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Dale Lusby
06-16-2010, 05:08 PM
I'm looking at purchasing a surface plate from Enco and wanted to get some thoughts on grade A vs grade B. The site says that the tolerance for Grade A is .0001 and Grade B is .0003. I'm a hobbyist so I figure grade B is good enough for most any application I do. Any thoughts?

Thanks!

duckman
06-16-2010, 05:48 PM
Get the best and biggest plate that you can afford, then there are no second thoughts. :D :D

Dale Lusby
06-16-2010, 06:14 PM
That certainly would be the motto I have lived by for a long time;) . The choice is between a 12x18x3 grade A or a 18x24x3 grade B. I'm leaning towards the grade B since the tolerance isn't too much different and I get twice the plate.

Mcruff
06-16-2010, 06:54 PM
Lets put this more into perspective,

Grade B = Toolroom grade.
Grade A = Inspection grade.
Grade AA = Lab grade.

There are very few people on this board that would ever need anything better than a Toolroom B grade.
I have a Toolroom grade Starrett Crystal pink, that I have had for over 25 years now, it was relapped about 3 years ago to an inspection grade plate. The company I work for re lapped all the plates in the plant, mine worked fine for a B grade for them for many years, the company just insisted on spending money, who was I to turn it down.
Just for more info, Starrett pink granite plates are harder than black granite. They have a higher quartz content so they will also last longer as far as being flat and such.

DICKEYBIRD
06-16-2010, 07:14 PM
Keep in mind the bigger one weighs twice as much as the smaller one. If I recall correctly, my 12x18x3 weighs more than 70 lbs. so the bigger one would weigh over almost 150 lbs.

When I bought mine, I planned on keeping it under the bench and just pull it out when needed. HAH! I forgot how much 70 lbs. is so I made a stand for it. My back thanks me for it every time I use it. Oh yeah, B grade is fine for my HSM use.:)

DICKEYBIRD
06-16-2010, 07:21 PM
...and here's a link to my surface plate/buffer stand in case you're interested:
http://bbs.homeshopmachinist.net/showthread.php?t=36253&highlight=buffer

knudsen
06-16-2010, 07:22 PM
Don't forget your free shipping code: PFSJUN

What a bargain with the web price and free ship. Weights shown here: http://www.use-enco.com/CGI/INPDFF?PMPAGE=387&PMITEM=640-0140

:D :D :D

Fasttrack
06-16-2010, 07:38 PM
How big are you wanting?

I think the Enco Grade A big one (like 36 by 72 or something) goes on sale for far cheaper than the equally sized Grade B one. Something like 500 for Grade B or 340 for Grade A ;)

'Course then there is the discussion about whether these grades actually mean anything coming from China and with no NIST cert.

SGW
06-16-2010, 08:16 PM
Grade B will be fine. Any better than that and you'll have to start worrying about temperature differentials.

Personally, I've always found 12x18 big enough, and it's movable without a crane.

bob_s
06-16-2010, 08:58 PM
I've already arranged for mine to see double duty.

In this life I'll use it to lay out the various projects I have.

My heirs have been instructed to use it to lay me out (headstone), when I'm through with it.

Dale Lusby
06-16-2010, 08:59 PM
I was hoping for free delivery with the coupon but it looks like the coupon isn't good for heavy items that are shipped by truck. Anyone able to confirm this. May try it with the smaller plate and see if that works.

Dale

Fasttrack
06-16-2010, 09:18 PM
I was hoping for free delivery with the coupon but it looks like the coupon isn't good for heavy items that are shipped by truck. Anyone able to confirm this. May try it with the smaller plate and see if that works.

Dale

12" by 18" is the biggest plate that will get free shipping. Sometimes (especially if the order is big of you've placed big orders in the past) you can call them and convince them to give you free truck shipping, as long as you don't need a lift gate. I got free shipping on a vise this way, despite the fact that it weighed ~120 lbs.

doorknob
06-16-2010, 09:21 PM
How do they ship these things?

Inside a wooden crate of some sort?

bob_s
06-16-2010, 09:26 PM
heavy cardboard box, about 1/2 inch thick

spope14
06-16-2010, 09:39 PM
Get the bigger plate. I have had many times where I do precision assemblies on my plates that need to be lined up "just right" where indicators and angle irons are needed as well. A 12 x 18 does not hold a lot of extra "support gauging" like this, and a larger part, or indicators, angle irons and gauge blocks take up more room than you imagine. Just think 6 inch x 6 inch angle iron, 3 x 3 indicator stand, the overhang, parts, and maybe a 5 inch sine bar in the mix and a dial height gauge or vernier height gauge - normal day in my shop.......


Then someday you may wish to grind up a machine vise.....

I have two 24 x 36 inch, a 24 x 24 that is a cramped "heightmaster (the probe gauge type) station, and a couple of 12 x 18's, the 12 x 18's are "quick inspect" stations or flatness checkers.

Bigger, grade B will suffice for a HSM for the most part.

Mike of the North
06-16-2010, 09:48 PM
I just picked up a 36" X 48" X 6", and it lowered my trailed so much I had to remove the fenders because thy where rubbing, but I got it for $65 so it was worth stressing the trailer a little. If you have some time and don't have a problem with used, watch auctions and Craigslist and you may get lucky, I got mine at an auction for a company that was moving and decided to sell there surface plate it came with a stand so I just need to get it off the trailer and in the garage.

oldbikerdude37
06-16-2010, 10:15 PM
Mcruff
Lets put this more into perspective,

Grade B = Toolroom grade.
Grade A = Inspection grade.
Grade AA = Lab grade.

There are very few people on this board that would ever need anything better than a Toolroom B grade.


Oh yes,most home shop guys would stick sand paper to it and lap plates and stuff. Not a thing wrong with that. Use the tools you have, they are worthless in the grave. nothing last forever.

wooleybooger
06-16-2010, 10:52 PM
must not be many poorboys here. i was given a piece of 1x16x24 granite counter top that works for me for layout with a height gage. i understand the deficiencies with heat distortion and inaccuracies with the finished surface but you have to work with what you have. if i were bill gates or warren buffet,jr i probably wouldnt be doing some of the embarrassing things i do. i would love to have an old home depot building to fill with tools and turn into my personal playhouse.

darryl
06-16-2010, 11:26 PM
Well, maybe if Bob was buying the surface plate it would have to be the bigger one. That way his relatives would have a harder time laying him out with it. He might live longer-

I have the 12x18- so far it's been big enough for anything I've wanted to do with it. Don't know if it a grade A or B, but the specs say accurate to .0001 over the entire surface. Doesn't matter anyway since it's hard enough getting something to be flatter than 1/2 thou over several inches anyway. I have some granite slabs one inch thick that I've checked against it and couldn't find any rocking, so those become sanding backups when the work is small enough. I have seen those where they are full of ripples, so you'd want to be careful going that route.

Make do with what you have- I have a couple of automatic transmission valve body castings that I've embedded in concrete which I used to use as flats. They make unique workholding jigs since they are both full of tapped holes. Still use them every long now and then.

Black_Moons
06-17-2010, 12:34 AM
I've already arranged for mine to see double duty.

In this life I'll use it to lay out the various projects I have.

My heirs have been instructed to use it to lay me out (headstone), when I'm through with it.

Awsome idea! next time im at an auction this will give me an excuse to bid on one of those 6' by 3' by 1' surface plates.

'Here lies Blackmoons, His headstone accurate to 0.0001 over 6 feet'

Dale Lusby
06-17-2010, 10:50 AM
I called Enco and I couldn't get the to go free shipping on the larger one. Figured it was worth a shot:D

I went with the 12x18x3 which I'm sure will be good enough for now. I'm curious to compare it to some scrap granite pieces I have from counters I did. I might have to make up a few extras from them if they're pretty straight.

EVguru
06-17-2010, 11:41 AM
There's been a 2 foot by 3 foot cast iron surface plate sitting in the back of my car since last Saturday. It was all I and the dealer could do to comfortably lift it. My friend Roy is down with the Lurghi at the moment and hasn't been able to help me get it out and into the workshop.

sidneyt
06-17-2010, 02:04 PM
How do they ship these things?

Inside a wooden crate of some sort?

They shipped the first one I ordered in a cardboard box with virtually no packing. It arrived with a corner chipped off. I suggested that it might work better with a little more packing in the box. The second one arrived in the same type of box, but undamaged. They didn't ask for the damaged one so I got two for the price of one. They came via UPS in both cases. This is the 12 x 18 plate (B grade).

Forrest Addy
06-17-2010, 02:57 PM
Maybe we're going about this backwaeds - or maybe we hould work backwards.

Imagine your largest anticpated work piece is a tree standing in your yard and it's raining. The "drip line" is where the branch tips hang to drip on the ground; a critical concept when it come to spreading weed killer and fertilizer. Consider the "drip line" of your largest part, double it and make that the width of you proposed surface plate. A rectangular plate will be about 1/3 longer than the width.

You need a plate double the size of your largest work because you have to have space to go all the way around it with a surface gage, height gage, transfer stand, etc. Maybe have two smaller jobs in progress at the same time. OK that takes care of size.

Next comes grade. The closest tolerance most of us work to is 0.001". It's commonly accepted that inspection tooling should theoretically be 10 times as accurate as the work it's used for. No less than 4 times is a workable compromise for us Earthlings who have to be practical.

Using "this 4X rule," if your work is in the 0.001 range then the surface plate should be a grade allowing 0.00025" or better flatness in a patch the size of your largest part's "dripline". Remember that your surface plate is roughly double the size of your largest part so you should select a grade offering 0.0005" or less departure from a true flat for 0.001" accuracy work. Naturally, closer is better. Yes, I ignored a number of mathematical considerations in offering thi rule of thumb.

The weight of the plate is immaterial. It will be as heavy as it needs to be for its size and grade. Once its placed on its stand or bench it stays there. Surface plates are not safely hand portable except for the very small sizes. A big powerful chap can conceivably muscle a 18" x 24" granite plate but they are very heavy (140 lb,) awkward to lift, and have no "handles". It's very easy to drop one. I was once a powerful chap (6' 4" 240 lb, 19" neck at age 32) and I've dropped two, broke one in three pieces. I never man-handle a granite plate over 9" x 12".

Some wth small work space may have to limit the size of the plate they acquire. That's OK. Some ingenuity may be required but the work can be done if not so conveniently. One neat trick is to locate the plate in a shallow drawer just under the benchtop and slide it out when you need it. An outrigger with a caster attached to the drawer front may be necessary so the weight of the plate doesn't dump the whole shebang on its face.