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Damaged Surface Plate

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Bob Korves

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#2
The damage to the plate probably does not change its accuracy. The bigger issue is perhaps value. Any used surface plate, without evidence of current calibration and careful usage, is about as valuable as any other rock in the woods. It is an unknown quantity. Furthermore, new import surface plates are not that much more expensive, aside from the shipping. Import plates are known for less than good quality control, so even a new one is subject to concern regarding accuracy. Some are very good, others are not, and we hobby machinists do not normally have the tools and skills to check them. So it is a gamble, and you never know if you have won or lost the bet. Getting someone to come and calibrate and certify a surface plate, or ship it for that work, is expensive. Buying a new USA made plate is also fairly expensive, including shipping. Bottom line and back to your original question: You could use the damaged plate for a lot of work, like general layout work, but you could never trust it to meet any standard. Using unknowns as reference surfaces is a fool's guessing game.
 

chips&more

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#3
If I’m going to spend $50 bucks on a SP that size. It better be darn nice! And not with a big chunk/corner missing. It should be FREE! With that kind of a problem, I would be concerned about the reorganization of internal stresses and change in calibration.
 

Rustrp

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#5
I would look at the shipping costs, deduct this from the $50 they are asking and make an offer, or deduct the cost of the short road trip. Otherwise I wouldn't consider it. As Bob said; There's to many if's and unknowns, but if there's an itch that needs to be scratched, post a photo of what you bought instead of the plate. :D
 

Bob Korves

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#6
If there is a company near you that sells, calibrates, and certifies surface plates, then the costs of ending up with a nice one at a decent price might decrease dramatically. You would do the delivery and pickup, or they might come to you for a decent price. I have no idea what is available in Minn. You could buy a used one and get it calibrated or buy a used and calibrated one from the same people. That is worth looking into. Uglydog http://www.hobby-machinist.com/conversations/add?to=Uglydog on this forum lives in your area and may know what is possible there.
 

ddickey

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#7
Thanks guys. Think I shall pass on that one.
 

scwhite

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#11
I had to laugh cause there's people over here that try to sell chuncks of misc granite as surface plates.
If it is a Granite surface plate it would have some
Kind of calabration tag on it . Grade A
- or AA or AAA.
On a tag with the company that makes it
Like Starrett
 

darkzero

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#12
If it is a Granite surface plate it would have some
Kind of calabration tag on it . Grade A
- or AA or AAA.
On a tag with the company that makes it
Like Starrett
Well yes if it's US made or some other reputable company. Import ones don't, the "certificate" comes separate. I got a 12x18 grade A import with ledges from Enco years ago when they used to go on sale & that's how it came. Best $25 I ever spent & shipping was free!

Oh I also have a MHC brand 9x12 grade B surface plate from MSC, came the same way.
 

darkzero

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#13
If anyone is in the Los Angeles area, there's still a 24"x18" Standridge with ledges for $100 in Chatsworth. If I had the room I would have snatched it up when I first saw it.
 

scwhite

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#14
Well yes if it's US made or some other reputable company. Import ones don't, the "certificate" comes separate. I got a 12x18 grade A import with ledges from Enco years ago when they used to go on sale & that's how it came. Best $25 I ever spent & shipping was free!

Oh I also have a MHC brand 9x12 grade B surface plate from MSC, came the same way.
Mine is cast iron it has the manufacturers tag on it
The grade is left blank . I doubt if it is very close
Might be .001 - .002
 

Bob Korves

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#16
If it is a Granite surface plate it would have some
Kind of calabration tag on it . Grade A
- or AA or AAA.
On a tag with the company that makes it
Like Starrett
There is also grade B which is typically used on the shop floor unless you are at an aerospace, semiconductor or other high end company. Grade B is good enough for most work. No certification and calibration to a standards bureau means that somebody is guessing or pencil whipping. If someone is not willing to stake his reputation on his work, then what do you think, or rather know, you have?
 

Bob Korves

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#19
Yea I know the grade B is a lot closer that my cast iron
My cast iron plate is not even graded .
I expect it might be .001 which is not very close
But it is cast iron & not Granite
I have a 8x16" cast iron surface plate that I have scraped in. It is pretty accurate, and was spotted in to my AA tolerance, recently certified granite surface plate. If you have an accurate reference surface, it opens up lots more things you can do accurately and with confidence.
 

scwhite

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#20
I have a 8x16" cast iron surface plate that I have scraped in. It is pretty accurate, and was spotted in to my AA tolerance, recently certified granite surface plate. If you have an accurate reference surface, it opens up lots more things you can do accurately and with confidence.
I agree
I got my cast iron free . I can't complain about that .
 
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darkzero

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#22
The 9x12 grade B surface plate I bought a couple of months ago was $33 from MSC. They have 12x18 grade be for $66. Not sure how much shipping costs but if you have an enco merged account shipping is free over $50.
 

Charles Spencer

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#23
Mine is cast iron it has the manufacturers tag on it
The grade is left blank . I doubt if it is very close
Might be .001 - .002
At the shop where I worked in the 1970s we all had cast iron surface plates at our benches. There was one granite plate that could be used if needed. I don't recall ever needing it.

Of course we also had a large Blanchard grinder with a dedicated operator. Periodically they would inspect the cast iron plates and regrind where necessary.

Nowadays I have a pretty good Stanbridge plate. I keep it covered unless I need it. Most of the time I use a 6" piece of iron that I milled, faced, and lightly sanded. It is close enough and large enough for most layout work I do. It fits easily in my benchwork area and I just flip it over to protect the surface when not in use.
 
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