Grinding surfaces

[Stephen FollowsParticipant @stephenfollows82099]

Can anyone. Recommend the best type of stone for grinding machined surfaces true? I need to true my milling table.

[Stephen FollowsParticipant @stephenfollows82099]

[Nigel Graham 2Participant @nigelgraham2]

I would be very wary of using any abrasive on it. No matter how careful you are it would be extremely difficult to avoid particles finding their sneaky way into the wrong places.

Also, even if you do grind your mill table, how do you guarantee it actually being true afterwards?

By "truing" it though, in what respect?

[Stephen FollowsParticipant @stephenfollows82099]

I had a water leak in my shop which went unnoticed for a few days. The table rusted. Cleaned the rust but some very minor pitting. Watched videos where people finished surfaces with a stone but don’t know what stone. Looked very like oil stone used for sharpening.

[Bill PhinnParticipant @billphinn90025]

Posted by Stephen Follows on 02/11/2022 20:44:43:

stone for grinding machined surfaces true? I need to true my milling table.

Posted by Stephen Follows on 02/11/2022 21:54:28:

The table rusted. Cleaned the rust but some very minor pitting. Watched videos where people finished surfaces with a stone but don’t know what stone.

Grinding your milling table true and just stoning it are very different things, Stephen.

After cleaning the worst of the rust off have you run your bare hand over it to confirm that there are any real protrusions on it? Pitting won't matter unless there is rust standing up around the outside of the pits.

[HopperParticipant @hopper]

Posted by Stephen Follows on 02/11/2022 21:54:28:

I had a water leak in my shop which went unnoticed for a few days. The table rusted. Cleaned the rust but some very minor pitting. Watched videos where people finished surfaces with a stone but don’t know what stone. Looked very like oil stone used for sharpening.

If you are talking about stoning, not grinding (which is a powered operation with a revolving grinding stone), then yes an oilstone used to sharpen knives will do the job. Or you can use other similar smaller stones known commonly as rubbing stones. Best to use a fine grade. You want to use it conservatively though as overuse could wear a low spot on your table. Usually stoning is done to remove burrs sticking upwards, such as if something has hit the table and raised a burr etc. It can be used to lightly remove surface rust sitting on top of the table.

But it will not remove pitting. To get down to the level of the bottom of the pit, you would have to remove all the surrounding metal down to that level, which would do more damage to your table surface than the original pit.

[David George 1Participant @davidgeorge1]

If you want the table actually ground it would need to be done by a company which needs to know what they are doing, on a grinder which is suitable to do the job, and large enough to cover the area which needs grinding in one pass accurately. I use an India double sided stone, similar used to sharpen chisels, run over my beds etc to check for any damage ie damage caused by dropped item or swarf trapped under a clamped jig of vice etc but using oil and the fine side only.

David

[Howard LewisParticipant @howardlewis46836]

If the pitting is only minor, it will be unsightly, but not affect the accuracy of items clamped to the table

(A pit 0.25" across is not going to misalign something like a milling vice. As long as it is a pit and protruding above the general surface ).

To clean up the table, just wrap some fine emery around a block of wood or steel and use it to polish the table until any it cleans up. Hopefully, you will not be removing even 0.00001", just removing any rust that stands above the surface, and then just lightly polishing. But, as Hopper says, polish all over; do not concentrate in one small area and produce a low spot.

An Apprentice who left his his tea cup, on a Surface table staining it was given this this task to remove the marks. Obviously this is for surface staining, if the are of pitting is large,and deep, you have to think min terms of milling or grinding to make the surface pristine again. This is not really a practicable process for the average home machinist, either in terms of equipment or skills, and will require the table to removed and taken to a professional machine shop.

Howard

Edited By Howard Lewis on 03/11/2022 06:31:10

[Martin KyteParticipant @martinkyte99762]

For getting rid of bumps and you don't need to worry about pitting you could do worse than invest in a diamond whetstone which are very flat (at least the 3M ones are). They are usefull for flattening other types of stone and they will not embed in the surface.

regards Martin

[Robert Atkinson 2Participant @robertatkinson2]

There is a school of thought that you should use "precision" ground stones for this task. See:

https://www.model-engineer.co.uk/forums/postings.asp?th=177218

I'm not advocating one way or the other, just pointing to the discussion….

Robert.

[Martin Johnson 1Participant @martinjohnson1]

For taking out the odd dents and dings, a rub over with one of these does the trick

https://www.ebay.co.uk/itm/323972427605?hash=item4b6e42ef55:g:8hkAAOSwNxNhEfvz&amdata=enc%3AAQAHAAAA4K2azx4zpPGpjWlmYLsOtkbfqj1XNPcmX48H52k2RwIHBSX9NlYkNG1EeNNk4dsNmmuK9BlMXkm06jNm7J9phXZCDuApV5fRP6zwygFowqwbDJu%2BsfPp3WfzIpud0AVtnLuhwQ3Z5sVsXtA5keRJoAyzefRDNjRI%2FT3cpBNWlzJ5jtjXBp6iQXUjCGONdhLaPPgdnuBJNUPCoirxcNGazGI%2BywbiWxb9h825hSBVhK0NtxXOqgSQcI91qyceWPDpz4MADHGHIG%2For6D4pgjpqaZ2JPvxxdtvbmF5GprYMA%2Bz%7Ctkp%3ABk9SR5qHktmHYQ

If you dont go mad it will take you millenia to put the machine out of true.

Martin

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Stephen Follows on 02/11/2022 21:54:28:

I had a water leak in my shop which went unnoticed for a few days. The table rusted. Cleaned the rust but some very minor pitting. Watched videos where people finished surfaces with a stone but don’t know what stone. Looked very like oil stone used for sharpening.

.

Here’s a similar, but rougher, job in progress

.

The base of this bench drill was not only rusty but significantly bumpy [having originally been finished with a linisher], so I set-about-it with a suitably large flat stone.

As you can see …There is a way to go yet !

MichaelG.

[colin hawesParticipant @colinhawes85982]

I use a flat oilstone 25x80mm with white spirit or paraffin to clean recently rusty marks. Colin

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