# Surface Plate Restoration or Machine Base?



## vtcnc (Apr 5, 2021)

Found this little gem on Craigslist over the weekend....



















Had to part with $20 in order to bring it home!

The PO covered the top surface with a zinc coating for “long term corrosion protection”.

Question: the zinc coating is used to protect boat surfaces or docks. Can this coating/paint be removed easily? If so, any recommendations how?

Follow up: if it can’t be restored I will likely use it as a small machine base for my gear hobber project.


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## benmychree (Apr 5, 2021)

It may be just electroplated, it could likely be removed by re scraping or by using hydrochloric acid.  I wonder if it is some sort of paint?


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## MrWhoopee (Apr 5, 2021)

Assuming this is something like ZRC or other zinc rich spray paints, I'd be trying chemical stripper. It won't hurt the CI.


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## Peyton Price 17 (Apr 5, 2021)

What is the size? Looks better shape than one I have.


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## C-Bag (Apr 5, 2021)

NICE! $20...wow your really

SUCK!


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## vtcnc (Apr 5, 2021)

18” x 24” is the size.

It is some sort of zinc coating or paint. The previous owner said as much but couldn’t tell me how he applied it. I’m guessing by brush or spray can. He said people use the zinc product on boat bottoms??


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## darkzero (Apr 5, 2021)

Nice score!

At the local college thay had like 4 CI plates like that. We used them for general lapping with sandpaper. They had a big granite surface plate for inspection purposes. I'm assuming they just kept them around & repurposed them for that eventually.

A couple of them also had handles on them, just like the holes on yours. Was told that the purpose was to be able to take the plate to the part to be checked if it couldn't be brought to the plate. Advantage of the CI over granite is the lighter weight.

If I had that I would use it for the same thing, general lapping. I bought a 9x12 granite surface plate for 20 something dollars at MSC (before tarrifs) & use it for that same purpose.


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## Dabbler (Apr 5, 2021)

A muriatic acid bath, rinse, repeat as necessary.  The top will need to be refurbished, but that is one seriously nice piece of iron!!


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## vtcnc (Apr 5, 2021)

I have a lapping block already with a grid milled in the surface for charging with compound. It’s pretty sweet. I’ll take pics sometime. It is smaller but heavier than this surface plate.

I saw this on Craigslist and he had it on for $40. I literally have been really good about not spending money on things I don’t need.

Then he dropped the price to $20...and the stupid took over and started driving my brain.


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## Dabbler (Apr 5, 2021)

If were both there we'd have to fight for it!! nice score!


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## C-Bag (Apr 5, 2021)

One of those is on my long range radar...$20...I’d a been stupid at $40.


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## darkzero (Apr 5, 2021)

Dabbler said:


> If were both there we'd have to fight for it!! nice score!


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## Cadillac (Apr 5, 2021)

I bought a 3x4 CI plate similar to that acouple years back and it had some surface rust on it and some staining from a tapping machine the PO had on it. I took the blue paper towels in a roll and soak enough of them in vinegar to cover the top surface. Let it sit for acouple hours and got this. Would still loved to get it scraped back in but the surface is great no pitting just discolor from the bad spots


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## extropic (Apr 5, 2021)

Great find Bryan.

It is absolutely restorable. I would try removing the coating by spraying with Easy-Off Heavy Duty BBQ Grill Cleaner.
Rinse & repeat as required.

One issue with using CI for precision surface plates is that any ding raises an annulus. Granite may chip, but no raised annulus.
That means you have to be even more careful with CI. If you get a ding, you have to stone it. What?

Clean it up and survey it for flatness. I don't know if you have a large enough granite, but I'm hoping you have access to one. Maybe, as is, it's flat enough for your desires at this time.

If you drill holes in it to mount a Chinese arbor press (or the like), I will shed a tear.


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## vtcnc (Apr 5, 2021)

extropic said:


> Great find Bryan.
> 
> It is absolutely restorable. I would try removing the coating by spraying with Easy-Off Heavy Duty BBQ Grill Cleaner.
> Rinse & repeat as required.
> ...


Thanks for the advice. I'll try the degreaser. Ok, I PROMISE, I will not drill into this and use it as a machine base. What was I thinking?!


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## vtcnc (Apr 5, 2021)

extropic said:


> One issue with using CI for precision surface plates is that any ding raises an annulus. Granite may chip, but no raised annulus.
> That means you have to be even more careful with CI. If you get a ding, you have to stone it. What?
> 
> Clean it up and survey it for flatness. I don't know if you have a large enough granite, but I'm hoping you have access to one. Maybe, as is, it's flat enough for your desires at this time.


Stoning won't be an issue and have done this before to remove burrs and raised sections you describe. I can feel a few raised areas around some pits and dings, so it will require some love and attention.

I have my eye on a 3x4 granite surface plate. Despite being in the temperate Vermont climate, the granite will be far more stable than the cast iron.

Having both won't hurt my feelings!


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## JRaut (Apr 5, 2021)

I've got a smaller one (12 x 18 or so) that I use as a sanding plate. I use it ALL THE TIME. Cannot recommend it enough.

One or several of the YouTube dudes have done videos on the topic. I don't remember who at the moment, maybe Renzetti?

I've also got a pretty decent granite plate that I use for measuring stuff. I try not to use it as a sanding plate too, but, well, we all do from time to time.


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## Downunder Bob (Apr 5, 2021)

Nice find, you guys in the industrialised North America have so many opportunities to buy second hand stuff, it's very scarce here.


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## Ulma Doctor (Apr 6, 2021)

nice score!!!


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## Braeden P (Apr 6, 2021)

I just got a 15 by 18 ci plate used some scotch brite and some wd 40 cleaned right up the thing was sitting in a barn for 10 years my plate it has six feet not three


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## macardoso (Apr 6, 2021)

Looks like a great scraping project to me! I'd definitely not drill it.


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## Richard King 2 (Apr 6, 2021)

It looks lie it has been sitting  for a long time.  Depending on how accurate you need it.  You could leave it alone.  If I wanted more accuracy I would have it Blanchard Ground.   That would zip of any plating real fast.  before being ground I would tap the holes for handles.  Before sending it out to be ground I would also screw in an eye-bolt, hang it up and on a crane and use a dead blow hammer or 4 x 4 and hit it like a bell to vibration stress relieve it.  Parts sitting for a long time causes cast iron to set a twist.  It may or may not have set on 3 points, or sitting on 2 x 4's cockeyed.   It is a preventative thing to do.


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## vtcnc (Apr 6, 2021)

Richard King 2 said:


> It looks lie it has been sitting  for a long time.  Depending on how accurate you need it.  You could leave it alone.  If I wanted more accuracy I would have it Blanchard Ground.   That would zip of any plating real fast.  before being ground I would tap the holes for handles.  Before sending it out to be ground I would also screw in an eye-bolt, hang it up and on a crane and use a dead blow hammer or 4 x 4 and hit it like a bell to vibration stress relieve it.  Parts sitting for a long time causes cast iron to set a twist.  It may or may not have set on 3 points, or sitting on 2 x 4's cockeyed.   It is a preventative thing to do.


It has three points to rest on cast into the base. The bottom has some rust, so I would expect it to not be flat after however many years it has been neglected.

For now, my logical brain is kicking in and cursing myself for buying it. My emotional brain is happy I saved it from the scrap heap. My problem solving brain is figuring out a plan for a stand to weld up for it.


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## macardoso (Apr 6, 2021)

vtcnc said:


> It has three points to rest on cast into the base. The bottom has some rust, so I would expect it to not be flat after however many years it has been neglected.
> 
> For now, my logical brain is kicking in and cursing myself for buying it. My emotional brain is happy I saved it from the scrap heap. My problem solving brain is figuring out a plan for a stand to weld up for it.


I bet there are a few people here happy to take it off your hands


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## Dhal22 (Apr 6, 2021)

extropic said:


> Great find Bryan.
> 
> It is absolutely restorable. I would try removing the coating by spraying with Easy-Off Heavy Duty BBQ Grill Cleaner.
> Rinse & repeat as required.
> ...




Dawn power scrubber or whatever dawn used to sell is a wonderful metal cleaner.   Too bad they don't sell it anymore.


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