Myford Super-7 chuck – unacceptable run-out??

[flatlineParticipant @flatline]

Hi,

 

I have just rebuilt my 1955 Super-7B; had the bed, saddle & cross-slide reground, etc…

I also fitted 2 x new angular ball-races to the spindle, I left the phosphor-bronze bearing alone, as the spindle run-out at the nose was pretty much zero.

However, when I fit a 3-jaw Chuck, a 4-jaw or a ER-32 collet holder I get the same result, which is about 0.05mm run-out… I have tried to load short videos of the DTI readings… but there seems to be some technical issue…

Any ideas what is causing this run-out??

 

 

 

[John HaineParticipant @johnhaine32865]

Where did you measure the spindle run-out, and what type of collet holder?

If the measurement was on the inside of the MT2 bore but the collet holder fits on the nose thread, the observed runout could be because the external register is not quite true.

[JasonBModerator @jasonb]

You would need to host the video somewhere like Youtube.

A photo of what you are measuring and where may suffice.

[flatlineParticipant @flatline]

Here are 2 photos of where I measured the spindle run-out…

 

[John HaineParticipant @johnhaine32865]

Thanks.  So on the cylindrical part and the flange of the register, and you measured negligible run-out?  Assuming that your collet holder fits on the register as well, maybe something is stopping the chucks seating on the register properly.  It looks like there’s a little bit of galling near where the cylinder meets the flange, could that be problematic?

[flatlineParticipant @flatline]

There is galling present, but it doesn’t affect the seating of the chucks or collet-holder.

Of note is that neither of the chucks nor collet-holder use that cylindrical portion of the spindle to locate/register… it appears that they use the vertical back face on the spindle  & the threaded nose only…(?!)

[JasonBModerator @jasonb]

And where are you measuring your 0.05mm (2 thou) runout? 3-jaws can vary in accuracy and hard to say a 4-jaw has runout. Are they threaded body chucks or on backlates?

[flatline]

On flatline Said:

There is galling present, but it doesn’t affect the seating of the chucks or collet-holder.

Of note is that neither of the chucks nor collet-holder use that cylindrical portion of the spindle to locate/register… it appears that they use the vertical back face on the spindle  & the threaded nose only…(?!)

Seems odd, perhaps therein lies your problem.
The thread is only there to keep the chuck attached, with the register being the cylindrical part, combined with the stepped face; the two surface where you are showing your DTI.

Bill

[flatlineParticipant @flatline]

Thanks Bill – yes, it’s a curious one for sure..

[flatlineParticipant @flatline]

JasonB … the 0.05mm run-out was measured on the chuck back-plate, threaded on to the spindle..

 

[Charles LamontParticipant @charleslamont71117]

The chucks should register on the cylindrical portion and shoulder face. The thread is only there to hold them on.

There are people who for some reason like to question this, but I would advise them to read the manual. It says this:

“Backplate register bores are held to very close limits. When backplates are supplied with the the machine, they are carefully selected and adjusted to suit the spindle nose so as to retain the closest possible contact between register bore and register diameter. When backplates are supplied either as separate units or fitted to chucks after the machine has left the works, the backplate bore may need very light scraping or polishing with fine emery cloth.”

It also says the same applies to threaded body chucks, and to use a bit of oil.

[ChrisLHParticipant @chrislh]

Your chucks are unusual in that they don’t locate on the plain 1.250 diameter of the shaft. Locating on a thread is never a good way to ensure concenricity. If your chucks did locate on the plain diameter, even 0.05 clearance on diameter could result 0.05 dti runout if you were unlucky with where the chuck, etc. decided to sit and it could be different the next time you fitted it. If the locating diameters of the chucks, etc. are greater than 1.250 inches (the standard Myford dimension) either a previous owner has deliberately bored them out to, perhaps, allow tapping them true or they are not intended for a Myford 7 lathe. Or an, extreme case, somebody has reduced the spindle nose diameter from 1.250 inches !

[ChrisLHParticipant @chrislh]

Flatline

Just seen your 15:12 post. The runout of this part of the chuck doesn’t matter, it’s the runout of a decently round and finished piece of material gripped in the jaws that’s crucial.

[ChrisLHParticipant @chrislh]

And I own a Myford S7 as old as yours complete with handbook. If you do not have one of the latter and would like a copy please PM me.

[flatlineParticipant @flatline]

ChrisLH … many thanks for your input, I do have a copy of the relevant manual as the machine came with a host of tooling & paperwork.

whin I get home I’ll mic’ the spindle to see if I do have a 1.250” dia… or not!!

[Dave HalfordParticipant @davehalford22513]

When people fit a new backplate, chuck etc the backplate step that engages with the back of the chuck is trued to fit the chuck. The outside edge of the backplate that you are measuring is not important.

Some people allow a tolerance there to tap a 3 jaw to more accurately hold the work, which of course throws out the chuck body

[John HaineParticipant @johnhaine32865]

I have always understood that they should register with the cylindrical bit, clamping against the flange.  If the counterbores in the backplates are a smidgen too large (say 0.05mm) then gravity will give them that much runout before clamping.

[old martParticipant @oldmart]

As already mentioned, the runout of the OD of the backplate is meaningless, what matters most is the face which the chuck bolts onto. It is normal for a backplate to require skimming on its face, after screwing it on and off several times to settle down the threaded connection, both halves of which must be absolutely clean. We have about 10 backplates for the museum’s Smart & Brown model A which have register diameters varying from plus 0.0005″ to 0.020″ relative to the spindle, and they all repeat perfectly, the tight one is a pain to fit and remove.

You could skim the OD of the backplate if you want to, it will not harm anything.

With a replacement second hand backplate, if the register which the chuck fits on has radial eccentricity, it will either have to be reduced slightly, or the backplate will have to be faced back to allow a new register. This can be done if there is enough thickness, or as I recommend, leave it loose, you will be able to adjust the running of the jaws to zero at any holding diameter. The bolts will stop anything slipping, after all, you only use bolts and clamps on a mill bed to hold things, and nobody worrys much about that.

[Neil LickfoldParticipant @neillickfold44316]

Did you get the bearings from Myford or another supplier ? I have seen where I used different bearings, other than from Myford, where the spindle showed to be zero like yours, but when a piece was placed in the chuck, or the collet chuck placed on the nose, the chuck was running out of being true. I then got a new set of the Myford bearings and it was just fine.

Old mart is correct about chuck registers on backplates.

At work , I have 4 plates on the backplate that have screws to micro shift the chuck like a 4 jaw does, and then tighten up the bolts to hold in place. This is better than using the 4jaw , as there is no swash adjustment required.  I did the same with my collet chuck, to make it adjustable for the poor concentric collets.

The Myford front bearing arrangement is extremely good if fitted correctly and if the spindle taper is round and concentric to the rest of the spindle. With the face and the register showing zero or very near to zero, your spindle taper is correct.

Neil

[DiogenesParticipant @diogenes]

Never had an S7, but if you’ve “just” fitted new bearings wonder if it’s worth a couple of sessions cutting metal to warm everything up and settle it all down before re-adjusting and checking again..?

 

[JasonBModerator @jasonb]

Did the spindle have any runout or play before you started to refurbish the machine? If it did and the backplates were machined on the wonky spindle then they should be remachined on the new one.

Also as you have not long had the lathe do you know if the chucks etc were being used on that machine, if a dealer has put them together as a package or bought separately then the backplates will not have been machined in situ on that machine so again will want remachining.

have you had the chucks off their backplates as part of the refurb? If so are they a close fit on the spigot or did a previous owner allow some play so the chuck could be fine tuned for position, that latter you may not have done.

At the very least take the chucks off their backplates and measure any runout to the face and spigot which are the ones that affect working accuracy not the OD that is irrelevant and check the fit of the spigots in the chucks.

[David George 1Participant @davidgeorge1]

On my Lathe the only thing that matters is how are the jaws holding the workpiece. I was taught to use the same chuck key hole which is marked by a 0 every time i hold a piece of steel and check with a dial indicator every time i put piece of steel into a chuck. This means if there is an anomaly I can find out before cutting a job unless it is a piece of black bar or cast material etc. If i find a problem I remove the jaws clean them and using a short stiff bristled brush rotate the scroll with the brush in the bottom jaw slot to mack sure any fine swarf of dirt is removed. I then reassemble the jaws and put a 3/4″ diameter dowel  into the chuck and recheck for runout. If there is a problem I would remove the chuck from spindle and inspect both the spindle location and face and the chuck also. if any damage has been caused by swarf etc a fine stone locally can help but usually all is well as I wipe all parts before putting on a chuck the spindle and the chuck location and face.  The diameter that you are checking for runout is the wrong diameter to check as if this runs out it doesn’t matter unless you have skimmed this previously and now runs out  I hope this helps.

David

[Howard LewisParticipant @howardlewis46836]

We are all making the assumption that the register has zero run out compared to the spindle bearing diameters.

If the spindle nose is showing zero run out, the 0.05 mm is within whatever you fit to the spindle.

To have a 3 jaw chuck that holds work concentric within  0.05 mm (2 thou) suggests that it is a good one.

To engage any chuck on the cylindrical register, there HAS to be a finite clearance, probably about 0.05 mm. You would have a struggle fitting or removing if register on spindle and chuck were size and size!

If you think about the clearance necessary between register and backplate and then the clearances within a 3 jaw chuck (individual jaw / scroll, scroll/body) getting work held to less than 0.127 mm (5 thou) run out is pretty good.

If you want to have work absolutely concentric, then use a four independent chuck and keep clocking and adjusting until the eccentricity falls within your standards of acceptability.

If you really want to work to tighter tolerances, you had better have your workshop temperature and humidity controlled, like an industrial Standards or Calibration room.

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