Corrosion or Stale Oil (in joint face)?

The "joint face " concerned is between the rear tool-post and the saddle on my Myford 7 - and indeed between the 2 steel blocks of the post itself.

Removing the tool-post today for the first time for months, to gain more access for the next set-up, I was disturbed to find dark stains on the contact surfaces.

I had assembled them with grease or oil (I think the former) in the first place, but is this just staining from old oil?

Or is it corrosion? If so, is it from breakdown products in the oil, or possibly from soluble cutting fluid that had leached into the joint?

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I have noticed this on other machine tools, too, such as under accessories I'd left bolted to the milling-machine table for some time, and below the top-slide on another lathe.

Cutting fluid will discolor like that sometimes.

That is the downside of soluble cutting oils, neat oils avoid that problem.

Hi there, back in the far off days of my apprenticeship when setting up automatic lathes with multiple tool blocks for form tools I was told to wipe the joint face clean & adorn it with Vaseline, this solved the black staining problem, necessary because most of these machines were running on soluble oil, also endowed their operators with the characteristic smell that identified them as Machine Shop persons, my mother had a few words to say on that subject!

Bob H

I shouldn't worry about the stains, you might try rubbing them with wire wool and wd40, but not anything more abrasive.

When I first took the Smart & Brown model A spindle out, I took the whole head off the bed and the staining made by the soluble oil was amazing. It very likely had been undisturbed in 70 years. The joint surfaces got a minimum clean and lined up perfectly when it was bolted back down. I now know how to remove the spindle, it takes ten minutes.

Thank you all!

Oh, I wouldn't use an abrasive as such on a machine-tool!

I'll go with Robjon's hint to use Vaseline.

I have a tool-post to assemble, on a Harrison L5, so there's a good starting point.

I'd acquired a Dickson ( or similar) QCTP for it to obviate the old Hunt The Shims game, and this evening made a pair of locating bushes to hold it reasonably centrally on the rather care-worn 1/2 " BSF pillar already in place. I'd considered making a new pillar but could not see how to dismantle the top-slide itself to gain access.

[Pauses to watch the progress of a spider descending gracefully halfway between my eyes and the monitor - I'm not sure where it's gone now! Web-browsing probably... ]

I've still to put spanner flats on the lower bush, which I threaded so it also acts as a nut holding the slightly loose pillar rigidly in the top-slide, and once everything's assembled I don't envisage removing it often. Hence my asking the question.

I also believe that the bacteria that thrive in soluble oil when its stale cause this type of corrosion. It also give it the characteristic smell.

I think modern soluble oils don't taste nice to bacteria, but I know the problem with the older "suds" type that makes a while fluid.

A lathe at one place I worked was not used very often - the company made special electronic equipment to order - and the suds in that used to acquire a brown gelatinous bacterial "skin".

As others indicate, the answer is either a different emulsion or neat cutting-oil.

Anyway, I completed the WCTP for the Harrison lathe today - the finishing touch being two spanner-flats on the lower location bush so it is also the tool-stud's securing nut.

(I suspect the stud might be a bit of studding to replace the original, as it is threaded for its full height and apparently screwed into the top-slide then peened on the underside.)

Taking Robjon's advice I coated all parts in petroleum jelly on assembly, and it all went together most satisfactorily!

Celebration cuppa, then I discovered the next problem. The fixed steady won't fix! Goodness knows what lathe it's for, as it's un-named, but Harrison L5 it isn't!

Hi there, again with the soluble oil coolant problems, back in the day our coolant was mixed (automatically) in a large tank to the correct ratio then piped to each section so you didn't have to lug it too far to your machine, so far so good, however at that time it was customary to use Jeyes Fluid as a biocide, not the maidens water it is today I might add, it was often difficult to determine whether a coolant splash or a poke in the eye with a sharp stick was the more painful, throw in people spitting in it, throwing cigarette ends in it & my own favourite washing their hands with it (ugh!). Help is at hand however, due to Cast Steel & Cast Iron denaturing the coolant, when it got too rank we would demand a litre of a modern purpose made biocide, pour it in & run the very large CNC lathe for 24 hours to give it time dissolve any gunk in the pipework & then drag it out with a big sludge gulper, job done. So I would suggest a similar regime would be the way to go in the home workshop, substituting an extremely ratty old wet & dry workshop vac to get the last dregs out after draining off.

Bob H.

It is surprising where bacteria can live and thrive and the consequences from their proliferation, there are bacteria that live and thrive quite happily in aviation fuel (kerosene), nowadays the fuels are dosed with inhibitors to control their growth. Prior to the widespread use of inhibitors it was not uncommon to find extensive corrosion of aircraft fuel tanks from the products of the bacteria that were highly corrosive to certain grades of aluminium alloys that the aircraft were constructed from. Not surprising that bacterial growth in coolants and oils has an effect on steel and cast iron.

Dave W

Thank you for al this information & experience. I'd been thinking of making a pumped-coolant system on a small trolley, moveable from machine to machine, but may be better off staying with brushes, simple drip-cans or spray bottles (ex-kitchen cleanser).

The stuff to use though would be one of the modern soluble oils, either indigestible to bacteria, or containing biocides.

Re bacteria living in odd places; at school, many years ago, we had a large bottle of fuming sulphuric acid. Complete with some white fungus apparently thriving on the bottom, inside the glass Winchester!

Obvioiusly, no accounting for tastes!

Howard

I was advised by an industrial chemist that nothing is really proof against bacteria, moulds etc. He put it this way:
Throw whatever you like out in the open air, and sooner or later something will come and live on it'.

The brown top layer (Nigel Graham 2) was, I suspect, a layer of un-mixed oil which had risen to the top and any remaining water had evaporated from it.

And remember that in order to work well, cutting oil needs to form a layer on the work or tool (ideally both) which sticks there and resists being wiped off by the shaving. The layer only needs to be a few molecules thick, but over time, it can build up and stain. The same trick is used in hypoid axles (etc) which are worm drives with an extra wiping action. The hypoid additive reduces friction and wear by forming this thin layer of resistant compound. We are warned on the tin (sometimes) not to use it where there are bronze or brass components as the friction-proofing attacks copper compounds badly.

And finally I wonder if the white stuff at the bottom of a conc sulphuric acid jar was actually silica dissolved from the glass by the acid?

Cheers, Tim

Hydrofluoric acid will attack glass, many years ago when I worked in electroplating, I intentionally put a 10% HF solution in a glass bottle, left it overnight, and when it was rinsed out, the immersed part of the bottle was a couple of mm larger diameter. HF is stored in lead or polypropylene. Sulfuric acid, H2SO4, will not attack glass, the sediment must have some other explanation. Be afraid, always, when handling conc sulphuric acid, I got one drip on my hand once and was rinsing it off under running water within a second, too late of course.

old mart claims: Sulfuric acid, H2SO4, will not attack glass, the sediment must have some other explanation.

I beg to differ, but I hope that someone more up to date with industrial chemistry can advise. Glass includes Calcium Silicate and Sodium Silicate, and the conc acid will be dead keen to change them to calcium sulfate and sodium sulfate - as the Silica is a much less 'strong' acid. But what do I know?

Cheers, Tim

We kept concentrated sulphuric acid in glass carboys, in straw, within a steel frame. There was no health and safety then. And nitric, hydrochloric, and glacial acetic acid.