Centec 2B Mill Table—Surface Grind or Scrape?

[Graham Horne 2Participant @grahamhorne2]

I am learning to ask specific questions in threads as answers have a tendency of exploding, so to be specific, I have a Centec 2B mill, and my concern in this thread is the mill table. It’s not terrible, but not great either—there are no major dings or mill marks, which is a plus, but it has a ±0.25mm concave bend and noticeable wear in the middle of the ways.

My first thought was to get the table surface ground, but I’ve struggled to find anyone willing to take on the job near me in the midlands around Rugby. While I’d still prefer surface grinding for the table, I’m now considering scraping it flat instead. It won’t look as nice as a ground finish (I’m sure options will vary) but scraping the ways also gives the benefit of oil retention.

For those with experience, would you go for scraping in this case? Are there any pitfalls I should watch out for, or alternative approaches worth considering?

[Andrew TinsleyParticipant @andrewtinsley63637]

Not an expert at scraping, but I have never tried to scrape such a large amount of material. It would take me forever to do such a task!

How are you measuring the plus or minus 0.25mm? would it be by putting a DTI in the quill and then traversing the table underneath it?. If so, then there are other reasons you could be observing the plus or minus 0.25mm.

Other more experienced people will be able to comment.

Andrew.

[duncan webster 1Participant @duncanwebster1]

Unislide grinding in Coventry advertise doing Bridgeports. Whether they can be bothered with smaller machines requires a phone call

Tell them you’re not in a hurry and they can use it as a fill in job

[peak4Participant @peak4]

I’m absolutely no expert, having only attempted a job like this once, and without any training whatsoever.

During the first lockdown, I scraped in the table on a Herbert Junior surface grinder.
It was similarly bowed; the top surface was flat, so I scraped away any high points, so that it showed a uniform blue transfer all over from a surface plate.

The underside was bowed, with about 14 thou wear in the middle, so I effectively need to take of about 15 thou from each end. The dovetail was well worn too, so I made an angles straight edge from a length of cast iron for that job.
It was all done by hand, but did take rather a long time; a better scraper would have helped.

Essentially I flattened the top, and made the underside parallel to it within a couple of tenths.
Scraped the front edge square to the top and bottom, so I could then use that as a reference for scraping the fixed dovetail parallel to it.

The flat table then had a handle attached to either end, so I could use it as a portable surface plate to scape in the column.

Lots of photos in a Flickr album, many showing the various lashups for measuring wear.

The photos seem to show an excess of blue on the surfaces; in reality, it wasn’t as thick as it looks at the later stages.

Bill

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