Myford Super 7 headstock taper bearing

[Andrew Moyes 1Participant @andrewmoyes1]

The following might be of interest to others who enjoy scraping and lapping bearings.

My lathe was the big bore machine that Myford hawked around exhibitions and used to demonstrate headstock spindle adjustment.  When I bought it in their liquidation sale, the lathe was as-new except the headstock bearings had suffered rough treatment and the spindle had been swapped.  I had to replace the noisy rear ball bearings and rescrape the front bearing as the bush did not match the spindle and had caused the spindle to seize at some point.

On reassembly, there was a slight alignment error of 0.15thou/inch towards the operator.  After two years’ use in this state, I revisited the bearing with the intention of further scraping to correct the alignment.  I then discovered I could achieve perfect alignment simply by slackening the four headstock holding down cap screws and fully tightening the right hand alignment screw.  While the spindle was out, I naturally inspected it for wear and found that apart from a few tiny high spots, there had been no metal-to-metal contact.  The scraper marks were just as I made them.  On this evidence the life of the bearing will be indefinite.

Now – and the point of this posting – during this initial use, the oil consumption of the bearing was surprisingly high.  I needed to add 2-3 drops of oil every second turning session or so.  All the oil dribbled out of the left hand end of the bearing and none out of the right hand end, which seemed to defy gravity.  Out of curiosity, I ran the lathe in reverse for 30 minutes and the oil all came out of the right hand end and none out of the left.  The only explanation I can offer for this asymmetrical behaviour is that the original factory ground finish on the spindle left a microscopic screw thread which acted like an Archimedes screw.

I decided to lap the bearing with Timesaver powder using the yellow label fine grade.  I lapped it by hand, lifting and turning the spindle regularly by 1/3 turn.  After only 5 or 6 minutes of this treatment, I cleaned off the paste and found the spindle had a uniform matt grey finish over its entire surface.  About 50% of the bronze had lapped to the spindle.  I decided to stop lapping at this point as I wished to keep some scraper marks for oil retention in the light of the previous experience.

Now in use, I would say the oil consumption has reduced by at least an order of magnitude.  I need to add 2-3 drops after 20 or 30 hours of running and there is a faint trace of oil running down both ends of the headstock bearings.  My thinking is that the striations in the spindle are now truly circular and not spiral.  I wonder if there is an expert out there, perhaps with industrial experience, who could either confirm my thinking or offer another explanation.

Incidentally, the countershaft has a related issue.  If I top up both oil cups and run the lathe forwards, the right hand cup draws in all the oil within 10-20 seconds whereas the left hand cup dumps most of its contents into the belt guard.  If I top up the cups again and run the lathe in reverse, the opposite happens.  I now top up one cup at a time and run the lathe in the appropriate direction.  Again, I wonder if this is due to the way the shaft was ground.  Curious!

 

[Tony Pratt 1Participant @tonypratt1]

I don’t think I would have used lapping paste in this situation but each to their own:)

Tony

[mgnbukParticipant @mgnbuk]

I don’t think I would have used lapping paste in this situation but each to their own:)

The OP did say he used “Timesaver” – a product specifically designed for the purpose described which doesn’t embed & breaks down to an inert compound after limited cutting life – instructions for use here.

Nigel B.

 

[Andrew Moyes 1Participant @andrewmoyes1]

Thank you Nigel – that’s why I use Timesaver.  I did plug the oilway first and clean off the lapping paste afterwards but it is reassuring to know that any traces left behind will do no damage.

Andrew

[noel shelleyParticipant @noelshelley55608]

Rover cars used a reverse scroll on the first motion shaft to keep the oil in the gearbox – No seal ! So I think what you have observed is the same idea, ie that a spiral will move the oil, depending on which direction it rotates. Noel

[Neil LickfoldParticipant @neillickfold44316]

When grinding or turning parts that rotate together, use a fine scotchbrite pad over the surfaces to take away the microscopic high spots. It will make a noise initially and then when the noise stops those high spots are gone.  A very fine stone can also be used, but a 900 grit stone can cause deformation of the surface or rounding of outer edges so great care needs to be taken.

Lapping is good as it makes the microscopic lines now in a radial form not a scroll.

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