View Full Version : Stoning grit size

05-28-2016, 04:33 AM
My mill table and tools have some dimples and burrs I want to get rid of, so I bought a set of stones in diferent grit sizes. They start in 80 up to 1000. What grit size do you usually use/recomend to clean your tools?

I have been using 150 for biggest dimples and 240 for the general work. I have my stones soaked in gasoil to keep them wet and avoid clogging them.

05-28-2016, 06:28 AM
Sounds ok, the slip stones I have are Gershwin the finest is about 400 ish, mostly I grab somthing about 180, think that's a blue one for de lumping, handy things it must be said,

05-28-2016, 07:42 AM
That's about the same grits I use on the very rare occasion when I bump something hard enough to cause a divot. LOL!
However, what's gasoil!
Gas with oil in it? Like for a 2 stroke motor?

05-28-2016, 09:34 AM
I use medium India oilstones, or soft Arkansas in the shop.

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05-28-2016, 09:57 AM
what are you guys doing to your tables?

it would be good to add to your arsenal a scraping file. For the unfamiliar its a piece of file , 4" inches or so, where you've stone off the sharp ends of the teeth. It just skids across a flat surfaces but catches and removes protrusions. After that a hard Arkansas stone - they remove very slowly so are safe. If you've a lot of large bruises, use coarser stones, but with a lot caution. Shiny smooth tables that aren't flat are the booby prize.

Also, if you have a real mess to deal with, consider getting a hockey puck stone - google Norton machine knife stone. These are large round stones great for this task....what makes them different is they're a little wider surface area so you're sampling and knocking of material over a broader area and the groove makes them easy to hold on to. In a business, a machine is consumable over the long haul so it make sense run one of these over the table periodically to ensure good parts. Stuff happens and less than perfect machines follow us home, but in general, at home I more want to keep things pristine so would be gentle with the table which should considered a precision surface so heavy remediation isn't needed

05-28-2016, 10:07 AM
Clean up the table the minimum amount necessary. Add wooden table covers on both sides of the vice to prevent future damage and create a place to safely rest tools and parts.

J Harp
05-28-2016, 11:32 AM
My Google search didn't find it, but I seem to remember seeing ads' for Gasoil in Popular Mechanics or some such magazine. The ad showed a fellow holding up a small can, about pint size, I think the can came with a spout.

I never used the product, but I think it was a penetrating lubricant.

Forrest Addy
05-28-2016, 11:33 AM
Dimples? That suggests a small abrupt defect below the net surface of the table like a hammer peck, a drill start, or an impacted chip depression.

Ideally a machine table is a reference plane. A work plane set on it is referenced to the table and saddle axis plane. Any raised metal on the table (bruises, burrs, scratches, etc) has to be reduced/restored to the table surface if it is to continue as an accurate reference surface

Usually there is some raised metal surrounding compression defects (hammer pecks, bruises from dropped items, chips or grit crushed under clamped articles.) The metal flows laterally from the depression to form what might be called a crater with a raised rim. Yes, flow. Even cast iron will flow a bit.

The raised rim of the crater holds work set on it above the table plane and important trifle. The raised portion of the defect has to be removed by stoning or filing to the plane of the table but no further. The appearance of the defect will look something like the bull's eye of a target. In the center the residual pit. Surrounding the pit (or scratch,) the glossy finish where the stoned or filed raised material was removed. This has a vague margin where it blends into the table surface. A sensitive dial indicator on a surface gage scanned over the surface will register zero setting as it passes over the stoned defect, then "falls off a cliff" at its abrupt intersection with the residual pit. An inadequately stoned defect will still have raised metal and the dial test indicator will find it. If the defect was over-dressed the dial test indicator will show a depression below the table surface. Localized depressions - products of over-dressing - in the table are very bad. Work clamped over them may be deflected even deformed.

Table dressing is a delicate art. A machine tool used properly has a finite life that must be prolonged by proper maintenance and care in operation. A stone glided by the fingertips over a clean table is a sensitive raised metal detector. No wear will result, not ever minute scratches when the stone is in "glide mode." The stone will catch on raised metal. This is both felt and heard by the canny operator. A few strokes (just enough - no more) will remove the raised metal to restore the table to a reference plane. The pit is left as a reminder to be careful next time.

Resist the temptation to stone the pit or defect to oblivion. Excessive dressing may result in a depression a few thousandths deep and inches wide. How may depressions may be tolerated in a machine table before its no longer useful as a reference surface?

A machine table is not fine furniture where scratches and defects are blemishes to irritate a fastidious owner. A machine tool table is a working surface sure to collect small defects and wear with proper use over time. These defects may be considered honorable battle scars. A machine table does not have to be shiny and pristine to fulfill its function but it does have to be a plane parallel to the table and saddle axis.

My preferred table dressing stone is a triangle slip stone 3/4" on a side about 4" long (broken in line of duty). This I deliberately dulled on a coarse diamond bench stone. I Like the triangle shape because its easily manipulated and glided over the surface by my fingertips. It detects every little catch and burr and erases them with a little focused work. Being dull it has little tendency to over-dress.

A new sharp stone can be very aggressive so be careful as you break them in. Dull them by 180 grit (wet or dry) abrasive sheet lapping. Sharpen them with a light media blasting using sharp coarse grit at low (15 PSI) pressure.

"So, Grasshopper," said the benevolent old Shaolin machinist, "Preserve the plane. Glide gently, do not scrub intently."

05-28-2016, 11:40 AM
Yeah that's the point, getting off the raised material around small impacts.

Thanks guys! I just was a bit concerned about using too big grit on it.

Gasoil is diesel fuel here, not sure how you call it in English speaking countries!

05-28-2016, 12:25 PM
where's here? Most of us trying and put location in out profile, its helpful to know where people are from, especially as sources and nomenclature are often localized

05-28-2016, 12:32 PM
Gasoil is diesel fuel here, not sure how you call it in English speaking countries!

Diesel fuel is called Diesel fuel or Diesel in English speaking countries.:)

05-28-2016, 02:06 PM
Mcgyver you're right, already put Cervantes land in the location.

05-28-2016, 03:42 PM
The odd time I've had to do this I always used a fine cut file used in small short strokes concentrated on the bump and resting with minimal pressure on the flat area round the bump. And I stop when the file starts to cut into the surrounding flat area by more than a kiss.

As mentioned by someone above you don't really want to abrade the table other than at the high spots. And it makes sense that we'd want to deal with the problem but in a way that doesn't affect the area around it. And a hand stone would make focusing the pressure on these high spots while not rubbing on the good areas rather tough to do.

Another option which I read about a while back but have not used yet is to use a small to mid weight hammer to knock such burrs back down into the table before removing any residual high spot with a file or scraper.

05-28-2016, 11:08 PM
Visited a machine shop several years ago that was doing some repair on one of our machines. The owner was preparing his Blanchard for a tight tolerance job. He was using a 6 inch diameter grinding wheel with the label/blotter removed and the corners rounded over. Said he had been using it for years to check for bumps from dings.

05-28-2016, 11:34 PM
Just because an "old timer" uses such a trick doesn't make it a good idea. Bubba has been around for centuries.

At best if he uses it in a proper manner that sweeps the whole area of the table evenly it would do no harm. But what are the odds that he's using it that way?

05-29-2016, 10:52 AM
Just because an "old timer" uses such a trick doesn't make it a good idea. Bubba has been around for centuries.

amen to that. I don't need no highfalutin' learnin', me pappy did it so i do it :D

05-31-2016, 03:45 AM
I was waiting to see if any one mentioned that hand-scraped surfaces address this very subject.

Forrest, as always - addressed the subject very well.

I just clean down my table/surface and then when clean rub my open hand over it. It will soon tell what the"dings" are and where they are. "Cotton wool" works very well in finding them too.

I usually use a good flat "emery" stone - about 8" long x 2" wide by 1" thick/high - same as many wood-workers do to "finish" their "sharpening/dressing" of plane blades and chisels etc.

I use "sewing machine" grade oil and soak the stone in it and then "break the stone in" to knock off all the bumps, high spots and "snots" off the stone and its ready to go.

The stone surfaces can be re-covered/restored on a surface grinder if needs be. When the stone is no further fit for purpose it gets "binned".

Their cost (for a stone that is "good enough") is very cheap by any measure - and once it had reached its "limit" - out it goes.

"Stoning" milled and ground surfaces can improve them considerably as regards "looks", "surface finish" and in may cases "accuracy" too.

"Wet and dry" ('emery") paper used "wet" works pretty well too.

I often use a small/medium a ball-pein hammer (both ends) to knock some of the larger "stand-outs" back to where they came from if bad enough then back to previous.

It is no "big deal" at all as it is just a normal part of "shop maintenance" which requires very little time, effort, or money to get a very good and serviceable restoration result.