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JoeLee
12-06-2016, 09:36 PM
MSC has a sale on the import black granite surface plates with free shipping on orders over $25.
I always wanted a knock-a-round plate for stuff like inking and rubbing parts and when I need to tape a piece of sandpaper down and work a part flat etc. I won't use my good Starrett plate for anything like this.
These are graded just like any other plate, tool room grade etc. But........ are they really as graded??

JL..................

Toolguy
12-06-2016, 09:45 PM
I have found them to be perfectly good in general. You can get a bad one of anything made, if unlucky.

Andre3127
12-06-2016, 09:57 PM
Your sandpaper backing paper isn't perfectly flat, it will also ripple and create rounded edges around the part. An import surface plate will be more than enough :)

(woodcraft also sells them)

Mcgyver
12-06-2016, 10:37 PM
For layout and holding a piece of emery they will be more than good enough. What is "inking". Are you meaning bluing as in scraping? That is something you should reserve for your best plate, its the most demanding of accuracy of any work you're likely to do.

BCRider
12-06-2016, 11:02 PM
For layout and holding a piece of emery they will be more than good enough. What is "inking". Are you meaning bluing as in scraping? That is something you should reserve for your best plate, its the most demanding of accuracy of any work you're likely to do.

If you're doing demanding work then I'd agree. But if working something to a "flat enough" grade there's nothing wrong with a lower grade of plate. It all just depends on what sort of final product we require.

J Tiers
12-06-2016, 11:19 PM
I have two "chinese tombstones".

They blue up fine against each other, but were bought years apart, from different sources. Barring an outlandish coincidence, they are both flat enough for any normal scraping reference use, and have proved to be so. As mentioned, you can get a bad one of anything, but in general they seem to be fine.

Mcgyver
12-07-2016, 08:45 AM
If you're doing demanding work then I'd agree. But if working something to a "flat enough" grade there's nothing wrong with a lower grade of plate. It all just depends on what sort of final product we require.

I think that's kind of what I said....or at least meant. Remember, Joe says he has a good plate so its not a question of whether a crap plate is good enough. If you are reserving one for the most demanding work, that's obviously the one to use for blueing (if that is what inking means) where you need the most accuracy. What are any of us up to that would need more accuracy than that? Unlike milling or grinding, with scraping you can't just move the tolerance around ie 'people who say good ' nuff' lol....you are somewhat constrained by whats a normal thickness of blue and the small DOC.




I have two "chinese tombstones". They blue up fine against each other

how did you do you that? I think it would be a challenge to assess how thick the blue is, and hence how well they matched. Unlike a scraped part, it s difficult to get a read of granite and also know there was no rocking. Plus you need do to in different directions.

I can tell you scraping to a crap plate can be very frustrating. Take a largish piece of cast iron, say 8x8 or 10 x 10 and scrap it flat. Notice as you're trying to move from zones to points you get different readings every time as you spot. Arg. BTDT, waste of time.

In any event, the point is not whether a crap plate good enough or not, you go with what you've got. its that if you have choice as the OP declared, having more than one plate, its a no brainer that you use the higher grade banded one (assuming its in good shape, not worn out) that should be the one to use for scraping. It may all be academic as we still don't what inking is. Perhaps Joe is tattooing up the plates :)

Spin Doctor
12-07-2016, 09:13 AM
One thing about a black granite versus pink. They clean up easier. In my experience it is very hard to get all the blueing out. Besides I think that Starrett uses pink as if it is something special. Remember granite and glass were initially war time substitutes as cast iron surface plates could not be produced fast enough. Lapping is a lot faster than scrapping. In a home shop most times a shop grade plate is fine. Inspection would be nice. Lab rated is overkill

J Tiers
12-07-2016, 09:33 AM
...


how did you do you that? I think it would be a challenge to assess how thick the blue is, and hence how well they matched. Unlike a scraped part, it s difficult to get a read of granite and also know there was no rocking. Plus you need do to in different directions.

...

How do you spread blue on the plate normally to scrape to an iron piece?

Right... that's how I did it for the assessment. IIRC, I did check it with an iron piece (short straightedge) to verify that the blue was normal. Both are black granite so the blue is harder to see. Normally one can judge pretty well from the sheen the blue gives the otherwise slightly dull surface, but that is not a "measurement".

Yes, checked in two directions, and took care to keep from allowing tilt.

Is it a perfect check? No. I have thought of rigging up a Repeat-O-Meter with a scraped block, a smaller scraped block, and an indicator, to verify if there are any humps or valleys on the two, but have not bothered as of yet. I would probably want an indicator significantly more sensitive than the ones I have.

But what is scraped to one also checks as flat by the other, so with that as a secondary check, I declared them to be both as flat as they needed to be.

BCRider
12-07-2016, 02:01 PM
I think that's kind of what I said....or at least meant. .....

Ah... fair enough. I'd taken it to be that you intended that ANY scraping jobs should use the Starret.

Mind you if I had a good plate and a cheap import plate I'd likely use the good one for anything involving dye marking and scraping. For that sort of use why work with second best even if the job doesn't need to be THAT close? And with an import to use for sand paper lapping and other such jobs it would keep the abrasives away from the Starret. And that's what having a second plate is all about anyway. Right? So it looks like you were right the first time in a round about way? Circular logic at it's best? :)

Mcgyver
12-07-2016, 02:15 PM
Ah... fair enough. I'd taken it to be that you intended that ANY scraping jobs should use the Starret.
.

I did mean that.....what I didn't intend mean was some idea like "the only way is with such and such a plate". You can, and I have, used a crap plate, but it can be bloody frustrating. I agree with you the idea of usings abrasives is best done on the cheapo


Mind you if I had a good plate and a cheap import plate I'd likely use the good one for anything involving dye marking and scraping

why? I don't think wear is overt using the plate; spotting is almost lubricated by the blue

imo its the most demanding of work our shops will see, its the work the good plate should be used for. I might be difficult explain if you haven't done a lot of scraping, but I tried to convey the idea it just doesn't lend itself to low classes work: accuracy from scraping is mix of of the thickness of the blue and DOC and the reference flat.....they all kind of want to be in the range for it to work. It just doesn't lend itself well to say, "well today scraping to 1/2 a thou is good enough". It just doesn't work like that...you could try but you might go mental lol. A reference much flatter than the DOC is what you typical, but one less flat would be very frustrating. This is I grant a unconventional way of looking it, just trying to explain that there is sort of an accuracy sweet spot for scraping....driven by a appropriateness of flat reference, blue depth and DOC. Its also not a hard and fast thing, how good is good and how crap is crap (who believes the offshore certs?)....but all things being equal,....

I would say abrasives and laying out are for sure for the cheapo, tenths indicator inspections and bluing for scraping are the for the good one.

J Tiers
12-07-2016, 02:27 PM
[QUOTE=Mcgyver;1084274.....
why?

imo its the most demanding of work our shops will see, its the work the good plate should be used for. I might be difficult explain if you haven't done a lot of scraping, but I tried to convey the idea it just doesn't lend itself to low classes work: accuracy from scraping is mix of of the thickness of the blue and DOC and the reference flat.....they all kind of want to be in the range for it to work. It just doesn't lend itself well to say, "well today scraping to 1/2 a thou is good enough". It just doesn't work like that...you could try but you might go mental lol. A reference much flatter than the DOC is what you typical, but one less flat would be very frustrating. This is I grant a unconventional way of looking it, just trying to explain the reality and some the they whys as the accuracy sweet spot for scraping

.....[/QUOTE]

With scraping you don;t necessarily hit a specific tolerance on the low side.

It has TWO components of accuracy aside from the plate, as you know (but others may not).

1) The number of contact points per unit square (commonly an inch)

2) The degree to which you can see different heights of contact points as being different (not a "measurement"). ideally there are sufficient points per inch, and they are all the same height within the ability to distinguish them.

They are related. Thicker blue contacts points that are lower as well as higher, and that gives you more or less points with thickness. And, to some extent the thickness affects whether the high spots create "bulls-eyes" that show you that they ARE the highest points.

A crap plate is one that is not flat, basically, so it would fail to show you similar markings all over a truly flat surface. Therefore you will assume the need to work over the flat surface, and end up making it un-flat. More likely, you would simply make a surface that is not flat, conforming to one position on the plate. if you mark vs a different area, your marks will change.

In the worst case, you end up chasing your tail all over as the marks change depending on just where you put down the part do do the marking.

Mcgyver
12-07-2016, 02:27 PM
How do you spread blue on the plate normally to scrape to an iron piece? .

yeah, i figure that out. but very smooth surfaces do not spot well and are harder to read - ie why a ground surface makes a poor reference for bluing. They are also heavy so hard to know if you got any rocking. Without 3 and a lot of care, its doesn't tell you that much. I guess it gives some comfort its not a washboard

pinstripe
12-07-2016, 02:27 PM
I would say abrasives and laying out are for sure for the cheapo, tenths indicator inspections and bluing for scraping are the for the good one.

I think that's what BCRider was saying.

Mcgyver
12-07-2016, 02:50 PM
In the worst case, you end up chasing your tail all over as the marks change depending on just where you put down the part do do the marking.

No one dies, but that is still a bloody awful case and why you want to use your best plate. actually there is a worse one, your plate is smooth but not flat. say convex. you make a reference from it, replicating the curve and proceed to scrape this error into some big machine rebuild.

Blue thickness can be varied somewhat (there is a optimal thickness you end up with for finish work) but DOC is a also both a constraint and there is what I will call (with license to make the point) the sweet spot of accuracy when scraping. Of the three DOC is not easily varied, its a around a tenth on point with a hand scraper. Those unfamiliar (and I know you're not one) might think anyone involved in scraping is a hotie totie HSM elitist or such BS conclusions with all this talk of tenths.....but the reality is that's just what a typical pair of Mark I arms generate. That and the fact that machine tool bearing surfaces do benefit from that level of accuracy.

In most things we do its reasonable to say well I only need .002" on this part so I'm just going to make to the .002" I need, even if on the previous job you needed something smaller. You use the machines in a manner that produces the part within tolerance. Scraping isn't like that its not sensible to extend that sort of thinking to it because it just creates frustrations

BCRider
12-07-2016, 03:12 PM
I think that's what BCRider was saying.

I think we were talking in circles around each other but in the end thinking the same thing. Such is the joy of discussing things on a forum instead of over a beer where each other can see the nodding heads.....

Mcgyver, I totally understand that "sweet spot" thing. Looking at Stefan's "roughing" of his reference flat side it's apparent that it's easy to get into the ball park and get a generally decent flatness. The serious time comes in the finish work of achieving more contact spots per area for a more even surface.


.....you make a reference from it, replicating the curve and proceed to scrap this error into some big machine rebuild

I had a few choice words flying around my wood shop when I discovered that a previously flat wood body jointer had developed an arch to the sole. I'd dressed off about half of my new wood working bench when I got suspicious and started checking...... Oh yeah, the air was as blue as a bottle o' Dykem for a while. A good lesson in trusting nothing without checking first when doing the serious jobs.

J Tiers
12-07-2016, 04:50 PM
...
Mcgyver, I totally understand that "sweet spot" thing. Looking at Stefan's "roughing" of his reference flat side it's apparent that it's easy to get into the ball park and get a generally decent flatness. The serious time comes in the finish work of achieving more contact spots per area for a more even surface.
...

Contact spots AND what KIND of contact spots....

Yes, that IS basically the difference between roughing and finish work when scraping.

oldtiffie
12-07-2016, 08:40 PM
The "flatness"/"accuracy of the OT's plate does not seem to be included here - well I can't recall seeing it anyway.

The "B" or "D" plates have been designated/used as "shop" plates \for many years.

So far as I can see they are quite adequate for the vast majority of "shop" work with "C" and perhaps "B" plates used for "inspection" grade work.

"A" class plates are for "Laboratory" and the like work.

I've always "got by" with a "B" grade plate and so that is all I really need.

http://qcssindy.com/index.php?option=com_content&view=article&id=15:surface-plate-tolerances&catid=2

My two surface plates rarely see the light of day as I really do quite well with a sheet of "float" glass, the top of my mill and grinder tables and the top of my surface grinder magnetic chucks.

I have no issue with others who may want to and perhaps do need flat surfaces to be "better" or optimum "flatness".

oldtiffie
12-07-2016, 10:46 PM
There seems to be an underlying supposition here that the shop/space where the "part" is scraped to a required accuracy is quite stable as regards environmental stability as regards temperature and random impinging light and heat etc. and that this will have no significant effect as regards the stability of the plate and the "work".

That may be so but how sure of it are you and how do/will you check and correct it if or as required?

Just how accurately "flat" must the job be when finished and how did you decide on that figure/flatness that needed to be achieved?

JoeLee
12-07-2016, 11:51 PM
I forgot to mention one thing......... these plates are NOT traceable to NIST. Should that be telling me something???? I know there are a lot of import plates, not sure weather any of them are traceable.

McGyver.......... Inking, yes scraping.

JL.............

J Tiers
12-08-2016, 12:04 AM
JoeLee:

So do they NEED to be traceable?

If there is no contractual agreement that requires it, plates can verify flatness of each other, and with an intermediate piece, such as a somewhat wide straightedge, to use for the comparisons, YOU can be sure they are quite "flat enough" without the rigmarole of getting anything "certified".

Tiffie:

As the OP wants a chunk of stone to tape down sandpaper to, I can't see it being an issue of any significance.

With regard to the shop space, I certainly know in my case, because the shop space is partly underground, and I own thermometers.... It's quite reasonably consistent year around, obviously varying but not varying fast.

Paul Alciatore
12-08-2016, 01:50 AM
I have a piece of thick glass that I use for sandpaper backing. It works just fine. You can do a quick inspection of the glass at the supplier before they cut it. Just look at the reflections at a grazing angle from two sides that are 90 degrees apart. If the reflections at that narrow angle look distorted, don't buy it. If they look OK, then it is quite flat; good enough for backing sandpaper, which has absolutely no flatness or thickness spec. I believe I paid about $5 or $10 for it and since it was purchased locally, there was no shipping charge.

I recently did some sharpening on some wood planes here:

http://img.photobucket.com/albums/v55/EPAIII/Web%20Post%20Photos/Misc%20Web%20Posts/PC080010_zpsy8rmh5zm.jpg (http://smg.photobucket.com/user/EPAIII/media/Web%20Post%20Photos/Misc%20Web%20Posts/PC080010_zpsy8rmh5zm.jpg.html)

And they came out near perfect. I used some of that foam shelf and drawer liner under it to support it evenly. Not exactly Airy point suspension, but it does do a good job for less critical applications like this.




Your sandpaper backing paper isn't perfectly flat, it will also ripple and create rounded edges around the part. An import surface plate will be more than enough :)

(woodcraft also sells them)

oldtiffie
12-08-2016, 02:34 AM
I forgot to mention one thing......... these plates are NOT traceable to NIST. Should that be telling me something???? I know there are a lot of import plates, not sure weather any of them are traceable.

McGyver.......... Inking, yes scraping.

JL.............

A lot of this quest for insistence for "NIST" in a home or commercial jobbing shop is in most cases a fallacy pure and simple and in terms from OZ (Australia) is a pure "wank" and to that end many are co-ersed by others who should but all too often do know better.

"NIST" calibration only certifies the accuracy of the plate between specifies limits at the "test date" and an arbitrary "end of certificate" whether the plate has been use or not as it is then "out of test" (and "Certificate").Most or most of the"import" plates (yeh -from China) are at or exceed Class B - mostly better.

If the say the plate etc. is required to be at "NIST" standards then so must the Camelback and/or level be and that usually means that it must be at least one grade better/higher than the reference plate.

I can't see me getting a plate re-lapped or re-scraped - too dear - and same appliesto re-scraping.

I really do detest physical plate scaping as I promised myself years ago that I'd never do it (again) unless absolutely essential and vital.

If I had to scrape it I'd consider buying a new plate and if I really had to "do it" I'd buy a NEW scraping tool/machine (which are really expensive).

https://www.google.com.au/search?q=scraping+tool+or+machine&rls=com.microsoft:en-AU:IE-SearchBox&rlz=1I7IRFC_enAU360&biw=1280&bih=560&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwibnMfriOTQAhVBqY8KHYauAqgQsAQIVA

But in the end I'd probably just put up with the surface/s that "needed" scraping or just scrape and perhaps replace with a new machine.

My shop is small and so a new machine would suffice.

Getting enough (any?) space/s to strip down, clean, scrape, re-assemble and "set to work" for an extensive period would be beyond the space available as well as time and patience.

In my shop, a new machine is the best option - and the old one straight to scrap.

oldtiffie
12-08-2016, 02:41 AM
I forgot to mention one thing......... these plates are NOT traceable to NIST. Should that be telling me something???? I know there are a lot of import plates, not sure weather any of them are traceable.

McGyver.......... Inking, yes scraping.

JL.............

Nope - those plates do not need to be "NISTED" and they are quite good as they are.

JoeLee
12-08-2016, 10:47 AM
JoeLee:

So do they NEED to be traceable?

If there is no contractual agreement that requires it, plates can verify flatness of each other, and with an intermediate piece, such as a somewhat wide straightedge, to use for the comparisons, YOU can be sure they are quite "flat enough" without the rigmarole of getting anything "certified".

Tiffie:

As the OP wants a chunk of stone to tape down sandpaper to, I can't see it being an issue of any significance.
u
With regard to the shop space, I certainly know in my case, because the shop space is partly underground, and I own thermometers.... It's quite reasonably consistent year around, obviously varying but not varying fast.This plate wouldn't have to be traceable for any of my uses but when a manufacturer doesn't have it certified and traceable they can hide a multitude of sins and the average guy would never know it because how many of us have the proper equipment to test a surface plates accuracy??
At least when a plate is certified like my Starrett you know you can rely on it.

JL..................

pinstripe
12-08-2016, 11:06 AM
Even if it said that it was traceable back to NIST, would you trust it from a nameless offshore manufacturer? The only way to know it's flat is to get it checked yourself.

J Tiers
12-08-2016, 11:07 AM
This plate wouldn't have to be traceable for any of my uses but when a manufacturer doesn't have it certified and traceable they can hide a multitude of sins and the average guy would never know it because how many of us have the proper equipment to test a surface plates accuracy??
....

JL..................

As I mentioned, it is actually QUITE EASY to make a test of the plate with no special equipment other than equipment for scraping.

1) Scrape a surface to the plate, picking any consistent area on it to use as reference. The thing you scrape is convenient if it is like a scraping straightedge.

2) Scrape a SECOND similar item TO THE STRAIGHTEDGE FIRST SCRAPED

3) Try BOTH of the scraped pieces in various positions on the plate. Corner-to-corner both ways, across in the middle both ways, down each side.

If both pieces show up marked the same with your usual marking process, then as far as you are concerned, they are all flat. Your test methods do not detect a difference, so they are as good as you need.

QSIMDO
12-08-2016, 11:27 AM
Is there any way to repair a pock-marked plate?

I was given a 18x24 plate with more potholes than a spring New England road.


That should read "inexpensive" as well.

Mcgyver
12-08-2016, 11:56 AM
I forgot to mention one thing......... these plates are NOT traceable to NIST. Should that be telling me something???? I know there are a lot of import plates, not sure weather any of them are traceable.
.

Having been involved in two businesses that had plants in China, I have this image of China plates coming off some single conveyor assembly line. At the end are workers packaging and filling in test and cert cards after receiving a forecast of what was suppose ship tomorrow.

I doesn't matter to me if its NIST traceable as I don't have to answer to the next party down the line. BUT it does matter that I can believe the cert that came with as true. I'd be inclined to trust Starrett, and I'd not trust whatever the non branded offshore plate cert says. Of course for those who never use their tools that point won't registerr lol. The only cert you can go by, imo, on the non branded offshore plate are the internet claims of some guy you really don't know - either skill level, type of work being performed or expectations and even then you no reason to believe the plate that arrives will be to the same.

Being one of those guys giving an internet opinion, I'll say the offshore plates are ok for certain tasks and I do own one (as well as aa Starrett A). However they are not that good and have caused problems for me scraping. If you really need something traceable and/or a reliable cert, ie something better than a guy on the internet, a China crap plate isn't the thing to pursue.

J Tiers
12-08-2016, 01:07 PM
NO "internet guy" has ANY idea what the specific plate the OP has is like. Good, bad, indifferent, we are not there and can have no opinion.

Some of us CAN know the import plates CAN be good, because we have ones that are good enough that routine scraping of precision stuff does not show up a problem. Any individual plate is unknown until checked, because the inspection is probably a lie.

If the work you do (scraping as suggested in my post) does not show up a problem, then your plate is good enough for what you do and the way you do it. A better plate, if one existed, would be no better for you. If you detect no problem, then there is no information about HOW good the plate is, in absolute terms. You cannot prove that it is, or is not, absolutely perfect.

That proof is what the NIST certification says.

A "B" grade is essentially flat with no deviation more than about a tenth (0.7 tenth) for a 12 x 18 plate.

One scraping pass is in the area of one to 2 tenths, on average, with moderately hard scraping pressure and it is easy to see the difference between two scraping passes. The scraping test doubles the error. So for an estimate, you can likely distinguish about a tenth, and the test suggested can therefore show if you are within about a "B" grade plate spec.

For most machine scraping purposes, that will be sufficient unless you have requirements stated past that.

Remember, most machines folks here will have are designed to be accurate to around a thou. The do not hold tenths reliably. So "B" grade standards meet the 10:1 requirement on measurements.

http://www.qualitydigest.com/aug03/articles/03_article.shtml

Mark Rand
12-08-2016, 03:40 PM
The cost of getting a cheap import surface plate calibrated is identical to the cost of getting an expensive non-import plate calibrated. Without a current calibration, the flatness and error map of a plate isn't traceable no matter who it came from.

oldtiffie
12-08-2016, 05:36 PM
I agree with you Mark but having got your plate calibrated and if it meets or exceeds your real requirement for what it is needed to do - well and good.

But if it does not meet your requirements then you have a problem - lower your requirement to a level that the plate can achieve or scrap the plate and/or start all over.

Its even more of a problem if say you want to scrape (or have to) a say straight-edge or camelback straight edge or angle/bevel for say a dove-tail slide (both male and female) as they must meet or exceed the accuracy require for the finished job.

You might just "get lucky" and the seller (to you) will have convinced (sold you) that its the "real deal" and of course he will "love you in the morning".

If it were me I'd hope that I got the deal I wanted but I could only be sure ( or just sufficiently confident) by having it calibrated - and I'd have gone full circle - back to where I started.

I bought my surface plates new from a trusted seller to the trade with a good history of supporting his name and warranty - like this:

https://www.machineryhouse.com.au/M710

https://www.machineryhouse.com.au/Q810

http://www.shars.com/products/measuring/surface-plates

Depending on the job and given that "new" plates are expensive then perhaps its not so much how much you have to pay with confidence as apposed to the risk if to buy one that may not be what you wanted or were sold by buying a "cheapie".

Its the scrapers "call" after all - and the level of risk and cost that he must make his judgement on.

In other words - "ya pays ya money and ya take ya chances" and perhaps you just get/got "reamed" - or hopefully all works out well.

J Tiers
12-08-2016, 05:46 PM
I agree with you Mark but having got your plate calibrated and if it meets or exceeds your real requirement for what it is needed to do - well and good.

But if it does not meet your requirements then you have a problem - lower your requirement to a level that the plate can achieve or scrap the plate and/or start all over.

Its even more of a problem if say you want to scrape (or have to) a say straight-edge or camelback straight edge or angle/bevel for say a dove-tail slide (both male and female) as they must meet or exceed the accuracy require for the finished job.

You might just "get lucky" and the seller (to you) will have convinced (sold you) that its the "real deal" and of course he will "love you in the morning".
////
Depending on the job and given that "new" plates are expensive then perhaps its not so much how much you have to pay with confidence as apposed to the risk if to buy one that may not be what you wanted or were sold by buying a "cheapie".

Its the scrapers "call" after all - and the level of risk and cost that he must make his judgement on.

In other words - "ya pays ya money and ya take ya chances" and perhaps you just get/got "reamed" - or hopefully all works out well.

Well, Tiffie, if the plate is out of spec, that is not a case of "bin it".

It can be brought back into spec by any competent calibration and checking outfit. This typically involves lapping with another plate, and is quite effective, and not a long process. It is commonly done because even expensive certified plates will wear and be out of spec later.

The only difficulty is if you get a snooty outfit that refuses to bother with an import plate on principle. Some apparently have been known to say things like "Oh, it will warp and be out of spec in a week, we don't waste your money on them".

While one can imagine cases in which that might be true, in most cases it is BS, and the stone is stone, it will last a year without turning into an out of spec pretzel.

JoeLee
12-08-2016, 05:59 PM
Even if it said that it was traceable back to NIST, would you trust it from a nameless offshore manufacturer? The only way to know it's flat is to get it checked yourself.It depends on how NIST accepts certifications??? I'm sure they have strict requirements. I have no idea how it or they work. But I find it highly unlikely that NIST would just accept the word of some mfg. and a certificate that the plate is within a given spec or grade. Even not knowing I would think that a certified person with certified and calibrated equipment would have to do the inspection and that they would have to be an approved inspector. There has to be some system of reliability in place.
I doubt that NIST sends an employee to every mfg. to inspect the plates and we all know that the mfg. sure as hell doesn't send all their plates to NIST for approval.

I did find this but haven't gone over it. NIST has quite an extensive website.

http://nvlpubs.nist.gov/nistpubs/jres/68C/jresv68Cn2p83_A1b.pdf

JL................

oldtiffie
12-08-2016, 06:00 PM
You are right JT.

Scraping a granite plate may be more difficult that scraping cast iron one - but that's up to the user.

Calibration usually (only??) refers to calibrating a granite plate as its very difficult to apply to cast iron.

Scaping one plate to another is OK if the plate to be scraped is not too heavy to lift up and down - otherwise its a PITA - and possibly risky and dangerous as well - and its real easy to get fed up with.

"Lapping" a plate to another is a PITA if the plate is heavy as well.

Paul Alciatore
12-08-2016, 06:09 PM
After reading all the comments about certification I need to make a few comments.

Sometime ago someone posted a thread, either here or on the PM board where he showed a video of a calibration service which came to this shop and measured, re-figured, and certified his granite plate. To check it they used two instruments; a Repeat-O-Meter and a laser autocollimator. And they used a LOT of experience, which was not visible in the video images. To correct the plate they used a smaller, diamond charged lapping plate. And, of course, they checked it again after the corrections were made.

My comments:

First, certifications against an external standard is NOT needed for something like a surface plate where the primary requirement is that it be flat. Flatness can be determined, to any degree of precision needed without any external standards. There was no NIST when the first surface plates were made and yet, they were made. There are multiple ways in which the flatness of a plate can be determined. A comparison to an external standard may be a convenient and fast way to do this, but it is not the only way. And, if you are talking about a standard that exists in a NIST laboratory or facility, then there must be multiple steps in copying that standard to field plates and then the field plates would be compared to the plate you are testing. So, in fact, when you say it is traceable to NIST, you are, in fact, saying that there were multiple stages where errors could creep in. So being traceable to a NIST standard plate may be a less accurate way to determine the figure of a plate in the field.

Second, neither of the instruments that they used are capable of determining the flatness on their own. It is only the combination of the two and some logic and knowledge on the part of the man using them that allows them to be used in that manner. Consider: a Repeat-O-Meter used on a plate that is uniformly concave or uniformly convex over it's entire surface will show the exact same reading at all points. And yet the plate is curved. On the other hand, an autocollimator will show that a given line is straight, but it can say nothing about how co-planer that line is to one of the other lines across the plate. So a plate with a warp will show no errors with it.

Third, even with both of those instruments, they were relying on the plate being flat at some point in the past and there being a good chance that the corners and edges where they started from were flat and co-planer at that past time and they are not very worn at the present. They start both instruments from those corners and edges. Generally, this is probably a good assumption. But it is possible for there to be exceptions.

Finally, they depend on their smaller, lapping plate to be reasonably flat. It is not clear how they have determined that.

I am sure that the calibration service shown in the video was competent. But I am also sure that just by observing the video you can not learn or see everything that was taking place. Much of the process was in their heads and was heavily drawn from their experience and education in the field. I am sure that there were multiple things that they were on the look-out for that were never mentioned. But these things would have triggered warning bells in their heads and other instruments or tools would have been brought into play. Or, in the worst case, the plate they were certifying would have been taken to their shop/lab for further tests and work.

I am sure that when they certify a plate in a given grade that it actually tested to a grade better than that as they stated in the video. I am also sure that their instruments were calibrated with reference to NIST or other standards. But there is nothing magic about "NIST". And in the case of surface plate flatness, it may not even be the best way to ensure it.

And for gosh sakes, if the OP is looking for something to back up sandpaper, almost any plate, even a worn one, even my sheet of glass, is plenty good enough. He does not need NIST or any of the other instruments used for surface plate measurements. I mean, WHO makes sandpaper that is accurate to tenths? I really want their name.

enl
12-08-2016, 06:25 PM
It depends on how NIST accepts certifications???.

I haven't had much to say in this thread, given that if A plate meets the requirements for the job, that is what matters, most import plates and tools I have seen from reputable suppliers seem to meet the stated spec (with a few exceptions), and that most jobs don't require traceability.

But this is something a lot of people don't understand so a summary (incomplete, but good enough): The NIST has noting to do with your NIST traceable plate. The plate (or any other tool) is certified by the manufacturer (or test agency) that it meets the stated specification and that the testing of this was done with instruments and standards that have been calibrated either by NIST (pricey) or using standards with a pedigree that is traceable through other standards to NIST.

For example, my shop gauge blocks have a very out of date cert from a lab whose standards were certified by another lab whose standards were certified directly by NIST (according to the paperwork). Likely the standards used have another generation in there between the shop master and the ones used on the floor, but maybe not. The paper only specifies the accumulated uncertainty. My good Mitutoyo set for doing Mic's has the Mitu cert, and their masters are done by NIST. The specified uncertainty is significantly lower, though the stated values are no more accurate than the shop set. None of these ever saw NIST, and NIST doesn't know of their existance, unless someone that works there reads this.

The reputable manufacturers have in house QC programs with outside review (like ISO9000, for example), but any of them can cheat. The only exceptions I know of are a few companies that do gov't contract work and nuke industry work, where there is fairly constant oversight, though the end result is still based on trust, since the inspectors can't see everything and themselves need to be honest.

oldtiffie
12-08-2016, 06:31 PM
Excellent analytical reports from both Paul and enl - many thanks.

I do think that many here may not either need a surface plate at all and even if they say that they "need" it that really they "want" the "biggest and bestest" around more for "bragging rights" than real "need".

To some extent the same might well apply to "1 micron" test dial indicators (where 1 micron is pretty close to 0.00004" - say "about 0.4 of a "tenth"").

Same seems to attract a lot of similar comment when the topic is "tramming a mill" or "setting up a really really good milling machine vyce" which - of course - must absolutely be at least a "top of the line" "Kirt" vyce (no surprises there either).

I can understand all that - and like some others, I've done my share of it at times.

But I do see of lot of very remarkable work by some very remarkable people here using some "ordinary" tools but some very high skill levels.

J Tiers
12-08-2016, 08:14 PM
ENL has described the gist of "traceable to NIST".

In short, it means that the item (of any sort) was measured against things which in turn were measured against others, in a line back to a primary standard. "Traceable" means that this line is documented, each device is listed on the succeeding device's cal sheet, and if you follow back, you end up at an NIST primary standard.

Yes there is an error in each measurement, although it is intended to be minimal. If one insists that each device be 10x more accurate than the device measured with it, one will quickly run out of decimal places if the "line" of devices is very long.

Typically, a meter, for instance is calibrated against a "meter calibrator" unit. The manufacturer of that calibrated it against some standard which was calibrated against the company standard(s). The company standards were sent to the NIST and calibrated against the NIST primary standard, and there are probably several of each.

So, any meter calibrated with a "company X" meter calibrator is 4 "jumps" away from the NIST in the scenario suggested. The company and NIST standards are likely basic standards, and the actual standard used is calibrated with several comppany standards of different types, resistance, voltage, current, time, etc, depending on what the meter in question measures.

Similar considerations apply to distance measuring tools, such as the indicator used in a Planikator or Repeat-O-Meter.

Now, as for Tiffie's deprecation of the need for a good granite flat or whatever.

As McGyver has said, there is nothing worse than trying to scrape to a bent standard. Nothing comes out right, and in the end, you spend the same effort it would take to do it right, to very carefully do it WRONG. And that will show up in the use of a machine so scraped. Ther will be errors, a grinder will grind a bow into parts, the lathe faces a bow, or ripples into parts, etc, etc.

The errors show up.

Now, if, as I have mentioned, your methods of bluing and marking against a flat, do not show up a problem, then you can be sure that no better plate can help you. Your methods will not do better than you do with the plate you have. To do better, you would have to detect errors of a smaller amount, and you do not have the ability to detect them unless you use a different method (Dykem instead of Canode, alcohol "haze" instead of Dykem, etc).

So if you scrape something to your plate, as well as you can, and then scrape another item to that first piece, the second piece should reproduce the errors in the plate. If you then spot THAT against the plate, the errors are doubled, easier to see. If at that point you see no errors, then you can do NO BETTER, your plate is flat enough for your methods.

This is not to say your methods are bad... Every method has a limit, and all we are saying is that your methods see no error, so it's known to be flat enough within your limit of error.

THAT is one way to verify for yourself that your plate is good enough, using NO external references or services. And it is NOT a "make-do". However, it does not give a "number".

TGTool
12-08-2016, 09:28 PM
The autocollimator or differential levels can map errors on a plate without reference to an external comparison. In the video referenced on PM, the Repeat-O-Meter was used in two ways. First, after an autocollimator check of the standard pattern, the meter was zeroed on a section of the plate that was tested as flat, then used to check for localized high or low spots. The autocollimator could have been used to do the same thing if they tested more points. (Finer grained check)

The second way it was used was again to zero on a known good plate, then use it alone on a second smaller plate rather than getting out the autocollimator. That's especially helpful on a smaller plate since the collimator setup has a length that makes it more awkward in short distances. For instance, if the autocollimator itself is 1/4 the length of the plate, you can't tell anything about the first 1/3 to 1/2 the plate where it's sitting. So you check what you can from that corner, then go to the opposite corner and check your way back. If you've got the Repeat-O-Meter calibrated, you just swing it around the plate and you're done.

JoeLee
12-08-2016, 09:54 PM
This is interesting..................

https://www.youtube.com/watch?v=NWObTpn6dTk

JL................

J Tiers
12-08-2016, 10:26 PM
...

The second way it was used was again to zero on a known good plate, then use it alone on a second smaller plate rather than getting out the autocollimator. ....

Notice that this procedure neatly eliminates the issue mentioned by Paul A.

By zeroing it on a good plate, the parallel condition is the zero. Now, supposing the spherical error as he described, it is in fact detected, since it is not flat like the original "zeroing plate". The error is apparent the very instant the Repeat-O-Meter is set down on the bad plate.

The Repeat-O-Meter is in essence a sort of comparator, not an absolute measurement device. It measures deviations. If there is the "perfect potato chip" surface, that has an error, but the error is the same all over, it will not be detected by an internal comparison. But if compared to an external standard, the error is instantly detected.

The key is in the words "compared to".

As far as the auto-collimator, there I believe Paul is dead wrong.

Yes, it can only establish a straight line. So, if poorly utilized, the "perfect potato chip" would have a lot of straight lines, and the Auto-collimator would not detect a problem if it is ONLY oriented along them.

But, even with that device, if all random orientations on the plate give a straight line, then the "perfect potato chip" is in fact perfect..... perfectly flat.

The argument that the auto-ollimator does not, or cannot find an error is false because it assumes a limited number and orientation of measurements. That is a USAGE problem, simply not being thorough. ANY non-flat surface must be either convex, concave, or a combination of those. That being the case, there necessarily exists at least one test line that will cross one or more of the convexities or concavities, and so the error will be detected.

None of this matters much if the OP just wants a plate to tape down sandpaper to.

TGTool
12-09-2016, 12:16 AM
The standard check of a surface plate with either the autocollimator or differential levels is a union jack pattern that traverses the four edges, the two diagonals and the two midlines. It's showing if the reflected light from the target is perfectly coincident so if there's any angular change it's visible. In any shape you can imagine, other than perfectly flat, you will observe some change in the angle as the target moves over a concave, convex or other curve.

The data you collect is from the number of measurements you take and the span of the base of the target. A wide base target could miss a small local deviation. Similarly, if you only took two checks down one of the lines you might miss what's happening in between. Differential levels will give the same information. If you knew ABSOLUTELY that the plate wouldn't move as you walked around it, you'd only need one, but with two, the stationary one gives you essentially a zero reference compared to the one you're moving around the plate. It won't matter if the floor shifts slightly since they're referenced together. Since the autocollimator is always on the plate it self references in a way unless the stone itself flexes. If you put it on a bench and the target was a surface plate on a separate stand you'd never know what changed, the plate surface or one or other of the supports.

oldtiffie
12-09-2016, 04:33 AM
For a good "retro" read this thread:

http://bbs.homeshopmachinist.net/threads/45859-Surface-Plate-Reconditioner

Mcgyver
12-09-2016, 08:48 AM
I haven't had much to say in this thread, given that if A plate meets the requirements for the job, that is what matters, most import plates and tools I have seen from reputable suppliers seem to meet the stated spec (with a few exceptions), and that most jobs don't require traceability.

But this is something a lot of people don't understand so a summary (incomplete, but good enough): The NIST has noting to do with your NIST traceable plate. The plate (or any other tool) is certified by the manufacturer (or test agency) that it meets the stated specification and that the testing of this was done with instruments and standards that have been calibrated either by NIST (pricey) or using standards with a pedigree that is traceable through other standards to NIST.

For example, my shop gauge blocks have a very out of date cert from a lab whose standards were certified by another lab whose standards were certified directly by NIST (according to the paperwork). Likely the standards used have another generation in there between the shop master and the ones used on the floor, but maybe not. The paper only specifies the accumulated uncertainty. My good Mitutoyo set for doing Mic's has the Mitu cert, and their masters are done by NIST. The specified uncertainty is significantly lower, though the stated values are no more accurate than the shop set. None of these ever saw NIST, and NIST doesn't know of their existance, unless someone that works there reads this.

The reputable manufacturers have in house QC programs with outside review (like ISO9000, for example), but any of them can cheat. The only exceptions I know of are a few companies that do gov't contract work and nuke industry work, where there is fairly constant oversight, though the end result is still based on trust, since the inspectors can't see everything and themselves need to be honest.

good post...I'd like it if we had likes lol