting-off, cutting multi-start worms etc.on mine with great success, although the fact remains that if you put a clock on a work-piece and adjust the levelling screws or lean on the bed you will see the needle move but so what? The machine performs its allotted tasks admirably, it's just that such a deflection does not occur on my Student which obviously has a much more substantial bed casting.

In terms of performance as a lathe, the Colchester walks all over the Myford but only as a 'lathe'. The little Myford, with all its attachments, both proprietary and shop-made, is a complete machining centre in itself. There is hardly any task, within its capacity, that cannot be performed on the Myford.

[Mike DonnerstagParticipant @mikedonnerstag]

Many thanks to everyone who replied.

Tony: It is radial run-out, which I measured on a ground spindle held in an ER40 collet chuck, with a backplate screwed onto the spindle.

Martin/blowlamp: Measured on the OD of the the spindle register, the total runout I can measure with my half-thou indicator is around 0.0007" when in lowest back-gear. Perhaps this isn't too bad – let me know what you think. I hadn't realised that the oil film in the front bearing needs to stabilise. How does this affect DTI readings?

The belts have been recently replaced and I have also adjusted the bearings recently.

My theory is that the balls in a ball race rotate at half of the speed of the spindle. Am I right?

Mike

[Tony Pratt 1Participant @tonypratt1]

Mike, you are not actually measuring the spindle run out but a 'ground spindle held in an ER40 collet chuck, with a backplate screwed onto the spindle.' I suggest you remove the collet back plate & check for run out on the spindle outside register & internal taper, not sure about the ball race rotating at half spindle speed though.

Tony

[SillyOldDufferModerator @sillyoldduffer]

Posted by Chris Crew on 21/06/2022 01:05:36:

"I really am fed up with people calling super 7s flimsy I regularly part off 2 inch 304, maybe its the blunt tools !!!"

Bernard, my remark was not meant as a criticism of the Myford 7 series of lathes. …

I didn't read the comment as a criticism, just a statement of fact. Compared with many other lathes, Super 7s are lightly built, there's no denying it.

Doesn't matter provided the machine is driven within it's envelope, and this is true of all tools. It's all relative, I was amazed to find professional users often consider Bridgeports 'flimsy'! I think they're monsters, massively heavy and rigid compared with my little mill, and too big for my workshop.

I expect someone, somewhere, considers this vertical lathe to be a middle-weight! Max turning diameter 14 metres, max weight 500 tons, turning power 300kW plus 100kW milling power:

I wonder what they do with the swarf?

Dave

[Howard LewisParticipant @howardlewis46836]

The way to make a machine tool accurate /precise to the highest degree is to make it rigid, which implies weight and metal where it will do most good.

MANY years ago, in Shrewsbury there was a company making Boring Mills. The slideways were coated with Formica, which apparently when oiled resulted in a very low coefficient of friction.

Needed for a machine that was assembled in a hole in the ground large enough to swallow a house, but containing only the lower half of the machine.

My current lathe weighs 300Kg and replaced a ML7 which did flex, when used for milling..

No doubt this one does, but under a much great load than I have ever applied.

Used sensibly, a 7 Series Myford will do excellent work, but overload it at your peril if you want long life and consistently precise output.

As we regularly say, "Horses for Courses"

It might well be that a new belt, if it has a fat joint, will increase tension sufficiently to change bearing clearances temporarily and result in run out.

And single phase motors are not renowned for producing a consistent angular speed..

If it could be incorporated into the drive, maybe a hefty flywheel would provide some inprovement?

Howard

[duncan webster 1Participant @duncanwebster1]

they've probably got a conveyor system to take it away. Then they centrifuge it to recover the coolant and sell the scrap. Friend of mine got a job machining some exotic alloy once, he made more selling the swarf than doing the machining. Must have been a bit bottom clenching hoping he didn't scrap one tho'

How about trading your ML7 for this little lathe. Note operator platform on toolpost

[HopperParticipant @hopper]

If you are running it in backgear it could be the meshing of the gears causing runout. Do it with no belt on the pulley, no gears engaged and rotate by hand. With dial indicator directly on the spindle.

[old martParticipant @oldmart]

Can you check the runout of the left end of the spindle to find if it coincides with the right end? If you were to remove the left end bearing and clean it before replacing it, the inside and outside races would end up in different positions to where they are now, which might change the unusual charactistics. Building up the oil film before testing has already been mentioned. Link belts may help if there is a suspect stiff belt section. The odd behaviour is annoying, but not a vital flaw, I wish all the machines I use were as good as your lathe.

[Kiwi BlokeParticipant @kiwibloke62605]

A S7 in good condition should do better than that! Ignore comments that it doesn't matter. The thing is built to perform better, and it should. That's what matters.

It's not clear whether this runout appears when the spindle is effectively in isolation, or only when it is being acted upon by the machine's drive train. If you haven't already done so, I suggest that the spindle drive belt is slackened, and the spindle bearing set-up procedure is gone through. Then, begin the hunt starting with the isolated spindle, then add components of the drive train, one by one, measure, rinse and repeat…

Also, I'm not clear whether you're measuring runout, where there's no 'slop', or free movement that appears on alternate rotations. The rear bearing ball set will indeed orbit at half spindle speed.

You have measured runout when back-gear is engaged. Is there a little backlash in the back-gear train? If it's too tight, any eccentricity of a gear may cause radial forces on the spindle. Turn by hand and check.

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