Surface Plate purchase question.

[Micscience]

I just purchased a used Starrett 24x18x6 pink crystal grade AA surface plate which brand new it is certified to be within a 0.000075 tolerance. It has five times better the wear resisting qualities of the dark granite versions.

Now, I do think I got a good deal but I do feel a few tiny little holes in the surface which are barely visible to the eye. I know there are many machinists here who have plates I was hoping you could throw your 2 cents in if ya don't mind. The plate came from a shop not sure if it was a machinist shop or some type of engineering shop and was given to the seller for free then sold to me.

My question is if it was a decent buy? This is my first surface plate so I don't know how they come brand new.

Also are those tiny holes normal wear?

 

[Qrazy]

IMO the tiny holes won't hurt anything as the items you place on the surface plate will easily span them. keep it clean, I use to use an aerosol product called kleen surf to clean the surface plate. It was a foamy spray that smelled like glass cleaner that did a good job of penetrating those little holes and bring the dirt and debris to the surface, just spray and wipe down. Build a wooden cover for it to protect it when not in use, it will not only keep dirt and grit off of it but will also help protect it from something dropping on it. Grats, I would love to have one of my own.

 

[Hemlock]

Hard to say if it was a good buy since you don't say what it cost, you can price comparable new ones at McMaster. They are companies that will come to you, check and grind to true them if needed. Nice slab to have, I agree you should make a cover to protect it.

 

[A_Pmech]

Granite is used for making surface plates because it offers better dimensional stability than metals. Another useful property is that when the plate surface is damaged, the damage does not leave a raised burr as a metallic plate would. Granite is not ductile. Thus, the gauging surface is not harmed by light gouges.

A small plate like that can be calibrated for not a lot of cash. Whether your work requires that it be calibrated is something only you can decide.

 

[Micscience]

Sorry I forgot to say how much I paid for it. It cost me $75 bucs and a one hour drive to go get it. I was either going to buy this Enco 24x18x4 with ledges (http://www.use-enco.com/CGI/INSRIT?PMAKA=640-0142&PMPXNO=951630&PARTPG=INLMK3) but then I saw this Starrett one on Craigslist.

John/Hemlock that is good to know. So basically it is normal wear I'm assuming. I don't think I would need to resurface it or re-calibrate it for the hobby stuff I do, but I would like to see how it is done since I have just started taking up scraping and I find it kind of fascinating all the things that are derived from having a flat reference.

On another note, when I brought the stone in with my cousin, it was a pain to move with a weight at 248lbs. It occurred to me how the hell did them Egyptians move those lime stones from miles away and how did some of the other ancient people flatten the stone so true at puma punku.

edit: I would like to note that there does have a sticker saying calibration not required. I'm curious to know why that is there because I have heard 3-5 years is the average before you need to re-calibrate a pink stone.
http://i14.photobucket.com/albums/a318/Micscience/100_7187.jpg

 

[larry_g]

edit: I would like to note that there does have a sticker saying calibration not required. I'm curious to know why that is there because I have heard 3-5 years is the average before you need to re-calibrate a pink stone.
http://i14.photobucket.com/albums/a318/Micscience/100_7187.jpg

The calibration sticker comes from HP. It was used in an area where it was not a reference surface therefore no calibration required. Granite makes a good base to isolate vibration as it has a very low resonate frequency.

lg
no neat sig line

 

[Jbizzle]

What do you use a surfacing stone for?

 

[Adam.C]

Sorry I forgot to say how much I paid for it. It cost me $75 bucs and a one hour drive to go get it. I was either going to buy this Enco 24x18x4 with ledges (http://www.use-enco.com/CGI/INSRIT?PMAKA=640-0142&PMPXNO=951630&PARTPG=INLMK3) but then I saw this Starrett one on Craigslist.

John/Hemlock that is good to know. So basically it is normal wear I'm assuming. I don't think I would need to resurface it or re-calibrate it for the hobby stuff I do, but I would like to see how it is done since I have just started taking up scraping and I find it kind of fascinating all the things that are derived from having a flat reference.

Pits, scratches, or even small chips do not effect the performance or accuracy of a surface plate. They may indicate abuse however. This plate was a fantastic deal. It's worth 10X what you paid (for new that is).

Couple words for you:
1) These plates are designed to be supported in specific places. You may find three marks in a triangle shape on the bottom of the stone where it was supported during final lapping.

2) Crystal Pink is very slow wearing. It has a high quartz content. I clean mine with gojo grit-less hand cleaner. Keep it super clean and covered when not in use. I also level mine. My surface gage will float across it when the plate is clean.

3) If you use it for spotting, you won't be able to get 100% of the dye out. If you use the blue paste, (prussian blue oil paint? or Dykem spotting dye) you will end up with a purple surface plate. I use mine only as an inspection plate, and not for spotting. I prefer the black granite plates for that. But mine is not as large or as accurate as yours (12X18 B grade).

Surface plates are used as reference surfaces to determine how straight or flat an object is, but also as a common (flat) surface used to compare objects, determining parallel or square.

For hobby or part time machinists like me, a good reference plate is really helpful. I recommend looking for exactly a plate like yours because they are expensive new, slow wearing and often super cheap (as yours was).

I buy a lot of used tools and it is impossible to determine what the tool is without a way to measure/inspect it. For example: every machinist needs a master square (Starrett No 20). These are super expensive new and worth little used since few people have the means to calibrate them to determine if they still retain their original accuracy (.0002"/6"). Other examples include used parallels, used 123 blocks, and other tooling. Such things can be inspected accurately with a surface gage holding a good tenths indicator, or a planer gage holding something similar.

 

[Carla]

I just purchased a used Starrett 24x18x6 pink crystal grade AA surface plate which brand new it is certified to be within a 0.000075 tolerance. It has five times better the wear resisting qualities of the dark granite versions.

Now, I do think I got a good deal but I do feel a few tiny little holes in the surface which are barely visible to the eye. I know there are many machinists here who have plates I was hoping you could throw your 2 cents in if ya don't mind. The plate came from a shop not sure if it was a machinist shop or some type of engineering shop and was given to the seller for free then sold to me.

My question is if it was a decent buy? This is my first surface plate so I don't know how they come brand new.

Also are those tiny holes normal wear?

You got a truly excellent deal on one of the best grade of surface plates (tiny twinge of envy, mine is an old black granite Collins)

The obvious question would be, how close do you wish to work?

Any used plate is an 'unknown', which may have been abused.

A plate of that quality, gotten at the 'give-away' price you paid, justifies the cost of having a specialist metrology firm inspect it, and re-lap if necessary.

Only then will you know what you have.

As has been mentioned, it should have three thick rubber pads, at specific points....if those are missing, get new ones.

cheers

Carla

 

[davethorik]

What do you use a surfacing stone for?

The main use I am aware of is for machining metal. If they are kept flat and level, then you can use the top surface as a reference for measurements, commonly with a height gage or surface gage.

I have a similar size Starrett, except mine is the normal black granite. 4x18x24" with 2 ledges, Grade A. I got mine off CL for $50 plus an hr and 10 minute drive. It had been relapped recently, p/o had paperwork from 2 yrs prior. Mine does not have spots for feet, however the original 3 rubber pads used had left profiles of shop swarf on the bottom and I put the new pads in the same place let it acclimate to where I work, and had it checked when the granite-checker dude came in and certed all of our big granites. It had a dish in the center that was .00005 deep, but I only ever go out to 4 decimals anyhow, usually more like 3, so good enough for my use.

 

[Micscience]

Larry- Thanks I just wonder why HP would use a grade AA for a stand when they could get a cheaper one but I get what you are saying and the plate could have had many different jobs during it's life at the shop.


Adam- It does have the three feet at the bottom and it stands level since my bench is level however I need to build a stand and some kind of casing.

I also am curious how to clean this plate. You mentioned gogo cleaner but I have read some soaps can be harmful to the plate. I am going to have to research what counter top cleaner to use which will clean and not harm the plate.

==========================================================================
("3) If you use it for spotting, you won't be able to get 100% of the dye out. If you use the blue paste, (prussian blue oil paint? or Dykem spotting dye) you will end up with a purple surface plate.")
==========================================================================
That is precisely why I bought the plate for. I was hoping to scrape some items and I was going to use the plate as the reference by prussian bluing it up. That kind of ***** there has to be a way around this.

Carla-Thank you, I was hoping to hand scrape my lathe bed to within a tolerance of .001, if I can get better then that, so be it. I wanted to have an accuracy of at least .001 on parts made from this lathe I am building. I have no machinist experience so my goals are set a bit low to accommodate my learning curve. Thanks for the feedback guys.

 

[ez-duzit]

That's a fair price for an excellent surface plate. My black 4x18x24 plate cost me ~$50 plus 1.5-hour round trip drive.

Besides their use as a base from which to take precise measurements, they can be used as lapping plates, fixing a sheet of appropriate grit sandpaper for dressing a flat part.

 

[larry_g]

Larry- Thanks I just wonder why HP would use a grade AA for a stand when they could get a cheaper one but I get what you are saying and the plate could have had many different jobs during it's life at the shop.




I also am curious how to clean this plate.

A lot of the labs would have precision scales on old plates that no longer met the standards of the metrology department.

As far as cleaner, go to the source,, http://www.use-enco.com/CGI/INPDFF?PMPAGE=363&PARTPG=INLMK3&PMITEM=640-0082 Look to the bottom of the page linked.

lg
no neat sig line

 

[INSP380]

Starrett sells surface plate cleaner. I use it on my Crystal Pink plate.


Steve

 

[Adam.C]

Adam- It does have the three feet at the bottom and it stands level since my bench is level however I need to build a stand and some kind of casing.

I also am curious how to clean this plate. You mentioned gogo cleaner but I have read some soaps can be harmful to the plate. I am going to have to research what counter top cleaner to use which will clean and not harm the plate.

==========================================================================
("3) If you use it for spotting, you won't be able to get 100% of the dye out. If you use the blue paste, (prussian blue oil paint? or Dykem spotting dye) you will end up with a purple surface plate.")
==========================================================================
That is precisely why I bought the plate for. I was hoping to scrape some items and I was going to use the plate as the reference by prussian bluing it up. That kind of ***** there has to be a way around this.

Carla-Thank you, I was hoping to hand scrape my lathe bed to within a tolerance of .001, if I can get better then that, so be it. I wanted to have an accuracy of at least .001 on parts made from this lathe I am building. I have no machinist experience so my goals are set a bit low to accommodate my learning curve. Thanks for the feedback guys.

With respect to my friends here, this is the wrong forum for this sort of discussion. You should ask in the metrology section of practicalmachinist.com Ditto for the scraping. And BTW, scraping a lathe bed to .001 produces better then .001 on a cylinder turned on that lathe. Remember what that bed does. You can easily produce parts to .001 on a lathe with a worn bed. Turning perfect cylinders is the problem. And scraping a lathe bed (depending on the bed, is about the hardest thing you can do. You will need other masters besides the plate.

For surface plate cleaners, many old timer machinists recommend the gojo. Some use windex, others plain old rubbing alcohol, some even recommend WD-40. I forget what the Starrett plate cleaner is, but it is nothing special.

There are significant issues with some other cleaners. I would not use granite counter top cleaners until you know they are safe. Some leave stuff that attract dust. Alcohol actually cools the surface of the plate which can be a problem for stuff on top of it.

Cleaning Dykem off a plate is different from cleaning a plate normally. You have to remove dust and oil from hands and tools off a normal plate. Cleaning spotting usually requires mineral spirits followed by gojo or something similar.

Couple thoughts:
1) Assuming your plate is AA grade, it might be a good idea to not touch it AT ALL. Don't use it for spotting, don't put your coffee cup on it. Use it for inspections only and only when you get the experience you need (assuming you aren't experienced) to use it properly. You bought a Ferrari cheap. Don't use it as your daily commuter car. I would assume you bought a $750 surface plate and treat it accordingly.

2) If you must use it for spotting, maybe use the red dye! You will never get it all out of the pores of the stone, but maybe it won't look so bad.

Be sure to check out practicalmachinist for more information on surface plates and scraping.

What lathe are you working on?

 

[Micscience]

Adam thank you for that response. I have tried asking or figuring out what you just mentioned about the accuracy of a cylinder from a bed that is flat to .001 and I never got a clear answer before.

I read yesterday that some guy who calibrates the plates uses gojo so I might give it a shot til I can get the real stuff.

Ok I get what you are saying that I shouldn't use this plate for basic stuff but if I would have known that from the beginning I wouldn't have even bought it. My main goal was to scrape many parts for my lathe and make my own straight edge. I tested an area and it came off better then I expected however if blued often the plate will eventually show a trace of blue on it.

I am in the middle of building the Gingery lathe and I am well aware of the lathes capabilities. I am almost half way done. If you notice in the background of the picture you can see the bed and with the ways installed on the plate. I was lucky someone sent me a box with all the patterns of the lathe so I didn't have to make them except for the bed, I did that myself. I am addicted to this build believe it or not, that is how much fun I been having. That being said I am still going to buy a lathe. I have been looking around craigslist and many lathes are selling really cheap. So it won't be long before I'm turning some parts.

 

[Adam.C]

The other way of looking at this is that you can do what you want with your plate. I've spent WAY more on drinks than you paid for this surface plate. You probably have too. The guys on PM say acetone will remove the spotting dye. So forget it.

Only flip side....in my experience as a HSM, we are unique in that we have to replicate an entire shop full of people and tools. If you buy all your tooling brand new and top quality, you're good. But if you buy second hand or second quality, it is important to be able to check stuff out. A good surface plate is absolutely essential. I'm just trying to advise you so you will have no regrets.

Pro machinists have the advantage that they can use their employers QC depts to calibrate stuff or use the shops masters to check stuff.

You may find you can check your lathes bed with a precision machinists level. These are adjustable. But you need a flat surface to adjust them. If you want to turn with high precision, you will likely need a ton of special tools- check tools, ...even stuff to check your grinder tables. The old adage is you will spend as much on tooling as you do on your machines.

 

[ttpete]

When you make the stand, also make a cover for it so it stays clean.

 

[macgee]

With respect to my friends here, this is the wrong forum for this sort of discussion. You should ask in the metrology section of practicalmachinist.com Ditto for the scraping.

Couple thoughts:
Use it for inspections only and only when you get the experience you need (assuming you aren't experienced) to use it properly. You bought a Ferrari cheap. Don't use it as your daily commuter car. I would assume you bought a $750 surface plate and treat it accordingly.

Be sure to check out practicalmachinist for more information on surface plates and scraping.

Micscience,

I'll first say congratulation on getting a nice coveted pink Starrett surface plate. While we will all see used tool grade surface plates on cragislist going cheap and not so cheap, it's very rare to find a AA pink starrett especially a 6" thick one in that size and at $75 it's a practically free when compared to a new price and to what these typically sell used for.
For the most part random small tiny holes will most likely not effect the accuracy that you need. I do see what looks like a scratch but that maybe part of the granite?

Not trying to stir the pot but in regards to not asking on this forum and instead you should go to Practical machinist. I have never been to a more arrogant, rude egoistical forum site in my life, it's very sad. If your new and ask a silly newbie question they will rudely rip you apart, call you names and then close the thread. It's like they are licking there chops waiting for newbie's, they almost seem to live for it. While not everyone on that site is like that (they're some very helpful members) but the bad ones are very loud and sadly wide spread including the moderators. The site does give you enormous and valuable information but wanted you to warn you and be aware on how that site operates. I think your getting some good information here on GJ in regard to your questions


I recommend using it for whatever you want to use it for, its used and it's yours.
Don't be afraid to use it. Your eyes & fingers are an excellent source in seeing problems with a surface plate. Do you see any wear spots, maybe from repeated use in one area? Your probably not in the position to have two different surface plates so try using it. Does it really matter if it gets stained? I know its a bit sacrilegious but what are your options? If you feel that way then sell it and get a cheap new fresh black one from Enco or Grizzly.

**For the most part it's probably an excellent plate in the current condition for your level of metrology needed, I would leave it alone unless you see some glaring damage or uneven areas. This pink granite is very, very hard and it was made so well and accurately that you have a better chance of this plate being in good shape compared to any others you'll see on craigslist.

I've been down this path and I know how frustrating it is not knowing if your plate can be trusted or not. Getting a plate like that tested can be very expensive but not always. I suggest to call around and you might get lucky finding someone near you that will take pity and give you a smoking deal to test it.

I was able to get mine tested for $30 and a six pack at local calibration shop after asking if they could help me. I brought my 18 x 24 plate to there shop when they were slow, they were very kind to explain and show me how they test surface plates. They were happy to see a surface plate being saved and being used by someone.

The comment about don't drive a Ferrari as a commuter? I say go for it. I see plenty of 1980 $300K Rolls Royces being sold now for $15K being used every day, some with surf racks and a big smile on the driver.

EDIT: These also make for very good platforms for vinyl record players, audiophiles love them. I also highly recommend making a cover for it

 

[Micscience]

macgee - Thank you, that black screech doesn't seem to be a scratch as far as there being an indentation on it. When I rub my fingers on it you feel nothing protruding or indenting so I think I'm ok.

=============================================================
"Do you see any wear spots, maybe from repeated use in one area?
=============================================================
No I do not, that was the first thing I did and I don't see any faded out areas or nothing of the sort. The craigslist ad said the plate was in very good condition and I agree. Especially after the feedback about the tiny holes.

I appreciate the input macgee and everyone else who participated. I am excited to have my surface plate finally so thanks for steering me in the right direction folks.

 

[Kevin54]

On our large plate at work, we used it off and on for bluing up parts. We always use Prussian Blue as it does not dry. Starrett make a cleaner which is basically a liquid cleaner wax. I found the best thing to clean it was to use WD-40 and a clean rag. Spray it on, wipe it off, then give it a slight buff. And no, it won't hurt the plate as the Calibration guy even uses it.

As far as getting one calibrated, they use a meehanite cast plate and a fine diamond grit, then check it with a laser I believe. All of our large plates were within .00001 in the Toolroom, the smaller desk plates were calibrated to .00005 or better. None of our desk plates set on three points, they just set on the tops of our benches. Out large plates just set in a metal frame. One was a 3x4 plate, and the largest was a 4x8 plate. The large plate was hauled out and moved to another room by riggers, and set on the floor with nothing leveled, then it was cal'd and all was still within specs. So they can take a little punishment. You don't want to pound on them, but if you set it down on a flat surface, it should remain flat for as long as you own it. Most home shops aren't working that close that even a half a thousandth out will affect the work. Just make sure that wherever you set it that the surface is relatively flat. A good way to insure that the the plate will take a flat set is go to WallyWorld, and back around the paint section somewhere, they sell round disk of felt pads with a sticky back. Get the ones that are about 1" in diameter. Put one at each corner and one in the middle. The weight of the plate will settle down to where it needs to be without distorting the plate. Remember that the granite plate is nothing more than a rock that has been ground smooth. Plus the felt pads will not scratch your desktop if you have to turn it 90 degrees for any reason.

 

[ttpete]

On our large plate at work, we used it off and on for bluing up parts. We always use Prussian Blue as it does not dry. Starrett make a cleaner which is basically a liquid cleaner wax. I found the best thing to clean it was to use WD-40 and a clean rag. Spray it on, wipe it off, then give it a slight buff. And no, it won't hurt the plate as the Calibration guy even uses it.

As far as getting one calibrated, they use a meehanite cast plate and a fine diamond grit, then check it with a laser I believe. All of our large plates were within .00001 in the Toolroom, the smaller desk plates were calibrated to .00005 or better. None of our desk plates set on three points, they just set on the tops of our benches. Out large plates just set in a metal frame. One was a 3x4 plate, and the largest was a 4x8 plate. The large plate was hauled out and moved to another room by riggers, and set on the floor with nothing leveled, then it was cal'd and all was still within specs. So they can take a little punishment. You don't want to pound on them, but if you set it down on a flat surface, it should remain flat for as long as you own it. Most home shops aren't working that close that even a half a thousandth out will affect the work. Just make sure that wherever you set it that the surface is relatively flat. A good way to insure that the the plate will take a flat set is go to WallyWorld, and back around the paint section somewhere, they sell round disk of felt pads with a sticky back. Get the ones that are about 1" in diameter. Put one at each corner and one in the middle. The weight of the plate will settle down to where it needs to be without distorting the plate. Remember that the granite plate is nothing more than a rock that has been ground smooth. Plus the felt pads will not scratch your desktop if you have to turn it 90 degrees for any reason.

I worked with big plates almost every day. We had a 5'X10' Mitutoyo granite plate that wasn't used often, and two vehicle size iron plates about 20'X30'.

They were mainly used to set up and scribe vehicle bodies. Every vehicle had locating holes on the underside and using a print, we'd locate stands using the scribed lines on the plate, then drill and tap the plate to tie them down. Then, we'd adjust the height to design height, ending with a pilot tip the size of the holes.

The bare body would have a thin coat of white paint, and once it was on the pins, we'd scribe it using height gauges and large gauge blocks every 100 mm in X,Y, and Z planes. Using the scribed lines, it was then possible to locate any point on the vehicle, given the XYZ coordinates.

From time to time, the millwrights would come and check the plates using a transit and a target. Using the screw jacks spaced in the plate, they could usually get it within .005" plus or minus across the plate, which was all we needed.

 

[Micscience]

Kevin54- You know the spray wax sounds like a really good idea. I used to be an auto reconditioner and we used to use that spray wax a lot with a ball of clay. Spray wax can clean and leave a really nice finish, it is not as slippery as regular waxes, I might give that a shot.

 

[Adam.C]

I don't like the idea of spray wax. It is possible it would fill the pores in the granite, making spotting dye come off easier. It is also possible it would dry on the top surface and effect the flatness of the plate.

Surface plates are a subject that lots of folks (on PM for example) might talk about in theory. And some curmudgeonly types like to ask if you are working for NASA and really need anything that accurate.

In my modest experience making items that require very little accuracy, having a flat surface you can trust is absolutely essential. And in practical applications, (which are often hard to enumerate) I can't see how to work without one.

Here's the root of it: The home shop machinist typically buys second hand or second rate tooling. And all that stuff conspires against us at night while we sleep. I bought a set of matched Starrett V-blocks on ebay. Are they really a matched set? Are my parallels from China actually parallel? What about my squares? Are they square? Is the fixed jaw of my vise actually perpendicular to its base?

Thinking about part tolerances is completely irrelevant. HSMs need to inspect their tools, correct what can be corrected, then learn techniques for reducing the impact of inaccuracies in their tooling.

Once you achieve the capability to inspect tools, you'll be surprised at how many items are not properly adjusted, aligned etc and can be corrected easily.

The items from my shop I find complete necessities (that are rarely discussed by HSMs)
1) Surface plate- mine is a Starrett B grade 12X18, which is pretty good since it's small. (the grade is based on the diagonal measurement).
2) Ottovino Granite square
3) Mitutoyo Granite parallels
4) Starrett inspection grade 123 blocks
5) Mitutoyo gage blocks
6) Mitutoyo digital indicators
7) Mitutoyo Digital mics and mic stands
8) test indicators (mine are all Giordtast- swiss made but inexpensive, sometimes sold by Fowler).
9) I also have some precision ball bearings which are very helpful for inspections.
10) Starrett no20 master squares (which tho used, appear to be good).

For the OP, before you can even think about scraping a machine, you need to develop the ability to measure what you have- i.e. both the machines tools and the tools and fixtures you use to check the machine tools. You can buy this stuff new, but it is typically too expensive.

 

[IanB]

I've had it for a long time, but I have a small bottle (maybe 10 ounces) of the Starrett surface plate cleaner. A gallon would do much more cleaning than I would ever do.