• This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn more.
  • PLEASE: Read the FORUM RULES BEFORE registering!

Surface plate support quick question

expressline99

H-M Supporter - Premium Content
H-M Supporter-Premium
#1
I just read in an excerpt from a early 1900's book that it's best to support your surface plate in a 3 point configuration. The part I read didn't go into any detail at all about what this was about. So is this valid or a typo? I'm sure it was referencing cast iron plates. (I think.)

Paul
 

MonkMan

H-M Supporter - Premium Content
H-M Supporter-Premium
#2
Found this on Rock of Ages site.

SURFACE PLATE SUPPORT

In accordance to GGG-P-463c, Rock of Ages insures accurate readings of surface plates by supporting the plate properly on three support points. Three points are preferred and are located 1/5 the length and width from the ends and sides. Three supports are used because it is the only way to consistently support a surface plate object without the weight shifting from one leg to another. Any attempt to use more than 3 points may cause the plate to receive its support on various combinations of three points and the plate will settle differently and possibly deflect out of tolerance.

Rock of Ages provides various options for supporting surface plates:

  • stationary stands with leveling screws
  • stands with casters
  • stands with casters and leveling screws
All models with casters come with wheel locks as standard. Any working height can be specified to meet your application need.

- See more at: http://www.rockofages.com/en/industrial/products/surface-plates/#sthash.zSMXeVRf.dpuf
 

ewkearns

Active Member
Active Member
#3
I just read in an excerpt from a early 1900's book that it's best to support your surface plate in a 3 point configuration. The part I read didn't go into any detail at all about what this was about. So is this valid or a typo? I'm sure it was referencing cast iron plates. (I think.)

Paul
A plane is defined by three points, therefore is much easier to level. Personally, I would think one would find a surface plate on casters less useful than one carefully leveled and stable.
 

Rustrp

Active Member
Active Member
#5
A plane is defined by three points, therefore is much easier to level. Personally, I would think one would find a surface plate on casters less useful than one carefully leveled and stable.
Given the weight and it's setup location, a surface plate on casters may expedite shop projects. Level isn't the primary purpose of a surface plate, although having one set up in the level position seems to jump out as important. My concern would be the possibility of it getting tipped over and damaged.
 

ewkearns

Active Member
Active Member
#6
Given the weight and it's setup location, a surface plate on casters may expedite shop projects. Level isn't the primary purpose of a surface plate, although having one set up in the level position seems to jump out as important. My concern would be the possibility of it getting tipped over and damaged.
Yeah, in my downsized shop, I'm looking at casters for a LOT of things, but I'm going to arrange them such that I can have a hardened point leveling the [whatever] against the floor.
 

Rustrp

Active Member
Active Member
#7
Yeah, in my downsized shop, I'm looking at casters for a LOT of things, but I'm going to arrange them such that I can have a hardened point leveling the [whatever] against the floor.
In many of the carts and movable frames I've fabricated I like the foot operated brake that has about 3/4" of travel to use on the caster side of the table.
 

expressline99

H-M Supporter - Premium Content
H-M Supporter-Premium
#8
So is there a possibility of tipping on a 3 point stand? I'm considering a 24 x 24 plate. Probably the heaviest thing I would put on it would be 30-60 pound cross slides.
 

ezduzit

Active User
Active Member
#10
On a small surface plate I wouldn't worry about 3-point mounting. And I likewise wouldn't worry about it tipping, using a 3-point mount, as long as there was a full support surface just beneath the 3 points. Mine is 12" x 18" (IIRC) and sits on a rollaway cabinet.
 

Rustrp

Active Member
Active Member
#11
So is there a possibility of tipping on a 3 point stand? I'm considering a 24 x 24 plate. Probably the heaviest thing I would put on it would be 30-60 pound cross slides.
Three legged milk stools have been around a long time. :)

As ezduzit stated, the support for the three points would be the important factor. Most of the signage I've seen on the work benches or carts in machine shops always detail a **DO NOT** preceeding a list, with some type of physical harm done if said action was ignored. I think by the very nature of the surface plate being a precision tool, logic says we treat it with care. With that said; I stopped using "Would you treat your tools that way?" years ago.

I've seen plenty of surface plates supported on work benches and carts. I don't think I would be inclined to place one on a three point stand. Many websites show the plate inset into or surrounded by a protective frame to prevent a **what if**. My experience in fabrication is the employee struggle with when to use a level versus a square. It isn't necessary for the plate support to be precicely level, just structurally sound.
 
Last edited:

tertiaryjim

Active User
H-M Supporter-Premium
#13
I would think a cart should have a frame slightly larger than the plate so the plate couldn't bump anything as it's rolled around.
You could still mount the plate on three points with a square or rectangular frame and support the frame with four wheels.
 

todd774

Active Member
Active Member
#14
Given the weight and it's setup location, a surface plate on casters may expedite shop projects. Level isn't the primary purpose of a surface plate, although having one set up in the level position seems to jump out as important. My concern would be the possibility of it getting tipped over and damaged.

Leveling could be an important factor if you what to do some static balancing. As with 2 knife edge straight edges.
 

Rustrp

Active Member
Active Member
#15
Leveling could be an important factor if you what to do some static balancing. As with 2 knife edge straight edges.
Yes it would, but if the intent was to facilitate timeliness in a machining project(s) to save steps back to the surface plate, it isn't likely related to static balancing. There's multiple tasks where a surface plate needs to be level.
 

todd774

Active Member
Active Member
#16
I suppose you could seat the knife edges on 4 posts. 3 of which are adjustable.
The reason I even mentioned it was because I just very recently purchased a surface plate. I was thinking of how I should mount it. While planning it out in my head I realized I could
Balance Harley Davidson fly wheels with that kind of set up. My original purpose of purchasing the plate was to scrape the ways of a cheap Chinese milling machine.
Mine will also be on a heavy duty cart with casters.
 

Rustrp

Active Member
Active Member
#18
Static balancing... well it's gone over my head again. lol
Imagine a round rod placed in the mounting hole of a lawnmower blade so you can tell which side needs to be ground down to balance the blade. Something requiring more accuracy might be the stone/wheel for a surface grinder. Static balancing would be the least expensive way to check for an out of balance condition, but it's also a quick way to answer a vibration question. e.g. vibrating bench grinder.

PS. Okay, I just assumed you had balanced a lawnmower blade, or that you had lawn that needs mowing. :)
 

Rustrp

Active Member
Active Member
#19
I suppose you could seat the knife edges on 4 posts. 3 of which are adjustable.
The reason I even mentioned it was because I just very recently purchased a surface plate. I was thinking of how I should mount it. While planning it out in my head I realized I could
Balance Harley Davidson fly wheels with that kind of set up. My original purpose of purchasing the plate was to scrape the ways of a cheap Chinese milling machine.
Mine will also be on a heavy duty cart with casters.
I did chuckle. I imagine a guy sitting on a Harley thinking; Hmmm, maybe my flywheel is out of balance. :D
 

Dabbler

H-M Supporter - Premium Content
H-M Supporter-Premium
#21
All of the higher end Standridge stands use two adjustable elevator bolts, and two more on a rocker arm, making the leveling as per a 3 point system, but supporting on all 4 Bessel points. For long term flatness, the surface plate (especially large ones) need to be supported equally on all 4 Bessel points. (.2204 from the edges, as I dimly recall)
 

expressline99

H-M Supporter - Premium Content
H-M Supporter-Premium
#22
All of the higher end Standridge stands use two adjustable elevator bolts, and two more on a rocker arm, making the leveling as per a 3 point system, but supporting on all 4 Bessel points. For long term flatness, the surface plate (especially large ones) need to be supported equally on all 4 Bessel points. (.2204 from the edges, as I dimly recall)
>.2204 from the edges... are you a suspect for photographic memory?

So after re-reading all this is it a yea or nay for 3 points? It sounds like on the large plates (3'x3' Or bigger?) that they need 4. At the largest I would have a 3' x 3' . I just wonder at what width or thickness would it start to flex, twist or distort. If I'm using it to scrape small ways my wooden workbench might not be where I want to set this thing up. I know my garage floor is bowed like >insert anything you want here< . I know I won't have a Harley in there. So I guess I'm still up in the air on this. Then it gets back to will I ever get my work to a level quality that would require this amount of OCD in advance. :chemist: Perhaps!

Paul
 

Dabbler

H-M Supporter - Premium Content
H-M Supporter-Premium
#24
I have 3 surface plates, and here's what I'm doing with them:

- an 11"X 9"X2.5" (unknown grade) from China - used only as a bench plate, for lapping only. supported by bench. stored in a drawer.
- a 12"X18"X3", (B grade) - just unmounted it from its stand, because I'm reusing the stand. It will be mounted on 3 points, just because it's easier.
- a newly acquired 18" X 24" Mitutoyo A grade plate. see below...

... first a short story: I have a friend that bought a Mitutoyo AA grade surface plate in the 36 X 48 X 5 inch size - and mounted it using the 4 corners... After 36 years, it has dropped about .006 in the centre. It is now worse than a shop grade plate. I wouldn't take it if he gave it to me.

So being a little OCD and/or anal-retentitive (yes it does have a hyphen BTW), and because I'm not from Standridge Granite I am mounting my new surface plate on a rolling Tool and Die cart, also recently acquired, which is made of 10 gauge pressed steel. The plate will be mounted using 4 Bessel points with a pivot...

The best advice I can give to you is that if you are mounting it on a non-movable table, make the feet of the table adjustable so ti is properly supported( so the table won't twist) . No use twisting your surface plate for the lack of 1$ worth of leveling bolts. If it is on a moving base, the your plate's sub-base must be overly rigid, so as to support the plate properly. No matter what, the plate has to ber very rigidly supported to maintain calibration.

3 or 4? your choice - if your manufacturer won't commit, I'd use 4. If you go with a Standridge 24 X 36, they explicitly say use 3 because they calibrate them that way. I hope this is more helpful than confusing,...
 

expressline99

H-M Supporter - Premium Content
H-M Supporter-Premium
#25
This guy is great. I'm surprised he wasn't on my subscribed to list.
Paul
I have 3 surface plates, and here's what I'm doing with them:

- an 11"X 9"X2.5" (unknown grade) from China - used only as a bench plate, for lapping only. supported by bench. stored in a drawer.
- a 12"X18"X3", (B grade) - just unmounted it from its stand, because I'm reusing the stand. It will be mounted on 3 points, just because it's easier.
- a newly acquired 18" X 24" Mitutoyo A grade plate. see below...

... first a short story: I have a friend that bought a Mitutoyo AA grade surface plate in the 36 X 48 X 5 inch size - and mounted it using the 4 corners... After 36 years, it has dropped about .006 in the centre. It is now worse than a shop grade plate. I wouldn't take it if he gave it to me.

So being a little OCD and/or anal-retentitive (yes it does have a hyphen BTW), and because I'm not from Standridge Granite I am mounting my new surface plate on a rolling Tool and Die cart, also recently acquired, which is made of 10 gauge pressed steel. The plate will be mounted using 4 Bessel points with a pivot...

The best advice I can give to you is that if you are mounting it on a non-movable table, make the feet of the table adjustable so ti is properly supported( so the table won't twist) . No use twisting your surface plate for the lack of 1$ worth of leveling bolts. If it is on a moving base, the your plate's sub-base must be overly rigid, so as to support the plate properly. No matter what, the plate has to ber very rigidly supported to maintain calibration.

3 or 4? your choice - if your manufacturer won't commit, I'd use 4. If you go with a Standridge 24 X 36, they explicitly say use 3 because they calibrate them that way. I hope this is more helpful than confusing,...
Unreal how multi-million year old granite moves in a few years. This does help me quite a bit. I'll have to buy some really ridged box tubing to weld up once I select a plate. I've got a lot of measuring equipment to purchase going forward. Seems the surface plate is the base point for being able to measure with accuracy.

Being as new to it as I am I've got a long way to go. Since there is never an end to the learning on this topic I think I've picked the perfect hobby.

Paul
 

Rustrp

Active Member
Active Member
#26
Being as new to it as I am I've got a long way to go. Since there is never an end to the learning on this topic I think I've picked the perfect hobby.
Yes there is! Door #3 has a tunnel with an infinite length filled with infinite cubby holes just waiting for someone to say; "I didn't know that."

Now, I'll say I was with him up to the point where he puts a beam on the third support. I still think we get stuck thinking **level** when all we are really striving for is flat. The plate is certified (if it is of certifiable quality) and it needs to be supported so there's no force or tension on any specific point. I don't think there's been proof that a plate supported on three points ends up with to of the corners drooping. I think if we replace the word support with suspend we arrive where we need to be.

With that said, I wouldn't want the workbench or support to be out of level to a point where things roll off the plate.
 

Tony Wells

Former Vice President
Staff member
Administrator
#27
I think if I ever get room and need for a larger plate, I will build a heavy stand with leveling feet, just because it may have to move some time in the future.....never know. But I will build the top as a tray and fill it about an inch deep with self leveling floor compound. That stuff seems to flow out really nicely and should give even support. HOWEVER, the catch is that there is no guarantee that the top and bottom of any plate are parallel, nor that the bottom is actually flat. But if I time it right and sit the plate in the compound just before it sets up, then I would have virtually 100% contact and therefore support for the entire plate. It wouldn't matter so much if it weren't perfectly level at that point, as I would adjust it with the feet. It doesn't have to be level, but it sure is nice at times to have a known level surface. And I mean really level, so close I could use it (to a degree) to calibrate levels. Like the one I'm about to build as soon as I talk Ken into scrounging me a piece of nice, aged CI.
 

ezduzit

Active User
Active Member
#28
TW--that is bound to fail as changes in the mounting surface will impart stress on the surface plate. If that were a workable solution, the big guys would be using it already.
 

expressline99

H-M Supporter - Premium Content
H-M Supporter-Premium
#29
TW--that is bound to fail as changes in the mounting surface will impart stress on the surface plate. If that were a workable solution, the big guys would be using it already.
OK to take this a step beyond this. Could you mount the surface plate support system in a way that it would be stabilized and protected from vibration. Much like they earth quake proof buildings? Almost in a stiffened rubberized mount that would take the stress or any expansion of the bench material?
 

Rustrp

Active Member
Active Member
#30
OK to take this a step beyond this. Could you mount the surface plate support system in a way that it would be stabilized and protected from vibration. Much like they earth quake proof buildings? Almost in a stiffened rubberized mount that would take the stress or any expansion of the bench material?
There's no such thing as an earthquake proof building. :grin big::grin big:

....but we do keep trying.