Help needed truing ways on mill

[egaParticipant @ega]

Here is a photo of the bluing on the defective ways:

By way of explanation, I applied the thinnest and most even coat of blue I could achieve to the corresponding ways on the fixed base of the mill, offered up the casting without touching the blued areas, lowered the casting into contact, moved to and fro once and then lifted and removed the casting. I had previously confirmed that there is no corner-to-corner rocking by testing with a dial gauge and the bluing seems to support this although it looks as though my bluing was too thick on the inner edges.

Ironic that the operator seems to have machined the parallel, non-contact, faces visible in the photo to a respectable finish.

Ketan Swali: thanks for your kind advice. As an occasional customer, I find it very gratifying that you are prepared to take an interest.

[John McNamaraParticipant @johnmcnamara74883]

Scraping is still alive and well

**LINK**

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Only scraping can correct the microscopic movement that unpredictably happens after a machine component is milled or ground. It is particularly noticeable in large frame parts.

Also skilled scrapers can compensate for and correct sag or other stresses in a part. This is very difficult to do with CNC because each assembled machine is different and will require different compensation.

Regards
John

[egaParticipant @ega]

Graham Meek:

Thank you again – I am minded to follow your advice.

The reason I dismantled was that I wanted to provide some better means of lubricating the y-axis ways and associated leadscrew and nut. However, I recall GHT advising the removal of the Myford cross slide when necessary for cleaning. This assembly does not have the advantage of oil nipples and oilways, unlike the saddle, and I suppose this may be one occasion when dismantling is justified.

[Ian PParticipant @ianp]

Having seen the picture of the blued slide I would definitely go along with the 'leave it alone' philosophy, (I'm assuming that there was not such an excess of blue that it spread to look as if it made contact over a greater area than it really does)

Gray, your comment that slides never go back the same, is something I have found happens with everything I touch! Actually I exaggerate but there are many components that this sort of thing happens with, (ball races are one). I have ultrasonically cleaned new ballraces and put then together meticulously carefully but they rarely feel the same as an untouched bearing.

Whilst on the subject of slideways and lubrication, having the surfaces with little pits to contain lubricant is a askew with some other types of bearing surfaces that are very close fitting and have highly polished bearing surfaces. I have examined many mechanical parts of video, audio, computer equipment where it appears the rotating surface is so smooth and hard that it wont cause any wear on its opposite number.

Ian

[Clive HartlandParticipant @clivehartland94829]

When moving bearing surfaces are lubed the 'Oil wedge' effect is apparent, shafts rotate and build an oil wedge and stay lubed. I would assume it still occurs with a sliding surface like a milling table as oil is dragged backwards and forwards by the table motion. Making forced lub. conditions in a mill is maybe only to ensure the debris are forced out of the slideways. A machine that has a continually moving slide as a CNC perhaps does need this. Manual operation and occasional lub. is fine. Modern lubricants are made tah adhere to the surface and it is hard to break down that surface and in fact some are applied before assembly.

Clive

[jonathan heppelParticipant @jonathanheppel43280]

Slideway grinding leaves the telltale marks that you have in your high areas, which is purposely done to provide oil reservoirs as in flaking. I suspect you slide was milled, then it distorted due to stress and was finished on a slide grinder. The distortion was more than the grinding tolerance allowed, hence your little problem, and why the "good" finish is low.

As far as bearing surface finish is concerned, it is quite true that when the surface speed is enough to promote hydrodynamic lubrication, a "broken up finish is unnecessary. This never happens on a manual machine tool, and squeezing out the oil film and the resulting adhesion which causes stick-slip becomes an issue. This is why it is rare to see two finely ground mating surfaces; fine scraped or surface ground finishes are usually mated with the traditional slideway ground finish or a polymer bearing material, whose finish is usually broken up also because of said stick slip.

It's no big deal but there's rather too much blue there to get a good print.

Edit. looking at the print again, there isn't too much; it's just not very good contact. Would benefit from a few passes with a scraper. My mistake.

Edited By jonathan heppel on 23/02/2014 18:30:19

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