Surface plate stand

[theGallery]

I just bought a 3 x 12 x 18 granite surface plate from Enco, shop grade. They had it on sale plus free shipping($70. total). I am going to build a metal stand and plan on support only at the perimeter. The question , is this enough support or do I need center support?

[Chris Evans]

Yes at 3" thickness. Nice find.

[Video Man]

There is a standard mounting convention for surface plates that is a 3 point suspension. Here's a link to the Starrett site, look at question #12 for info: http://www.tru-stone.com/pages/faq.asp#question12

[DICKEYBIRD]

The 3 point mounting system calculation is called "airy points." Here's a thread where I made a crude stand that works very well. http://bbs.homeshopmachinist.net/thr...ght=AIRY+POINT

[Andre3127]

The Airy points are extremely close to 5/9ths of the overall length of the plate (but centered). The distance of Airy points can be important because it is such that when a piece is supported by them it is at minimal flex opposed to any other point configuration.

Will it matter with a thick B grade shop plate? No.

[softtail]

I've got a plate that came out of a Pratt and Whitney shop that is 5" thick and over 4' long and only has legs on the ends similar to older lathe legs. No trussing of any kind under table. Fwiw.

[Forestgnome]

Mine's sitting on top of my desk. I'm sure there's some airy points under there somewhere.

I doubt any measuring tool I have could tell the difference. If the plate was much larger then it would be advisable to support it properly.

[theGallery]

Thanks for the input. It did raise several additional questions. What material and what size (contact area) should the three points be?

[Andre3127]

Thanks for the input. It did raise several additional questions. What material and what size (contact area) should the three points be?

Any type of furniture felt or rubber pads will do nicely.

[Paul Alciatore]

More important, they are the points where the plate was supported during it's manufacturer. So when the plate is supported at those points, any flexing will be the same as when it was made and tested so the plate will be at it's flattest.

Now, if you have a plate that is supported in another manner, and it is resurfaced while supported that manner, then it will be at it's flattest when it is supported in that, alternate manner.

The key here is consistency.

The Airy points are extremely close to 5/9ths of the overall length of the plate (but centered). The distance of Airy points can be important because it is such that when a piece is supported by them it is at minimal flex opposed to any other point configuration.

Will it matter with a thick B grade shop plate? No.

[Paul Alciatore]

The size of these "points" would depend on the size of the plate. For a relatively small plate, 2 feet and under, about one inch (diameter or square) would be nice. For larger plates, you are going to need larger support pads. I would use a hard rubber or similar material.

I have a small, 9" x 12", shop grade plate and I doubt that the points are very important. I just have it on a piece of that foam shelf liner material to distribute the weight over the whole bottom surface. It does not have any points marked on it's bottom.

Any type of furniture felt or rubber pads will do nicely.

[theGallery]

Thanks for the information and comments. I think I now have a plan that is probably way over kill for a shop grade plate in a home hobby machine shop. Out of curiosity I spent about a half hour researching the web for commercial stands and not a single one mentioned a three point support.

[Dan Dubeau]

It's 3" thick, and only 12x18" You could support it at one end only and suspend the other in mid air and not be able to detect any sort of practical or measurable difference with typical home shop equipment. Build whatever kind of stand you want. Perimeter support only will be totally fine on a plate of that size.

[Mcgyver]

Thanks for the information and comments. I think I now have a plan that is probably way over kill for a shop grade plate in a home hobby machine shop. Out of curiosity I spent about a half hour researching the web for commercial stands and not a single one mentioned a three point support.

its hard to comment with seeing their offering....but the stand manufacturer is a fabricator, its the plate manufacturer who'll tell you how to support it. Starrets I've had came with the the feet so it wasn't a question. I agree with Dan, its a small plate and it does't much matter.....The advantage of 3 is also it won't rock, so you use three bits of rubber and you are done.