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gregl
12-29-2008, 05:48 PM
The header says it. We'll have some left over from the kitchen remodel and I hate to just toss it since I paid for it . I don't need inspection room accuracy, plus or minus .001 is more than good enough for what I do. THANKS!

derekm
12-29-2008, 06:00 PM
measure it ... if its good its good

a piece of float glass and some blue will tell you

SGW
12-29-2008, 06:13 PM
An old gent I knew who built absolutely beautiful model steam engines used a piece of busted-off granite facing veneer from an old store front for his surface plate. ("It drops off about three thou towards that corner, but I allow for it.") So I expect a piece of granite countertop will be at least that good, and at least that usable.

But the only way to tell, for sure, is to measure the piece of granite you have and see what it's like. Put a dial indicator on a surface gage and sweep it across the surface in several directions.

And let us know what you find. I'm curious.

dp
12-29-2008, 07:03 PM
I bought a 12" square of black granite at Home Depot some time back and used it with great success for a lot of projects. I have a granite surface plate now but I still use this one for sanding and quick checks of non-critical parts.

You can easily check the flatness by placing the tiles face to face. Any two that resist spinning (surface tension) are good fits to each other. If a third is found that is also a good fit you probably have found as good a set as exists in the store. The store floor people will look at you oddly.

lazlo
12-29-2008, 07:11 PM
The Enco 12x18, Grade B surface plate is $24.95 with free shipping:

http://www.use-enco.com/CGI/INSRIT?PARTPG=INLMKD&PMPXNO=949402&PMAKA=640-0120

Frank Ford
12-29-2008, 07:17 PM
Unfortunately, I believe they ship granite plates by truck now, so I don't think you can get the free shipping deal on them.

Bones
12-29-2008, 07:33 PM
Ijust received a 12x18 surface plate from enco, free shipping, delivered to my door by ups.

bones

BobC
12-29-2008, 07:34 PM
Unfortunately, I believe they ship granite plates by truck now, so I don't think you can get the free shipping deal on them.

Enco may have changed its policy but I purchased a 12x18 a few months back at the $24-$26 price and it came with free shipping via UPS or FedEX, forget which.
Bob

Teenage_Machinist
12-29-2008, 07:39 PM
The two smallest sizes of surface plate are shippable by truck. Highly reccomend using the free UPS, there are still a few days left for a 25 dollar minimum.

If there is a Woodcraft store near you you can do that as well, They sell 9x12 grade B, as some woodworking tools need careful alignment aided by a reference..

Wish there was such a thing as "MetalCraft" sort of is in LMS but we could use some more variety.

It depends on what you consider a surface plate. Granite is good because it does not expand too much when heated, is abrasion resistant and cannot get burs, which mean that good counter top may be useable for less precise stuff such as marking.

Scraping and toolmaking == NO! NOT PRECISE ENOUGH!

Just Bob Again
12-29-2008, 07:41 PM
You have to check the piece you get. I have a sink cutout from a granite counter. Nice and smooth but nowhere near flat. Out at least 20 thou from corner to corner. Over a small area, it's fairly flat. Too thin for a real surface plate. On the plus side, mine is 20 by 30 inches and I can lift it.

John Stevenson
12-29-2008, 07:47 PM
Ironically this has just come up tonight on a UK forum.
I have taken the liberty of copy and pasting the post from a well know and respected UK member Jim Petagrid and all the following is Jim's work.


*****************

Having recently aquired a 6" optical flat I thought it would be
interesting to checkout the granite placemats and chopping boards
now stocked by the supermarkets. These are 15 to 20mm thick and
small enough and light enough to be kept in a drawer when not in
use.
Although the working surface is polished, it is only
polished sufficiently to give a shine. There's severe "orange
peel" surface disturbance - not good enough for optical
interferometry checks. However the surface is ideal for the
capillary/surface tension method.

http://xs434.xs.to/xs434/08011/granite_1a910.jpg

http://xs134.xs.to/xs134/08011/granite_1b902.jpg

http://xs134.xs.to/xs134/08011/granite_2a522.jpg

http://xs134.xs.to/xs134/08011/granite_2b880.jpg

Show the test results on two 15mm thick placemats. The 6"
flat was supported at the top end with an 0.005" shim to give an
airgap slope of about 5/6000. The equal thickness capillary
edge displays a 6000/5 amplification of the flatness error -
approx 1" per 0.001" Each plate was tested at 0deg and 90deg and
showed errors of less than 0.0004".

The tests were repeated on a 300 x 400 x 15mm chopping board.

http://xs134.xs.to/xs134/08011/chop_board_0.005925.jpg

http://xs134.xs.to/xs134/08011/chop_board90_0.005344.jpg

http://xs134.xs.to/xs134/08011/chop_board_0.001674.jpg

The first two show the 0deg and 90deg results The third is a
repeat of the 90deg result but with an 0.001" shim.

http://xs134.xs.to/xs134/08011/plglass_0.001_x_2in878.jpg

Is the result using an 0.001" slope on a 12" length of 2" x
1/2" plate glass (ex shop window display shelf)

http://xs134.xs.to/xs134/08011/splatemeths0.005256.jpg

Is an 0.005" slope test on a 12" x 18" surface plate. Although
the lower faint capillary edge is fairly visible by eye, the
contrast is too low for satisfactory photography. Both Meths and
ispropanol (rubbing alcohol) gave similar results but a marking
out fluid which appears to be heavily dyed alcohol gave
excellent contrast. The snag is that the higher viscosity
results in a long settling time.

http://xs134.xs.to/xs134/08011/splatemkgbu0.005571.jpg

http://xs134.xs.to/xs134/08011/splate0.001start328.jpg

http://xs134.xs.to/xs134/08011/splate0.001finish758.jpg

The fist JPG is an 0.005" slope test. The second shows the
beginning of an 0.001" slope test. the third is the result
1/2hour later. The results show up the comparative roughness of a
ground and scraped surface.

Jim

dp
12-29-2008, 07:48 PM
Scraping and toolmaking == NO! NOT PRECISE ENOUGH!

They're perfectly suitable where 0.0002 is not necessary which at home is quite a bit. I used mine for scraping and improved the surface of the work immensely. I've done side by side checks with my granite surface plate and the granite tile and the differences for my environment are not significant.

Given the cost of true surface plates today the only justification for using a tile is convenience - they're easy to put away, and abuse. You can beat the hell out of them and not feel bad.

Evan
12-29-2008, 07:56 PM
By a piece and test it. From my web site:

http://metalshopborealis.ca/laser/flattest.htm

If it doesn't make the grade it is still a handy work surface.

Teenage_Machinist
12-29-2008, 07:58 PM
Not only that but they do not get burs from being beaten, in fact a good piece of tile may be better than the mill table.

dp
12-29-2008, 08:07 PM
Not only that but they do not get burs from being beaten, in fact a good piece of tile may be better than the mill table.

They're the hot new thing on table saws and joiners, and probably router tables, soon enough. They're probably cheaper than casting iron for the same purpose.

darryl
12-29-2008, 09:15 PM
The few pieces of granite and who-knows-what-else slabs I have check out pretty good on my surface plate. Over about 8 inches wide by about 10 long, I can't detect any rocking at all. If I put one layer of zigzag paper (.001) under any corner, I can feel the rocking that it induces. For me, and for probably 90% of uses, that is more than good enough. Of course, I do have the surface plate to be able to reference to, and I do recommend that a surface plate be purchased anyway instead of relying of some substitute that can't be verified as to flatness and overall accuracy. The plates are not expensive, as others have suggested. Float glass may be decently flat, but it's not something to automatically trust either. Test the pieces you might use before going any further. They might be fine, or you may find some warping. That would not be a surprise to me.

After I checked my pieces, I was then able to consider using them as sort of 'expendable' flats. If I want to sand something flat, the paper lays on one of these slabs and the workpiece is carefully 'slid around' on the paper. Any non-critical assembly could be done on them as well, where there may be a chance of contaminating the slab. Better these than the surface plate.

I did check the granite and ceramic tiles at one of our local stores. The granite surface looks rough, though it may be reasonably flat overall. The ceramic tile I considered was way smoother than the granite, but for either I would have to make the purchase, then bring them home for an actual test against my surface plate. I may do that in the new year.

Some of the inaccuracy figures that have been reported here are way too much- if I had found even .003 of warpage on the slabs I checked, they would be useless, except for my first application which was a base to do soldering on so I wouldn't mark up my desktop.

Interesting to hear more of experiences on all this-

lazlo
12-29-2008, 11:20 PM
If there is a Woodcraft store near you you can do that as well, They sell 9x12 grade B, as some woodworking tools need careful alignment aided by a reference..

Scraping and toolmaking == NO! NOT PRECISE ENOUGH!

A Grade B surface plate is flat to within 2 tenths over an 18" surface plate. I think even Forrest, Lane et al would be more than happy with a Grade B plate. ;)

http://i164.photobucket.com/albums/u15/rtgeorge_album/surfaceplate.gif

Teenage_Machinist
12-30-2008, 12:16 AM
WHOOOPS! A purchased granite plate is great for scraping and toolmaking, I would not use countertop without :p measuring with whatever instruments are used. Misled you.

dp
12-30-2008, 12:22 AM
WHOOOPS! A purchased granite plate is great for scraping and toolmaking, I would not use countertop without :p measuring with whatever instruments are used. Misled you.

Nice recovery :) How long before we have to call you Teenage_Machinist_Emeritus?

Rich Carlstedt
12-30-2008, 12:27 AM
I got a piece of granite from a neighbor that was 12 x 12 inches and about 1 1/4" thick
I set it on my Precision surface plate and graphed the surface contour.
I first shimmed it so 3 points were flat to my indicator (Plane = 3 points)
I then used my surface gage and marked the ridges/valleys with a marker pen
it looked like a typographical map of a mountain range.
No rhyme or reason, with dimensions =/- .010 from median.

Perfect for making fudge.
Rich

dp
12-30-2008, 12:37 AM
When I had granite counters installed in the kitchen I talked to the vendor about the process. They do all their own finish grinding and sizing. He said they can finish to what ever flatness you need. They make surface plates as well as counter tops. But he said not all granite is appropriate for surface plates and of the type that is only a subset is going to be useable.

The stuff has a lot of stresses built into it while it's part of a mountain and when it's pulled from there and subjected to changes in orientation, temperature, and humidity (the inside of a mountain can get pretty dry) they can move quite a bit. Some stresses form pressure ridges that continue to relax over time and that may be what you saw in your sample.

They often have to repair blow-outs with epoxy and stone rabble.

He said he could make me a 4" grade A plate, uncertified, for a fraction of store-bought.

darryl
12-30-2008, 05:03 AM
I guess it would be naive to think that granite wouldn't have stress in it. So it's millions of years old- what's going to happen when you mine it and cut it up- you might be relieving it of a lot of pressure- ah there's more to this than I care to think about right now. Except for one thing- is there anything industry does to stress relieve it?

Evan
12-30-2008, 07:07 AM
I was doing some searching and found this. Some interesting points here:



Sarla Exports, in the span of over one and a half decades has become a one-stop quality source for all major Indian dimensional stones, be it Marbles, Stones or Granites. While the company owns and controls some major deposits and processing facilities, it has strong strategic alliances with few external companies, thus being able to offer the complete range of building dimensional stones from India.

At Sarla Exports we always supply merchandise in its original form & never try to push 2nd choice material as the 1st choice. We wish to caution the buyers, of a practice, adopted by many producers of India. Like in any quarry, in India too there is abundant production of material having unpleasing / lighter shade. To push such material as premium choice, an artificial pigment is applied on the Polished Slabs / Tiles that hides all the shortcomings of the natural material. This is however a purely temporary treatment that steals the natural beauty of a natural material.

We strictly maintain the shade range of the merchandise as desired by the client. While producing cut to size/ Tiles, careful batching is done even when the material is cut from a same slab/block.

We do the repairing / netting to reasonable levels and not to the extent of joining two broken pieces. Moreover, more importantly, we use low viscosity epoxy based resins specially produced in Italy & Germany for stone application. We never use cheaper polyester-based resins, which have a limited life. While sawing, especially Green Marble, we take a lot of care, as it is a very brittle and pasty material.

We maintain a very low down feed and regularly monitor the sharpness of diamonds to ensure maximum tolerance of +/-0.5 mm within a same slab.

At Sarla Exports we have carefully controlled this very common and major problem. We never let the sawing result in slabs with a curve/bow, which makes the fabrication/ installation very difficult.We always maintain flatness of slabs to the permissible tolerance limit.

We polish the Marble Slabs & Tiles on automatic multiple head line polishing machines from Breton spa & Terzago spa of Italy. We never supply merchandise polished on "locally made table polishing machines".

We achieve the gloss between 75-90 and guarantee an excellent flatness, proper pre bed preparation and suitable life of the gloss at international Quality Standards.

We maintain perfect squareness in cut to size materials, thanks to the automatic bridge cutting machine from Breton SPA, Italy. We never use locally made bridge cutting machines or conventional hand driven edge cutting machines as it is far than difficult to maintain size and squareness accuracy on such machines.

http://www.worldstonex.com/en/SF/Sarla/AboutUs.asp

Heh. So, this Indian stone products supplier thinks their Indian produced machine tools are of inferior quality. What a surprise.

Circlip
12-30-2008, 07:59 AM
Had to go back to page one to see what the original question was, gee Gregl, if you want to sell your home machined parts to NASA you're going to have to spend lots of dollars/pounds to get the accuracy required (and don't forget to cost in recession tax). Thought I saw the key word FREE in the original question? T'aint free cos you already paid for it in the kitchen mod, but if you put it in the dumpster and someone else "Discovers" it, it will be the "Find" of the centuary.

In the mother country we used to recycle marble washstand tops and lumps of 1/2" thick plate glass and be exstatic. Oh how times have changed?

Regards Ian.

Your Old Dog
12-30-2008, 08:51 AM
I think the bigger question is will Enco's $25.00 12X18 grade B Surface plates with free shipping work well as counter tops? :D

I actually considered using them as paver blocks out to my shop.

oldtiffie
12-30-2008, 09:06 AM
I think the bigger question is will Enco's $25.00 12X18 grade B Surface plates with free shipping work well as counter tops? :D

I actually considered using them as paver blocks out to my shop.

So THAT'S wot John Stevenson used for that berluddie big paving job he had with those pallet-loads of pavers.

I've never seen John mention that he had or used a surface plate. Perhaps he has been saving them up.

I guess after it was finished both he and the paving were more than just slightly "stoned".

Circlip
12-30-2008, 09:56 AM
An i'll bet the air was slightly "Blued" :p

Evan
12-30-2008, 10:16 AM
I actually considered using them as paver blocks out to my shop.


Sure would make a nice hearth.

dp
12-30-2008, 01:13 PM
I guess it would be naive to think that granite wouldn't have stress in it. So it's millions of years old- what's going to happen when you mine it and cut it up- you might be relieving it of a lot of pressure- ah there's more to this than I care to think about right now. Except for one thing- is there anything industry does to stress relieve it?

Dunno, but my wife just showed me a blowout on our kitchen counter. A dime size shallow divot showed up under an area we keep our cook books in. No abuse possible there, it just let go.

Jpfalt
12-30-2008, 03:02 PM
Granite is basically a cast silicon dioxide and aluminum oxide with some other minerals thrown in. Grain size, shape and color is driven by the composition and cooling rates. As a result, granite has all the issues normal for a casting. Granite is solidified liquid magma and the grain size and residual stresses are going to depend on the thickness and cooling rate of the original slab when it solidified. I've seen some writeups on granite surface plates that talk about using specially selected granite from specific locations. I have to assume that a particular quarry is tapping into a specific granite "casting" that just happened to come out better than the rest. Arkansas sharpening stones are similar in that the type and quality was determined by the quarry they came from in Arkansas.

I've made some tools for scraping and measurement using countertop material. A lot of what you can use depends on what you need from it.

I made two 12" straightedges from emerald pearl granite and the results were OK. I was told that emerald pearl comes from a specific location in Norway and is selected for large grains (up to an inch across) angle of reflection and color. I polished it mostly with harbor freight diamond plated hones and used yellow oil based artist color thinned with WD40 as the transfer spotting compound. I also made a 6" x 6" flat from paradiso granite sample, which is fine grained and pinkish red. The top surface was initially flat within about .002 and finished at about .0001 flatness.

Cutting was done using a 4-1/2" wet diamond saw blade (also Harbor Freight) on an angle grinder with a trickle of water put in at the entry to the cut. Messy, but effectice. A tile cutting saw would probably work better. I also use a 7" saw blade under flood coolant on a tool and cutter grinder.

You would be really surprised at how quickly the diamond plated hones in water will flatten granite. It's basically the same process as scraping, but you are snading rather than scraping. With the plastic back removed from the hone, the metal mesh domes slightly where you press aginst it, which works well for removing a local spot of material. With stiff backing, the mesh is stiff enough to avoid rounding over edges.

After taking the scraping class from Forrest last June, This has launched me on a path to see how accurately I can scrape and then measure to verify the accuracy. So far that's been limited to the accuracy of my best dial indicator and the measuring tools i've made to use the indicator.

derekm
12-30-2008, 03:33 PM
...
After taking the scraping class from Forrest last June, This has launched me on a path to see how accurately I can scrape and then measure to verify the accuracy. So far that's been limited to the accuracy of my best dial indicator and the measuring tools i've made to use the indicator.

I think you need to start researching interferometry... It sounds scarier than it is ... but its just a standards room practice dating back many many decades etc... now made a lot simpler by cheap lasers. Essentially you have an optical flat separated from the surface under test whih you illuminate with a coherent light source (originally a sodium lamp behind a fine slit) and you observe the shape and count of the fringes formed by the interference patterns.

fasto
12-30-2008, 05:41 PM
now made a lot simpler by cheap lasers
...
illuminate with a coherent light source

A perfectly acceptable coherent light source is a COLORED LED flashlight. A white LED flashlight WILL NOT WORK as it's closer in operation to a fluorescent tube (uv light changed to visible by phosphor).

Evan
12-30-2008, 06:29 PM
Not all LEDs are the same. Some LED colors have multiple wavelength emissions which is responsible for the color we perceive. The best for optical interference work is what is called Pure Green. These are emitters at 560 to 555 nanometers. They are single mode LEDs and have a narrow bandwidth. It is also the wavelength where the human eye is most sensitive.

radkins
12-30-2008, 06:43 PM
The Enco 12x18, Grade B surface plate is $24.95 with free shipping:

http://www.use-enco.com/CGI/INSRIT?PARTPG=INLMKD&PMPXNO=949402&PMAKA=640-0120



The $25 free shipping is still in effect? Do you have the code?

Teenage_Machinist
12-30-2008, 06:59 PM
Laser Pointer?

derekm
12-30-2008, 07:06 PM
Laser Pointer?

yep but use a lens to spread the beam out .. and if you want to get real fancy, use a pin hole to do some spatial filtering :)

lazlo
12-30-2008, 10:07 PM
The $25 free shipping is still in effect? Do you have the code?

One more day:

Hurry, you have just 2 days left to get the best deal of the season at Enco! Get Free UPS Shipping* on your order of $25 or more today through Wednesday!

See below for details and Act Fast...this Free UPS Shipping* offer expires Wednesday, December 31, 2008 at 11:00pm EST!

* To get Free UPS Shipping on your order, apply promo code RFS85 when you order $25 or more online or mention the code to your friendly sales associate when you call 800-USE-ENCO.

Evan
12-30-2008, 10:17 PM
yep but use a lens to spread the beam out .. and if you want to get real fancy, use a pin hole to do some spatial filtering


The average dollar store laser pointer won't work well. My experiments show that they are very unstable and usually run mixed mode. To do interferometry with a laser you need a stable laser that runs in TEMoo mode with no mode switching. This especially includes green lasers. Green lasers are feedback controlled by an integral photodiode that regulates current by sensing brightness. External lightsources, especially reflections of the lasers own light will cause instability in the regulation function and can even shut down the laser. There is a very big difference between just any old laser and a stable mode controlled laser. When a laser changes modes constantly the phase of the light wavefront changes and that makes it unsuitable for inteference measurements.

Jpfalt
12-30-2008, 10:49 PM
Interferometry doesn't require a coherent light source, but does need a monochromatic light source. When I was first learning metrology, the standard was a green filtered mercury vapor lamp. The method i learned was using gage blocks to stack up to a particular dimension and then set the optical flat across the gage block and onto the workpiece. You could then count the interference lines across the top of the gage block to figure out the tilt angle on the optical flat.

My problem with using interferometry is that it first requires an optical flat, which I don't have.

tony ennis
12-31-2008, 12:25 AM
Heh. So, this Indian stone products supplier thinks their Indian produced machine tools are of inferior quality.

Or, they understand and accept our prejudices and have altered their business model accordingly.

Evan
12-31-2008, 01:53 AM
Interferometry doesn't require a coherent light source, but does need a monochromatic light source

True. But, if a coherent source is used it must be a stable single mode source. Because all of the modes produce coherent light but of varying phases it causes the position of the inteference fringes to vary. With incoherent monochromatic light the fringes are an average of the jumble of phases and are stable.

Forrest Addy
12-31-2008, 04:44 AM
There's a couple of points to conisder when selecting a planar references - that is a flat or a surface plate. One is flatness that is certifiable. This may be of no particular importance to most home shop machinists but more than a few have legitimate need for a accurate flatness reference. Another is stability and rigidity. Granite tiles and thick float glass have been low cost convenient expedients for generations. Much of it is quite flat but its flatness of a byproduce of the finishing process not a product attribute in itself. Also these materials are thick enough to give the impression of rigidity but when work of any weight is placed on them the apparentlt stiff material may sag somewhat perhaps enough to allow error to creep into work where greater than usual precision is desired.

Those of you on a budget may find a 12" granite tile 1/2 thick or a hunk of 3/8 float glass is well suited for your model steam engine work. A piece of granite countertop an inch thick may be even more satisfactory. Most of the time I use my milling machine table for quick and dirty layout. The T slots are there and much of the equipment I need are handy to it. My DaAll Class "A" 24" x 36" granite flat is always buried under stuff (it IS a flat surface after all and so it's the default repository for stuff I haven't put away) and the smaller granite flats are always in the scraping class box. So I use expedients too.

If it works for you fine but there is always a "but..." . Many of us do work where a certified or at least a certifiable flatness reference is required. Also weighty work and inspection requipment has to remain in a plane if accurate work is to be accomplished. Everything deflects to some degree under load; what was flat enough when unloaded on a bench may deflect excessively when loaded with an indexing head with a chuck on it, a 12" height gage, and a height reference. This application requires greater stiffness that a granite tile or a piece of float glass can provide.

I'm always scraping things that require better than machined flatness as examples for my scraping classes, restoration of machine tool components etc. I don't think anyone will quibble my choice of a granite flat as a reference for this class of work.

These days of cheap but very serviceable granite flats and promotions offering free shipping for smaller sizes means no US home shop owner needs to resort to budget expedients unless he does without on principle. Sad to say our European and Southern Hemisphere brethren haven't our access to low cost import machine shop goodies. I wish there was a way we in the US could send them a share of our bounty but shipping of granite surface plates, chucks, and other heavy stuff is prohibitive.

You who use granite tiles, countertop remnents, and plate glass as flatness reference do so with my blessing combined with a caveat: all that appears flat may not be adequate for all classes of work.

Parenthetically speaking: I won't allow mystery metal in my shop; only materials whose identity can be supported by factory markings, invoice description, calalog reference, color code, etc, will be placed in my stock racks. No measuring tool in my posession is without a standard of some kind for in-shop checks. That includes my straightness and flatness references. This may be a fussy way to run a shop but I was well trained in an exacting work environnment and a bit paranoid about tracible accuracy. There's been too many instances in my past where work was screwed up because tooling that was presumed accurate was, in fact, not.

So if I sound off excessvely about accuracy and certifiability allow me a little slack. OTH, It's been a long long time since any product of my shop was defective as a result of inaccurate tools. I've screwed up plenty of times but my personal shop equipment has been very much up to snuff since the early 1970's even when I was not.