# Tools and Surface Plate Questions



## Splat (Mar 22, 2019)

So I'm starting to do more projects now that require more accurate measuring than I've been doing. I don't do many big >12" parts so I'm considering a 12x18 size plate. I can pick up locally a grade-B  Standridge surface plate via McMaster Carr (love that place!). I know I can get much cheaper via Woodcraft or MSC but shipping is killer or the quality might be/is  suspect. From what I've read most home shops are using the 12x18 so I think I'd be ok with that size. Any opinions on the size? How are you guys supporting your plate?

As far as measuring I now have:  good 123 and few angle blocks, good set of parallels, good hole gauges,  good analog and a decent digital micrometers. Should I get a height gauge, combo square set, or something else? I'm leaning towards a height gauge but but figured I'd ask you guys. If height gage what type? Vernier, dial, etc? Thank you.


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## f350ca (Mar 22, 2019)

A height gauge is necessary, but I use a surface gage more. Gets used a lot setting up parts in the mill as well. Its a deep hole once you start buying tools. 







Greg


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## JimDawson (Mar 22, 2019)

I personally prefer vernier height gauges, pretty much bullet proof.  A dial is OK, but I wouldn't have a digital as my only height gauge, and I do own a cheap one, guaranteed that the battery will be dead just when you need it.


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## mmcmdl (Mar 22, 2019)

Height gage will measure and scribe lines . Surface gage has many uses . You'll use them all . I'm getting ready to unload a lot of both .


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## benmychree (Mar 22, 2019)

I have both a vernier height gage (12" Starrett with 50 division vernier) and a few sizes of surface gage.  The surface gage is good for rough layout work and many other jobs, if used on the surface plate for layout, a rule holder that clamps your rule vertically is handy; also I would not be without a combination square set, and don't settle for cheap crap, buy a (very) good name brand; I found two sets at an estate sale, both unused B&S from the 1940s, one resides in my wood shop, the other in the machine shop.
Bottom line, I mostly use the height gage for any and all layout work.


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## darkzero (Mar 22, 2019)

I have a import 18x12 grade a granite w/ ledges that I got when enco was selling them for dirt cheap with free shipping. I get by with it but I really wish I had a bigger one. I also have a 12x9 that I picked up from my local MSC when they were cheap but I only use it for lapping. Perfect size for standard sheets of sandpaper.

I agree, I prefer vernier height gauges too but I use a 6" M-DRO/SRA digital most of the time. I like my 12" Mitutoyo vernier, it's in nice condition & it always goes back into the wood case when not in use. But most of the time it's too cumbersome to use. So I bought the 6" digital to use for laying out lines. Compact, much easier & quicker to use. I just leave it out. Yeah it's Chinese so it likes to eat up batteries but I still like it.

I don't work on big stuff & I easily run out of room with a 18x12. I'd say if you're able to, get at least 24x18 (or bigger) but that's about the size where the price jumps (from what I remember). Size of the plate doesn't dictate what size parts you can measure, remember you need space for the measuring tools to sweep the part, etc. 

That reminds me, I need a smaller surface gauge too, my Starrett surface gauge is kinda of too big. Well I guess it really means that I need a bigger surface plate (wish I had the room).


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## mikey (Mar 23, 2019)

I have a 18 x 12 and it is good enough since my work tends to be on the smaller side. I also have a little 8 X 12 Starrett toolmaker's flat for layout work. Depending on what you need to do, I would suggest you consider:

A height gauge - if you want a good one, look for a dual column Mitutoyo. Very rigid, heavy and accurate in the thousandths. My most used one is a little 6" Starrett dial height gauge - light, fast, accurate and easy to use. If you can, buy a carbide scribe for your height gauge; they last forever. Most height gauges can hold an indicator with the right attachment.
Surface gauge - get a big, heavy one and maybe a small one for basic layout work. These also hold an indicator for assessing flatness, just like the height gauges do. If you plan to do layout work with a surface gauge, buy a rule holder as this will save you time; Starrett makes a nice one or you can make your own.
Cylinder square - useful for checking if a square is actually square. I want a 6" high cylinder square but don't own one yet. I have a little 3" Murkens magnetic cylinder square that is perfect for evaluating how square a vise or angle plate is; very useful.
Make a box or at least a lid to cover your surface plate when it isn't in use. If you don't cover it then you'll sit something on top of it and nothing should touch the surface except for your measuring tools.
Here is some info from Starrett on supporting your plate: 



* How should my surface plate be supported? Does it need to be level?*

 *A)* A surface plate should be supported at 3 points, ideally located 20% of the length in from the ends of the plate.  Two supports should be located 20% of the width in from the long sides, and the remaining support should be centered. Only 3 points can rest solidly on anything but a precision surface.                             
The plate should be supported at these points during production, and it should be supported only at these three points while in use. Attempting to support the plate at more than three points will cause the plate to receive its support from various combinations of three points, which will not be the same 3 points on which it was supported during production. This will introduce errors as the plate deflects to conform to the new support arrangement. All Tru-Stone steel stands have support beams designed to line up with the proper support points.

If the plate is properly supported, precise leveling is only necessary if your application calls for it. Leveling is not necessary to maintain the accuracy of a properly supported plate.


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## hanermo2 (Mar 23, 2019)

I feel that the quality of the surface plate is immaterial for those using scribing etc. as their main marking out technique.

Airy points are also immaterial until one gets into volumetric single microns.
Aka x by y by z measurements for some datum in 3d space.

S:
Look at suburban tool videos on cylindrical squares and lapping.

A gage block set / stack can give a very good 1 micron (2 micron) length.
So will any medium-good import micrometer set.


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## Moderatemixed (Mar 23, 2019)

Initially I bought a 12 x 18 surface plate from Lee Valley Tools here in Canada. It was great, but I found it to be too small. I could measure or lay out most of the time but was putti g my height gage or surface gage onto the bench, which meant wiping the bottoms of each over and over. While it may seem trivial, after a while it just becomes aggravating. I purchased a second 18x12 plate (a Starrett) on Kijiji, Canada’s version of Craigs List for $100 and put them side by side which was ok, but not ideal. To my point then...... I ended up with a 24 x 36 x 4 Starrett, toolroom grade plate and I LOVE it. My wife sewed a vinyl cover for it and not once have I remarked that I wished it was smaller. My shop is 11 x 10 and that plate takes up a bunch if realestate, but it is worth every inch to have it. It cost me $250. I sold both 12 x 18’s; the Lee Valley one for $50 (lost $10) and the Starrett one for $150. Get a good plate and buy the largest one you can afford/have space for. And be patient, one will crop up. I only wish that there were people in Canada who could do the calibration/resurfacing like there are in the States. My plate is good, but I’f like it calibrated and cannot find anyone in Ontario to do so. As for height gages, Starrett or Mitutoyo digital all the way. Verniers are great, if you can figure out how to read them...... 

Cheers all. 


Sent from my iPhone using Tapatalk


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## francist (Mar 23, 2019)

Moderatemixed said:


> Initially I bought a 12 x 18 surface plate from Lee Valley Tools



Do you mean the 9 X 12 from Lee Valley? I don't remember them ever selling a larger 18 X 12, but if they did I should have bought it. The 9 x12 is a nice surface indeed a bit tight for anything bigger than a few inches square.

-frank


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## Bob Korves (Mar 23, 2019)

If you buy a used surface plate, you have an unknown.  You are not likely to be able to check it with any reliability by yourself in your home shop.  Buying a used plate by brand name and paying more for it is about the silliest thing I can imagine.  They are all chunks of rock that look visually flat.  I bought my 18x24x4", 2 ledge for $50 off a rack behind a machine shop, covered with junk and grime.  I "guessed" it was in pretty good shape by chasing various indicator setups and straightedges around it and scratching my head.  A group of local hobby machinists brought their plates to my shop and Standridge granite dropped by to calibrate the 5 plates.  Mine ended up costing ~$103 to be calibrated to AA grade and certified to A grade.  It turned out to have a .003" "hole" in the center.  To be used for precision work, guessing will not do.  A friend bought a very nice pristine looking 24x36" Starrett pink plate for a pretty high price, and it turned out to have a .005" hole in it, and had to be taken 400+ miles to Standridge's facility in SoCal to get it calibrated, they will not remove that much in the field.  IF THE PLATE HAS NOT BEEN IN YOUR POSSESSION AND UNDER YOUR CONTROL SINCE IT HAS LAST BEEN CALIBRATED, IT IS NOT A SURFACE PLATE, IT IS "AN UNKNOWN KINDA' FLAT LOOKING ROCK."  No exceptions.  The idea of a surface plate is it being a _known_ flat plane reference surface in your shop.  If it is not a known quantity, it is worthless for that job.  If you want to use it only for simple layout work or for lapping non critical parts, stacking parts and tools on, eating your lunch, a tombstone, or some other non precision use, then go for it.  Just don't hope that it is something it is not.


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## Moderatemixed (Mar 23, 2019)

francist said:


> Do you mean the 9 X 12 from Lee Valley? I don't remember them ever selling a larger 18 X 12, but if they did I should have bought it. The 9 x12 is a nice surface indeed a bit tight for anything bigger than a few inches square.
> 
> -frank



Yes, sorry. It was some time ago. The plate was very good however. 


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## Moderatemixed (Mar 23, 2019)

Bob is extremely knowledgeable and operates to a tolerance much higher than I. While I don’t have the entire chain of custody clearly mapped for my Starrett 24 x 36, my point was to say, buy the biggest that you can afford (cost and space limiting). Further that for the hobby Machinist, most surface plates, morsels of granite from counter top shops or even plate glass will suffice. If you are building the space shuttle replacement along side Bob then finding a hole .003 deep could be a problem..... I on the other hand am ok with that as a tolerance. All with a grain of salt.... 


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## Meta Key (Mar 23, 2019)

Splat said:


> so I'm considering a 12x18 size plate. I can pick up locally a grade-B  Standridge surface plate via McMaster Carr



I use a 12 x 18 pink surface plate (Starrett) and I've been frustrated only a few times in 20 or so years of use. It fits nicely on a Kennedy roll around that is dedicated to the job. I got it with the factory offered cover and also have an additional layer of padding under the cover.



The height gage is a Swiss Etalon of about the same vintage. It's 18" high and I've appreciated the height a few times. The surface gage on the left is a Starrett and the stubby one on the right is shop made.

The most important tools in the drawers are two nice sets of Jo Blocks which I use A LOT. Also, various other measuring and layout tools as you would expect.

(And, for you guys in Hawaii, that's two feet of snow outside the window...)

MetaKey


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## Bob Korves (Mar 23, 2019)

Moderatemixed said:


> Bob is extremely knowledgeable and operates to a tolerance much higher than I. While I don’t have the entire chain of custody clearly mapped for my Starrett 24 x 36, my point was to say, buy the biggest that you can afford (cost and space limiting). Further that for the hobby Machinist, most surface plates, morsels of granite from counter top shops or even plate glass will suffice. If you are building the space shuttle replacement along side Bob then finding a hole .003 deep could be a problem..... I on the other hand am ok with that as a tolerance. All with a grain of salt....
> 
> 
> Sent from my iPad using Tapatalk


My post was directed to all those reading this thread who might be considering purchasing a surface plate, Moderatedmixed, not directed toward you personally or your posts here at all.  I have seen many here and elsewhere who seem to have incorrect (in my mind) ideas about purchasing used surface plates.  When buying one used, we have no idea how it might have been used or cared for.  That was (and is) my message.  I am just another hobby machinist who cares to understand what I think I know, what I don't know, and how it affects my results.  I do the best I can with what I have, as do we all.  Much of the work in my shop is pretty crude.


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## mikey (Mar 23, 2019)

Meta Key said:


> (And, for you guys in Hawaii, that's two feet of snow outside the window...)



Yeah, I noticed that right away! Alas, it's 79 degrees here and not a snow flake in sight ...

Nice set up you have there, by the way. I'll have to look for a dual column Etalon - never knew they made them!


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## Larry42 (Mar 23, 2019)

I bought an 18x24 grade B from Shars with their steel stand. The stand supports the rock in three places. I don't work on large parts but I wouldn't get a smaller plate. I have no way of checking the trueness of the plate other than my gage blocks and dial test indicator, and moving about the surface plate I haven't been able to detect any variations. This is of course a very limited method because it is only comparing areas that are relatively close to each other. I also have a, less than ideal, import, dial ht. gage. Used for "close enough" ht. measurements and scribing layout lines. The two have very different uses so I would guess both are needed by most people.


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## Dabbler (Mar 23, 2019)

I have an 18X24 Mit AA grade plate, and it seems perfect size for all the work I do, and some of it gets near to being too big, but so far, it has sufficed. I do know of a shop I can work at that has a Mit A grade 36X48 I can use for the really big stuff.


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## Cadillac (Mar 24, 2019)

I have a 18x24 and it gets tight on some things. Blueing up parts eats up space quick. Then swinging gauges aroundfeels like I’m always on the edges of the plate. I’d go for the biggest you can afford. Shipping is a killer thankfully Im close enough to pickup than deliver. I use 12x18 cast iron ones for simple scribe and layout work near the machines, auction purchases.


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## KMoffett (Mar 24, 2019)

For something as heavy as a surface plate, check with McMaster-Carr on shipping cost before you order.  I got stuck with a $69 freight charge on a 1"x10' $7 PVC pipe from them because it was over 8 feet. Anything that exceeds FEDEX or UPS "limits" goes "$$$ freight $$$". 

Ken


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## Moderatemixed (Mar 24, 2019)

Bob Korves said:


> My post was directed to all those reading this thread who might be considering purchasing a surface plate, Moderatedmixed, not directed toward you personally or your posts here at all. I have seen many here and elsewhere who seem to have incorrect (in my mind) ideas about purchasing used surface plates. When buying one used, we have no idea how it might have been used or cared for. That was (and is) my message. I am just another hobby machinist who cares to understand what I think I know, what I don't know, and how it affects my results. I do the best I can with what I have, as do we all. Much of the work in my shop is pretty crude.



Hey Bob, no disrespect intended. I thought I had made that clear. You are far more advanced than most and see things from a different perspective. That’s what makes these forums great; collaboration. In my line of work we call it “Crew Resource Management” or CRM for short. I was just clarifying my points as they were more from a Kindergarten perspective than yourself at the College level, figuratively speaking. Regards all. 


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## eeler1 (Mar 24, 2019)

Tom Lipton recommended getting a small plate cheap from Shars and doing all the abrasive work on it, saving your bigger, more accurate plate for precision work.  I think my 9x12 Shars cost $35 with shipping at $45, or thereabouts.  It’s reserved for abrasive and small non-critical work.  

Agree with Bob that used stones, unless recently calibrated and certified, are a bit of a crapshoot.  I think the point was to not pay too much for used unless you can verify it’s flat.  Get it cheap enough and you can afford to have it calibrated if you decide you need to.


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## Toolmaker51 (Mar 26, 2019)

It's not mentioned descriptively, but used surface plates abound. In more accurate environments they are resurfaced on a regular basis. I've never seen a used plate for sale that was hopeless, depending on next owners commitment. 
Check with a local machine shop that gets their plate re-certs on a predictable schedule; have your plate there to save a service call charge. Reimburse them or arrange with the plate inspector and pay him direct. Done this many times over the years; they pocket a little cash for themselves. Your 12 or 18 x won't take them an hour.
When you run across a plate deal use a good straight edge, a bright flash light and feeler gauges. Check across corners and a grid divided by thirds or so. Put equal shims under ends of straight edge and start with feelers .001 or .0005 under size of those at end. 
Buy it, use it and wait for an opportunity to have it checked. It will withstand your individual private use decades.


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## petertha (Apr 11, 2019)

re Lee Valley, not bashing them because they offer some nice (woodworking) tools via their own Veritas line plus some other name brands. But they also have a increasing proliferation of Chinesium. Again, nothing wrong with that but I would suspect theirs isn't appreciably different than Busy Bee or similar vendors. For $54 (and that's deflated Canuck bucks) seems like decent value. Just not sure I would rely on all those decimal places LOL. I'm not even sure how Joe Hobbyist could verify it independently. One of the issues I'm noticing is shipping weight. There are some comparable offshore offerings through tool catalogs like KBC & Travers, but as they get larger footprint they also get thicker which means more weight. So sometimes what you are able to pick up locally counts for something too.

http://www.leevalley.com/US/wood/page.aspx?cat=1,43513,51657&p=32526


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## Dabbler (Apr 11, 2019)

I have both BB and a Lee Valley surface plates, and they seem ground to very acceptable precision.  I needed a little larger for the work I do, hence the 18X24 Mitutoyo.  Within my measuring instruments limits' I cannot tell the difference between any of them.


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## 38super (May 24, 2019)

Found a 3 stack of 18x24 surface plates, including my 12x18 reconditioning cost for all will cost between $325 to $450,   Average wear 0.0004", worst 0.0007" (might cost a bit more).   Ace (Glendale) and Precision Granite  (Santa Fe Springs) are local to me.  Reconditioning a surface plate is not that bad if the purchase price is reasonable.  Group reconditioning spreads the travel fee.  Made a small version of the Rahn RoM, hard to interpret on long slope wear troughs.


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## Bob Korves (May 24, 2019)

Standridge (which is also named Precision) Granite of Santa Fe Springs can do work on surface plates in their factory workshop for pretty cheap, even if they are out by a few thousandths.  On the road, where they lap by hand using diamond dust and cast iron surface plates to do the job, .002" is about the most they will do without incurring extra charges.  Standridge will often do them while you wait.  They also have some very good deals on surface plates, angle blocks, and other products that are "blems."  Only problem for me is that it is more than 400 miles away...


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## Dabbler (May 24, 2019)

Bob, think how far it is for me to go there!


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## Bob Korves (May 24, 2019)

Dabbler said:


> Bob, think how far it is for me to go there!


Ask your SO if she wants to go on vacation...  Stop by in Sacramento and say hi.


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## macardoso (May 24, 2019)

I bought a 18x24 Grade B Import locally from a tool supply shop. At $90 and no shipping charges I couldn't complain. I haven't outgrown it using a 7x26 table size benchtop mill or a 12x36 lathe so far. I am not doing NASA level parts or super precision scraping so the Grade B import was acceptable. The grain size on mine is rather large and the finish isn't the same as some of the Starrett ones I've used but I'm happy with the purchase. Plus I can carry it by meself, definitely couldn't move the 24x24 without help.


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## Bob Korves (May 24, 2019)

We asked the team who came around from Standridge Granite to do our plates what they thought about the Chinese surface plates sold in the US.  They told us that the plates are often very accurate and quite usable, but that a small percentage of them are WAY off, some could have been vetted with a yard stick.  Beyond that, the process that they use to make the plates is different than the process used for making surface plates here, and the Standridge team is not even able to make the Chinese plates correct in the field without excessive labor, so they will only test and certify Chinese plates, nothing else.  Obviously, like many things imported from China and some other countries, quality control and quality assurance do not enter into the equation for inexpensive products shipped to the US.  It costs a lot to send that stuff here, and they still want to make a profit while charging fire sale prices to the US distributor.  Part of that something is quality control and quality assurance.  I have seen it many times with their products.


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## darkzero (May 24, 2019)

Funny, just last night I was watching Tom Lipton's video where they came to his shop to resurface the plates. I had no idea it was done like that in the field with not much equipment. Pretty cool.


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## Bob Korves (May 24, 2019)

darkzero said:


> Funny, just last night I was watching Tom Lipton's video where they came to his shop to resurface the plates. I had no idea it was done like that in the field with not much equipment. Pretty cool.


The same team that came to Tom Lipton's shop also came to my shop.  I think they are the only team that does field work for Standridge.  Nice guys and hard workers, and aim to please their customers.  They bend over backwards to get things done that they probably really shouldn't.  The three of them did 5 plates at my shop to AA tolerances in less than an hour and a half.  Great team.


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## astjp2 (May 30, 2019)

I have a 48x72x10 plate that is grade b that I would love to get to grade a, but not really worth it for the shop I have it in or what I do with it, paid 400 for it used and I feel lucky to have bought it.


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## projectnut (May 30, 2019)

I know you mentioned you rarely do parts over 12", but in the scheme of things do you expect to do larger pieces in the future?  I ask this because I started out with a small 12"x 18" surface plate that did the job for a short period of time.  However in less than a year I found I was doing parts large enough that I needed to consider a larger plate.  

There are always "large" plates available on either Craigslist or eBay for nearly scrap prices.  In most cases you'll have to find them locally because shipping wouldn't be cost effective.  I happened to find a Challenge 24" x 36" plate that was recently certified for $100.00.  In my case the plate came from the shop I worked in.  When the company closed down the shop it was sold to a friend of mine who also happened to purchase it and several other larger Challenge and Starrett plates.  When he decided to his shop move to a different building he was willing to sell the "smaller" Challenge plate.  Even at it's "small" size it weighs nearly 600 lbs.  It was a beast to load it into my truck and get it on to the stand in the shop, but now that it's there I  use it far more often than I ever used the 12" x 18" plate.

A lot of people seem to prefer the Granite plates over the cast iron ones.  I on the other hand prefer cast iron.  I have no idea whether one is better than the other, but for some reason I always seemed to gravitate to the cast iron one in the shop rather than the granite ones.  Now I have the one I used at work in my own shop.


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## Bob Korves (May 30, 2019)

Cast iron surface plates are usually quite a bit less accurate than granite surface plates, because the cast iron ones typically have never been calibrated, or it was so long ago that it is meaningless.  Cast iron most definitely moves over time due to internal stresses.  If it it properly heat treated to remove the stress, life is a lot better, but it still moves.  The skill and patience of the person who scraped in a cast iron plate is also a real question.  Cast iron plates that are Blanchard ground or milled flat are not accurate enough for precision work.  Granite is much more stable.  Both wear with usage.

Rule #1.  Guessing the flatness of a surface plate is hopeless and worthless.  Vetting or creating a flat surface plate in your shop to a known standard is highly unlikely, but barely possible if you want to make it a long term project to prove a point, given enough time and effort.  It can be calibrated by pros quickly, fairly cheaply, and reliably to a known standard.  "Close enough" is a term that is used quite loosely and often, but is essentially meaningless, without answering both questions -- "close enough for what?" and "how do I know for sure what I actually have here?"


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## Dabbler (May 30, 2019)

I usually consider smaller cast iron surface plates as 'shop plates' - useful for work that doesn't require a lot of precision, like marking out, or lapping.  For really accurate work I've always used granite surface plates, lovingly cared for, as they are very expensive and easily damaged.

*projectnut,* you can buy an offshore A grade granite plate very cheaply, and use it to check your cast iron ones, and do some basic corrections with a scraper.  The only cast iron plate I used regularly was .002 out in the centre, and .002 low in one corner, with respect to the other 3 corners.


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## projectnut (May 30, 2019)

My Challenge surface plate is an older one that was hand scraped.  According to their website the tolerance was within .0005".  At the time I got mine hand scraped was still standard, but was more expensive than the ground plates.  The 24"x x26" size was a little over $3,700.00.  I see now they offer only ground plates as standard and the hand scraped are special order.  Also I was mistaken on my last post saying the plate was nearly 600 lbs.  The plate itself is only 475 lbs.  The stand is another 170 lbs.
 The plate was last certified in 2016.  It's hard to read the label, but I would assume it was certified to the original factory standard.


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## Dabbler (May 30, 2019)

Cast plates do move, but it takes time.  If your shop gets warm and cold during the seasons, it will mover farther and faster.  A stable environment, temperature and humidity keeps the pates closer to spec.


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## Bob Korves (Jun 1, 2019)

projectnut said:


> My Challenge surface plate is an older one that was hand scraped.  According to their website the tolerance was within .0005".


A plate with an "tolerance" of .0005" from the factory (when?) would likely be suitable (then!) for vetting work to around .003", and that is good enough for a lot of home shop work.  What was it certified to when it was last certified and what was is it's history since certification?  My 18x24x4" granite plate is recently "certified" to an overall accuracy of .00015" and repeatable to .000030".  I take care to keep it so, and no one else but me has used it or had access to it since it was certified...


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## Janderso (Jun 2, 2019)

While we are on the subject, thinking of the cast iron surface plates.
Once they are scraped flat, properly supported and stored, will they retain their flatness or will it need to be rescraped down the road?
I can see why you would want all the stress worked out of the iron.
Thinking of the cast iron plate Rex just finished, it would be a shame to have to repeat the process.


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## Bob Korves (Jun 2, 2019)

Janderso said:


> While we are on the subject, thinking of the cast iron surface plates.
> Once they are scraped flat, properly supported and stored, will they retain their flatness or will it need to be rescraped down the road?
> I can see why you would want all the stress worked out of the iron.
> Thinking of the cast iron plate Rex just finished, it would be a shame to have to repeat the process.


Hand scraped surface plates which are done by hobby machinists are usually ongoing works in progress, improving them as personal scraping skills improve.  You have the plate heat treated to remove stresses, and then ring the thing well before starting to scrape it.  It will probably move some more over time and need an occasional refresh of the scraping to deal with wear and any residual stresses being let out over time.  Not having a solid and stiff mounting to properly support the plate will tend to make it move around as well.  Bottom line, it will need to be tested at intervals, against a KNOWN accurate granite surface plate or by professional certification techs.  I have 2 nice cast iron surface plates, one 8x16" the other 14x18", both works in progress.  I have the smaller one fly cut to remove imperfections, and the larger one is a nice hand scraped Brown & Sharpe that has light surface corrosion from decades of proper storage.  I need to put together some sort of crane in my shop to move the cast iron plates back and forth from the scraping bench to the granite plate to mark them up for each scraping pass.  They are too heavy for moving them back and forth by hand and poor back for the number of times it takes to get them properly scraped in.


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## StevSmar (Jun 4, 2019)

Could you purchase three used granite surface plates and use the three plate method to level them?


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## Bob Korves (Jun 5, 2019)

StevSmar said:


> Could you purchase three used granite surface plates and use the three plate method to level them?


If you work at it for a LONG time and have the correct knowledge, skills, and patience -- and you stick to it -- you can get it to grade A or AA accuracy, maybe even better, but how will you know when you get there?  The three plate method requires strict care in how the stones are properly rubbed together and then carefully tested for improving results, and that is not easy when "lapping" very heavy chunks of granite.  It can certainly be proved to be possible, and perhaps actually has been, not just hyped, but it is in no way a quick, cheap, and easy way of acquiring a accurate surface plate -- it is the exact opposite of that.


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## astjp2 (Jun 5, 2019)

I bet my plate weighs about 1000 pounds, the forklift sure grunted when I lifted it up.  Tim


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## Fitter Bill (Jun 12, 2019)

astjp2 said:


> I bet my plate weighs about 1000 pounds, the forklift sure grunted when I lifted it up.  Tim


Assuming its granite and my math is correct.  4' X 6' X 0.833 = 20 cu ft @ 170# cu ft = 3400 #


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## 38super (Jun 12, 2019)

Meta Key said:


> (And, for you guys in Hawaii, that's two feet of snow outside the window...)



Hey, no prob shave ice


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## Toolmaker51 (Jul 4, 2019)

Cast iron plates have one distinct advantage; being ferrous, they accept magnets and wonderful surface for assembly or mock-up work.


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