Surface Plate Resurfacing

[durableoreo]

This.

Without a climate controlled room (no, your air conditioned spare room or basement does not cut it) and expert level practices much of this is academic.

Scrape it to within whatever measurement you like and you will distort it while taking your reading or doing your setup by resting your wrist on the edge.

This is why granite is a thing, but even then your body heat is affecting every tool you touch.

The above mentioned dished surface plate we use at work is in an uncontrolled room right under a HVAC vent and we somehow get by.

No need to go crazy with the temperature talk. You can measure 10ths reliably in most circumstances.

Granite is "a thing" because it is durable and brittle. It does not form burrs. In the war, they sometimes used glass. Glass is about as hard as steel, so they didn't last very well.

I don't think I could live with 0.002 systematic error. I had a cheap grade B plate and it was hard to get reliable readings for even basic stuff, like scraping a part flat and parallel within a tenth. So I picked up a much bigger grade A plate. Obviously this is not a reasonable solution for everyone but a reliable flat surface Is a great asset in the shop

You can investigate the status of the plate with a 4-footed gage, a level, an indicator set up for "repeat" readings

Surface grinding would be a good solution but you'll need to scrape some texture into it if you want to use it as a surface plate.

 

[dwall174]

You can measure 10ths reliably in most circumstances.

I don't even own an indicator that can read 10ths.

I don't think I could live with 0.002 systematic error.

Yeah, maybe if I had a milling machine, I would be more inclined to get a better surface plate.
However, for my needs laying out hole locations for brackets & simple fixtures, 0.002" over 24" is more than adequate.

 

[extropic]

Can folks supply specific recommendations for "precision ground stone(s)"?

I have a mill table with a ding in it as well as a cast iron flat plate.

Use the search function in H-M and eBay for plenty of info and sources.

Search "precision ground stones".

 

[SouthernChap]

Mine has the 3 mounting bosses, I just got finished cleaning it up & repainted the base.
View attachment 500998
I didn't get any pictures of the top after cleaning it up, but it came out pretty good.
I don't have a really good precision straight edge, but I do have a 24" ruler for my Starrett combination square. Using the ruler & some feeler gauges, I had a hard time getting a 0.002" gauge under the ruler. Way better than I expected & good enough for the type of work I'll be laying out with it.

I'm also going to be making a new stand for the plate since the one that came with it is not that square, plus those big wheels are way overkill for this surface plate & they're not locking swivels.
View attachment 501003

I guess you'd need a straight edge as long as the longest dimension.

I have a set of oldish Moore and Wright straight edges but the longest is only 6".

This is where people with surface grinders have an advantage; they can just make their own straight edges.

I'd love to have the space for a surface grinder but I'd struggle to fit even the smaller 'benchtop' models.

 

[MensaPE]

Could maybe use precision ground flat stones, to just knock rust/peaks off the high spots, very light pressure to prevent wearing a hole in it.

 

[SouthernChap]

Here in the UK, we're stuck with the 3 stone method. Precision flat stones are simply not available here unless one orders from the US and takes the shipping and import tax hit.

Stefan Gotteswinter used to supply to the UK but since Brexit...

 

[RaisedByWolves]

My point is that he bought a "used" item and , unless he bought it from you, neither of us have any idea of how it was cared for.
That's why I suggested he "search out" any high spots. Your apparent assumption that his purchase is in pristine condition seems overoptimistic to me.

Filling voids . . .

I have no idea what you’re on about.

I made no assumptions whatsoever.

 

[durableoreo]

for my needs laying out hole locations for brackets & simple fixtures, 0.002" over 24" is more than adequate.

Good point. Tenths would be excessive for that type of work.

 

[durableoreo]

Here in the UK, we're stuck with the 3 stone method. Precision flat stones are simply not available here unless one orders from the US and takes the shipping and import tax hit.

Stefan Gotteswinter used to supply to the UK but since Brexit...

Just to be clear, precision ground flat stones are ground flat with a diamond wheel. The cutting action is from the spaces between the abrasive particles. Sharing instead of scratching. So you can't make them with the 3-plate method. A harder abrasive must cut the jagged protrusions of the stone. They are expensive but really useful.

 

[SouthernChap]

So you can't make them with the 3-plate method.

Fair point but precision ground stones are unavailable in the UK. What do you suggest?