If the temp changes gradually, a flat table will stay flat. Temperature changes from one end to the other will cause the table to loose it's accuracy. Inspections rooms are kept at about 68 to70 degrees because inspection tools are calibrated at this temperature. As soon as you remove it from the inspection area, don't measure the part anymore. The surface table is still flat but a height gage measuring 24" off the table will change height with the temperature change, the surface table may be slightly larger or smaller depending on the temp but with a uniform, gradual change it will stay just as flat.
Dave Patterson
odd_kins@yahoo.com
http://home.comcast.net/~oddkins/foundry_home.html
--- On Wed, 8/24/11, Wonk <tiwonk@yahoo.com> wrote:
From: Wonk <tiwonk@yahoo.com>
Subject: [gingery_machines] Re: Surface plate support
To: gingery_machines@yahoogroups.com
Date: Wednesday, August 24, 2011, 9:38 PM
Temperature is important due to the fact that if you measure and lay out something on a cold day, the measurement will change if a hot day. A good machine shop will have a steady temperature where the surface table is located. I've installed many HVAC systems in such places over the last 40 years and it wasn't for the comfort of the employee! Same reason you heat or cool parts to make a close tollerance fit! Things move when temperatures change!
Wonk
--- In gingery_machines@yahoogroups.com, David Patterson <odd_kins@...> wrote:
>
> A surface table will hold it's accuracy regardless of temperature. As long as the change is gradual and uniform. having part of the surface table in the sun and part in shade, or having the whole thing in front of a window getting full sun where the temperature change is rapid, is a bad thing. Pick a dark corner of your shop and add enough lights to remove shadows. If kept clean and waxed, I used johnsons floor wax, you can use it a glueup table for making patterns. Also 4 point support works as long as the supports are adjustable and have a rubber pad under each support.Â
>
> Dave Patterson
> odd_kins@...
> http://home.comcast.net/~oddkins/foundry_home.html
>
> --- On Wed, 8/24/11, Wonk <tiwonk@...> wrote:
>
>
> From: Wonk <tiwonk@...>
> Subject: [gingery_machines] Re: Surface plate support
> To: gingery_machines@yahoogroups.com
> Date: Wednesday, August 24, 2011, 10:16 AM
>
>
> Â
>
>
>
> Unless you can control the temperature of where your surface plate lives and have a way to hold that temperature the plate might not give you true accuracy no matter how good it is. As a hobby machinist this seems non doable. My shop has a 50 deg F temp swing from summer to winter when I'm out there working, and probably much more when I'm not. Temperature along with dust and other problems plague most of us so how good is good?
>
> Wonk
>
> --- In gingery_machines@yahoogroups.com, Jim Ash <ashcan@> wrote:
> >
> > I didn't mean to denigrate the grade B surface plate. My concern was that the lower tolerances on it (as compared to an A or AA plate) would possibly approach bad enough to contribute negatively to my work, and I wouldn't really have a good way to find out how good is good or how bad is bad. I originally bought it with the expectation that even a grade B plate would probably be an order of magnitude better than I would care about for hobby machining and the Gingery road.
> >
> > Since I posted my original inquiry, I've done some reading/web surfing on the subject. A plate should be supported properly and calibrated while using those supports. Changing the support system changes the shape of the sag and could make it out of tolerance (admittedly, I haven't seen this quantified). A calibration sheet should also be included with the plate to indicate how it was supported during calibration, which should be used for the final setup. Mine did, but the paperwork got moved somewhere away from the plate to points unknown. Some plates have markings on the bottom indicating the support points, but mine doesn't. One claim (I think from a pissed US manufacturer) is that the surface plates coming from China haven't got this documentation and aren't traceable back to a NIST standard. The questions remain - How good are they and how much do I care?
> >
> > The Feds have a standard (http://www.vermontphotonics.com/FlatnessSpec.pdf) which I can't say I've read, but they do supply a suggested mounting which I'll probably use. There's a point where you've gotta decide for yourself how much reading and cogitatin' you're going to do versus just doing it and seeing what happens. I'm way past that point, so I'm just going to pick some mounting points and call it a win. Still, I find the reading interesting lunchtime activity when I'm stuck at my desk and can't get my hands dirty.
> >
> > I'd thought about using three globs of silicone. but this thing weighs a lot and I was thinking it might be enough to squish it down to the nuthins'. I've got some sheets of gasket rubber that I could probably stack a couple dots up at each point and call it a win. I like the hockey puck idea, but I don't want my plate raised higher than the edge of the rectangular angle-iron box around the perimeter. I'd also thought about using heavy adjustable furniture feet like Keith had suggested.
> >
> > My plan was to build a basic rectangular support out of angle iron, then drop a couple cross braces across it at the right place on the x-axis (like the slats on an old bed frame), then put the support points on them. I'm also going to fabricate a plywood box for a cover, with a felt lining inside. I've got a very bad habit of cluttering up my work areas, so I refuse to set this plate up until it's built. A friend (actually his wife) succinctly calls it the 'the Horizontal Surfaces Rule' - (paraphrasing) All horizontal surfaces are required to be covered with something. Although I live by it also, I find it amusing she has assigned this behavior a name.
> >
> > Jim
> >
> >
> >
> >
> >
> >
> > -----Original Message-----
> > From: Nelson Collar
> > Sent: Aug 23, 2011 9:41 PM
> > To: gingery_machines@yahoogroups.com
> > Subject: Re: [gingery_machines] Surface plate support
> >
> >
> >
> >
> >
> > Jim
> >
> > I myself go with the angle iron. As far as the three point, why not just put a nice bead of
> >
> > silicone alowing to dry then set your stone on it and see how level it is? If it is good lift the
> >
> > stone out and put another bead of silicone and set the stone on it soft, when dry it will give
> >
> > support all around and have a softer than steel. Wood is for furniture and raw wood will take
> >
> > on moisture and dry out, causing expansion and contraction. "B" grade is nothing to snub
> >
> > your nose at for it is better than most have and the tolerance of +/- is closer than we need
> >
> > in the home shop. Unless you are picky!
> >
> > Just an idea
> >
> > Nelson Collar
> >
> >
> > --- On Mon, 8/22/11, kabowers@ wrote:
> >
> > From: kabowers@
> > Subject: Re: [gingery_machines] Surface plate support
> > To: gingery_machines@yahoogroups.com
> > Date: Monday, August 22, 2011, 12:55 PM
> >
> >
> >
> > On Sun, 21 Aug 2011 22:50:16 -0400 (GMT-04:00), you wrote:
> >
> > >
> > >I've had a B-grade surface plate from Enco for quite some time and am interested in setting it up on a stand. The plate is 18x24x3, 0-ledge. I've got some heavy 2" angle with which I can fabricate a sturdy stand. Here and there I've read a surface plate should be supported at three points (called Airy points). Normally, I would have just supported the plate around its perimeter out of ignorance. The commercially-available stands I've seen on the web for this-sized plate appear to be supported by intermediate cross-members, but they don't look like they're providing 3-point support.
> > >
> > >I guess I have two questions here. What have those of you with these surface plates done to support yours? And am I being overly-anal about this or is improperly supporting it going to significantly effect the flatness of the plate within the tolerances I'm going to care (this is, after all, a cheap B-grade surface plate)?
> > >
> > >Jim Ash
> > >
> >
> > [Non-text portions of this message have been removed]
> >
>
>
>
>
>
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>
>
> [Non-text portions of this message have been removed]
>
[Non-text portions of this message have been removed]
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