Which Quality For Surface Plate? | The Hobby-Machinist

Dear all,
First thing first i'm very new to forum so i would like to salute you from Turkey. My name is Yavuz and have mechanical engineering degree. I'm also hobby machinist, don't have a dedicated garage. Just working on my spare times in a dedicated room inside my flat.

Nowadays i am looking for a granite plate in size of max 400x400 mm (~12 in) and reasonable weight to handle it. Just looked for suppliers and learnt about their different standarts, quality etc..
One of them returned me that they have A and B grades in din 876 standart, also, for both south african and chinese stones. I think that A and B reffers to 0 and 1 grades in standart. (attached image)

I would like to have your opinion, in my case which of them should i choose? I'm not so pro right now and my machines / tools are not in space engineering grade Actually i would like to have that plate for some bed way scraping. With a bit of limited budget i'd like have the most suitable one.

Can you help me on that issue, would grade B (1) and chinese stone be so bad?

thanks

Yavuz, welcome the forum. I think you will find this a friendly and helpful forum.

I am not so sure that your attached flatness chart corresponds at all to the grades A and B for surface plates, but I am in the US, and we have our own standards. Here in the US we also have grade AA, along with A and B. The tolerances are different for different sizes of plates, and also include repeatablility limits.

http://standridgegranite.com/products/surface-plates
http://standridgegranite.com/images/stories/docs/forms/fed spec ggg-p-463c.pdf

What you need in a surface plate depends on what you are going to measure, to what tolerances, and to what repeatability. Grade B is commonly used for in-shop surface plates. If you plan to scrape things into higher tolerances, or do high precision grinding or layout work, you may want to go to a higher grade. Grade AA only really makes sense in climate controlled metrology labs. All that said, inaccuracies are to some extent cumulative, so a higher tolerance surface plate helps to build confidence in your home workshop measuring capabilities.

In my opinion, everyone making accurate parts needs measuring tools including flat (surface plate), length (gage blocks), and angles [sine bar/table, known accurate square (certified granite angle block and/or cylinder square.)]

You should be able to prove your tools and machines to your needed accuracy... Firstly, please accept our condolences for the attack on your airport.

Second, from your chart I see that the DIN876II is listed as accurate to within 1.06 mils (0.) in your chart. That's almost twice as accurate as the lower grade one.

In my experience, when I'm not exactly sure what to buy, I have a simple rule: Never buy the cheapest or the most expensive. I use this for all types of purchases.

I think I'd go with the one I mentioned above unless the price is really the most important factor. Hello Yavuz,
welcome to the forum!
i try this rule when buying, buy the best you can afford.
you can upgrade later, if necessary, as your needs demand.
sometimes you can sell the old items you no longer use to fund the purchase of something you will use.
all the best
mike Yep, consider your projected needs and your current budget.
Get the best you can afford.
But, also consider the sequence in which you need/want to purchase machines/tooling/inspection/etc equipment.
Obviously, if the deal of the year comes along. then you may need to scramble.
But, keeping priorities in line is critical.

Also, (and don't tell my wife I wrote this) don't forget the kids need winter boots and breakfast.

Daryl
MN

Firstly, please accept our condolences for the attack on your airport.

Thank you for your kind feelings, also same here about Orlando, Paris, Brussels, Ankara also.. A wicked universal thing.

I think i will go with sum of your suggestions, top quality until to affordable budget (i dont need winter boots ). But i think for hobby purposes 12x12 in^2 is more than enough.
In the first time i will use it to take referances while reconditioning my lathe bed ways and gibs mostly. You see there are visible cutting left overs on gib surface, of course that's a cheap mini lathe i own (7x12).
While making projects (double acting steam engine / bollaero diesel) i clearly understood required tolerances and finishing detail.

Thanks again for your help, i'd like to join other issues and threads later.