Sheraton 9A Headstock Lapping

[electrosteam]

The Sheraton 9A is close cousin of a Southbend 9A, and a close copy of the Hercus 9A both built in Australia.

My 9A #1167 was purchased in 2007 and operated successfully for a couple of years.
I read all the books and diligently kept a good supply of oil up to the headstock bearings.
I taught myself machining on this lathe, corrected several problems and was getting good results.
Then, it developed hot headstock bearings and the occasional seizing.

An inspection revealed bad bearing surfaces with significant scouring and quantities of loose debris.
The spindle runs directly in the CI housing, with helical grooves in the housing to distribute the oil.
I formed the opinion that the debris had been flushed out by the oiling and was moving into jam-up positions.

There was the prospect of significant difficult work to correct, so a replacement lathe was purchased.

I enrolled in a local techinical school and eventually was able to use the cylindrical grinder and horizontal borer.
The spindle was ground, the headstock bored out, bronze liner glue fitted and bored to suit the new spindle size.
Then I got kicked out of the school due to cut-backs by the Government.

Years have passed, but now has come the time to get the old girl going again.

The photo shows the headstock after slitting with a gap now of 2 mm.
Measuring the chuck end, bore is 45.76 mm and spindle is 45.73 mm, so clearance of 0.03 mm or 0.0012 ".
They won't go together easily, and I have not tried to force it.

Requesting comments on a couple of subjects:
- what bore size should I have,
- how to go about lapping the bores,
- size of hole to drill through the bronze for the oil,
- source for suitable oilers (I think 5/16" BSF),
- advice on grooves in the bronze to distribute the oil.

Considering positioning the headstock vertical on the table of my CNC turret mill with a lap in the quill.
Then program repetitive Z-axis mill cycles while the headstock is held in the hands and loaded against the lap.

Keep well,
John.

 

[Charles Lamont]

For the ideal bearing surface you would scrape the bearings rather than lapping them, but that would be a whole lot of work. Could you spring the bearings open a couple of thou with a wedge in the slit to see how the spindle fits?

 

[goldstar31]

I'm an Imperialist(?) and this sounds like you need 1 and 3/4" bearings which are cheap and easy to obtain.
I'm simply playing with my Vernier and and looked at things differently.
Let us know how you get on

Norman

 

[Gabe J DiMarino]

Do not use lapping compound on brass or bronze the grit will impregnate the surface and you will destroy the bearings .You need to blue and scrape in the bearing surface .

 

[electrosteam]

Thanks for all the comments, especially the warning on lapping with a grit.
I have made a timber lap, and tried it with just light oil.
The CNC repetitive cycles works a treat.

Scraping is a big step for me, I have only ever done small flat CI surfaces as test pieces.
And, I cannot get the spindle to enter yet.
This is a solid housing with a single slit, no bearing half to lift.

Purchased some kitchen cleaner today, perhaps something like the old 'Bon Ami'.
It has a very fine light duty abrasive in a water based carrier.
Can anyone confirm that this approach would not be too aggressive.

Keep well,
John.

 

[Dubi]

Thanks for all the comments, especially the warning on lapping with a grit.
I have made a timber lap, and tried it with just light oil.
The CNC repetitive cycles works a treat.

Scraping is a big step for me, I have only ever done small flat CI surfaces as test pieces.
And, I cannot get the spindle to enter yet.
This is a solid housing with a single slit, no bearing half to lift.

Purchased some kitchen cleaner today, perhaps something like the old 'Bon Ami'.
It has a very fine light duty abrasive in a water based carrier.
Can anyone confirm that this approach would not be too aggressive.

Keep well,
John.

Toothpaste works quite well.

 

[Charles Lamont]

Brasso is good too.

 

[ajoeiam]

Toothpaste works quite well.

If your trying for very fine abrasives - - - baking soda is about par with toothpaste.
If you really want to get serious and go for seriously fine abrasives - - - - then I would suggest you for a company called gotgrit.com .
They supply grit for optical grinding - - - - right down to rouge level (you know the stuff your wife uses except their stuff is very accurately sized).

 

[Gabe J DiMarino]

You have a circular bearing with a slit cut in it . In that slit is supposed to be a shim pack .Many pieces or one that makes up the space of the slit .When you tighten the bearing slit bolt it compresses the shim pack to establishs final running fit .If the bolts are lose and you can not fit the spindle in , your bearings are way to small i.d. dimension . With the bolts lose you should be able to install the spindle .Tighten the bolts put an indicator on the spindle to measure up and down moment .Then adjust the shim to get the desired running fit .Sounds like you may either need to re-grind the spindle or re-cut the bearings .Someone suggested that you try to open up the slit in the head stock casting with a wedge . If you try this and the spindle wont enter you will not be able to remove enough material with a fine abrasive . You need to remove more material than polishing will allow.

 

[wthomas]

Hi John:
If you look in the Machinery Handbook for a running fit I think you will find you need .002-.003" clearance
between the shaft and the bore. if you have a vert. mill just set it up and skin one bore then flip it over and do
the other bore. Be sure to indicated them close in vertical alinement before boring. Just a skim cut and it is done!
Bill Thomas

 

[BaronJ]

Hi Guys,

Why not use an adjustable reamer to remove the few thou needed.

 

[goldstar31]

Hi Guys,

Why not use an adjustable reamer to remove the few thou needed.

I suggested a pair of oilte bearings from 'off the shelf with all the dimensions correct and no work necessary other than drawing the old bearings out and pulling the new ones in.
So much for what seemed to be straightforward.
But- BUT this headstock has bearings held by a single clamp bolt--- and if one gets it wrong----CRACK.
Cracking old headstocks WAS quite a normal hobby.
Say no more, nudge, nudge wink, wink. Ah well?

 

[Scott_M]

I suggested a pair of oilte bearings from 'off the shelf with all the dimensions correct and no work necessary other than drawing the old bearings out and pulling the new ones in.
So much for what seemed to be straightforward

Norman
You should check your math or look at your calipers a little closer. 45.73mm is 1.8003". Not a stock size. Would still need to machine to size.

Scott

 

[goldstar31]

Norman
You should check your math or look at your calipers a little closer. 45.73mm is 1.8003". Not a stock size. Would still need to machine to size.

Scott

Apologies but I am 90 and have macular degeneration in both eyes. One wet one dry
So in this case, I would have bought some scrap lead indium bearings and 'tinned' the worn ones.
Not a lot to scrape in . I did it on a Pools Major which you probably never heard of----- After WW2.
I'm now at that wonderful twilight in life where I have been retired for longer than I have ever worked and despite the the Covid-19 I am still able to buy 'as new' and still have money accruing.
Apart from the sheer boredom- I might have got the important things 'spot on'
Best Wishes

N

 

[abby]

Might be easier to polish the mandrel !
Old lathes using a headstock with cast iron bearings the mandrel was was rarely hardened .
With pb bearings the mandrel should be hardened for best results.
Note that in use the shaft/mandrel should rotate easily with very little resistance because in use it will heat up rapidly , taking up insufficient clearance and seizing up , this applies to length as well as diameter .
If you can't fit the mandrel you can't scrape it in ! how can you see the high spots ?

Dan.

 

[goldstar31]

There is 'something wrong here.
I did a Worden tool grinder which would not admit the spindle assembly. i cured it in less time that it takes me to type

 

[electrosteam]

Job done, for now.

Made a timber lap mounted on a M12 stud with a Dia 20 mm cylindrical nut at one end.
Mounted in the lathe with an ER32 20 mm collet, sized the lap to about Dia 44.5 mm.
Reduced an ER32 collet nut down to Dia 43 mm so that it would enter into the headstock bore.
(The nut reduction needed frequent freshening up of a brazed tungsten tool !)

Mounted the lap/nut in the mill and programmed Z-axis repetitive cycles +/- 47 mm.
Ran the lap at 400 RPM, feed speed 100 mm/min.
Made up a slurry of kitchen cleaning powder in linseed oil and brushed it on.
Checked that headstock sat vertical on the mill table, and used a metal tray to keep the slurry off the table.
Held headstock in hands and loaded it against the lap in a cyclic manner.

After 3 cycles, the timber was black, so I cleaned up and tested the fit.
Spindle and bore lubricated with linseed oil, went in about 10 mm.

Did another 3 cycles and tested.
Now spindle goes all the way, and can even 'slip' a little.
It is a tight fit, measured now at Dia 45.80 mm.

I will now attack the rear bearing.
This one, I think, may require a honing step before lapping.

Keep well,
John.

 

[electrosteam]

The rear bearing was an exact fit, bore to shaft, so some work expected.
Side-stepped the possibility of using a hone for now.
Used the previous approach, timber lap in the mill with Z-axis cycles programmed on the CNC.
Worked for some time before I could achieve entry of the spindle.

Then, very pleasingly, when I tried a dry (no lubricant) entry into both bearings - success.
The alignment was excellent, fit very tight, but there.

If I rotate the spindle a number of times, then remove it, I can see the localized contact rub marks in the bronze.
I use a small buffing wheel, dia 30 mm x 5 mm thick impregnated with the lapping slurry, on the rub marks to reduce the contact.
Expect some work now to get a reasonable operable fit.

Once I think it operable, I will fit the shims and lubrication, then run for a few hours at low speed, with frequent check on temperature.

The slitting saw was 2 mm, so the first trial shims will be 2.1 mm.
The old ones were steel, so making them again in steel makes it easy to surface grind to thickness.

Not yet resolved just where I will put the oil distribution grooves.

Keep well,
John.

 

[Dubi]

Thanks for all the comments, especially the warning on lapping with a grit.
I have made a timber lap, and tried it with just light oil.
The CNC repetitive cycles works a treat.

Scraping is a big step for me, I have only ever done small flat CI surfaces as test pieces.
And, I cannot get the spindle to enter yet.
This is a solid housing with a single slit, no bearing half to lift.

Purchased some kitchen cleaner today, perhaps something like the old 'Bon Ami'.
It has a very fine light duty abrasive in a water based carrier.
Can anyone confirm that this approach would not be too aggressive.

Keep well,
John.

I made a comment about toothpaste and to follow up please see the pic. This reflector was machined from solid bar because I needed to use it as a heat sink as well. (Machined fins at the backside)

 

[electrosteam]

Dubi,
Thanks for the comments, and photo.

Each spindle end inserts into its respective bore without any looseness, and rotates firmly.
Started adding longitudinal marks with non-permanent wick pen to assist assessment.
Can insert spindle all the way axially by hand without twist, then extract axially, but with plastic dead-blow hammer.
Inspection of marks shows the contact areas, see photo.

Size is now virtually spot-on, and the bores concentric.
Now must get some clearance for the oil film.

Busy making laps from PVC pipe.
Made a sample, slit and sized to fit, then multiple holes drilled for the slurry.
Have to get a length to make it practicable to hold and rotate on axis.

I will start with slurry to achieve some sense of spindle rotation, then swap to toothpaste as you suggested.
Do you have a recommendation for the flavour ? Ha, Ha.

Have started on the shims also.

Keep well,
John