Myford-S7 Rear Thrust bearings.

[Neil LickfoldParticipant @neillickfold44316]

Some time ago, I came across a section about setting up the spindle on the S7 lathes and the procedures for setting the front taper clearance. Amongst it was about setting up the rear thrust bearings, Angular contact bearing pairs and their oil spacer shim.

Some have added taper roller bearings to replace the pair of Angular contact Bearings. Is their a link to that discussion anywhere? I have tried to find what I vaguely recall reading, and only find the information for replacing the bearings and setting the front bush clearance.

While thinking about the front taper bearing, has anyone tried an air bearing for the front of the spindle at all ?

Any links or info will be greatly appreciated.

Neil Lickfold

[Michael GilliganParticipant @michaelgilligan61133]

This, or something adjacent, might be the post you seek Neil:

super 7 headstock bearings

https://www.model-engineer.co.uk/forums/topic/super-7-headstock-bearings-2/#post-394892

MichaelG.

[John HaineParticipant @johnhaine32865]

Look for Dan Gelbart on YouTube for air bearings on a lathe.

[Brian WoodParticipant @brianwood45127]

Hello Neil,

Dealing first with the question of taper thrust bearings. Ken Wilson published a three page article in MEW 175 dated April 2011 which fully described the modification in detail and the rework that needs to be done on the screwed rings that hold the bearing stack in place. Having made the modification myself to taper bearings in place of the angular contact bearings I fully endorse the change and have not had to make any further adjustments to spindle clearance since that time. If you can’t track down the article I have a copy which I can email you, PM me if I can help in this way.

Now air bearings. I am no expert on the subject but I believe things like dental drills use them extensively to achieve the very high speeds, upwards of 50k rpm, that they run on. Rolls-Royce Aero in the 1960s were experimenting with multi positional air bearing measurement of components in the one fixture with no contact other than air.

I don’t think the technology is appropriate for machine tools with variable loadings from cuttings forces, and at the much lower shaft speeds they work at.

Regards   Brian

[Dave WoottonParticipant @davewootton]

I did the conversion mentioned by Brian above, following Ken Wilson’s article to the letter, to my late 60’s S7. The machine had stood for a considerable time in a concrete garage before I bought it to rebuild, and the original bearings were suffering from some very light corrosion. Very pleased with the results, can’t really compare performance against the originals, but they were easy to adjust initially and have not needed adjustment since. In my case the bearings were in need of replacement anyway so it was an easy choice to make.

[Neil LickfoldParticipant @neillickfold44316]

Thanks very much for the responses. I will make up a couple of taper bushes and have a play with things. If the Air bearing does not work, will just put it back to the wick oil bush. While apart, I will be adding the link belt, and will make a new spacer for the spindle shaft also.

Neil

[Kiwi BlokeParticipant @kiwibloke62605]

Dan Gelbart made an air-bearing lathe, capable, apparently, of micron accuracy. Most impressive. Video in usual place…

I don’t know much about air bearings, and was surprised to discover that they can be sufficiently stiff for a lathe spindle bearing. My intuition suggests that a tapered bearing (if this is what you’re hinting at) may be a challenge, because the leakage path’s cross-sectional area will increase from one end to the other. Wouldn’t this lead to the bearing ‘air cushion’ collapsing? Sounds interesting, if a technical challenge…

[Michael GilliganParticipant @michaelgilligan61133]

I hope this isn’t too far off-topic

Having seen the references to Dan Gelbert … I happened across ‘Cyclo’

https://youtu.be/kezh294OO-w?feature=shared

… slow paced, but very informative

MichaelG.

.

[Kiwi Bloke]

On Kiwi Bloke Said:

Dan Gelbart made an air-bearing lathe, capable, apparently, of micron accuracy. Most impressive. Video in usual place…

I don’t know much about air bearings, and was surprised to discover that they can be sufficiently stiff for a lathe spindle bearing. My intuition suggests that a tapered bearing (if this is what you’re hinting at) may be a challenge, because the leakage path’s cross-sectional area will increase from one end to the other. Wouldn’t this lead to the bearing ‘air cushion’ collapsing? Sounds interesting, if a technical challenge…

I’m with Kiwi Bloke in thinking that an air bearing isn’t suitable for a lathe being used for heavy/light cuts, drilling, parting off, high/low speeds etc. but I’m open to persuasion.

Tony

[Tony Pratt 1]

On Tony Pratt 1 Said:

On Kiwi Bloke Said:

Dan Gelbart made an air-bearing lathe, capable, apparently, of micron accuracy. Most impressive. Video in usual place…

I don’t know much about air bearings, and was surprised to discover that they can be sufficiently stiff for a lathe spindle bearing. My intuition suggests that a tapered bearing (if this is what you’re hinting at) may be a challenge, because the leakage path’s cross-sectional area will increase from one end to the other. Wouldn’t this lead to the bearing ‘air cushion’ collapsing? Sounds interesting, if a technical challenge…

I’m with Kiwi Bloke in thinking that an air bearing isn’t suitable for a lathe being used for heavy/light cuts, drilling, parting off, high/low speeds etc. but I’m open to persuasion.

Tony

He says toward the start of the video, when showing those pins in the chuck, that the machine is only for light duty work. So I would guess it is basically a cylindrical grinder with a bit of light turning capacity. A specialised finishing machine. Roughing out, (to the nearest 10 microns!) would be done on a regular lathe and then transferred to this one for final turning and finish grinding perhaps?

Certainly impressive demonstration at the beginning with his plug in a hole that will spin freely but let no air out of the captured space. I wish I could get the power cylinder and piston on my current Stirling engine project so nice!

[Tony Pratt 1]

On Tony Pratt 1 Said:

I’m with Kiwi Bloke in thinking that an air bearing isn’t suitable for a lathe being used for heavy/light cuts, drilling, parting off, high/low speeds etc. but I’m open to persuasion

Discussed quite helpfully in the video that I linked

MichaelG.

[Brian WoodParticipant @brianwood45127]

Hello Neil,

Did you get the Ken Wilson article I sent to you by email, using the address you gave in your PM reply? I have since had a rather abrupt note from Morton’s webmaster informing me that it would not be delivered and should be sent via the Forum.

I thought that action was rather high handed and intrusive and it certainly adds to the task of sending an article copy from a simple one to learning how to do that as a Forum input.

Regards   Brian

 

[Neil LickfoldParticipant @neillickfold44316]

Hi Brian, no email has arrived.

Neil

[Brian WoodParticipant @brianwood45127]

Hello again Neil,

Second attempt send to your alternative address; it would be helpful to know if this one gets through to you.

Failing that I suggest we communicate directly by email. Mine is as follows;    wood_y(at)btinternet(dot)com   There is an underscore between the d and y, address all in lower case with no spaces

Best wishes   Brian

[Neil LickfoldParticipant @neillickfold44316]

So the air bearing on a taper spindle really is a fail. Plan B, is to make an air bearing headstock for a sieg6 lathe bed that I have. Convert the carriage to be on linear rails, and make it specifically for finish only and light duty things. The new spindle will be a parallel one and will look into the carbon air bearing pads like Dan Gilbert did making it adjustable for the loads etc. I just need to learn a lot more about air bearings for sure.

Made a replacement bronze bush for the S7 and recut the 12deg,25 mins (12.4166 deg) inclusive taper on the spindle matching the bush.  The bush needs to be scraped and fitted to the shaft after it is pressed into the housing.

I did not have that much success with the taper roller bearings. They worked, but there is a coupling happening from the slight error of the bearings concentricity and the concentricity of the shaft to the shaft taper. It may have been that they were not the high precision taper roller bearings.

Switched back to the angular contact bearings and it was better but not where I wanted it.

Hence the reason for the re cutting of the shaft taper and making sure it was concentric to the existing diameters of where the bearings sit and the chuck register diameter.  It was very close  just over 0.01 mm TIR

The new coated carbide cut the taper very well at around 400 rpm or so.

[old martParticipant @oldmart]

Air bearings suit grinders better than lathes where the forces are less. Particularly small diameter internal grinding.

[Author]

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