used granite surface plate buying advice

hi,
I'm looking to get my first small granite surface plate and came across a used one that I think fits the bill but don't know what to watch out for and how much it should be worth. Can anyone give some input on it? As to how I might use it, see the final questions below.

The plates:

There are two for sale:

Plate with "496" written on its side



Plate with "171" written on its side







I think the "171" plate is DIN 876/1 flatness grade based on the yellow label on the side (translates to "usable to precision class 1", which is relatively poor as far as I see from THOME Prazision GmbH | DIN 876 - Tolerance of flatness, no idea what grade the plate "496" is.

The size of plate "171" is 450 x 350 x 65mm (17.7 x 13.8 x 2.56"). I think the other plate is the same size.

The plates have been online for at least half a year at ~$90 so I'm guessing that price is high (it's Europe so add at least a 1.5-2x "tax" over what you'd expect to pay in the US). They guy had some Grade 00 plates but they got sold.

To give you some reference points for cost, these are the cheapest new surface plates of roughly similar size but higher grade that I found on amazon and ebay:

450x450x75mm (17.7 x 17.7 x 2.95") DIN 876/0 for ~$200
WABECO Granit Messplatte Prufplatte Tuschierplatte 450x450x75 Messtisch: Amazon.de: Gewerbe, Industrie & Wissenschaft

400x250x70mm (15.75 x 9.8 x 2.76") DIN 876/00 for ~$163
Messplatte Hartgestein Kontrollplatte Granit Platte Tuschierplatte Anreissplatte | eBay

I don't think it's relevant but I'll mention it just in case--
I just got a height gauge, used, this model:
Machine DRO ME-HG-PRO-300 Digital Scribing Height Gauge n/a 300mm (12 inch)|allendale-metrology.co.uk


The questions:

1) how might I be limited by this "Grade 1" surface as I evolve and do more precise machining and layout work? You know, sometimes it's ok to buy a cheap tool, grow with it, then buy something better, other times it's just frustration and you end up buying a better tool almost immediately after using the cheaper one. To start with I will use it for aligning assemblies and laying out lines for drilling/cutting during builds of small projects in my basic basement workshop, then will use it during my build of a cnc mill (I aspire to something like what this guy did in UHPC but doubt mine will be that precise: Projektstart MiniVMC/BAZ "Elke" aus Beton (MiniVMC Part 1) - YouTube) and probably while making a mount for a binoscope I'm building (dual telescopes used like binoculars. The best d.i.y. example I've seen is: https://www.youtube.com/watch?v=akFaEhcuHcQ). Not quite optics in terms of wavelength precision, but some precision required. I also might like to try scraping at some point, maybe for making some small ways.

2) what would a good price for one of these plates be?

3) are there any things I should look at closely if I go in person to check out the plates? Any subtle but show-stopper problems in particular?

4) how bad can chipping or pitting or grooves be before I'd start getting problems (and frustration) using the plate?

5) might it be cost effective to get this low-grade plate then somehow turn it into Grade 0 or 00? (0 and 00 might be similar to A or AA but I don't find a page showing the conversion) Plate conditioning does not look really d.i.y. based on videos I saw of the process, but maybe someone has some experience in upgrading their plate and can share it.

6) is a surface plate the kind of thing you're better off buying new because if you're an inexperienced user the risk is too high that you buy an old one you think is ok but after a few weeks of using it understand that it's full of limitations and problems?

Any thoughts on all this would be appreciated.
Randy

i would never get a grade 1 plate, for me its useless. you know, mdf is pretty flat too. also get a 600 x 800 plate, much more useful. in view of the low pricec of new chinese plates it doesnt make sense to buy used. i have four plates,iget them from german dealers and have them shipped to a service address on the border.

edit: last time i looked a 880 x 600 "00" was around 300 euros.

Thanks a lot for the reply. I'm very (very) limited in terms of space so is there any particular reason you find 600x800 more useful? I'm limited enough in space that I might be putting the plate away after I use it, so that's another consideration I maybe should have mentioned. 450x350x70 is ~30kg which is fine for me to lift but 600x800x100 would be ~130kg which would be a hassle.

Since I've never had a surface plate, I don't quite understand why a grade 1 would be useless. It seems like for making marks for say drilling holes or cut lines, it should still be ok since the height gauge base I'd use is ~150x115mm so shouldn't it kind of average out any irregularities?

I probably will go visit the seller this Sat. (day after tomorrow) and was thinking to get the plate if he took my offer of $70 (rather than the ask of $90). Seems like at least then I'd have something and could get a feel for how it will work. My main concern would be that it's bad to the point of causing problems that I only see after using it a while. Unfortunately, I don't know how to judge it when I go see it, besides maybe taking my height gauge, sliding it around on the surface and seeing it if feels smooth or not.

A surface plate is only guaranteed to be a particular grade at the time when it was calibrated.

A grade zero plate that was calibrated 10 years ago and has been used hard in a factory since then is very unlikely to be a grade zero now!

Without a optical collimator really the only thing you can check it with is something like a repeat o meter it's sort of like a hight gauge with a long narrow base. Google it.

I bought a new in crate 24x36x5 Granite grade B for $300 US at a going out of business sale.

It's probably not a good idea to have it as your only flat reference. However it's probably better than nothing. Clean it and look it over a worn granite plate may look different in the worn spots

Mark Rand said:

A surface plate is only guaranteed to be a particular grade at the time when it was calibrated.

A grade zero plate that was calibrated 10 years ago and has been used hard in a factory since then is very unlikely to be a grade zero now!

Click to expand...

I get how that could be an issue. The only indication of flatness I see on one of these plates is the yellow label "usable up to grade 1" which is already pretty low quality and I have no idea when that label was applied or how much it was used afterwards. The plate kind of looks ok to me in the pictures...but maybe that's not very meaningful?

Two other plates he already sold had labels with more info--Grade 00, one from 1993, one from 2001. I kept copies of those pics. These are NOT available anymore, but from what you say they might not have been any better than the Grade 1 that remains. But I mention it since it's possible, I would guess even likely, the remaining plates come from the same manufacturer.






I just don't know how 'bad' a plate can be before it's not useful to me even as a complete newcomer to surface plates with initially relatively simple requirements.

carlherrnstein said:

Without a optical collimator really the only thing you can check it with is something like a repeat o meter it's sort of like a hight gauge with a long narrow base. Google it.

I bought a new in crate 24x36x5 Granite grade B for $300 US at a going out of business sale.

It's probably not a good idea to have it as your only flat reference. However it's probably better than nothing. Clean it and look it over a worn granite plate may look different in the worn spots

Click to expand...

I might be able to do something simple like this:
"How to determine if your surface plate is out of tolerance."

although I don't have any gauge blocks, just a height gauge and some indicators (a couple 0.01 and one .001mm).

I've been searching the classifieds/ebay for used surface plates about this size for probably a year and this was the best chance at getting one I've seen as most of the others you have to collect yourself (I have to collect this one too but it's close enough) which then negates any savings from buying used--for me, with no car and most such offers being many hundreds mi./km away and in a different country. Like you say, maybe it's better than nothing, although maybe it's not better than just buying a big marble floor tile at the hardware store or a big flat marble/granite piece from a local gravestone cutter or a big piece of thick plate glass? Someday I hope someone does a definitive comparison between those on the relevant flatness parameters for typical examples. I've found scattered info on surface plate alternatives but nothing comprehensive.


>It's probably not a good idea to have it as your only flat reference.

Because I have no experience with surface plates, I still can't really see where it's going to fall short, particularly for the first few months of getting to know it. Seems like I will be able to scribe lines, mark holes and lay parts on it to square them up pretty precisely if the parts are large enough they should average out most deviations from surface flatness that are significantly smaller than the length of the parts?
A few concrete examples of where it could fall short would really help me understand.

Save yourself the money/time/frustration of a cheep plate.
Wait and save up if you have to and buy a quality product
Take care of it and it will probably last a lifetime in a home shop

The art of scraping has a very high resolution its relatively easy to see a.0002 error in a plate when hinging a part

I'm now the proud owner of a surface plate of questionable quality and unknown utility.

I got the aforementioned used plate despite some of the cautions in comments above to get a new one instead because:

1) as mentioned, this was the best deal I found in the past year and I didn't want to keep waiting, nor spend 2-4x more for known-good plate.

2) by chance I was visiting the seller's city which is ~1 1/2 hrs. drive away and it was a rare opportunity to be able to pick up a plate rather than have a shipping hassle.

3) as far as I can tell, the plate is not bad. I know above commenters said I might have problems but since I couldn't figure out specifically what kind of problems I'd have given my newbie use cases, and I'm up for trial by fire, I pulled the trigger on it. It ended up being $80, which is a lot less than a new plate (here).

I will try to continue reporting on the plate as I get familiar with it since I think other beginner users like me might be in a similar situation with buying used/cheaper plates and could benefit from seeing any problems I get from it.

And...the very first action I did on the plate was to damage it! Fantastic. I put the used height gauge which I just received a couple days ago on it and slide it around to two or three locations, like I've seen done in surface plate videos on youtube. I thought maybe I could use it like a crude repeat-o-meter. After just a few seconds of this I noticed a white line scratched in the surface of the plate. I have no idea what it came from. I did wipe the bottom of the height gauge off with my hand before putting it down. I have no 'stone' to stone it nor really know what kind of stone to get for future use but it felt smooth, I thought. However I can't feel the white line by rubbing a fingernail hard over it and I used some alcohol and a cotton shirt to wipe over it and it became about 1/2 as visible so maybe it's not a disaster.

Below are some pics of the plate in case anyone's interested or it sparks any comments. It has three feet on the bottom which I think is a nice extra feature and makes me wonder if it started out as a higher-quality plate since I don't recall any of the new plates I was looking at on ebay/amazon as having feet, but maybe they just weren't pictured.

The old height gauge I got, the main suspect in the case of the scratch:

metamaterial said:

The old height gauge I got, the main suspect in the case of the scratch:

View attachment 296845

View attachment 296846

View attachment 296847

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...in case this post seems out of place/lacks context it's because the other posts I posted have not shown up yet. I guess they are still in moderation.

Like as not, someone reconditions and or recerts plates in your area, call and get a quote.

Since you are in Switzerland, my answer is probably not relevant but I just bought a toolroom grade 24"x36"x4" granite plate with 2 ledges for $275 delivered to a dock near me from Grizzly. They were having a shipping reduction sale. With granite plates, the delivery/shipping cost can be more than the actual plate.

My plate seems to be a pretty decent plate and is the dark granite type, which should ware well. There was minimal paperwork but it did have a calibration map with it (for what that's worth). It weighs about 300 lbs. I needed to use my engine hoist to lift it. I looked at a lot of used plates before I bought this one and in my opinion, all of them would have needed to be resurfaced to be at least as accurate as my new toolroom plate and with shipping were a lot more expensive.

i think your "scratch" is not a scratch. not easy to damage granite. did you check with the test indicator?

and, btw, i dont put my plates away, i have hard covers for them (made from the crates they came in) and use them as working surfaces.

Any plate is better than none.
Chips and dings are not a big deal. Same with the scratch in the base of your height gauge, stone it.
Advice will vary.
Do not get crazy or anal in this world. For sure one wants a AA or plus in pink but that silly land for most.
What is your shipped to home cost for the common import plate in this size?
Going on a stand or workbench?

For 99.999 percent of the people out there the thought of resurfacing your own plate is no-no. This an art learned the hard way and very expensive equipment.
Have Planekator and HP laser in house and would not take this on.
Bob

Wonderful I'm glad you got it I had to get the ok from the boss (wife) to get mine the 300 I paid would have covered the shipping let alone the plate. The shipping on this is borderline robbery.

The basics of the repeat o meter is a long narrow base you don't have to use a gauge block the check for flatness. Imagine the plate being a bowl which is a common condition of worn plates. You zero the indicator with the base parallel and close to an edge you then rotate it 90 degrees so the indicator is now towards the center. It the plate has a belly worn in it the indicator will show a highter reading, then rotate 180 degrees ect

MisterFixIt1952 said:

Since you are in Switzerland, my answer is probably not relevant but I just bought a toolroom grade 24"x36"x4" granite plate with 2 ledges for $275 delivered to a dock near me from Grizzly. They were having a shipping reduction sale. With granite plates, the delivery/shipping cost can be more than the actual plate.

My plate seems to be a pretty decent plate and is the dark granite type, which should ware well. There was minimal paperwork but it did have a calibration map with it (for what that's worth). It weighs about 300 lbs. I needed to use my engine hoist to lift it. I looked at a lot of used plates before I bought this one and in my opinion, all of them would have needed to be resurfaced to be at least as accurate as my new toolroom plate and with shipping were a lot more expensive.

Click to expand...

Although CH (Swit.) is my current location, I'm originally from Oregon, which is apparently your location, so kind of funny.

As to the plate and price you got relative to prices here, in case you're interested in the comparison:
These were the best deals I found on amazon.de and ebay.de for plates in the size I wanted (I didn't even look in CH because I know the prices will be at least 1.5-2x Germany):

450x450x75mm (17.7" x 17.7" x 2.95") DIN 876/0 for ~$200, amazon.de
WABECO Granit Messplatte Prufplatte Tuschierplatte 450x450x75

400x250x70mm (15.75" x 9.8" x 2.76") DIN 876/00 for ~$163 ebay.de

And, the used plate, below, just popped up in the local classifieds. In terms of size, it's 36% the size (volume) of your plate, almost 20yrs old and no delivery and it's about the same price as the plate you got.

630 x 400 x 80 (24.8" x 15.75" x 3.15"), 60kg, $275 (says is/was ~$635 new)
It's Din 876/00 which I think is more or less like AA but I'm not sure when it was last calibrated.
(I include the pics since the link will disappear as soon as someone buys it)

dian said:

i think your "scratch" is not a scratch. not easy to damage granite. did you check with the test indicator?

and, btw, i dont put my plates away, i have hard covers for them (made from the crates they came in) and use them as working surfaces.

Click to expand...

I really hope it is not scratched. I'm not totally sure how I'd use an indicator to check it...drag the tip over the scratch while it's attached to a magnet base and watch for a wiggle in the dial?

I did not feel any blip when I dragged a fingernail over it and I guess that means it's probably less than 15 microns.
(I'm guessing that because "...the casual usable dynamic tactioception discrimination limit to be around 9 microns. So if you have a really smooth surface with a 10 x 10 x 10 micron cubical bump, you will feel it when you slide your (untreated/unprepared) fingers over it if you are mildly attentive. There are many other factors (pressure, surface feature elasticity, glabrousness, sweat induced adhesion..) at play in these situations however."
Error 404 - Quora interestingly in some cases, patterned surfaces, you can feel down to 13nm !, "One of the authors, Mark Rutland, Professor of Surface Chemistry, says that the human finger can discriminate between surfaces patterned with ridges as small as 13 nanometres in amplitude and non-patterned surfaces." Feeling small: Fingers can detect nano-scale wrinkles even on a seemingly smooth surface -- ScienceDaily)

That's a good idea about keeping the plate out. I could cut a hole in my table top and recess the plate in it and when not in use put a hard surface over it that's flush with the normal table top and I can use the whole table top again (I am short on space).

CarbideBob said:

Any plate is better than none.
Chips and dings are not a big deal. Same with the scratch in the base of your height gauge, stone it.
Advice will vary.
Do not get crazy or anal in this world. For sure one wants a AA or plus in pink but that silly land for most.
What is your shipped to home cost for the common import plate in this size?
Going on a stand or workbench?

For 99.999 percent of the people out there the thought of resurfacing your own plate is no-no. This an art learned the hard way and very expensive equipment.
Have Planekator and HP laser in house and would not take this on.
Bob

Click to expand...

> Same with the scratch in the base of your height gauge, stone it.

I see "now I'll just stone the (xy table, bases, etc.)..." in many youtube videos on machining but I'm having a hard time figuring out what is this magic stone? Any smooth grinding stone? Like 3000+ grit? I have a 1000 grit diamond sharpening 'stone' but it looks really rough compared to the near-mirror finish on the bottom of my height gauge.
Japanese water stone? Arkansas kind of oil stone? Some kind of special "machinist's" stone?

> What is your shipped to home cost for the common import plate in this size?
oh, I just replied about this to the previous comment before seeing your comment. But in short, prices for a smaller plate like this are around $160 (amazon.de) to $270 (Switzerland, example Mess- und Kontrollplatte aus Granit 500x315x70mm Grade 0 | TOSAG AG, 174,45 CHF, $193 + ~$77 shipping)

I am just starting out and have a very basic basement workshop with extremely limited space. I will put this small plate on a table when I need it and get it out of the way when I don't need it (or possibly cut a hole in the table and recess it in the hole, cover with hard surface when not in use to reclaim the table top space).

I am definitely not going to try--and probably ruin--this plate by trying to resurface it.

carlherrnstein said:

Wonderful I'm glad you got it I had to get the ok from the boss (wife) to get mine the 300 I paid would have covered the shipping let alone the plate. The shipping on this is borderline robbery.

Click to expand...

Thanks. I'm excited to start using it.